IMR 4227 in 308 Win

T

thelongranger

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I recently loaded some 308 Win with IMR 4227 .2 grn above the suggested starting load which I got from my Lee manual. 23.5 grns behind Hornady 150gr fmj . I experienced gas in my face on the 4th round. Ejection of the brass revealed the neck had not sealed leaving significant carbon along the entire brass case. 1st round showed it only making it to the shoulder. Number 2 and 3 were fine. I stopped immediately after being gassed.

I have loaded 10,000 or more of reduced loads using cast bullet and jacketed bullets using powders from Red Dot on the fast end to IMR 4198 on the slower end of the burning rate. This has never happened before.

I suspect the rifle has a loose chamber and that the reduced charges created pressures so low that the brass failed to seal the chamber. Just asking to ensure I'm not missing anything.
 
Just as I suspected.

220 , you're absolutely right about it being dirty.

Chose 4227 for it's burning rate. With a mid level charge, the barrel is slower to heat up and pressures are low significantly​ extending barrel life yet giving me enough velocity to hit out to 400m. All I need to do is crank the turret.

Why is it so hard to find Accurate powders? XMP 4744 would be perfect for my application.
 
You're concerned about barrel life with reduced cast loads? That seems odd....
Barrel life to pressure is non-linear already so reducing pressure even a little will exponentially increase barrel life. Cast bullets further reduce barrel wear. My guess would be that a moderate reduced load (25-30% pressure reduction) and cast bullets will increase barrel life 10x over full-pressure, jacketed loads. I mean a match .308 barrel remains match grade for 1500-2500rnds where as a .22lr barrel will last pretty much indefinitely; cleaning does more damage than shooting it.

With regular cast loads using fast rifle powders I probably couldn't shoot out a bore in my lifetime.
 
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