8mm AR Barrels and Other 7.92x33 Kurz Case-specific Questions

I can't answer most of those questions, but the bolt for the .458 Socom is cut for a .473 bolt face. It is a low pressure (35KSI) cartridge, partly because the wall around the boltface becomes very thin. This is for a standard AR15 size frame as opposed to the larger .308 frames. I don't know of anyone selling just bolts buy you may want to call/email SBR Ammunition as they are taking over manufacturing and sales for Teppo Jutsu in Marty's absence.

A gas block is simply a manifold which redirects high pressure gasses from a port in the barrel back into the bolt carrier in order to cycle the semi automatic system. In the case of most military type rifles the gas block is incorporated into the front sight base and is pinned in place. In other builds, the block encircles the barrel and is either pinned, clamped, or held in place by set screws. Ajustable models typically have a set screw which can be screwed in to reduce the amount of gas diverted to the bolt carrier or backed out to increase the gas flow.

Most dedicated subsonic rifles I have seen use the pistol length gas system, but I don't have specific measurements for that. In that case the port on the barrel is roughly 4 inches from the receiver at top dead center. Given the use of fast burning powders typical in this application this allows for gas to be diverted while still at a fairly high pressure, and the bullet still has a fair amount of time in the barrel before exiting and dropping pressure dramatically (dwell time). The amount of gas diverted back to the receiver is controlled by the diameter of the port and the amount of gas allowed to flow through the gas block and gas tube. Ideally the port would be the correct diameter to function the rifle without adjustment in the gas block, but since this is experimental the adjustable block allows you to tune the amount of gas.

I keep them around, I'm sure some of the advertisers have them here too. 450 Bushmaster bolts is what you want to search for. Shouldn't be significantly more expensive than a quality 223 bolt.

You should probably investigate the 300 Blackout heavily.

It´s a .223 case shortened and blown out to take a .30 Cal bullet. (and therefore uses a normal .223 magazine and bolt, the only change is the barrel and the gas system)
The 300BLK (7.62x35) is designed for both Supersonic and Subsonic use and utilizes bullets between 125gr and 220 gr (Subs obviously) and will run em both in semi automatic fashion. It´s like a 7.62x39 (AK round) from an AR, but works a lot better then 7.62x39 in an AR, which can be problematic. A 8mm kurz will have the same problems in an AR.

300BLK rifles usually come in 1/7, 1/7.5 and 1/8 twist rates. In 16 inch barrels, the 300BLK uses a carbine lenght gas system. In 8-9" barrels it utilizes a pistol gas system. (these are the two most common offerings available as of yet)

If the 8mm bullet would fit in a regular .223 case (with some work), then you might want to ditch the x33 brass and make an 8mm Blackout instead with the big pro that the only thing that will differ from a .223 or 300BLK rifle will be the barrel, but you can keep the same bolt and mags without alteration that are used in an AR15 in .223/5.56/300BLK.

If you´re dead set on using the whole 8mm Kurz cartridge, the 300BLK can still give you a lot of hints as for twist rate, gas hole location/gastube lenght i think.

You´ll probably have to order an 8mm barrel blank, fit a barrel extension to it, chamber it and drill the gastube with either decision.



But if i where you, i´d ditch the 8mm kurz project (in an AR), and just get a one in 300BLK. Remington UMC should soon have 20rd boxes of 300BLK with an open tip Match bullet for 12.99$, and you, as a reloader will get away much cheaper as you can utilize all the widely available 7.62 bullets, casts and whatnot. Hey, you probably already reload .308, .30-30 or 30-06 so i don´t have to tell you that bullet selection in this caliber range is BIG compared to 8mm......

I´m from a metric country and let me tell you: 0.3mm difference in Diameter.... that´s nothing. 300BLK will do everything AND MORE then you want from your subsonic 8mm kurz.


Don´t get me wrong, i´ve toyed with the idea too lately and thought it would be cool to revitalize that old middy cartridge that lives right along the lines of 7.62x39 and 300BLK, but IMHO, it´s not worth the hassle.

An AK 47 would be better suited to be re-barreled in 8mm kurz if you ask me (but AK´s are harder to work on, the barrel is pressed in).
Or the AK-ish VZ 58.... now that would be cool!!!

First off Welcome Paul! I'm not sure I can answer all your questions, but I'll do what I can.


8mm Kurz, an interesting project for sure!


Yep they cost more, nothing can be done about it.

The above idea of using the .50 Beowulf bolt is a great idea, not only would it be big enough, but it was designed for the AR-15 bolt carrier.


I'm not going to get into the gas issue other than to say adjustable blocks/tubes generally allow one to have a larger than needed gas port and can dial down the volume (like a faucet).

Too much gas and you get 'overfunctioning' which strangly enough has symptoms that look similar to not having enough gas. Some timing issues can be resolved with adjustable gas blocks/tubes others may required the gas port to be in a different location. Adding in subsonic requirements is way out of my league.


Nobody knows as I don't think anyone's tried the project. As I see it the 8mm Kurtz has a pronounced taper similar to the 7.62x39 you will probably have feeding issues if you try to load more than 7 or so cartridges.


Probably not, but I wwere going to try I'd look at modding a PMAG as changing the ribs on an aluminum magazines is more a pain than dremeling the inside of a plastic mag.



Yes. The C-Producs/ASC magazines have more of a curve and a different follower. They are probably your best bet for this project.

There was a similar wildcat cartridge called the 30 Kurz that was orginally designed as an improvement over the 30 M1 carbine cartridge. The cartridge case was built on the 30-06 or 308 cartridge case shortened to 1.290" which is almost what your 7.92X33 Kurz measures. the 30 Kurz was designed to work out of an M1 Carbine magazine but your rounds with the longer spire point type bullets may be a little more of a problem as far as magazines go. If you were planning on just shooting subsonics then you might want to look into a pistol length gas system –– parts are easy to find. I have some odd little rounds that have short cases and long bullets and I can feed some of them from the M1 Carbine magazines but some of my cartridges are loaded with really long bullets that give the cartridge a COL of 1.85" (close to your cartridge overall length) and I can feed them out of a slightly modified Magpul Pmag. In your case, with the fatter cartridges, you might have luck with the Pmags if you can modify them. You're not the first person I've seen on here wanting to do a 7.92 Kurz and I imagine it will be a one-of-a-kind –– best of luck.

Edit to add; By the way, there are two companies that I know of that offer 7.92X33 Kurz ammo. One is Hornady and the other is Prvi Partizan. If you wanted to locate some commercial ammo for comparison you can find it here; 7.92X33 Kurz ammo The Hornady ammo is reloadable the Prvi is not.

If it's not too much trouble, could you do updates as the project moves along.

Thank you all!

While the .300 Blackout is a 'no go' for me, (no slam on the cartridge, just a personal preference on my part), an 8mm "Whisper" (.323x.223 Rem) is high on the list of alternatives. The primary reason I don't opt for that right off is that I can buy factory Kurz brass. Were I to go with a blown out .223 (Whisper) case, I'd probably just step on up to the .338 caliber.

I'm afraid I have to disagree on the significance of 0.015" in bullet diameter, Krautling. I've shot a number of caribou with .308 Win and 8x57 Mauser, and there is a REAL difference in terminal performance. I'd be the first one to agree were it not for first-hand and even some side-by-side comparisons. Also, lotsa folks that would equate the .308 and .323 calibers (I'm not saying you are one of them), would say the .338 is "way" "tougher" than the 8mm when in fact, as I'm sure you well know, the .338 is the same 15 thou bigger than the 8mm that the 8mm is bigger than the .308. Over the years I have come to respect bullet diameter WAY more than I do case capacity. Honestly though, I just have a "thing" for 8mm. By the way, I have a 58 SHE. Tough getting that 8x45 brass though.

I have the Kurz on some single shot actions, so I suppose I could be talked out of it for the AR-15 in favor of the 8x223 or the .338 Whisper.

I will definitely keep this thread alive as long as it is viable. I plan on getting a couple of "80%" receivers to start with, so maybe when I get that going I'll start a new thread for that.

Thanks,
Paul

Another alternative in the .338 caliber is the .338 Specter, another Teppo Jutsu development. Brass and loaded ammo are available from SBR Ammunition or should be soon and they are supposed to be making barrels and bolts available in the near future as well. That would be my choice if I were to build another upper for subsonic rounds besides the .458 Socom. I believe the original brass was made from 10mm pistol brass, but is now a factory offering from SBR

http://www.sbrammunition.com/custom_shop.html

There's the bolt for you. Brownells sells the barrel extensions and barrel extension wrench.

Marty of Teppo Jutsu has mentioned in the past that he has made one 8mm version of his 30 hrt. the .30 hrt is a modern rimless version of the 30 herrett on a 6.8spc case. IIRC Marty just necked it up to 8mm for the custom build.....he probably would be a better source for info than I, though. If you went the 8mmHRT route then you could use readily available 6.8spc bolts and magazines. It would probably match the supersonic performance of the 8mmKurz with ease and should do subs nicely.

advntrjnky

You stold my thunder...lol...I was going to suggest the same thing...It would be much easier to base the round on a 6.8 SPC case Instead, you correctly noted that Marty did do some
work with a 8mm version which would put it in the 7.92X33 circle...The bolt is also stronger, able to handle +35K PSI and mags are fairly easy to get, as is the barrel extension etc.

The other suggestion would be to do a shortened ,300 Fireball/.300 BLK case (as noted by another arf forum member) which is even cheaper/easier as it would use 223 Rem. cases
and components etc.

Good Luck.


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You can also use the "big Bolt" made by AR15performance. It is stressed for ~60 ksi chamber pressure and comes with a bolt and barrel extension. Harrison uses these bolts to make 6.5 BR AR15 uppers. You can see it on his new products page: http://ar15performance.com/new_products

Several folks have already covered the bulk of your questions, I will see if I can add anything useful...

- for the bolt, you can opt to purchase a .450 Bushmaster bolt or a .458 SOCOM bolt, the latter can be bought from RRA. Or, as you have access to a lathe, you can simply take a .223 bolt and open it up in a lathe. As rims get dinged an such, I suggest opening to 0.480 -0/+.002 to give enough room for any burrs etc on the rims. Also, do NOT taper the inside of the bolt face (as is done on the .223 bolt) as this reduces the material between the lugs to a knife edge that will cut into rims and cause feeding stoppages.

- you will have to do some work on the extension, blending the two existing ramps into one large one, to help feed the larger bullet and case reliably

- for the gas system, I would suggest a pistol length gas system as your case volume with the long bullets will be limited. Powders will be on the faster side, like Re7, Win296, H110, perhaps Lil Gun and amounts limited (around 9 to 12 grain) and you should be able to keep pressures low (with that large rim, the bolt loses strength and you will want to keep the peak pressure to 35,000 psi to keep the bolt alive longer). There are different types of adjustable gas blocks out there, if you intend to run only subsonic and only your reloads, then you likely don't need one and can start with an undersized port and work up. Should you accidentally oversize the port, you can always install an adjustable block then. PRI and JP make nice versions.

- extractor - this one is tricky, as camming over the larger rim can cause binding with the extension if the extractor is not shaped properly - this is where buying a factory bolt (.458 SOCOM) will help as the extractor is already tuned and shaped.

- Magazines... the Kurz is based off the most prevalent case diameter, the good ole .47x". Only problem is that there is not a singular reliable magazine THAT FITS THE AR-15 MAGWELL out there that fits that case size... I tried .44 AMP (.308 case cut to 1.29", you could use these for your Kurz as well, Starline makes them) in AK magazines, it seemed like it would work but after 7 rounds, they bind and bulge even the heavy steel AK mags. Largest case diameter that appears to work in the AR-15 mag well is the Grendel/AK-47 case (note that those magazines typically lack the "ribs" found in other magazines). So your case size is one of your first challenges - to find a magazine that works. Single stacking would be an option, but there is no magazine that reliably will SINGLE stack this case diameter either (at least, not one that fits the AR mag well...). Seems the diameter is too big to double stack and too narrow to stay between the feed lips...

- bullet diameter - I think 8mm is one of those overlooked calibers, like .257. For some reason, those two just don't seem to get much love (in the US, at least). You could make a 8mm-221 Fireball/Whisper, BUT.... note that the 300 Whisper requires trimming of the front rib in the magazines. The 7.62 x 40 - a slightly longer version of the .300 FB/BO - requires it too, such that Wilson will sell modified magazines (the Lancer mags turn out to be easiest to modify for this). Going to the 8mm bullet will only make this more pronounced of an issue, but it can be resolved by going to a 6.8 SPC magazine - if you do that, then you can step up case size... so nothing wrong with 8mm, just beware if you go the 8-221 FB route... also, you will have next to NO shoulder on that case, so crimping will require a bit more finesse as likely you will head space on the case mouth.

(BTW, there are a few different 338 subsonic rounds out and folks who have compared .308 and .338 performance have noted the significant difference in terminal performance on game animals when using these types of rounds, that 10% extra diameter and 25% extra mass (240 SMK v 300 SMK) DOES make a difference)

It might indeed be easier to make something like the 8mm HRT, which is the 6.8 SPC slightly shortened and opened up to take 8mm bullets. We did one for a customer who had an 8mm MG barrel (a beauty, we really did not want to use it, but he insisted) and a boat load of 8mm bullets. It affords the use of factory bolts and magazines and should work well in your application. I looked but did not find any pictures that I had saved...

Hope this helps

Paul, lacking a set of calipers, I tried to reverse engineer the dimensions of your rimmed wildcat, and it appears have a base (not rim) diameter of .374" - have you tried making the rimless version from .223 or similar brass?
And that said, have you tried seating these in an AR magazine? Your dimensions suggest that the loaded length of your existing wildcat is 1.8" to 2.0" so they will fit in an AR magazine as shown in your drawings...

Paul, IIRC, the minimum chamber pressure needed to cycle the AR-15 action is about 19,700 PSI in a 223 Rem., this is also dependent
on gasport location and gas pressure/volume...I believe the pistol gas position needs the most chamber PSI and gas volume the rifle
gas system needs the least...all of which amount to dwell timing etc.

So in a nutshell the shorter gas system will need the most pressure/gas to cycle the action due to the extra gas lost due to the shorter
barrel and gas system and visa versa...Again, I going from memory here.

Feel free to email me to dicuss this further If you like...

Regards,
Dr69er

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Your analysis is pretty much on point.

One of the problems of the D.I. gas system is the fouling caused by unburnt powder and carbon build-up, so in order to keep this
to a minimum reloaders try fo find a clean burning powder suitable for their round and sometimes that means using a faster
burning powder. This is especially true for subsonic loads and loads for pistol position gas systems.

The buffer in the recoil system of the AR-15 is the primary link balancing the recoil timing and bolt velocity. So this Includes
three or four buffer lengths/ types like :Pistol buffer, Carbine with various weights, and Rifle etc. The buffer weights vary
from 3.4 oz. to 11.0 oz. The buffer springs come in two basic lengths 12-3/4" Rifle, 11-1/4" Carbine (AR-15) and 13-3/4"
for the AR-10/LR-308.

The recoil springs themselves don't vary much they come in two basic lengths and two tension levels: standard and heavy (x-tra power).

Regards,
Dr69er

The 'fog' clears... slowly.

Thanks,
Paul

I have the 8mm-30HRT Marty built. I would not go through the trouble of the 7.92x33 Kurz as the AR magazine is not particularly suited.

There is no doubt the AR platform can handle the relatively low pressure Kurz cartridge.

The 6.8 bolt is known for taking loads in the 70K pressure range w/o issues. So if you follow Marty's advice and use the 6.8 brass for your 8mm cartridge you won't have any issues with pressure.

With the concern being the ability of the Kurz to function the rifle with low pressures in an AR-15, I would have to believe that making an AR-10 function with its much heavier bolt carrier and buffer might approach impossible.

Point taken.

Paul

The gas tube will not get fouled too bad, all that unburned powder will wind up in your reciever area. Part of the AR-15 way of doing things. I've never seen a clogged gas tube, but I guess that doesn't mean it couldn't happen, if you are worried just keep a couple "higher" power loads around to blow out the tube at the end of the shooting session. I know people that do that with their cast loads to prevent any lead fouling in the tube, but as one man put it, "Losing a $10 gas tube doesn't outweigh the savings of cast bullets."


Daniel

Just some thought, having some subsonic rounds under my belt...

With the small cases and relatively large and heavy bullets, the pressure is not there to drive the operating system as much as being needed to get the bullet to the desired velocity. Your powder volume is limited, but you need gas volume to fill the bore and the gas system (and the bore tends to be much larger than typical). So you have a few factors fighting each other, and not all the .223 related aspects work the same with these "large for caliber" rounds. In the .338 Spectre, which is a 10mm Magnum case necked to .338, you have a 1.25" case with a 300 gr bullet sticking out. Case volume is all of 29 gr or so, but the 300 gr HPBT eats up a good chunk, leaving all of about 13 gr available. In this you have to fit a powder that will yield enough energy to get that 300 gr bullet down the barrel (and the longer 16" barrel will be more challenging) plus operate the rifle. Oh, and a clean burn... You end up with loads along the idea of 12 gr of Win296 that fill all the remaining area of the case and burn at close to 37,000 psi and with a pistol gas system offer just enough to get the job done. Even smaller cases (think 7.62x25 with a 200 gr HPBT) suffer even more and studies have shown that the longer barrels actually have LOWER velocities - the gas pressure is all used up, the bullet no longer get accelerated as friction force has exceeded what little pressure remains. And you can go too low - I have stuck a bullet more than once

Do you HAVE to operate at 35000 psi? No, think of it as your top end with the larger .47x rim. Keeping the pressure down, like you said, helps with the sound. You might even look at VV 3N39 which is developed specifically for subsonic 9mm to give the lowest temperature (=pressure) for suppression....

If you are going to the larger platform, you might wish to explore the 7mm BR based rounds... such as the .338-7BR and similar ones... these work well

Randall (AR15barrels) did a .357 MAX on the .223 case so you may be able to do your 8mm version, the only concern might be case wall taper (interior). I still think the rimless version of your .357Max wildcat will work in the AR15... wish I were stateside, I would ask for some dummy rounds just to see how they fit in the magazine...

Anything else, just ask, happy to help

Marty built me a carbine setup years ago for that 7.62X25 cartridge using much heavier bullets –– it uses the pistol length gas system. One cartridge example is pictured below.

Note the case size to the quarter or the .223 cartridge case. It uses a 168gr bullet and 9.3gr of AA#9 and is close to subsonic although I have not run this through a Chrony. I'm not saying that this is a way to go but just an example of a very small case being able to do subsonic work with heavy bullets. I would imagine the case capacity of the 7.92 Kurz or whatever similar cartridge case you decide on will have much more capacity than the little 7.62X25 Tokarev case. Another thing, you seem to be using gas checked lead bullets that seem to go down the bore a lot easier than copper jacketed bullets. I've shot 200gr Sierra spitzer bullets out of this carbine although I have the wrong twist rate and some would kinda keyhole. That 180gr gas checked lead spire point bullet you showed is really nice and should work really well in whatever cartridge case you decide on.

Thanks AR-Fan - I'm gaining confidence in the viability of this project on the AR-15 platform.

What kind of precision (accuracy) were you able to get from that rifle/cartridge combination?

Paul

Aaahhh yes the true beauty of the AR-15 platform...a wilcatters dream

That is the one big reason for using the AR platform it has the flexability and
more Importantly the accuracy potential with just about any wildcat you can
think of...

Just think about it from .17 caliber to .50 caliber and beond... All with MOA
accuracy in many cases.

How many platforms can do what the AR platform can...? Hardly any...Its the lego
of rifles...


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It is indeed. I have been tinkering with wildcats for a while and I am genuinely impressed with the extraordinary modularity of the AR platform. It is 'something'. I am really looking forward to learning how it works - gas operation, etc. - in 'real life'.

I tell those folks new to reloading, and maybe firearms in general, that there is no better way to learn the truth about reloading and firearms construction and operation that to "build" a wildcat. With this project, I am back in the 'learning mode'. While I wouldn't say I was jaded, the learning opportunities here seem considerable.

Paul

Patrick Sweeney shot this group at 100 yards, using 125 gr bullets and a 10.5" barrel, in the snow....

My best accuracy was with the Barnes 110gr TTSX bullet –– almost one hole groups. The Barnes bullet is extra long since it's solid copper, not a lead filled jacket. Now I was driving these supersonic –– at 1955fps –– I have not tried them at slower subsonic speeds because I figures there wasn't that much energy in a 110gr bullet at say 1000fps. I actually got even better accuracy with 150gr spire point boat tail bullets but I haven't shot those in a long time. The 168gr bullet shoots just as well as the 110gr bullet only its moving in the subsonic range and has a real rainbow trajectory. The picture below is the cartridges with the 110gr Barnes bullets and next to them is the 168gr bullet I've used.


In the picture that Marty just showed of the carbine using 125gr bullets notice that they were shot using a red dot –– darn good shooting.

This was just a test to see how much room was vailable in a cartridge case similar to the 7.92 Kurz case with a larger bullet inserted and adjusted to an overall length of 2.26" for use in an AR magazine. I just happened to have cartridge cases that are almost the same length (1.33") as the 7.92 Kurz case (1.30") so I opened the neck and installed some 168gr bullets and set the COL to 2.26" and put them in a GI magazine. They are pictured below.


Now this cartridge is based on the .223 case so if you decided to go with something like the 6.8 spc cartridge you would have much more capacity. There are magazines designed to handle the 6.8 spc cartridge. Now if you decided to go with the full 2.26" length you will have a pretty good amount of room in the case for powder. I set a 168gr bullet next to the cartridge case to give an example of just how far it actually seats into this test cartridge case. I can't sure but I would imagine that your 180gr 8mm bullets are probably about the same length as that 168gr 30 caliber bullet. A 200 grain bullet would work just as well with just a bit more reduced capacity.


I don't know if this is any help at all –– just figured it might give you something more to think about.

I don't know how I possibly missed your second post above AR-fan. That's a great help!

The .223-based cartridge - 8x.223 - is a great idea, but I don't need more case capacity for sub-sonic use. That said, it seem clear that at least as far as filling the magazine goes, the Kurz case seems OK. If those are 7.62x39 cases, the issue remains one of the head diameters. For the x39 cases I have in hand the head is 0.446" while the Kurz case head is 0.468". I wonder if that extra 0.022" (0.044" for two side-by-side cartridges) will make a difference in the magazine or with feeding. I don't think so, but...

Thanks,
Paul

Trust me, it will. I would consider doing an 8mm Grendel as the largest case, or 8mm HRT. Since you have the ability to form your rimmed version (in your pictures) and it shares base diameter with .223 case, I would highly recommend getting some .223 cases and trying to make the rimless version - you must have the reamer for that version already as well, and it will be easy enough to make a barrel (or even just a stub with a chamber) to test feeding. If that does not work, make the 6.8 based version, not necessarily for the extra case capacity but for slightly different case geometry to make feeding easier. You can then rechamber that test barrel/stub to test feeding - easier and cheaper than that is hard to come by.

Like Marty said, there are a lot of cartridge possibilities for you. I wanted to show that there would be powder capacity but, not actually having it built for a great big 8mm bullet, I was not sure how much capacity you needed. I don't know how it is were you live but down here .223 brass availability is limited only by how much you can pick up. The .223 brass is pretty straight sided so that helps in working with standard AR magazines and helps to cut down on the thrust on the bolt face when fired. I get the impression you have a nice little shop to make your own stuff in –– you're a a lucky guy –– hope you have some fun with this project.

edit to add; Note the ribs near the middle and rear of the magazine. If by chance you try to stay close to the original 7.92 Kurz design the Kurz shoulder at 0.966" will work with those ribs –– my case shoulder was a little further forward.

I think that an 8mm Tok might be a better choice that an 8mm-.223 variant because of the extra .015" of case diameter that might help "build" a shoulder for headspace. I have seen some very nice wildcats that headspace on the case mouth....but just don't trust them myself (probably due to some slight ignorance). IMHO the 6.8spc case shortened to 33mm and necked to 8mm would be pretty sweet.......however that would be virtually the same as necking down the .338spectre to 8mm. Those of you more knowledgeable than I please chime in....but a couple more grains of powder by going to the 6.8spc case over the .223 would offer more powder options to get the pressure curve where you want it for reliable sub-sonic semi-auto operation.

I am also and 8mm aficionado.....I just bought a bunch of 8x60s brass because it was on sale and am now building a rifle to take advantage of my available brass.....and have been thinking of a way to justify an 8mm/376steyr wildcat build.

advntrjnky

Gee... I've never done anything like that... And if you believe that, I've got some swampland I'm trying to sell.

One of the nice aspects of the 8x376 Steyr is that the relatively short case - 61mm - fits just fine in a milsurp Mauser action. One NOT so nice aspect is that Steyr 'started from scratch' when they designed the .376 case. Therefore is has dimensions - particularly the slightly rebated rim at nominal 0.496" and head at nominal 0.500" - that are larger than the standard 0.473" .308 head and smaller than the standard 0.535" "magnum" head. Therefore, if you want to build a rifle using the Steyr case, you'll have to open up a standard 0.473 bolt face. Not too big a deal, but there are a couple of reasonable - to me - alternatives that sidestep that issue.

The first one I would choose is the relatively new .375 Ruger case. Steyr came out with their case a year or two before Ruger came out with theirs, or I would have started with the "RCM" case myself. It has the standard "magnum" head of 0.535 but without the belt. While I like the Steyr case A LOT, cost, availability and compatibility set it worlds apart from the RCM case. Just as folks are recommending that I 'move off" of the Kurz case, I would recommend that you give consideration to using the Ruger case for your "big" 8mm wildcat.

The second good choice - in my opinion - is the .338 Win Mag case. Remember that the 7mm Rem Mag - an excellent cartridge in both "real" performance AND commercial "performance" - is just the .338 Win Mag necked down to 7mm. In my opinion, Remington just took the necking down a mm too far. Another little-known and widely denied FACT is that the .338 Mag shoots flatter than the 7mm version. Therefore, guess what: The 8x338WM also shoots flatter than the 7mm factory cartridge, and hits "harder" too.The Win Mag case is an outstanding case for wildcats - if you don't mind belted magnums. Personally, among belted cases I prefer it over the .300 Win Mag case because it is more compact. Furthermore, if one wants "more" magnum than the .338 Win Mag, one might as well go to the 8mm Rem Mag case. As most of you probably know, the 8mm RM case is the parent for all of the Shooting Times Western wildcats turned "factory" chamberings. The 8mm Rem Mag is an excellent cartridge that has been marginalized because of the silly refusal of American hunters to accept ANY 8mm cartridge. Don't get me started on that.

All of that said, use what ya wanna. That's one of the benefits of having the wealth of choices we have here in The States. As for me, when I can, I try not to make choices... I just make all of them.

I am considering ALL of the options you all have suggested. However, nowadays, I don't NEED any more rifles. The firearms I make now are purely to scratch some 'itch'. The Kurz case on the AR platform is still "itching" a bit.

Thanks,
Paul

Because I said I'd keep this thread alive as long as I was working on it, the AR-15/AR-10 Kit from Tactical Machining went in the mail to me on the 15th. I'm expecting it next Tuesday. Still haven't settled on a chambering for sure, but I do have a 16", 8mm barrel threaded (on both ends), and ordered a DPMS barrel extension from Midway today. (I don't have any .223 barrels on hand.) I also found (on Midway) an adjustable gas TUBE. They're mighty proud of it at something over $40, BUT, I like the idea of an adjustable gas tube even more than the adjustable gas block. I'm going to see if it is reasonable to modify my own gas tube for adjust-ability.

Paul

If you are going to replace the handguards, I would go with a Samson Evolution model. You won't have to remove the barrel on the 5.56 upper, just remove the plastic handguards and dremel off the delta ring and spring. You will probably need to remove the gas block and handguard cap as well, but I'm not certain. The Samson's mount directly to the standard barrel nut and only have an integral rail on the top. There are mounting/vent holes where you can add rail section if you need them, but as it leaves the factory it is smooth, light weight, fairly narrow and easy to grip.

Paul, it would of been easier to mill-out the FCP/THC first and then proceed to the drilling operations.
The TM forgings are 7075 aluminum and are fairly tough to drill through when you are dealing with
almost a Inch of material...

Anyway, good luck with your project.

I'm surprised to hear you say that Dr69er as I read your comments on the TM forum, and I thought you were in agreement with "Nathan" on the "drill first" philosophy. Apparently not, I guess.

It was tedious drilling first, no doubt, and I would have thought milling first WAS the way to go, but I was just following TM's advice/suggestion/instruction.

Thanks,
Paul

nice updates! keep us posted.

advntrjnky

You are correct in that both myself and Nathan were In agreement, however, the smaller diameter 5/16 drill bits do tend to "walk" so we should amend that to
mill the FCP first for ease of drilling,since the material is hardend 7075 aluminum with nearly .900" material to cut through.

It should be noted that it is correct to "peck" drill till you go through the material your drilling.

The other note is that the TM jigs do not have drill guides both sides, only one side (I had thought they had them on both sides originally).
If there were hardend drill guides on both sides I would have reccomended drilling the holes to .150" deep on both sides and then milling
out the FCP.

In the end it shouldn't be a big difference, but you diffinately want the most accurate drilled holes for the hammer & trigger pin holes, if they
are not within spec. then you run the risk of the lower not firing properly when assembled, or a unsafe condition of firing out of battery
or even multiburst (bouble firing) etc.

I doubt if this will happen in your case though, just something to be aware of once you assemble your lower, always use a dryfire device and
test that the safety and disconnector work properly before firing your rifle.


Thanks.

Oooccchhh ! Ah man that hurts when everything else comes out fine, then something like tha thappens and kills the job. I will address this on the website site tommorrow nite...laying-
out your work first using some prussian blue (layout fluid),line scriber,calipers and maybe a steel compass is all you need to do a proper job for your layout work and then start cutting.

I think the jig should be mainly used to drill your holes...the other parts of the jig should be mainly used to help you orient the outlines of the FCP and Rear Takedown Shelf etc.

I think it still is usable Paul, but it going to depend how far off it is from spec...last resort would be to center the slot and the put in a trigger module.

I think the jig should be mainly used to drill your holes...the other parts of the jig should be mainly used to help you orient the outlines of the FCP and Rear Takedown Shelf etc.
Couldn't agree more.

"last resort would be to center the slot and the put in a trigger module."

Not following that. "Trigger Module"?

My intent is to work it "square" with 8th inch radius corners. It would then be "large", but I don't think too large. When I get the lower parts kit in hand I'll be able to tell "what's what".

Paul

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