How hot is too hot?

[PinesAndProjectiles]

Yesterday I was able to get in some range time with the 308. I had a load of 155 SMKs over IMR-4895 ranging from 42.0 - 45.5 grains. My best group (by far) was the 45.5 grains. It chronied at 3073, 3074, 3075, and 3066. The group (minus .308) measured .3345" which is by far the best group I've ever put on paper.

I started to see some flattening of the primer pockets at 44.5 grains. It continued (obviously) into the higher charges. I've attached a picture. The brass on the left is of the 44.5 group, the 45.5 on the right.

The brass is RA 61 with the NATO stamp, primer is Remington 9-1/2.

Rifle is a Savage with a 30" barrel.

Are these loads too hot?
Thanks in advance!






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[Hoodlum]

Nothing wrong with those primers... There is still a very pronounced round edge on them.... As long as the bolt wasn't sticky, I would say load em up!!!!
Hoodlum

 

[Geno C.]

Not even remotely flat primers. Like above if the bolt ain't stick it looks like you got your load.

 

[witchhunter]

When you see a flat primer, you will know it! Those look good to me,

 

[damoncali]

The higher load is starting to flatten. Proceed with caution. Primers are an imperfect indicator, but the fact that you can see a difference between 44.5 and 45.5 means you're getting up there.

 

[stockdoc]

What were the environmental conditions you shot those at?

Primer flattening is not a very reliable indicator of pressure. By the time you notice flattening you may be way over on the pressure

If you shot that group at cooler temps you might get in trouble with that load in the heat

 

[Mike_Honcho]

Primers are fine. Like others have said - what were the enviros? More importantly - what were the groups like? and then the numbers (Avg. / ES / SD)?

 

[steve123]

Try the hotter load a few more times to make sure the average is still tight.

By July you'll know if that load is too hot or not because you'll begin to get bolt stick, ejector smear, loosening of primer pockets and most likely the group sizes will suffer. If you want to stay with that powder then back the load off to get the FPS you now have. Next winter you might have to put a few more tenths in.

 

[FLIGHT762]

The 45.5 load may look okay now, but be sure to note the temperature you tested them at. Be aware when you shoot in higher temperatures, you'll likely get overpressure. At 45.5, you're getting at the top. I use 45.0 grains of IMR 4895, H-4895 and Surplus RG-4895 with 155's in my bolt guns. If it were me, I'd stay in the 44.5-55.0 range.

I have a 43.0 gr. of IMR 3031 load with 155's that shoot great @ 70º, but when I shot them @ 95º+, I stretched the primer pockets past usefulness. I Had to toss all of the brass.
No problem since I have a lifetime supply of free Federal GMM 308 brass, but if the brass was Lapua @ .75¢ ea., I'd be pissed.

 

[lostcoyote]

these are TOO hot...

flat primers, crater rims, hard to get out of chamber (cylinder in this case)

 

[former naval person]

Try this...measure an unfired case rim.Load that case stepwise .5 grains upward, measuring the base each time. When you reach .001 expansion, stop...the case will maintain that dimension for a long time. When you increase the loading above that, it will increase with each firing till the primers fall out.

 

[PinesAndProjectiles]

Holy cow! I didn't expect so many replies! Thanks to everyone for all the input. Temps were in the low seventies when I shot these rounds.

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