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Posted: 3/23/2018 1:12:51 PM EDT
....seems to work. Uppers side by side.
 First off the upper fits; 
albeit not as tight as other upper/lower sets I have: 
I also bought a BCG from Brownells advertised as for a DPMS .308. Here it is next to the ArmaLite one (black one); 
It fits as well; 
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These two pictures show the distance from breach face to front of barrel extension lugs. If you zoom in you can see that the 32s mark is dead nuts on for both.
I have assembled and hand functioned the MEGA upper on my AR-10A4 B lower and it functions fine. Bolt feeds round, extracts, ejects and holds open on empty magazine. I recognize that there is no shelf for the magazine to abut to so all stresses on the magazine are going to be on the hole for the magazine catch. I think that as long as one is aware of this and does not subject the magazine to much stress it should be OK. I'm going to use the ArmaLite BCG in this because that is the bolt that went with that barrel on my ArmaLite upper. |
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Earl, you and I have been talking about this some, and I gotta admit I'm seeing way more consistency on all of the components than I would have believed before. Some/many of the DPMS-style upper/lower efforts made with an Armalite that I've seen pics of here on the site have not been that great for the most part. Also there are often cases of the barrel extension, bolt, and other components not being compatible always. Your measurements on the critical components seem to suggest otherwise.
I'm certainly no expert, and I would like to see some observations and/or experience with this setup from guys like LRRP and others. On your barrel, you told me it was a Lija. If you still have the OEM Armalite barrel, did you measure those critical areas on it for comparison? And if I recall, your Lija barrel was basically a DPMS-style and not Armalite specific, correct? |
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Lilja. I may have misspelled it. That barrel was made for an ArmaLite AR-10A4 B, way, WAY back in the day. It was a custom work but I think at that time ArmaLite was pretty much the only .308 AR game in town, besides Knight. Either way it went into an ArmaLite upper and I used the same bolt and carrier that came with the rifle from ArmaLite. The original barrel was another custom that was a bull barrel 7mm X 08. ArmaLite sent the rifle, sans barrel to this place (I had one or two beers since then and now can't remember their name, Okeechobee, FLA I think) and they made the barrel for it and sent it to me (my ffl). Back then (as I recall, (remember those beers?)) it was understood that bolts, BCG barrels, etc. ....and those uppers that have the angled back were all compatible. ArmaLite used to sell stripped uppers for the Knights Armament 10.
I'll have to wait till Monday now before I touch a couple rounds off, unless the wife goes out someplace this week end. It came to me. Outfit was Gunsmoke Enterpirses. https://www.gunsmokeenterprises.net/ Not a recommendation by any means. I think they are a shell of what they use to be and I remember angst getting my rifle from them. |
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Your verniers are sure "very near." 
That should be 1.1870 -.0005, IIRC. |
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Well, I am some what handicapped. I only have two hands. It's a little hard to hold a barrel, a set of calipers, a camera and then take a picture up side down while standing on my head on the kitchen cupboards. I know, I know. I'm not asking for a parking spot at the front of the parking lot but life is difficult sometimes.... 
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IT RUNS!!!! FLAWLESSLY!!! ...with my ArmaLite BCG in the MEGA upper
With the new Ni Boron BCG from Brownell's ( DPMS Version) it had a little trouble getting all the way into battery. It would take a single round loaded in a magazine but when there were more ( I loaded five) it would stall on the first round. I'm going to chalk that up to this bolt carrier is pretty stiff compared to my ArmaLite that's been around the block a few times. I'm confident it will break in and work just fine. It would take one round, go into battery and hold open on the empty magazine. I think I need to single load and fire a dozen rounds to get it loosened up a little. Next up when my X-Caliber barrel gets here (made for a DPMS) we will see how that functions in an ArmaLite upper. Going to be another 10 weeks though. |
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Quoted:
I have DPMS-rifle Criterions in Armalite uppers -- one with an Armalite bolt, one with an LMT (both in Armalite carriers, both with AR-15 rifle gas tubes). They work great. You want to check the headspace, of course, but it can work. |
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I have not swapped other brand barrels into my B-model, only Armalite barrels. I thought there was a "bugaboo" with using other brand/style barrels because of barrel extension and bolt incompatibility...upper and lower fitment issues aside. I'm no expert, so what did I miss in reading those past reports?
I contacted Rainier about getting a 6.5CM barrel for one of my B-models, and they said I'd have to have an Armalite barrel extension installed by them or a gunsmith. This seemed to fit with everything I had surmised from various sources...but of course not from personal experience. Seeing Earl's effort here seems indicate otherwise? |
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Quoted:
I have not swapped other brand barrels into my B-model, only Armalite barrels. I thought there was a "bugaboo" with using other brand/style barrels because of barrel extension and bolt incompatibility...upper and lower fitment issues aside. I'm no expert, so what did I miss in reading those past reports? I contacted Rainier about getting a 6.5CM barrel for one of my B-models, and they said I'd have to have an Armalite barrel extension installed by them or a gunsmith. This seemed to fit with everything I had surmised from various sources...but of course not from personal experience. Seeing Earl's effort here seems indicate otherwise? All these companies HAVE to say this partly because of the Armalite patents and trademarks on the name more than anything else. They dont want other industries saying "works with AR10" because that gives the Armalite AR10 a bad name, when it has nothing to do with Armalite parts or rifles. Make sense? Armalite does this to protect their brand image, other industry partners say this so you cant bitch at them when you put it in an Armalite AR10 and it doesnt work. A bullshit loophole really. Many people have posted success when mixing and matching BCGs and barrels. The main idea is to use Armalite bolts and carriers, or a DPMS bolt and carrier. Very slight differences here, but tolerance stacking can be a major bitch. However, there are plenty of people who have gotten lucky. And it seems like, as long as you stick with reputable company's parts, youll be good. You cant expect these mass produced parts to work well. Put good shit in, get good performance out. You can make all these rifles run with mixed parts. Youll just have to try a few different recipes, make some modifications to parts, try different ones, before you can settle on a "working rifle". That takes alot of time and effort most people are not willing to put in. Im getting the Stag receivers direct from Stag. Who knows when. And Im going to try a Faxon gunner barrel, and the Lantac BCGs. Im going to mix and match with this stuff to see what happens. Ive accumulated tons of overtime past few months, and I think Ive convinced the wife to let me build a few more rifles. |
| From what I remember going back to 1998 when I bought my first AR-10 it was pretty much understood that the major items were interchangeable. ArmaLite used to sell Knights Stoner stripped uppers that they made. There wasn't but Eagle/ArmaLite and Stoner back then. After the assault weapons ban sunset more and moar got into the AR-10 style .308s. Still it was kind of always held that BCGs, barrels, and somewhat depending on what style AR-10 it was, even uppers and lowers. I haven't been actively engaged in buying stuff as I was pretty well content with what I had (three AR-10A4 Bs) until I just recently decided I need an IronWood Stock set on an 18 inch, rifle gas length upper. That's what started my whole search for an alternative to ArmaLite. That's also what started all the confusion as everyone says there stuff is all proprietary. It's not. ArmaLite doesn't make anything anymore for the AR-10. Their business model sucks. It's we will decide what you want and how long you are going to wait for it. I will never buy anything from them again now that I know other's stuff works. |
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I get that, its kinda crappy, but they can guarantee better quality that way. I still get spare Armalite parts. Few bolts mainly, operating springs, thats pretty much all you really need. i wouldnt put an extractor made by DPMS in my Armalite bolt. That sort of thing. ITs the small parts like that, that really make a difference. |
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I just noticed something I hadn't seen before on the Mega site. It states that...
"Bolts & Barrels--Designed to accept any AR style .308 barrels and bolts*. This means you can use your AR10/Noveske or SR25/DPMS components." The only incompatible part they specified was the Armalite bolt catch. So, this makes more sense to me why the Mega Maten upper had a better chance of function. Pretty neat. |
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Quoted:
.....Its a Cover Your Ass type thing. The barrel extensions themselves are dimensional identical...... Quoted:
Quoted:
I have not swapped other brand barrels into my B-model, only Armalite barrels. I thought there was a "bugaboo" with using other brand/style barrels because of barrel extension and bolt incompatibility...upper and lower fitment issues aside. I'm no expert, so what did I miss in reading those past reports? I contacted Rainier about getting a 6.5CM barrel for one of my B-models, and they said I'd have to have an Armalite barrel extension installed by them or a gunsmith. This seemed to fit with everything I had surmised from various sources...but of course not from personal experience. Seeing Earl's effort here seems indicate otherwise? Just a note. There may be other differences. |
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Quoted: I'm bringing this back up to the top because they are NOT dimensionally identical. If you look closely at the pictures where I'm posting the out side diameters with my calipers you can see obvious differences in the feed ramp area (DPMS type barrel are much larger.). Also while I did measure inside diameters between lugs and on the lugs with no surprises, I cannot measure lug width and side angel to any degree that would make the measurements worth anything. Just a note. There may be other differences. There's slight variation in all extensions because machines aren't perfect, and people inspecting are far from perfect. |
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Quoted: Please correct me if I'm wrong, I'm not a machinist. But wouldn't that difference still be in the nominal +- ranges? There's slight variation in all extensions because machines aren't perfect, and people inspecting are far from perfect. |
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Maybe a couple of thou but you can get tolerance creep if you don't watch out. A few thou too shallow on the bolt face, a few thou to long on the barrel extension lugs. A few thou on screwing the barrel extension on, a few thou too short on the reamer in the chamber an KABOOM!! Well, maybe not that drastic but "this ain't no disco, this ain't no foolin around". Always check at least with go/no go gauges.
Also if you really really closely at the picture where I'm measuring the outside diameter of the barrel extensions, you can see that the lugs do in fact appear to be of different dimensions between the two barrel extensions. The bolts are not (noticeable by me and my calipers) different. |
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Quoted:
Maybe a couple of thou but you can get tolerance creep if you don't watch out. A few thou too shallow on the bolt face, a few thou to long on the barrel extension lugs. A few thou on screwing the barrel extension on, a few thou too short on the reamer in the chamber an KABOOM!! Well, maybe not that drastic but "this ain't no disco, this ain't no foolin around". Always check at least with go/no go gauges. Also if you really really closely at the picture where I'm measuring the outside diameter of the barrel extensions, you can see that the lugs do in fact appear to be of different dimensions between the two barrel extensions. The bolts are not (noticeable by me and my calipers) different. My screen sucks, so I cannot see the differences in your pictures, but can in others. |
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