Where to start?

[jschroed]

I have a new 6mm BR. I'm looking for some advise on how to start working up a load. I'm using Lapua brass, varget, CCI 450's and 107 SMK's. I plan to start at 29.5 gr. and work up in .2 gr. increments.

My question is about seating depth? What is a good and efficient way of finding ideal seating depth? Is it trial and error or is there a systematic approach?

Thanks

 

[Forum Boss]

Lawrence is correct that a systematic approach is good. However, I do NOT recommend starting "at the lands". The reason is that, in my experience, most people don't measure correctly so they are often a good .003-.005" in the lands when they think they are "just touching". Also, that entire zone of .004 out to .004 in the lands is a "no-mans land". If you have some base to ogive variance in your ammo (almost inevitable if you don't pre-sort those Sierras), some of your rounds will be contacting the rifling and some will be "jumping".

With the Sierra 107s. I would start .020 out, then move to .015 out, then 0.010 out. If the bullets don't want to jump I would go right to .015 into the lands, then .012, then .008, then .005. A lot of people find a good load .010-.015 in the lands, particularly with the Berger 105 VLDs or Scenar 105s.

Lawrence is correct that seating in the lands can create issues with very light neck tension. But seating in the lands can produce the best, most consistent accuracy with many bullet/barrel combinations for the 6mmBR.

IMPORTANT: if you are seeing pressure at 29.5 grains Varget when jumping the bullets, I would reduce the charge to 29.0 before trying seating in the lands.

Another technique that some guys follow is starting with a long seating, say .020 into the lands and then work back in one direction. There's some logic to that. I make my recommendation as most of the guys I know shooting 107 SMKs found a happy spot .010 to .020 OFF the lands. This all presumes, however, you get a good, repeatable measurement of length to lands in the first place.

Also -- I'm not ruling out that you make ultimately end up very close to touching. But for the reasons listed above, some of the benefits of jumping are diminished if you get within .005 or so with unsorted bullets.

 

[Shynloco]

If I might inquire, what brand of rifle is it? The two previous posts have good info, but if you have a Savage, you might be limited on the depth you can go into the lands. Thats because of the Accutrigger mechanism might "sense" pressure against the bolt face if you try to go too deep into the lands and the sear block COULD activate, preventing the trigger from engaging.

 

[Killshot]

JSCHROED, have you measured your chamber (distance from casehead to ogive contact in the lands) to establish the land's location first?

This should be done before any seating ensues.

As for your Sierras? I found them to shoot well with a .015" jump. Good luck.