I have a PA10 with a 20" 1-10" barrel equipped with an adjustable gas block.

In the process of working up a load, I decided to use IMR4064 since I have plenty of it.

As a generic data for all rounds, I am using Graf 168 HPBTs, CCI 200, and loading FC cases to OAL of 2.790"+/-

I have already tried 41.0 to 41.5 gr. I got awful accuracy, so I read further into the tacked thread above and noted that several have stated they were loading 42 to 43 grains of this powder. I think one person loaded 44 gr, but that may have been in a bolt rifle.
Also, it was stated that 42.8 closely resembled one of the typical factory match loads.

Anyway, I decided to load up a ladder with 4 rounds loaded in each 42.0 to 42.8 gr in .2 increments. I shot at 50 yards for convenience.

42.0 - no problems, but my first shot on a cold barrel messed up an otherwise tight group. <.5", but over 1" with 1st shot. I may load more and try again on a hot barrel.
42.2 - no problems, but worse accuracy
42.4 - 1st shot jammed the BCG to the rear and I had to pry it out. IDK what happened. Otherwise, 4 shot touching group and problem didnt happen again. A few swipes though out of the 4 shots.
42.6 - No problems, and once again all touching. No swipes
42.8 - FTExtract on 1st round. Then no problems. Tightest group of all. Oddly, No swipes.

My questions are:
-Do you think I may be having some pressure issues?
-Do you think the adjustable gas block may "fix" the problems I had?
-What do you think would/should be the upper end of the safe loading with these components?

I did not chrono the rounds, but it is obvious that I am getting a good bit more speed out of the upper end loads since my groups were dropping below the aiming point by the time I was at 42.8. .5" above POA at 42.0 to .5" below POA at 42.8"

Any other advice or suggestion.

42.0 to 42.5 grains of IMR-4064 is a known accuracy load using your brass and 168 grain match bullets. I would be more concerned about the malfunctions and getting to the bottom of why they are happening. You need to bump the case shoulder back at least -.003" (I use -.004") from the fired measurement in semi-auto rifles to insure reliable feeding and function.

.5 grain of powder in .308 caliber is approximately a 30 fps change in velocity. There is no reason to run your powder charges in such close intervals. I use .3 grains when working with .223, .5 grains when loading .308 or .30-06. 1 whole grain when loading .300 Winchester Magnum. Load up ten rounds at 41.5, 42.0, 42.5 and 43.0 grains of IMR-4064. This will give you a more useful window of operation and you can always fine tune once you find a load that shows promise.

From a 20" barrel I look at 2500 fps as being maximum velocity when loading 168 grain bullets in a semi-auto .308. A 24" barrel will net 2600 fps.

Try WIN WLR primers.  Always in my experience gotten better results with IMR 4895/4064.
Personally, I would look at using Sierra or Nosler OTM bullets.
More importantly, you want safety, reliability, and accuracy!

borderpatrol,
I respect your knowledge and I thank you for your input.

I want to add to your comment about normal max velocity with a 168 gr bullet, though, and please respond.
I did chrono the 41.0 grain 4064 load earlier this month on a chillier 50 degree day and got an avg velocity of 2519 on a 9 shot strand.

I am getting nearly 2500 fps out of my most accurate 175 grain load over 42.0 gr of Varget. (I am just trying out the 168 gr bullets to see if they are worth switching to for cost)

Extrapolating from your 30 fps per .5 grain, the 42.8 gr load would be pumping at about 2625 fps which doesn't seem excessive.

Back to the questions I asked, do you think that the failures I had could be related to the adjustable gas block not being adjusted properly for the load? Or could it be something else gun related?
I find it odd that I had a failure, then none, and then another failure on consecutive loads in the ladder. It seems that the failures would have gotten worse.

But, I also want to make sure I am not reaching safe limits from knowledgeable loaders of this round.

Probably should try switching, but I have a stash of CCI200s. I know that is not a good reason, but its all I got.

If I can get a 168 grn bullet to work well, I will likely opt for better manufactured bullets. The Graf were relatively cheap bulk bullets.

If you are getting 2519 fps with 168's and 41.0 grains of IMR-4064 then you are close to maxed out. Your 20" barrel loses 100 fps compared to a 24" barrel. Virtually every reloading manual uses 24" barrels to publish their velocities. Your 42.0 grain load of Varget with 175 grain bullets is about maximum too, your 2500 fps becomes 2600 fps when fired from the longer barrel.


Federal Gold Medal Match w/168 or 175 grain bullets usually runs around 2600 fps on the nose when fired from 24" barrels. So your speed is virtually identical with that standard bearer for the most accurate store bought ammo.

You can play with another .5 grain higher, but after that you're in no man's land.

If you want higher velocities switch to Winchester brand commercial brass, it has the highest internal capacity on the market. You might be able to add another grain or even more with those cases.

I shot my 16" AR10 two days ago in preparation for load development. I was getting 2375 fps using 42.0 grains of VihtaVuori N150 and 2340 fps using 41.0 grains of IMR-4064. Both charges were loaded in 7.62x51mm surplus brass. While surplus brass is not known for excellent quality, it is built for the abuse delivered by semi-auto firearms. That makes it my preferred brass for this role. This same ammo runs between 2475 and 2500 fps from my Super Match M1-A's.

41.5 grains of IMR-4064 is a maximum load when using Lake City brass and Sierra 168's. According to your testing so far your Federal brass appears to be performing very similar to Lake City as far as charge weights vs. velocity is concerned. Generic surplus 168's are not the same as Nosler, Hornady or Sierra match bullets. Unless they were seconds from one of the big three they are probably PRVI or some other knock-offs. Try Sierra bullets, they have always worked great for me. 1000 bullet boxes of 168 grain Nosler Custon Competition bullets can be purchased for around $230.00 (.23 cents each). Great bullet at a great price.

You should be okay at 43 grains of 4064 with the 168s as far as pressure.

I would measure the speed of Black Hills 168 in your rig as a reference point.

NJ Highpower Reloading Stuph.

Down towards the bottom are some Service Rifle Pet Loads for the .308 versions of the Garand and they show 43 grains of 4064 with regular primers.
I have shot tons of the Sierra 168 over 43 grains of 4064 and never had any pressure issues with Garand or M14.

I doubt your accuracy has anything to do with the loads, and more the barrel.

What build procedure did you use for this rifle?

I am not ignoring this thread. I just have not had time to do anymore with the load.

As far as the gun, I had a few more failures with the BCG locking back and me having to pry it loose. I had a couple arfcom guys look at it at the HTF shoot and the diagnosis so far appears to be that the buffer spring is out of spec. The diameter of the wire is larger than "normal" for an A2 or any other type AR spring I have ever seen. This is possibly causing the BCG to bind up in the buffer tube since there are no obstructions noticeable.

LRRP.
Forgive me for my blond moment, but what exactly do you mean?
How it was put together or my components?
I put it together myself with PSA upper/lower parts, a McGowen barrel, and MI FF tube. Gas block is adjustable(name brand eludes me right now, but is one of the good $100+ ones).  The buttstock is an A2 setup with A2 buffer and a MOE rifle stock on it.