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[ARCHIVED THREAD] - First Experiences with 6.8 SPC (Page 1 of 2)
Posted: 3/20/2007 1:55:02 PM EDT
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Well, over the weekend I finally got to try the 6.8 barrel/bolt in my LMT MRP. Results were a bit shakey. I had two boxes of SSA 115gr., and two boxes of Hornady TAP 110 gr.(one box V-Max, one box BTHP). Magazines: 2 C-products 10 rounders (yes, California). I encountered four total malfunctions. All except one malfunction were FTFs where the round was pounded into the feedramps leaving deep impressions on the case shoulder area. This happened once for each type of ammo listed. Can't be 100%, but I belive it happened with both mags, should have been paying more attention. The fourth malfunction occured with the SSA 115 gr. The primer blew out of the back of the case and got trapped between the bolt carrier and barrel extension. The anvil from the primer was found inside the barrel extension. Couple of observations. First, those SSA rounds seem much hotter than the Hornady stuff. Secondly, the recoil from the SSA ammo is noticalby more than a 5.56. I'm a little curious as to how well a standard AR lower will hold up over the long haul given a steady diet of SSA 6.8. Obviously, from CA, replacing a pre-ban Colt lower is not in the cards. Anyhow, not bashing any manufacturer/product, just relaying my experiences. Also, before anyone else says it, I know this thread is worthless without pics! 
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| I had similar problems with my first 6.8 build.It was a mid-length 16"Noveske SS 6.8 poly 1/10,pinned on Noveske gasblock,and a VLTOR MUR.The problem was narrowed down to the CProducts mags.I bought several PRI 6.8 mags and it functioned fine.I got four replacement mags from CProducts.Since I've tried one and it worked fine.My 12"6.8 LMT MRP works great. |
Where did you buy the SSA ammo? I ask because there are early lots of hot-loaded SSA rounds lingering around the market. Art has tried to recall them because of potential problems like yours. Art hangs arour ARFCOM as "kalwasart", if you want to send him an IM. You can tell if they are the early rounds if they are large primer (current production is small primer.) |
The small rifle primer SSA ammo is not as hot as the original load was. I have about 300 rounds down the tube so far in mine. My lower has KNS pins in it, so I don't think I'll see any wear in it. |
I have a Model 1 sales 16" upper on a Colt lower, and I have fired around 500 rounds through it so far. I had the same trouble with the SSA X-treme bullet in the beginning, too. I had a few FTF's as well, and a few rounds that cupped primers, and nicked off the first .001 of case mouth, which I found in the chamber. I talked to Art, and he was nice enough to exchange some of the small primer rounds for the Barnes-X 110 grain loading. I have shot over 100 rounds of this load with no problems whatsoever. They are accurate in my gun, too. This problem occurred 1) because the rounds were hotter, considered to be "combat" loads, and 2) once chambered, the 115 gr extreme bullet is more closely engaging the throat in the barrel, causing a stacking problem, thus increasing pressure. Most barrels, unless they have the new "6.8 SPC 2" throat dimensions will still potentially show pressure signs with that particular SSA round firing the 115 Gr extreme. The bullet shape and blunt nose are peculiar to that one load. 3) faster rifling, like the 1 in 9.5" twist on my upper, are exacerbating the pressure problems with the 115 grain extreme bullet, and the 1 in 11" with 4 groove rifling seems to have alleviated most of that pressure stacking. I only use PRI mags in my 6.8, and (once exchanging these loads) have never had even one stoppage in the last 475 rounds, with any ammo, including handloads. I love the 6.8. These are things that get worked out in the development process. I adopted this caliber early on, and I can tell you this; these professionals are working on getting this load and AR platform to its optimum right now. New barrels are being made by every major manufacturer, which address these small details. I am now convinced that 1 in 11" twist is the way to go, once I build my "DMR" type rifle in 6.8 SPC. Soon (weeks) you will be able to buy barrels that shoot even the hottest, most potent, SSA loads, as well as all the others. I believe (and I am no expert) that you should be able to shoot any 6.8 cartridge, except the SSA 15 gr extreme, with your current barrel with no fear, and your lowers should hold up just like any 5.56. for expert opinions, refer to Tim Hicks from Ko-Tonics, Randall Rausch, Art from SSA or Noveske, MSTN, Denny's. These ARFCOM sponsors are much better equipped than I to answer these things. |
I have had three 6.8 builds from my original MSTN 6.8 1/2 MOA tack driver, ...my LMT 6.8,  ...and finally my Noveske 6.8 blaster!! A famous qoute from Wes at MSTN, "if you need anything more than this, call in a JDAM." This is my CQB to 500 yard holy grail!  I have run thousands of 6.8 rounds that consisted Remington 115gr OTM's, Remington 115gr Match, Hornady 110 V-max and my own personal hand loads of Remington brass, Hornady 110 V-Max bullets with 28.8gr of H322 that puts a half MOA through my MSTN build on all occasions. I have had ZERO malfunctions and ZERO maintainability issues with any of the above mentioned gear. These above systems and load outs have worked flawlessly for my mission needs thus far. Hope this helps. Edited to add: All my mags have been PRI manufactured. Also, do not know where the 3 part holy grail 6.8 ammo thread went to? Zak Smith started this thread and was at the forefront IMHO of commercial loading of the 6.8. This particular thread was really the holy grail of 6.8 hand loading!! It was a great place we all posted our load outs and chrono results. I think Zak still has his web site with valuable 6.8 data as well. Maybe he will chime in here as I think he's shot every 6.8 load out there! |
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Here is the current incarnation of the 6.8 SPC FAQ thread: www.ar15.com/forums/topic.html?b=3&f=121&t=282708 Primers blowing out is definitely a sign of high pressure. I am sure SSA has the commercial-level loadings sorted out by now, but you should call them with your lot numbers to make sure. It could be your chamber setup, or it could be the ammo. My original PRI/MSTN upper and the Barrett M468 upper I borrowed for the SGN article last year both digested the hottest ammo I could get (or load semi-safely) without issue. That you saw malfs using the Hornady ammo too points to something in your setup: the barrel/chamber, or the magazines. To eliminate variables, get a PRI magazine and test using it. I know the PRI mags are good. Elsewhere I have seen variable reports of C-Products mag consistency lately. |
Why? Do the dimensions on the Barret M468 upper differ from a standard upper? Justin |
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Hey Victor, how much weight does that ARMS SIR system add to your MSTN build? Is the rifle still under the 8 lb mark without the NVD's and PAQ-4? I am right now, designing my next 6.8 build, and I am very much interested in the monlithic type rail in order to mount all my optics goodies. |
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Basically, and without remembering all the specifics, the chambers in the original guns like the PRI barrels and Barrett guns had dimensions, especially the throat dimensions, such that some of the original loadings shooting a 110-115 @ 2600-2650 from a 16" bbl were possible. This was before the SAAMI spec was submitted. As other vendors started to produce 6.8 SPC barrels, there were chamber reamers of many different dimension sets. Some just with a shorter throat, some tighter in other areas. Ammo that was 100% OK in the original guns causes gross overpressure in many of these barrels. Ultimately, commercial ammo offerings were dialed back to run safely in the spectrum of barrels that are out there. |
OK, so the uppers are all identical, it's just the barrels that vary? And do any of the manufacturers offer 110-115 gr. loads capable of moving @ 2650-2700 FPS from a 16" barrel anymore, or are those days long gone? Basically, something closer to the originally reported 2650-2700 FPS as opposed to the 150-200 FPS slower loads available now? Justin |
Silver State Armory does. Their 110gr Barnes TSX loaded to 'combat' pressure should do the trick - the 'standard' load for that runs around 2630fps from my 16" barrel. Also the 'Combat' version of the Extreme TMJ will run around 2630fps. You can only get the 'combat' stuff directly from Silver State Armoy these days. |
Just a shy under 8lbs bare bones. I went with the bi-level type SIR to give the extra clearence for NV rifle scopes large objectives. I could not be happier with this platform for the likes of D-760's and Raptors! Hope this helps. Vic |
So they compromise the ammo instead? I mean, there's a fairly big difference between 2700 FPS and 2500 FPS, The SSA combat load is great, but I wish someone would do it with the Hornady 110 gr. V-MAX bullet. |
Yep. Can't have factory ammo blowing primers in a substantial fraction of the guns out there.
Dillon 650. 
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True, but they could at least offer a more potent load for those with properly spec'ed chambers, sort of like how Hornady has 5.56 NATO pressure TAP, and .223 pressure TAP.
LOL, there isn't enough square footage in my place for a reloading setup, unless I put it in the shower!  EDIT: spelling. |
Lee makes a slick little unit that is loads one round at a time and doesn't require a bench... Slow, but if you gotta have it. Anyway the 'downloading' is not unheard of. Hornady also offters 2 leverl of TAP, one in .223 which is available to everyone and another in 5.56 for those LEOs that certify their ARs can handle it. At least SSA will sell the 'hot' stuff to us non-LEOs. |
After having talked to a few mfgs and monitored posts on this issue for some time, my admittedly imperfect understanding is as such: OK FOR COMBAT LOADINGS: -PRI -Barrett M468 -Ko-tonics with 1:11 twist, 4-groove -ar15barrels.com custom barrel with modified SAAMI chamber, 1:11 twist -any other truly custom one-off barrel with modified SAAMI chamber, 1:11 twist UNKNOWN: -RRA (probably NOT OK) -Noveske NOT OK FOR COMBAT LOADINGS: -everything else (Stag, WOA, CMMG, Bushmaster, ER Shaw, Model 1, DPMS, etc) |
| Thanks for getting right to the heart of the matter Hawkeye. Vmpglenn, am I to assume that LMT falls under the "everything else/No go" catagory? Perhaps a phone call to LMT is in order. I can only speculate to the cost of having an LMT 5.56 barrel torn down, rebored, and chromed to modified SAMMI 6.8 spec by a custom manufacturer! Not cheap, if anyone would dare do it at all. I'm just a guy who likes his rifle to function with all reasonable spec'd ammo of appropriate caliber. Having to shoot watered down ammo kind of sucks. |
Thanks. So, Barrett's are on the good list....interesting. They are chrome lined too.... I've been looking for a good reason to send Ronnie some of my money.... |
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Yep, as I understand it the original Remington loads (very hot) were the only game in town when Ronnie was developing the M468. The Barrett has always had the longer than SAAMI spec chamber. and in fact the first M468s were already on the market before SAAMI sent out their controversial drawings. If anything will handle SSA's combat loadings, the M468 will. Someone please correct me if I'm wrong. |
We didn't care for the SIR, but the M468 upper RAN GREAT [ link to LARGER image ] |
I had similar results the last couple times I took my 6.8 MRP out. First time around was with handloads - they worked great out of one CP mag and the other kept hanging up everytime it fed from the right side of the mag. Last time out I used some SSA Extreme stuff - I got one blown primer and I think it was due to feeding out of the bad mag and getting bullet set-back. Basically the buffer spring was pounding the bolt into the round and making the round shorter which effectivly increases the pressure in the round. I'm thinking of getting a couple PRI mags to compare with as well. I shot my handloads on a friends M4 lower on full-auto and it was awesome... Now if I can just find an extra $10k to $12k to get my own lower... Spooky |
| Take a peek at the 2004 NDIA Small Arms Symposium Presentation on the 6.8 SPC (Power Point File) link on the first page of the 6.8 thread in AR Variants. The ballistic gelatin tests show the M468 firing a Hornady 115gr OTM at 2608fps. The Hornady 110gr V-Max factory loads are rated at 2550fps. The M468 would be able to handle these at close to 2700fps. You do the math... |
Precisely. So why can't they offer two levels of 6.8 110 gr. V-MAX? One load capable of 2700 FPS out of a 16" barrel, intended for the properly spec'ed chambers, and another loaded at around 2500 FPS, for the tighter chambered rifles? |
Why would you want to download the current (works in everything) round? Currently the 110gr VMAX clocks in at 2543 @10' from a 16" barrel. But yeah, it would be nice if they offered a 'combat' version for those rifles that can take it. |
I didn't intend to suggest downloading the current offering, rather I was referring to the loads Remington has been putting out as of late, which hover around that figure. Mea culpa.
Do you think they would be interested in doing so? |
Because that goes against the whole reason of "standardazation". Someone with a SAAMI spec chamber would shoot the high pressure ammo and complain about it when there are problems. You can't have two "specs" floating around where crossing the specs is potentially dangerous. Until the specs get fixed, you either load your own or live with what's available on the market. I'll second Zak's recommendation: Dillon 650. |
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Updated (confirmed with Noveske over the phone): OK FOR COMBAT LOADINGS: -PRI -Barrett M468 -Ko-tonics with 1:11 twist, 4-groove -ar15barrels.com custom barrel with modified SAAMI chamber, 1:11 twist -any other truly custom one-off barrel with modified SAAMI chamber, 1:11 twist UNKNOWN: -RRA (probably NOT OK) NOT OK FOR COMBAT LOADINGS: -everything else (Noveske, Stag, WOA, CMMG, Bushmaster, ER Shaw, Model 1, DPMS, etc) |
In my opinion, it's unfair to seperate the different makers in the method above. What you SHOULD be seperating them by is the ability to shoot the "Extreme Bullet Combat Load" as that's really the only one that requires the lengthened throat. The high pressures with other bullets do not seem to have problems in SAAMI spec chambers unless the bullets are seated long and jammed into the throat. |
Is it the shape of the bullet that makes the difference: flat tip = fatter ogive profile near the lands? SSA also sells a combat loading with the enhanced fragmentation OTM bullet - will this round shoot OK out of a SAAMI spec chamber? |
I won't turn this into a pissing match, but I will just leave it at this: I have a low opinion of the Extreme Bullet's ability to function at "combat load" pressures in a SAAMI spec chamber and it's my OPINION that this bullet has caused the whole partitioning of 6.8 ammo into two different power levels. Please read through previous posts about this topic for the long drawn-out discussions about that particular plated bullet jacket's in-ability to keep from obturating in the neck. You will even find pictures showing what happens... |
No dog in the fight - just trying to understand. I get it now. ETA: I'd be happy with 2600fps out of a 16" barrel. That's just a bit hotter than the Hornady V-Max factory loads. |
+1 I have shot the "combat pressure" SSA loading with the Barnes XXX in my Model 1 sales gun, and never saw pressure signs. This is probably due to the different ogive, and the cannelures which obviously reduce pressure. The ONLY bullet with which I have ever seen problems was the Extreme bullet. |
+1 I have shot the "combat pressure" SSA loading with the Barnes XXX in my Model 1 sales gun, and never saw pressure signs. This is probably due to the different ogive, and the cannelures which obviously reduce pressure. The ONLY bullet with which I have ever seen problems was the Extreme bullet. OOPS, sorry for the dupe....my bad 
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FWIW, I was shooting the SSA 115 gr. Sierra Matchking load when I experienced the aforementioned primer blowout. I specifically stayed away from the X-treme load due to bad feedback from other users. As a general rule I find it's best to stay away from anything marketed as "extreme".
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With what loads? This is all about "standards"... It's entirely possible (and likely) that the "combat" loads do NOT meet SAAMI pressure specs in SAAMI chambers and that they would then require the longer throat in order to keep pressures at bay. It's certainly possible to develop hotter loads when you know that they will only be used with an extended "weatherby" type throat. It's even possible to sell these on the open market as long as the users understand what they are buying. I certainly don't advocate using LOADS that exceed SAAMI pressures in a chamber that CAUSES the load to exceed SAAMI pressures. These same type of loads should be completely safe in Weatherby type throats. |
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Another route for ammunition mfg's would be to work with SAAMI and get a +P loading standardized. This has been done for the .257 Roberts, it's not unheard of. Then it would be for each barrel maker to certify their chamber for the appropriate pressure level. What I'm not getting though is, if initial development included the longer throat, why did SAAMI ultimately standardize on the shorter throat? Did Remington let their failed sporting rifle 6.8 chambering drive the SAAMI standard? Was it to ensure better accuracy? |
[ARCHIVED THREAD] - First Experiences with 6.8 SPC (Page 1 of 2)
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