new to .308 loading

[Backr]

Hey gents, santa (wife) was pretty awesome this year and got me some new stuff to play with which includes:

some varget, lapua brass and a box of 165gr nosler partitions and a box of 180gr hornady interlock
I am curious about a few things, will my 1-12 twist 20 inch barrel stabilize the heavier 180gr bullets?

and what do i need to do to make sure i can get the most out of the lapua brass? 99% of the cases are at 2.0085, should i trim them all down to 2.005?


i am a fairly new reloader (+/- 5000 rounds) so any help would be greatly appreciated.

 

[tomt]

Start with 44 grains of Varget for the 165 partitions and tweak from there.

 

[Bart B]

Your 1:12 twist 20" barrel will stabilize 180's from maximum loads good enough in warm weather above 65 degrees F. As it gets cooler, you may see a little less accuracy; may not.

I'd trim 'em all back to 2.000" then again when they reach 2.010". You won't see any accuracy issues in that range of case lengths.

 

[Backr]

I am thinking of working up loads between 44-46 with the partitions and 41-43.7 with the interbonds, with a chrono as well, now theoretically wouldn't the trim lenght with the same bullet seating depht effect internal pressure in the case? Or am I thinking about this wrong? Thanks for the reply

 

[Bart B]

With everything perfect and uniform, a .308 case length changing .010" means a 4% to 7% change on its grip on a given bullet gripped by a .15" to .20" long section of the neck. How much does that change things?

A 4% to 7% change in how much force is needed to push a bullet out of a case is insignificant, in my opinion. There's normally a 20% spread in that force which will average between 10 and 60 or more pounds. Therefore, it'll be masked for the most part. Measure your own loads to see how many pounds of force it takes to pull seated bullets out.

If you want to see what the muzzle velocity difference is, then mount your barreled action in a fixed place so it doesn't move back in recoil. That'll produce the most uniform results. If you hand hold the rifle against your shoulder, the velocity spread for that load will be 3 to 5 times as great and several fps slower.

A .010" spread in case length is meaningless unless you and yours shoots no worse than .15 MOA so you can see the difference. But you may have to wear out a barrel proving it.

 

[Backr]

Ah that makes sense, thank you for the explanation, I definitely do not consistently shoot groups that tight, I average around .8 moa with fgmm factory ammo and want to drop that to 0.5 with reloads, the range has a sled I can use so will develop loads with that and a chrono to see what am I getting