Re: compact 308 home shop build
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 300sniper</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Downzero</div><div class="ubbcode-body">H4895 is pretty fast in my experience. IMR 4895 is slower and may produce more velocity, even in your short barrel.
Did you consider trying the staples of Varget and RL15? </div></div>
i haven't tried anything else yet. i was thinking that a faster powder and lighter bullet would be the best choice for a shorter barrel. i may have to reevaluate my thinking if i can't get this combo to work.
i dicked around with it again yesterday and it looks like 44.4 grains of h4895, once fired lapua brass, 210m primer and a 155 scenar seated to 2.810" (.007" jump) works pretty good at 100 yards. i didn't have my chrony with me as i don't trust it anyways. i will load up a batch of this load and mess with it again between 200 and 1000 yards this weekend. i'll only bring this rifle so i have time to really evaluate it. </div></div>
I don't think a faster powder will help you in a rifle. You need a powder that fills the case as much as possible to get max velocity.
It's not like loading for a pistol where burn rate can have substantial differences in whether or not the powder is completely burned by the time the bullet leaves the barrel. You have what, 18" of barrel? That's an awful long time when it comes to combustion. I'd imagine all of the powder is burned within that time, but the gasses are still heating and expanding.
I'm not a chemist or a physicist and I don't claim to have any knowledge of those subjects that'd be relevant here. In fact, I have never taken a physics class for credit.
But, my experience with H4985 vs. IMR 4895 with my M1 Garand suggests that there is a pretty serious difference in burn rate between the two, with IMR being more like Varget and H4895 quite a bit faster. Even a grain or a grain and a half lower still produced more velocity with the same bullet, to the point that I won't load like that again for fear of damaging the rifle.
If a faster powder (with less of it) results in higher velocity, that can mean only one thing--the pressure is unsafely high if you were at the max.
So the way I look at it, your options are push harder with a fast powder (more pressure) or try a slower powder.
Feel free to test my theory if you like. I am not a good enough shooter to be sure of the difference without going through a lot of rounds, and my .308 has a 24 inch barrel anyway.