Chasing The Lands

[bill123]

I have a 308 with 975 rounds on it. When new, the chamber CBTO w/ BERGER 175 OTM was 2.226" and the bullet grouped well with .030" jump. Now chamber CBTO IS 2.262", measured w/a Hornady gauge multiple times.

A few questions:
Is .036" a reasonable amount of erosion for 975 rounds?
Should I be able to seat the bullet .036" further out and get good results or do I need to do a new seating depth test? This is more of a general procedure question, not specifically one related to 175 OTM's since I realize they tend to be forgiving of seating depth.
Should I expect to have to adjust powder charge?
Finally, prior to checking the chamber CBTO, I Loaded 50 rounds with the old jump. Will I be ok pulling the bullets out a bit w/ an inertial "puller" and then reseating them to the new jump? Or, will this not give me as good precision as newly seated bullets.

 

[Raythemanroe]

Chasing the lands, I think you forgot about them for .036




Ray

 

[bill123]

Chasing the lands, I think you forgot about them for .036




Ray

You're saying that I should have measured sooner? My plan was to measure every 300 reds or so. Just didn't happen.

 

[FatBoy]

Only way to know is to shoot it. If it shoots, you're good. If not, push it out to the same jump you started with and try that.

308win is very forgiving. I bet you'll be fine as is.

 

[dmoran]

Try it both ways in a head to head comparison, from like 4 groups of each, alternating between the two.
Then report back and we all will know...........
Good Luck
Donovan

 

[bill123]

Try it both ways in a head to head comparison, from like 4 groups of each, alternating between the two.
Then report back and we all will know...........
Good Luck
Donovan

Will do.
Thanks.

 

[barefooter56]

bill123,
Make a dummy round to the lands so you can find what .030 off the lands is now with the erosion. You MAY also have to tweak the powder charge up to regain the velocity accuracy node if the velocity has gone low enough to take you off the node you had that worked. Do the bullet seating first then load if necessary. Bryan Litz has a good article on this on our website. Click on EXTERNAL BALLISTICS in the box in the lower right hand corner ( you may have to scroll down a bit to see it). Its a 2 part article on CBTO.

 

[jsthntn247]

Chasing the lands, I think you forgot about them for .036




Ray

You're saying that I should have measured sooner? My plan was to measure every 300 reds or so. Just didn't happen.

Need to check EVERY 100 rounds at a minimum. If it likes .030, keep it there.