"Jump to Lands" - What's Your Favorite?

[Grunt81]

Hey gents. I'm new to loading for .308. I picked up  a Savage 11 Trophy Hunter XP and have fired my first 140 rounds or so. My tightest group at 100 yards happened to be with a 168 grain match bullet, seated to an OAL of 2.833", atop a full-length sized LC case using Varget. I've determined that max OAL for this bullet to touch the lands is 2.853". This means my rounds were 0.020" off the lands. I can post a pic if you'd like, but it was a tight clover leaf, less than 0.2 MOA for a three shot group (too bad I thought I was missing the target and adjusted my scope, otherwise it'd be a 5-shot group). I haven't been able to duplicate a group anywhere that tight since then.

 

I talked to an old-timer who runs my local reloading store. He has a lot of competition experience and he suggested I seat my bullets from 0.005" - 0.010" of the lands. I was wondering what jmup to the lands some you all prefer for your bolt action rifles.

 

Thanks for your input.

[Tempest455]

Totally depends on the ogive of the bullet and chamber of your gun. Some like jammed, some like jumped. You just need to load a bunch up and see what your rifle likes.

 

I have one rifle that shoots best a .035-.040" jump.

[Grunt81]

Gotcha. I'm a little hesitant to seat 'em jammed into the lands, since this can spike pressure. Do you think jamming 'em would lead to quicker throat erosion?

[BJB]

I have built several accurate guns and have learned there is no set answer on OAL, powder, bullet or even primers. Best way to tell is load a lot document a lot until you find that magic spot that works. Good luck with that. .......it's been some of my most aggravating times shooting. But when you get it all together and can bust 5 Dumb-Dumb suckers at 300yrds with 5 shots. It's all worth the time. Good luck

[Grunt81]

Understood. That's some impressive shooting! I've shot about 22, 5-shot groups. Only a few of them were sub MOA and I haven't been able to duplicate that clover leaf. I have had a few vertical or horizontal strings, where 3 shots are touching and the other 2 open up the group to just barely sub MOA.

 

I'm going to put the Varget aside for the time being and start working through some IMR 4064. I've heard good things about it. I'll also take the man's advice and seat 'em longer, to around 10 thousandths off the lands or less and see how they do.

[gregintenn]

I've never found a standard distance that worked for all rifles. Trial and error is how I've found my best loads. Get a good group with a load you like, then start adjusting seating depth til you get the smallest group.

 

Mostly, I find the OAL specified in the reloading manual to be good enough. I don't usually tinker with it in a semi auto for sure.

Edited December 18, 2014 by gregintenn

[mikegideon]

I'll just leave this right here...

 

http://www.the-long-family.com/OBT_paper.htm

[gregintenn]

I'll just leave this right here...

 

http://www.the-long-family.com/OBT_paper.htm

I have ADD. You want to give us the cliff notes version?

[mikegideon]

You want the bullet to leave the muzzle at the time when the muzzle diameter is changing at the slowest rate. It's helpful to understand Dan's paper, but not totally necessary. Fact is, seating depth matters more than how much "jump" you have, assuming that you are shooting low runout ammo. You can use some math and set some practical limits on your test loads, or you can just shoot your way through it. As has already been mentioned, jamming the lands comes with a spike in pressure.