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[ARCHIVED THREAD] - 6.8mm SPC FAQ & Load Data Part III (Page 4 of 20)
| Just measured 3 cases that were fired Sunday in mid - upper eighties w/high humidity. base diminsion runs .418-.419. Virgin cases (unsized) from the same 1k batch run .4175-.418. I have the same flow marks on many of my cases. It is Remington brass and I still say the brass is soft. The primers are fairly flattened but still have a radius around the edge. While they are loaded pretty warm they are not excessive. I have been reloading for 20 yrs and know how to read primers. |
Our cases are a good 10-15 points harder (micro Hardness scale - Vickers) than our competitors, If your chamber is correct and timing is good with the case hardness up there you can flatten the primer so it looks like it was hit with a hammer. You will see very little case expansion and your velocities will be up there. I can tell you that very few guns out of the box can preform this way only someone who knows there stuff can tune a gun to max your preformance. The case can take a lot more than a primer, under ideal conditions (case harden to the max) the max pressure a case can with stand is 63,000 PSI. You can push it more with match cartridges in a match grade chamber in bolt actions as the case is better support and has very little room for growth when fired. We have one 6.8 AR gun here that we can shot cartridges that have pressures at 61,000 PSI. The primers are flat is a pan cake but the case is fine. This weapon as been reworked and tune to max out preformance. Art -SSA |
This is very well written and every gun owner should read his leak. Art-SSA |
With the X-Treme Combat loads it does matter as our test show around 49,000 PSI the rear portion of the projectile expands slightly. If the 45 degree angle is true it forces it back down with little effort and pressures do not spike. The graph shows a nice rounded curve at max pressure. With the angle being sharper this expanded area of the projectile encounters increases resistence and drives up the pressure. Basicly two wrongs does not make a right.. We have made changes to the X-treme's design but also I believe the issue of the angle should also be addressed. Art - SSA |
I got it now. So it's the chamfer angle that's important, not so much the actual LOCATION of the angle as long as there is safe clearance at the end of the case neck. The bullet is obturating at the base at the same time it's engraving into the lands. The 45 degree chamfer just allows a proper re-sizing of the bullet shank and base as they continue into the throat and leade right? |
Correct, you can put into better words than I can that's why you are the high paid writer!!!! Art - SSA |
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I have been following the 6.8 threads for a couple years. I read every post I see, cause my next build will be a 6.8 . I would like to thank Zak, Art, and Randall for their invaluable information with out getting into a peeing contest between 6.8 vs 6.x. Thank you |
Zak has provided the base for all the reloading data that I use now. He has provided anyone information that has asked. If he doesn't know the answer to your question, then he will tell you he doesn't know the answer to your question. He is one of the people that provideds information from real experience, and not what has been read or has been repeated like a parrot.
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We are reworking a State Cops 6.8 that can not handle the Combat X-treme and the timing is off with all ammunition types, the cases are ejecting in front of the gun. We are reworking the port and re-chambering the barrel to start with. We have already ran all kinds of ammo thru it in its present form to establish a base line. We will make changes and check how each effects the preformance of the weapon and or ammunition. We will post our progress so others may benefit from our testing. Art - SSA |
First off I can make a cartridge to the high end of SAAMI dimensional spec's and you make your chamber to the low end of SAAMI spec and the bolt will not close. If you need a copy of SAAMI'S drawings I will send it to you. More people than I can count has checked our cartridge dimensionally and NO ONE has ever said we where out of spec. Send me one unfired cartridge that is out of spec and I will buy you a steak dinner, if you can not look at your weapon Second. The Military works to their own spec's not SAAMI. I have made Billions of rounds for the Military and we have nearly all their Mil-Std spec's on hand and I have never seen an attribute that mentions SAAMI. Third. We have found an error on a drawing for the 6.8 chamber reamer (as mentioned earlier in this thread) so you are right chambers are out of spec in some guns, maybe yours. That is why some guns can handle the hotter loads and others can not. We have to call the Hotter Loads something (Combat) No Hogwash just fact. Basicly we have to make ammo that works in all weapons, but it is not fair to others with quality weapons. Yes you can shoot Remington's, dimensions to the bottom of the spec with velocites at 2,500 FPS and accuracy anything but impressive. Not me saying it but three different Magazine articles this year alone the latest being June's Issue of SWAT. In that article the X-Treme, our least expensive round was nearly 100FPS faster and had 50% better accuracy than their OTM. Again is it the gun or the Ammo you decide? Art _ SSA |
Art, Sorry I didn't get back to this sooner. This was a self-built rifle. Timing seems good as all cases are dumped at about 4 o'clock at 4-5 ft. from port in a fairly regular pile. It will also function as low as 2200 fps. The barrel is a Model 1 Sales non-chrome bought in '04. It is not my most accurate rig but with my loads I get slightly sub-MOA to an 1.5" or so. I think worst group has been around 2.5" while working up loads. I have not done any real accuracy work-up of loads so don't know just what it can do. I haven't tried H322 yet either. As far as velocity top loads with RL 10X are as follows: 110 gr. Sierra sp - 2609 fps 110 gr. Hornady hp - 2636 fps 110 gr. Hornady V-max - 2658 fps. Any obvious discrepencies/opinions? |
I would still like to get a copy of the 6.8SPC SAAMI page. Photocopy and drop it in the mail would be fine. I'll PM you the address. |
Art, What has been the neck size of your brass?.......I've been told anything exceeding .3065" is going to cause pressure problems in a SAAMI spec chamber and that anything under .302" should be fine. Can I get your opinion on this? Thanks, Sean |
Sean SAAMI calls for a neck in the chamber of .3085 + .002, we did have cases in the neck at .306 (SAAMI case dim's are .306 -.008). We now and have been for a while running at .299 - .301. And no running your neck at .306 will not increase your pressures, We have run test and have computerized results that supports this. If you think about it how could it increase pressures, is it increasing resistence for the bullet - NO - is it keeping the bullet better aligned with the bore - YES. What the larger neck does for you is improve your accuracy. An example of this would be match grade cartridges with match grade chambers. They hold dimensions much closer for a tighter fit = better accuracy and then they can increase their pressures via the powder for more velocity to give you overall better preformance. We had to reduce the neck size because gun manufactures did not adjust their chambers for chroming. There are guns out there that have necks in their chambers down to .304. Think of your weapon is a mechanical devise and like a car if it is not tune properly things can and do go wrong. Art - SSA |
Randall I have sent a scan copy of SAAMI to you via email. Art - SSA |
Art, Thanks for the response. Honestly, I know next to nothing (probably less) about loading or ammunition which is why I honestly don't know if a tighter neck would build more pressure or not, but your reasoning makes sense. I appreciate your patience with my stupid questions. What it sounds like to me (and perhaps it's b/c I don't fully understand all of this) is that the SAAMI spec for the ammunition and the spec for the chambers don't exactly coincide like they should (not that they'd be exactly the same....you have to have some tolerance gap). Am I correct though in believing your ammunition with its current .299-.301" neck sizing will run okay in my L-W 6.8 SPC upper that should have a chamber with chroming of .307? I ask b/c from what I've read of people actually using the 6.8 off the shelf loaded ammo, your's is the best in terms of velocity and accuracy and I'd prefer to use it over Remington. Again, thanks for the response and for trying to educate me on the subject. Sean |
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Sean Feel free to ask any question and read Randall's threads they are very good. Zak has posted a lot of good things too, he knows more about 6.8 loading and preformance than anyone I know. If you can get it out of him, he would tell you that "All guns are not created equal". Teacher; We already do offer empty cases for sale. We are changing over to the small rifle primer as we speak and we will start delivires the week of July 17th. Midway already has it posted on their site. If you are talking qty's come to us direct and we can cut you a deal. We are also making some wild cat cases based of the 6.8 for a company. Art - SSA |
Art- I have looked at the drawings and talked with Dave at PTG. The drawings are screwy for sure and the gun makers are NOT working to the drawings as far as maximum headspace and throat dimensions go. Here's what I know from talking with Dave: Clymer and or Remington produced the first drawings WAY back for Chris Murray. The reamer drawing dated 2/27/04 that I have posted on 68spc.com is the incorrect version dave got from Remington. SAAMI did clean up the throat dimension from 1.70185 to 1.7109 which corrects the chamfer angle. From talking with Dave, my reamer is also made this way, it's just my drawing that's incorrect (whew!). In the last 6 months or so, Barrett, PRI, DPMS and others have gone to a throat length of more like 0.100" to solve for pressure problems with the extreme bullet. Of course these throats are longer than SAAMI, that's the first reasoning behind why I stated above that gun makers are NOT following SAAMI. Second, the headspace length issue. SAAMI calls out 1.350-0.007 on cartridge headspace at the 0.360 diameter datum line. Dave confirmed for me that no-go gauges are being ground to 1.350 Go gauges are being ground to 1.346. The 1.356 dimensions is because the military folks requested an extended length spec. The error was in that military "field reject" length making it to the SAAMI print, where it does not belong. In my opinion, SAAMI should have called out 1.345-0.005 on the cartridge headspace dimension and 1.346/1.350 on the chamber headspace dimension. This seems to be about where the industry IS standardizing, even without SAAMI's help! |
Barrel makers such as myself buy our reamers and gauges from the reamer makers. It does not really matter to me what the dimensions are AS LONG AS they work with the ammo, which my barrels do. I can't say what John knows about it, but I bet it does not matter because John gets most of his barrels from Frank at Compass lake. Now, whose reamers and gauges Frank is using, I won't hazard a guess. I just hope that the other reamer and gauge makers have looked at the situation and come to the same (easy) conclusion as I have. If anyone has gauges from makers other than PTG, I would be happy to measure them and make notes to see how similar they are... |
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With all these chamber spec issues I have a question about my Savage/PacNor 6.8. As soon as I get my SSS recoil lug I am going to assemble my rifle. Fortunately I have PTG gauges. With the Savage headspace system it is quite easy to adj the headspace to the max spec or to the minimum spec. Any recommendations or is this something I will have to experiment with ? On all my rifles I adjust them so that there is no feel for the GO gauge [ stripped bolt head ]. On the target rifles I set them up with the bolt handle not closing very far on the NO GO. On a hunting rifle I set them up so the bolt handle travel is quite a bit farther down but no where near closing. This 6.8 Savage is just a sporter weight hunting rifle that will get shot at paper a pretty good bit. It will be interesting to see what the 22" hand lapped bore does for the velocity compared with my 20" Model 1. I keep finding myself wanting a 16" AR 6.8 with a lightweight bbl but everytime I see that pressure curve versus bbl length chart I talk myself out of it  . ETA, I just emailed Chris at PacNor asking about what brand reamer they use and including a link to this discussion. rj |
| I have a 16" middy build about half done. But I am going to wait until til this gets sorted out a little better. Until just very recently I hadn't decided who I was going to get the barrel from. I think that Randall has shown a desire to sort out the problem and get it right. Will be keeping a close eye on this discussion for the end result. Kudos goes to Art as well for trying to be sure that his ammo will work and to inform people of his findings as well. |
My friend knows Chris really good and helped him get into the CNC world. I believe that pac-nor may even be grinding their own reamers in-house now. |
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Sorry for posting such a big image, but this is important so that you can read all the details... Dies COULD be an issue depending on what dimension the die maker chooses to use when they set the shoulder location in the die. So far, this does not seem to have been a problem as dies are notoriously set short. 
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| If I am reading the drawing correctly it is possible to have as much as .013" headspace between a min. cartridge and a maximum chamber. This would explain some of what I have seen in Rem. virgin brass. I took some virgin cases to work and checked them on the optical comparator for headspace measurements, Between 3 cases I had .005" difference just in the brass. I don't remember what the readings are anymore since that was almost 2 yrs. ago. |
You ARE reading the drawing correctly, but thank goodness that you are not likely to encounter a chamber that actually measures 1.356". This is because the NO-GO gauge dimension being used (at least by PTG) is 1.350" So the maximum headspace you would likely encounter is 0.007". You can see how it gets REALLY sticky if Art were to produce ammo to 1.350" per the specs and I produce a chamber to 1.346" per the specs. NO WAY his ammo would go in my chamber as we have a 0.004" interference. As the ammo makers really have to conform to the guns being used while also trying to stay within the SAAMI specs, I'll hazard a guess that Art's right at 1.343" which is the bottom of the ammo spec. If Art stays within the specs and I stay within the specs with my barrels, he really only has 0.003" to work within which is tighter than I would want to be forced to be as an ammo maker. |
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Normally we would aim for the middle of the spec for head spacing to allow us manufacturing variances. But Randall is correct we are now at the bottom of the spec 1.343. But notice on the drawings that case shoulder height is 1.3012 and on the chamber it is 1.2956 - someone was sleeping at the controls. Art - SSA |
If you are not sizing it excessively, I should think at least 4-6 reloads. Autoloading guns are generally rough on brass. Just watch that you are sizing it enough that it chambers, but not a lot more. Beware that most sizing dies are setup on the short side of headspace specs and you can often run them a couple thousandths off the shell holder with good results. Best to have a case gauge to know for sure where you are sizing your brass. |
A case gauge AND calipers is best. What the gauge is used for is to check the length from the 0.360" datum point on the shoulder to the head of the case. Without a gauge, there's no feasible way to measure this dimension. |
When resizing you aren't adjusting case oal. The case may come out a little longer but you are squeezing the diameters and headspace length back closer to spec. The case expands upon firing against the chamber walls creating a seal. The case shrinks back slightly to allow extraction. If you try to chamber a fired case chances are it will not fully chamber. Bolt guns have more camming ability and can be closed on a tighter dim. case. Auto loaders do not have the same amount of camming action so the dims have to be closer to spec. You can do it without a case gauge but it takes a little more trial and error. The shoulder has to be bumped back and base dia. reduced enough for the case to chamber. The hardest part is to get this accomplihed for all cases as ther is some play in all presses and the amount of pressure you apply to the handle also varys. You just don't want to go to far and create a headspace problem. Also a correct gage will allow the loaded rounds to be chamber in other guns of the same caliber. |
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I have been very lucky, I have had four different barrels and all of my reloads have had flawless function! This seems odd, because the so called bad barrels have been apart of the four, some chrome lined and some not. But yet, all the loads worked perfect. This has been just my own experience. |
It really isn't difficult for an experienced or well tutored reloader. But for someone who is inexperienced and doesn't understand it can be very difficult to grasp. |
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Interesting to note that JGS has chosen 1.352" as their no-go dimension where PTG has chosen 1.350". Also, JGS has the old "Short" throat. I have posted the revised reamer drawing from PTG here: www.68spc.com/68spc-reamer2.pdf The 2nd version STILL has the wrong dimensions at the case neck chamfer, but it shows the longer throat. rjay- Can you please email me the full resolution images for my file? [email protected] |
I just don't understand why my reloads work in all my barrels and yet other folks say that the same uppers from the same manufacturer won't. I can understand a barrel being bad from time to time. I just sent one back. But, are all the other barrels just bad or is it the ammo that they are feeding them. It just seems odd.
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You are just "Special"  Ever work at McDonalds? The key element here is RELOADS. MOST reloading dies are on the short end. Are you gauging your sized brass, of just putting the die all the way down against the shell holder? If you put it all the way down, you are likely producing ammo which is shorter than standard and that's why it fits in all the uppers... If you are using a gauge, YOU can adjust the headspace of your ammo. How much headspace are you running? I like 0.003" myself. |
Thanks for the info - I assumed adjusting the die up and down over the shell holder would affect OAL, but it's obvious all the case dimensions change with this adjustment. Any suggestions on an in-spec case gauge? |
Done. Let me know if the attachment doesn't make it on my email. Back to the comparo of the JGS [ from Remington supplied specs ] reamer, my PTG headspace gauges, and the shorter throat's effect on the ammo; what issues may I end up having ? Am I going to need to lengthen the throat ? Thanks rj |
[ARCHIVED THREAD] - 6.8mm SPC FAQ & Load Data Part III (Page 4 of 20)
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