Case capacity question(s)...

daved20319 · Jul 22, 2019

So I have a new Howa 1500 Mini Action in 6.5 Grendel I'm getting ready to start doing some loading for. As my goal with this rifle is long range shooting, I've chosen to start with a small variety of 130 gr. bullets. ALL the published load data I can find has COAL at 2.26", i.e. AR mag length. Since I'm shooting a bolt action, I don't care about mag length, I'll be treating it as a single shot, anyway. I took some time this afternoon to check out max COAL for MY rifle with the bullets I have on hand. Book says 2.26" max with the Sierra TMK 130 gr., but my Howa is ~2.388" to the lands. Subtracting a reasonably conservative .010" gives me a COAL of 2.378", or almost .120" longer than book. Which finally brings me to a question.

What is that "extra" case capacity going to do to my velocity, assuming I stick to published loads? Logic tells me it'll reduce the pressure, thus also reducing velocity, yes, no, or it depends? Will I be okay exceeding published max loads in this case, with the qualifier that I will be watching velocity with a chronograph? I know I have a little extra wiggle room re: pressure with bolt vs. auto, but am I likely to net any real gains, or will I just be burning more powder for nothing much? Sorry if these sound like dumb question, folks, but although I'm not exactly new to reloading, it's been awhile, and I still have a lot to learn when it comes to loading for rifles, and especially for "precision" rifles. Thanks for your patience.

Dave

v0lcom13sn0w · Jul 22, 2019

id try reloading a few to max book COL and see where youre at on target. you might be surprised

. if not, move it closer to the lands and make changes to the powder charge accordingly by shooting ladders and watching for pressure signs. take your chrono with you!

i load 6.5 grendel for an AR. i am at max load and max COL. havent measured to my lands because im shooting out of an AR and just go at what the max length is in the book.

DizzyJ · Jul 28, 2019

You gained some case capacity and velocity as long as the pressure doesn't go too high.

Member 5605 · Jul 29, 2019

DizzyJ said:
You gained some case capacity and velocity as long as the pressure doesn't go too high.

(+) case capacity
(-) velocity

Right?
Greater capacity means powder gasses expands more before it acts on bullet giving a lower velocity? I ask because I run a .308 at 2.5gr over max at .025" from lands and I run the same velocity as 2.800" at 2.5gr less powder.

DizzyJ · Jul 29, 2019

Dyjital said:
(+) case capacity
(-) velocity

Right?
Greater capacity means powder gasses expands more before it acts on bullet giving a lower velocity? I ask because I run a .308 at 2.5gr over max at .025" from lands and I run the same velocity as 2.800" at 2.5gr less powder.

My thinking was he could theoretically stuff some more powder in there as long as his pressure didn't rise too much.