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[ARCHIVED THREAD] - 6.8mm SPC FAQ & Load Data Part III (Page 3 of 20)
I hate the cardboard boxes and stryo trays. Hinged plastic boxes are the way to go. Unfortunately, none of the frankford arsenal boxes are a good fit. You are going to want to get the MTM boxes designed for 22-250 / 250 Savage / 35 remington. Midway Link to the ones I am talking about... |
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Range Report Ok yesterday I loaded up my XJ and headed to the range. I had some 5.56 ARs to zero, and I really wanted to get my new Leupy Mk4 PR 3x9x40 (mil-dot) zeroed on my 6.8. I ended up shooting 100 rounds, 80 of SSA 115gr TMJ (the older stuff at 'combat' pressure) and 20 rounds of Remington 115gr OTM. I also managed to bring along my Chrony this time! Ok the Good: *The scope is nice! I got a great deal from Mike at CS Gunworks and I'm so glad I followed his advice and got this model - it works really well when you have good ammo and a good barrel to take advantage of the clarity, the magnification, and the target knobs. At 9x I can clearly see the .277" bullet holes at 100y. *Despite some popped primers - the SSA 115gr shoots very well. The Bad: *The Remington ammo would not hold a decent group compared to the SSA, otherwise it functioned fine. *I started getting popped primers with the SSA, one locked up the rifle. I've shot 200+ rounds of this lot and never noticed it before. Of course I wasn't interested in keeping the brass before, now I was inspecting the brass and noticed 3 (out of 80) with missing primers, and 2 others that had primers pushed halfway out. It also could be that I didn't clear out all the lube from my chamber after cleaning it earlier (just before shooting). The 2nd round in my 4th Chrony string felt/sounded different (MV was 2652.01 FPS @ 10'). I check the bolt and found it had some out by 1/4" or so. It did not respond to the charging handle or forward assist. Removing the magazine I found the bullets of the top 2 round sprayed with lube that had turned black from firing residue. I removed the scope, collapsed the M93B then cleared the weapon by banging on a bench while pulling on the charging handle. Rifle cleared immediately. I checked the case - not only was the primer missing, but it looks like brass from the case has flowed out from around the primer pocket (this was the only case that had this sign). I crushed the case neck, but kept the brass for photos. One thing I did notice about my brass was a circular mark on the back of all the cases - like the ejector was striking the case hard? Kinda strange, but it seems only a cosmetic issue. One of my PRI military floor plate magazines (#1) still has an occasional feed issue with the TMJ ammo. The Ugly: The Armalite scope mount I used ended up having issues.  Groups kept shifting to the right as the knobs would loosen. Then when I removed the optic (so I could clear the stuck brass) I found the mount did not come close to returning to zero (rounds were impacting 4"+ to the left @100y) There are other issues with the mount as well, all I can say is I'm saving up my pennies and getting a LaRue SPR mount at the first opportunity. I burned something like $68 in ammo and the rifle is now longer zeroed .The Data: (In order that they were fired - I shot some 30 rounds in zeroing/testing prior to starting with the chrony) Wx: 80degF, 40% humidity, 30.02, approx 800' ASL Rifle: 16" Match Stainless (barrel by AR15barrels.com), approx .80" diam, mid-length gas, Free Floated with a Troy MFR, YHM .308 Phantom Flash Suppressor, Armalite two stage match trigger, approx 290 round fired in it's life prior to the start of string 1. String 1 (10 rounds of SSA 115gr TMJ): 2668, 2590, 2656, 2659, 2617, 2655, 2640, 2619, 2613, 2626 Min: 2590, Max: 2668, Avg: 2634 SD: 25.13 String 2 (10 rounds of Remington 115gr OTM): 2550, 2576, 2503, 2481, 2525, 2497, 2554, 2496, 2531, 2570 Min: 2481, Max: 2576, Avg: 2528 SD: 33.43 String 3 (10 rounds of SSA 115gr TMJ): 2638, 2568, 2609, 2548, 2611, 2574, 2579, 2564, 2584, 2527 Min: 2527, Max: 2638, Avg: 2580 SD: 32.10 String 4 consisted of 2 rounds of SSA, the 2nd one locked up the rifle as noted above 2643, 2652 String 5 (10 rounds of SSA 115gr TMJ): 2637, 2580, 2661, 2572, 2616, 2616, 2582, 2601, 2557, 2673 Min: 2557, Max: 2673, Avg: 2610 SD: 38.10 Observations: I wish I kept my 100y zero target. I tossed it as there were several group on as I dialed in closer to the center. Once the scope was dialed in I had a nice 5-6 round group going on in the center (sub 1") then the magazine ran dry, I ran a magazine on the steel targets that dot the hillside (I couldn't miss with the scope dialed in so well) I then stopped to put up fresh targets. All shooting at paper was from a solid (cemented concrete block) bench using sandbags), when shooting at the steel I didn't use sandbags. When I started up again I ran 10 rounds of Remington. One thing I noticed with the Remington OTM; the first round of each magazine would shoot approx 4" to the left of what I was aiming at, while the next round would be where I had aimed. This behavior was repeated for both targets. Final group for the first attempt was in the 4" range (if you tossed that first round - other wise it was 5.9"). The Remington never clustered well in any event. Definitely NOT match/precision ammo. The second target (the one I did while shooting through the Chrony) had the rounds drifted to the right (thank you Armalite). With the initial 'flier' the group was 6.2", without it it still gave a pathetic 4.2". When I shot the SSA the group started out great (first round was literally dead center of the target, with the next 4 grouped 0.9"), then the group shifted right opening up my 10 shot group to 2.7". It looked more like a two 5 shot groups, a 0.9" and a 1.9" group to the right. When I started on string 4 both rounds impacted 0.9" from each other - shifted right. After this I noted the barrel was hot (I ran them through the chrony a bit quick). I shot a group using the irons (as the scope was removed). The group was large (6") but typical of what I'll normally shoot with irons. After reattaching the scope I had shot 8 rounds at the steel targets on the hill and couldn't figure out why I wasn't hearing any 'dings', so I put a couple on paper to test point-of-aim vs. point-of-impact; the group centered around a position 4" to the left and the rounds were spaced 2.1" apart. Time to call it quits with the 6.8 and practice with my M4. *photos will be posted as time allows* |
This is NOT a cosmetic issue. This is a symptom of the brass NOT being hard enough for the pressure at which the loads are being run. What's happening is that the brass is flowing back into the ejector recess in the bolt. Then, during unlocking, the bolt "wipes" the "flowed brass" as it rotates on the case head. The case is still expanded in the chamber at this point, so it does not rotate with the bolt. Lots more fun on my how it works thread. |
Those cases are 65 miles away, in my reloading shop, but I will try to remember to look at them this weekend. Maybe you could give me a call friday evening as a reminder? |
| Randall is correct. I have some '04 manufacture brass and that brass is soft thru and thru. Another thing I noticed with it was that the Datum point for the headspace of the cartridge varied by as much as .005". I found this out due to variations I was having in my handloads with this brass. I took three virgin cases to work and checked them out on the digital optical comparator we have there. |
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Wow, interesting thread here. I haven't read it in awhile. The 6,8mm has come along way. I have been using mine for the last 3 years to good effect. But last year was the best, here in Europe a few friends and I have been working with them. we managed to do some good killing with them on deer and wildboar. A friend of mine killed around 8 boar with his last year and 3 deer, my tally has been signifcantly less but now with deer hunting season open here I will be taking it out a bit more. I like the way it kills when I do my part right. We had two ARs built originally in 6,8mm with Model 1 sales; one 16" chrome-lined and mine in 20" chrome-moly. both rifles have worked flawlessly in sub-zero temps which is quite nice. the 16" gun w/a Rock River trigger floats accuracy wise at a little lesss than 1" at 100M (109yds) while the 20"gun w/ McCormick trigger floats around 1/2" moa at the same distance. We load on the middle of the road side (for big game) but just enough to make German law for muzzle energy with the heavier bullets (130s). I wish someone would make a 120gn bullet that was magazine capable for the 6,8-because the 130s are nice but they start to drop like a rock pretty quick. We have taken them up in velocity here but it is not worth it IMHO. Another friend has purchased an very expensive 20" "Custom Made Barrel" that might as well be a boat anchor, for it's reliability is terrible and it's accuracy is no better than my model 1 20". He has sent it back to it's maker and hopefully it will work now because for what he paid for it I could probably have built him 2ea 20" uppers from Model 1. Which gets me to the crux of the 6,8 dimensional tolerances problem. It seems to me it was such a race for people to get these guns on the market that not all did their homework all that well. Because Remington took almost 4 years to get the 6,8 ammo and specs out there and there were a few dimensional changes along the way that some people never fully caught up with. I had a 6,8 upper built in early 2002 but no ammo for quite awhile, but my old upper feeds everything I put through it nowadays but the guy who built it for me is the best of them all also in my opinion (not to mention he is the main designer of the 6,8). My only complaint about my Model 1 is that it is threaded to the M16 thread pattern not the correct one for the 6,8mm. Why you ask is it bigger? Because when we were in the planning phase of the 6,8mm it was decided that it would not be wise to have the same thread as the 5,56mm one. Because some hapless private in a DS unit would not have "Gotten the Memo" and put on a standard M16 one which would make for an interesting show. |
| Silentbushmaster be sure to keep us updated on the barrel. I have often wondered about the twist in those barrels. I can't understand why they would go with a 1:11 twist. I personally see no reason to go slower than 1:10. Slower twist would negate any possibility of using heavier bullets in my opinion. |
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I'm brand new to the 6.8 and I have to ask a question. Is it a good idea to purchase one of these uppers considering the fact that the ammunition is not really sorted out just yet? I ask b/c I'm looking at buying a Leitner-Wise gas piston 6.8 upper on Wednesday, but after reading this thread, I'm concerned that I could easily encounter ammo issues that could destroy the rifle..... I'm interested in 6.8 b/c of its better terminal ballistics vs. 5.56, but I'm also going to spend 5 times the amount for ammunition compared to 5.56 and it doesn't sound like the reliability of the ammo is all that great either. Am I crazy for even considering a 6.8 at this point? Thanks for any opinions. Sean **ETA** I don't reload and don't have time to start.....that said, who would you guys recommend for a brand of ammo? Silver State seems to be highly regarded (as long as I don't get the 2800 fps "hot" loads talked about on page 2) and Remington seems to be pretty bad from what I've read here. Any other options? |
As long as you don't get a min. spec. chamber you should not have any problems. The only real issue seems to be with min. spec. chambers and the hot "combat" loads. Some have had a few issues at first but I think most of those issues cleared up as the gun broke in. If I am wrong someone will be along soon to correct me. Part of Remington's problem is that their brass is soft. I know because I have a bunch from '04 that is and apparently still is. Plus they have downloaded their ammo from original specs. For know SSA seems the way to go. I wouldn't worry about blowing up your gun. I don't know of it happening yet with what is available. |
If you don't reload, you still have options. You can even use one of the barrels that have a tight chamber, just stay away from the hot loads. I can tell you that the SSA 110 grain Pro Hunter is a nice factory load as is the Hornady. I can also tell you that if you use a tight chamber with combat loads that are out there, you will be pushing your luck, these loads are for special chambers. They will cause you serious problems. You can also learn to reload or bribe a fellow shooter to load for you. Good luck!
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river_rat I am very sure that the barrel that I have is out of spec or that 1x11 twist is just not for the 6.8 SPC. All the other loads work in my other 6.8 SPC uppers. The 1x11 twist may shoot a 90 grain bullets fine, but results posted for this barrel showed 110 grain bullet groups that were sub MOA. I feel that if a barrel for the 6.8 SPC will not shoot a 110 grain bullet well, it isn't a barrel for the 6.8 SPC. I am open to recommendations from the point of purchase, but have not had a reply from my e-mail or my call made today. I am open to trade the barrel out for another 1X11 twist, but I have not been able to discuss this with the person that I purchased it from. I did order a Noveske barrel and am looking forward to testing that barrel out. Have heard great things about Noveske, but the proof is in the paper. If anyone here has a Noveske 6.8 SPC barrel, feel free to give results, or anyone with first hand knowledge. I will keep you posted.
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No way!
Silver State is tops, the only load you might want to steer clear of is the XTream in it's 'combat loading' the standard load should be fine in any barrel. The other option is Hornady, their 110gr V-VAX is a top performer. |
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L-W usually uses ER Shaw for their bbls. I don't know if this is the case for the 6.8 or not. They use Remington ammo for all their testing (although I guess at some point they evaluated SSA, hence the comment below). Their chambers are built to SAAMI spec, but wasn't there a question about the spec being backwards on page 2 of this thread? Here's what Paul Leitner-Wise had to say about the issue of high pressure and tight chambers: All our 6.8's run standard SAAMI spec chambers. That gives a neck size of .308" and after chroming this is around .307". With any semi-auto, you want to have .006" to .007" of clearance at the neck to allow obturation of the cartridge and reliable feed and extraction so ideally, the neck on the 6.8 should be .300" or less. Remington and Hornady are both in the .299" range and we have experienced no problems with either. The early Silver State rounds had neck sizes as large as .3065", all of these rounds would regularly blow primers, fail to extract or show excessive pressure signs. Both Barrett and PRI adjusted their chambers to suit but we maintain the SAAMI spec required for government use. We advised Silver State of our findings and understand that the are improving their QA to reflect the desired neck size on their latest production runs. Provided neck sizes do not exceed .302", you will not have problems. Based on this response, I'm going to go ahead and order.....any objections? If L-W is trying to sell the 6.8 to the govt. wouldn't their chamber have to be able to handle the "combat" loads? Thanks for the input guys. Oh, and can anyone tell me how to access the Armory forum? Wehn I click the "armory" button at the top, it takes me to a different page, but not the forum. Right now, I'm getting to it by using "my topics" b/c I started a post there. Thanks, Sean |
Hit the ARMS&TACTICS Button...Hope this helps... |
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Sean, all this talk of 'combat loads' is so much hogwash IMHO. A chamber is either SAAMI spec or it isn't, period. Ammo should conform with the same spec. The military isn't interested in anything other than SAAMI spec. ammo & chambers, bean counters HATE non-standard anything. I've seen, fired & inspected over 4,000 rnds of Rem 6.8 ammo thus far & I expect to shoot a lot more in the nexr few months. I have seen no evidence of soft brass or high pressures with Remington. I have not had the opportunity to test for pure accuracy as yet but I will willingly defer to those here who have & have reported their results. I expect great things from SSA in the near future but must add the caveat that thus far, QC & case dimensions have not been up to snuff, at least in my & LWRC experience. As the round gets more exposure, more popular & more ammo makers come on board, I would expect to see quality & accuracy improve & prices to come down across the board. Nature of the beast; anyone remember the teething problems the SS Magnums had when they came out a few years back? The 6.8 is a bit more difficult due to the case volumes, slightly tight specs on the cases & the fact of trying to run it in an AR 15 sized envelope rather than a bolt gun. Give it time, I can practically guarantee that until the military changes procurement procedures, we won't see 6.8 on widespread issue for a good few years, anyone remember the .276??? Goodwill to all here. |
The 'combat load' moniker refers to the chamber pressure not the chamber dimensions. Similar to how 5.56mm NATO is loaded slightly hotter than commercially available 5.56mm. Another example is the Black Hills Mk262 is loaded hotter than their commercially available 77 gr BTHP Match ammo. Stephen |
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I picked up a Leitner-Wise 6.8mm SPC 10.5" Piston Upper last week and so far it has digested everything I have put through including factory Remington MC, Silver State Matchking's, Hornady BTHP & BT, and my super heavy 150 gr Nosler BT handloads (moving at around 2300 fps and super accurate at 100 meters). No malfunctions of any kind through more than 500 varying cartridges and a hell of a lot of fun to shoot. It's also a pleasure to clean:D Stephen |
 Any reason you went with the 10.5" over the 10.3"? I think I'm getting the 10.3....mostly b/c that's what they have in stock. Sean |
It's probably 10.3" then. Like you I went with what they had in stock. You're going to love it! Nicest upper I have ever handled. Stephen |
George, That seemed to be the case earlier but IIRC, Paul and Darren worked with Art from SSA to rectify the discrepencies. Art from SSA:
www.ar15.com/forums/manageReply.html?a=quote&b=3&f=16&t=286986&r=2529824&page=1 I'd like to believe that will be a sufficient fix. By the way, Art says that they loaded a 110 gr. projectile to 2,815 FPS from a 16" barrel.
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haven't been on Zak's page for a while now but if it is the early pics I am sure that they are PRI mags. That's all that was available then. |
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Randall, check your 6.8 reamer drawing, at the 45 degree angle at the .2781 lead, is it 1.70185? I have received several drawings from different gun manufactures that have that same dimension. But from another gun manufacture I have 1.7109 which I believe is the correct dimension. If the 1.70185 is being used that means the 45 degree angle can not exist and you will end up with a sharp corner at the lead into the chamber. The X-Treme combat loads needs this angle otherwise pressure will peak. I have a 5 inch thick file on testing on the 6.8 and have to come to the following: 1. Neck size does not have anything to do with increasing pressure and I have the computerize test result to prove it. 2. Cartridges has to be made to the low end of the spec with regards to dimensions. 3. Recently found errors in chamber reamer drawings developed a sharp corner leading into the chamber, which is effecting the X-Treme combat loads. In the June issue of SWAT the Combat X-Treme had excellent results out prefoming all others rounds. You can blame the X-treme all you want but it works in some guns and not in others, so you decide, is it the ammo or the weapon? We however made adjustments to the X-treme to work in weapons with chamber issues. 3,. If your weapon can not shoot projectiles at 2,650 FPS than you have a weapons problem. 4. Some guns have very bad timing problems, where the bolt is trying to open while still under high pressure. Cases ejecting from the 1 to 3 o'clock position. The hotter the load the bigger the problem becomes. 5. If the case are blowing primers and expanding above .424 (being max chamber SAAMI) this is direct result of the bolt opening early. Our triple Shock thru a Barrett and CMMG is getting 2,715 FPS, can your gun handle it? The Military has tested the X-Treme at velocities of 2,625 FPS and had no problems. But again who's weapon did they test it in. We have made changes to the X-Treme so it will work with all weapons, mainly down loading it. We are try to offer a good round at a reasonable price unless everyone wants to shoot just the expensive stuff. If I was a gun manufacture I would be asking myself if a round is working in someone else gun why is it not working in mine? Or the quick answer is Blame the AMMO. Art - SSA |
My cases ran from 3:00-4:00
Art, when you say .424 is that the diameter of the base? If I were to measure my spent brass would this still be detectable? If it's just a timing issue I can always use a heavier buffer (right now I'm using a standard AR-15 carbine buffer). |
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Anything you can do to slow the timing down is good. Superior Shooting has a great flat spring that I highly recommand, they also sell a carbide weight that goes into the carrier. Competitive shooters do all this and more as a rule. They will also relocate the gas port as far down the barrel as they can, than they can open the port to get volume to release the bolt. Think about it, release the bolt at a lower pressure means less recoil equals faster target acquisition less pounding on your weapon, all good things. As I mentioned before, your case should eject behind you at the 4 o'clock position, now you have a well timed weapon. If it opens too early and the case is under pressure you can tear your extractor over time. Some people think that their extractor is going bad because it will not extractor a case from the chamber when in actuality the case is still being held by pressure and the extractor is over riding the rim of the case. Then you will have them complaining about the pull marks on the rim of the caee and blame the ammo. All this is less noticable with down loaded rounds. .424 is SAAMI max chamber, measure just above the chamfer of the extractor groove on the body. Spent cases will grow to around .419 - .420 max, this will be your hot loads. If it is over .424 the case is un-supported at high pressures and can cause damage to you or your weapon. With a 10.5 inch barrel I would think you be would around 2,475 - 2,500 FPS. But watch out if the gas port has not been adjusted (smaller). I am sure you will have one nice flame thrower and the recoil will be up there. If you reload the ideal thing to do is go to a faster burning powder, start with a light charge and work your way up then you can get the most from a short weapon. Your target re-acquisition will greatly improve and you will not burn anybody from the muzzel blast. Art - SSA |
So would a Enidine buffer be a good idea? It won't happen for a while since I'm blowing a wad on the rifle, SBR stamp, and 6.8 mags....but IYO, would it be a benefit? I'm going to trust L-W knows how to set up their gas piston in terms of the gas port size. I'd be interested in stephen's comments on this subject since he has exactly what I'm getting. Stephen, what are you running in terms of a flash supressor (if I may ask) and how's the recoil? Are you running a standard carbine buffer and spring or something esle? Oh and FYI Art this was in the L-W forum.....hope it helps. Quoted: The lastest revision of the 6.8 chamber was 2004. There was a previous one from remington and probably about 3 others floating around prior to SAAMI standardization. There has only ever been one SAAMI cert chamber. Sean |
My reamer drawing is published on the web here: 6.8 reamer specs It does show a length of 1.70185 at that junction. I looked into the dimensions you mention and I think you are right, they are transposed. I would have to go look at my reamer, but from memory, it has a 45 degree chamfer as part of the throat. I did a drawing for the benefit of those that might not understand the dimensions Art and I are talking about...  Don't worry about the angle dimensions, just subtract them from 180 and you get the angle convention that we are used to, so 45 degrees at the chamfer and 1.5 degrees at the throat. |
Nearly all our testing is with a 16 inch barrel and yes your 10.3 will not hit those velocities. You should lose 200 + FPS. Art - SSA |
As you know a 45 degree angle requires the length and height to be the same. If the 45 is maintained then something else has to change, and that can only be the 1.6964. Because you can not change the .308 or the .2781, at least you would not think so? Art - SSA |
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The man knows what he speaks about! Listen to him. Listen to me too, but read my How it works post first. |
I always listen to you two. Rifle has always had an M16 carrier for the extra weight; I'll throw in a H or H2 buffer as well. However, I don't think that's the entire issue. That might explain the primers, but if there is brass flowing into the ejector (as your writeup seems to diagnose) then wouldn't I still be dealing with a high pressure issue? |
Ok, new drawing. This one shows where the 1.6964 is at on the 0.307 neck and I drew in a proposed SHORTER (potential answer to ALL the chamber throat dim issues we have talked about) chamfer location if you were to anchor the 45 degree chamber at 1.70185 on the 0.2781 throat diameter instead of anchoring the 45 degree chamfer at 1.6964 on the 307 neck. 
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Brass flow into the extractor is purely a function of pressure and brass hardness. If the brass is too soft FOR THE PRESSURE, it will flow. Timing will accentuate the actual markings on the case though. If you wait longer to unlock the bolt, the pressure will subside more and the brass will not get wiped as strongly and the mark will not be as big/bright. |
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One more drawing and then I have to get back to real work... This one shows the case neck (yellow) and the bullet (blue) where they would be with the round chambered. Seeing this, I have to wonder if it really matters if that 45 degree chamfer moves 0.009" forward or back... In either case, there is ample safety room in front of the case mouth. My drawing shows the case trimmed to 1.675" which was just off the top of my head. If my trim length were wrong and the case trim length was more like 1.695, THEN we have a problem! 
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Art, I just measured 2 cases from each of these catagories: New brass, just resized and primed was .418 Fired brass (X-Treme) from that shooting session was .420 (with flattened primers and the marks mentioned earlier). Fired brass missing primers was .422-.423 (the needle was between the two) |
[ARCHIVED THREAD] - 6.8mm SPC FAQ & Load Data Part III (Page 3 of 20)
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