AIAX 308 20" with PP2000MR powder, also Factory M118LR Flattened Primers

[MattyG]

So I have shot some 208 AMAX, 178 AMAX and 178 BTHP over PP2000MR powder with varying results. For a baseline my M118LR gets 2640 out of this barrel.

So here is right to left 46.5, 47.0 and 47.5 gr with 178 BTHP and 220 yards (disregard far right group)



Looks like it likes something around 47.0 grains (2730 FPS).

The large groups are 208 AMAX at 45.0 and 46.0 grains of 2000MR. Results are no good. Anything over 2400 FPS and the groups open WAY up.



I also shot 178 AMAX's over various powder weights from 45.0 grains to 47.5 and got a group about 2" at 230 yards so I will be picking a load that matches the velocity I need with low SD's.

Last note is I have flattened primers randomly from M118LR (all the same lot). Below is a picture of two cases cleaned, both from the same box. Oddly enough I am also seeing flattened primers like this from 2000MR in all weights with velocities even as low as 2600 FPS! No other pressure signs though. Also notice the primer that did not flatten in fact has some push back around the firing pin impact point, as if this occurs after the firing pin hits and is pushed back (another owner of a .260 AIAX has this occur at safe load levels also).



Ambient temps on these shooting days are about 80-90 degress F (upper end of the spectrum that I shoot in). So I will continue to run the load at around 2730 with flattened primers, I may back of .2 grains and see but overall it seems this powder just does it in my 20". Also I am using LC LR 04 OFB.

 

[former naval person]

Are you sure those are from the same rifle? The cratering of the one on the left with the rounded edges looks like a Remington bolt face. The indents seem different also.

 

[MattyG]

Yup my AIAX has a large firing pin hole and the firing pin is pretty large. I will put a caliper on them both tonight. I have shot 2k rounds of this M118LR out of my AR-10's (3 different barrels), Sako TRG 22 20" and H-S Precision HTR 308 24". Never had flow back like this and I also never checked for flattened primers since it was factory ammo from the same lot. I do see random FAST rounds, like 2720 fps all the way down to 2600 from this ammo so consistency is not there, I guess for putting rounds on living targets this is acceptable.

I guess what I am saying is, seeing the primers flattening on factory ammo it makes me less worried with my hand loads doing the same. All I have ever really fired in .308's was M118SB, M118LR and M952 Match..... I do have a box or two of FGMM 168 gr I could try and see what the chrono says and see how the primers look. This Bartlein does seem to be on the fast side.

 

[former naval person]

I suspect that the 118 has enough headspace variation in some instances to allow the firing pin to drive the case forward until the fire is lit...then pressure builds and the forward case walls grip the case and the primer extrudes just a little bit...and then the pressure builds and drives the case head back against the bolt face, flattening the edges of the primer. Doesn't happen every time. I think that that batch of ammo may have too much variation for milspec acceptance. That may be why you have been able to have bought it surplus. Or it may be machine gun ammo, with a LOT of built in tolerance. JMHO

 

[MattyG]

I have that funky cratering EVERY round unless it flattens the primer. Those are the only two options, also it is about 10 to 1, 10 cratered primers to every 1 flattened primer. This was not mil surp I can assure you that. Machine gun ammo has shorter COAL, I know M118SB will not run through a M60, never tried a 240.

 

[JGorski]

So I have shot some 208 AMAX, 178 AMAX and 178 BTHP over PP2000MR powder with varying results. For a baseline my M118LR gets 2640 out of this barrel.

So here is right to left 46.5, 47.0 and 47.5 gr with 178 BTHP and 220 yards (disregard far right group)



Looks like it likes something around 47.0 grains (2730 FPS).

The large groups are 208 AMAX at 45.0 and 46.0 grains of 2000MR. Results are no good. Anything over 2400 FPS and the groups open WAY up.



I also shot 178 AMAX's over various powder weights from 45.0 grains to 47.5 and got a group about 2" at 230 yards so I will be picking a load that matches the velocity I need with low SD's.

Last note is I have flattened primers randomly from M118LR (all the same lot). Below is a picture of two cases cleaned, both from the same box. Oddly enough I am also seeing flattened primers like this from 2000MR in all weights with velocities even as low as 2600 FPS! No other pressure signs though. Also notice the primer that did not flatten in fact has some push back around the firing pin impact point, as if this occurs after the firing pin hits and is pushed back (another owner of a .260 AIAX has this occur at safe load levels also).



Ambient temps on these shooting days are about 80-90 degress F (upper end of the spectrum that I shoot in). So I will continue to run the load at around 2730 with flattened primers, I may back of .2 grains and see but overall it seems this powder just does it in my 20". Also I am using LC LR 04 OFB.

That primer on the right looks perfect to me. Are these the same primers? I fireformed some 22-250 brass in my 6 Creed with some WLR primers while my Hornady 6 Creed brass gets CCIBRs, those WLRs are much softer than the CCIs, they flatten out while the CCIs dont, they look just like the primer on the left.

 

[MattyG]

those in the picture are Mil CCI 34 primers. both are the same and came from the same box of ammo. Pressure I believe is what is causing the flattening on the right. My loads with federal 210's do the same thing.