Looking for Assistance With This Load Workup

[AnotherMadHatter]

Okay, so I bought 16lbs of WC820 when Jeff Bartlett had it for sale, and I am trying to work up a load using some blemished Midway bullets. The bullets are remarkably similar to the Hornady 123gr .310 (7.62x39mm) bullets that they sell. I resized them down to .308 with a CH4D bullet sizer.

Regarding the powder, there seems to be a few different lots floating around with burn rates between AA#9 and H-110. The lot that I have (Lot 47321) burns a bit faster than H-110, but this is where I am having difficulty. I ran out of CCI small rifle primers that I used for my H-110 load workups and started using the first of 5K CCI #41 primers for the WC820 workup, so that kind of skews the comparison.

My gun (at least the parts that matter):
CMMG 300BLK Flat top 16" M-4 Upper
Carbine Gas system
"H" Buffer
Standard carbine buffer spring


This is my current load I am trying to match:
Powder: H-110
Weight: 17.4gr
Bullet: 123gr V-MAX Resized from .310 to .308
Brass: Random Converted 5.56
Primer: CCI Small Rifle Standard
C.O.L.: 2.045"
Crimped with Lee FCD
AVG Vel. (5 shots): 2,198fps

I knew that switching from the standard primers to the #41 primers would cause an increase in velocity/pressure, so I reduced the load by 1gr, and I ASSUMED the WC820 was going to be faster than the H-110, so I reduced the powder load by 10% then rounded up to the next full grain, so my loads for the WC820 started at 14gr and went to 17gr in .5gr increments.

Using the same everything as above except:
WC820 instead of H-110
Using CCI #41 instead of Small Rifle Standard primers
14.0gr 1,971fps The gun did not load the next round for any of the shots.
14.5gr 2,016fps The gun did not load the next round for any of the shots.
15.0gr 2,059fps The gun did not load the next round for any of the shots.
15.5gr 2,098fps The gun did not load the next round for any of the shots.
16.0gr 2,124fps The gun did not load the next round for any of the shots. Some CHS.
16.5gr 2,165fps The gun did not load the next round for 3 of the shots. Moderate CHS.
17.0gr 2,236fps The gun did not load the next round for 3 of the shots. Bad CHS. Blown primers.

Link since the picture is too big.

Anyway, here is what is going on. It appears that the loads go from not being able to cycle the action to trying to cycle the action before the pressure drops. I only get to shoot infrequently, but this coming weekend I will be able to shoot another round, and I was wondering what you gals/guys think would be most effective in changing to get the gun to cycle properly.

Change the buffer from "H" to a standard?
Change buffer from an "H" to an "H2"?
Try a lighter bullet since it appears maybe the powder is too fast for the 123gr bullets?
Something else?
Did I forget to include any other pertinent info?

EDIT: When I refer to the "standard" buffer weight, I mean the standard weight for a carbine buffer.

[twcrowe12]

You're right about the burn rates varying. Unless you can confirm with a lot number, I'd say your data indicates that your particular lot is much closer to Accurate No. 9 than it is to H110. Looking at your picture you have some case head swipe starting as early as 15 grains, and it looks like it might be starting on on that tarnished round in your 14.5 group.

I'm at a loss as to how to get that powder to work safely for your rifle.

Not sure if it would matter, but what length gas system are you using?

[AnotherMadHatter]

It is a carbine gas system.

I think I may try using 110gr bullets and the standard buffer next weekend.

Do you think the powder would be good for that?

[plant.one]

you should consider switching to a standard carbine buffer & spring first and foremost - it seems to be the answer in that department that the most people have success with

its not a huge weight drop, but it might be enough.

going heavier is not going to help your cycling issues


as to working with the powder - i cant give you any first hand experience. i've never used surplus powders before, only consumer strength stuff

there some bright folks on this forum i'm sure they'll help you sort it out.

[AnotherMadHatter]

Thanks, yeah, this is my first foray into bulk powders, but since I got 16 lbs, I figured I only need to work up a load once for each cartridge and I'm set for quite a while.

I think I will definitely go to the standard buffer weight, and maybe load up some 110gr bullets as well and see if the lighter weight helps. I can always just use this for 110gr bullets if it came down to it.

I need to work up some loads for my 458Socom, but those discussions will be for another forum.