How often do you adjust seating depth as the throat erodes?

M

mks

Guest
I just made a huge adjustment in seating depth for a barrel I thought was shot out, and it came back to life. Seems like if I had been making small adjustments at regular intervals, it might have shot well all along. By my calculations, I should have made a 0.001" adjustment for every 134 shots. What is your experience? How often do you check for erosion and make adjustments? Is erosion at a constant rate, fast for a new barrel with a decreasing rate afterwards, or vice versa?

Thanks,
Keith
 
TB mentions in his book he checks after each day's match. To verify jam and adjusts accordingly.
If I remember correctly pg 257
 
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Hi Keith,

You must be shooting a cartridge that's pretty easy on barrels to need so little increase in loaded length. Another issue to stay after is constriction of the throat from fire cracking. Many shooters think the throat opens with erosion but it actually gets tighter and can benefit from being relieved with silicon carbide or diamond lapping. It's not good for accuracy to squish bullets with a tight throat and have them rattle up the rest of the bore. Finally, as the throat advances with firing and abrasive attention, increased loaded cartridge length needs to be accompanied with a modest increase in powder charge to maintain velocity and tune. 6.5mm thousand yard cartridges require the most frequent attention. They are all different but obviously the greater the expansion ratio of the cartridge, the more frequently it will benefit from this ritual. 30 BR's need not apply.

Best regards,

Greg
 
I have seen a .002 change become a .07 diff on a target.
I would think tracking wear and adjusting would be normal..
but i am the new shooter.
 
Tim, Tony told me in an interview that I did several years ago that once he finds the ideal seating depth on a barrel; he does not change it. Maybe he had a change of heart. Of course, Tony does not put more than a 1000 rounds on a barrel before replacing it. Good shooting....James
 
Erosion

another terrific thread.........
I wonder how much erosion varies in different barrels.... i.e. hardness.... I`ve noticed much difference in barrel hardness` from different barrel makers...???... some cut like butter......
one a few years ago was as hard a japanese arithmetic....
thank all who contribute......
bill larson
 
Tim Singleton said:
TB mentions in his book he checks after each day's match. To verify jam and adjusts accordingly.
If I remember correctly pg 257
Click to expand...

Yes, found it, page 257. TB says he checks seating depth every evening between matches.

Thanks,
Keith
 
mks said:
I just made a huge adjustment in seating depth for a barrel I thought was shot out, and it came back to life. Seems like if I had been making small adjustments at regular intervals, it might have shot well all along. By my calculations, I should have made a 0.001" adjustment for every 134 shots. What is your experience? How often do you check for erosion and make adjustments? Is erosion at a constant rate, fast for a new barrel with a decreasing rate afterwards, or vice versa?

Thanks,
Keith
Click to expand...

Back when I was shooting all the time in Group Matches, (and doing pretty good), I would set a barrel back .025 after about 250 rounds. Then again at about 500. The third time, if it was a really good barrel, I Would chop the entire chamber off and start over. This kept the throat pretty fresh.

This served me well. If I start shooting on that regular of a basis again, I will do the same. I am shooting more score than group now, and I do the same with my 30 caliber barrels.
 
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If it shoots I do nothing. So many other things change in the course of shooting a barrel 300 rounds. I have used same seat depth and powder all weekend or change one or the other during the match. Not sure how throat erosion effects the tune, which is all we are concerned with. I think Jackie is talking about putting barrel in lathe and cutting cone and shoulder but I could be wrong. I lately only shoot a barrel one or two matches..
Bill Greene
 
r44astro said:
If it shoots I do nothing. So many other things change in the course of shooting a barrel 300 rounds. I have used same seat depth and powder all weekend or change one or the other during the match. Not sure how throat erosion effects the tune, which is all we are concerned with. I think Jackie is talking about putting barrel in lathe and cutting cone and shoulder but I could be wrong. I lately only shoot a barrel one or two matches..
Bill Greene
Click to expand...

You are correct. My thoughts are to keep the throat fresh rather than chasing a corroded throat.
 
r44astro said:
do you ever just touch it with the reamer?
Bill
maybe a good way to keep a good barrel alive longer
Click to expand...


Bill, you can't just touch the leade ramp without changing the headspace if you are doing it with the chambering reamer because you would have to deepen the chamber to get to the leade ramp. That is why Jackie and some others "Set" the barrel back. They move the shoulder and the barrel cone then run the reamer deeper by that amount.

As to how often and how much, IMO, it depends on the bullet ogive relationship to the leade ramp. By that I think if you are jumping, say 0.020" then throat wear of 0.005" will not effect the performance as much as if you were jumping 0.005" initially. Same way on jam, a hard jam is not as effected by 0.005" wear as , say, a jam of 0.005". The dangerous, to performance, IMO, is where the gun wants to shoot best at a slight jump or a slight jam.

And all of this depends on the powder used, Some powders like V133 like a lot of startup resistance, some powders don't.


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