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Throat wear

RetiredArmy

Gold $$ Contributor
What is normal wear on a throat? 6mm br, 105 amax bullet since new. Varget powder, slower then most between 27.9 and 29 grains. Never ran hot! When barrel was new, round measured 1.783 bto. Measured now with same bullet and 601 rounds later it measures 1.866 bto. That is .083 of throat erosion. Of course I understand my measuring skill could be lacking some but not .083! I'm using the Wheeler stripped bolt method. It is a Savage prefit barrel. It shoots well one day and goes to heck the next. What say you?
Thanks Bill
 
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What is normal wear on a throat? 6mm br, 105 amax bullet since new. Varget powder, slower then most between 27.9 and 29 grains. Never ran hot! When barrel was new, round measured 1.783 bto. Measured now with same bullet and 601 rounds later it measures 1.866 bto. That is .083 of throat erosion. Of course I understand my measuring skill could be lacking some but not .083! I'm using the Wheeler stripped bolt method. It is a Savage prefit barrel. It shoots well one day and goes to heck the next. What day you?
Thanks Bill


Bill,
I agree that seems like a lot at 601 rounds,...I am guessing between possible error in measuring coupled with different ojive measurements from a different lot of bullets?....
Wayne
 
I have measured seating depth to touch on a few brand new unfired barrels where I found a significant increase in freebore after very few rounds fired. On the few that seemed to have huge initial jumps, they all settled down and grew "normally" after that. I figured that in those cases my initial reading was a false one from a minor burr or some machining irregularity in the lead. Perhaps that could be some of what you are finding.
 
You’ll get a decent amount of wear in the first 100-150 rounds with some chamberings as a barrel breaks in, then the growth should slow down significantly if not hot rodding the rounds.

I have noticed the same thing on all of my barrels as well over the years in various cartridges. For that reason, I have decided that i am going to start designing my reamers with about .015” - .020” less freebore than normal on the bullet i plan to shoot to help account for that initial wear as a barrel breaks in. I have a couple reamers for big magnums that i am going to send to JGS this week to get the freebore ground down shorter.

By the time my barrels break in with less freebore, I should be sitting pretty close to where i actually want the freebore to be.
 
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I agree that .080" is a lot. I have seen where if I clean with Iosso that I get accelerated throat erosion but no where near .080 in 500 rounds. If I use chems and JB I get much less throat erosion.

I think rounding of the rifling yields around .010, depending on the bullet.
 
Yeah .083” is a ton of wear on a small round with a fairly low round count...

Bullet lots can and will vary, but that seems excessive. Being a Savage pre fit barrel, im curious if the barrel has ever been removed and reinstalled since the first BTO measurement taken when the barrel was new? If not put back to the same exact position you could change the chamber length to the lands a lot.
 
Yeah .083” is a ton of wear on a small round with a fairly low round count...

Bullet lots can and will vary, but that seems excessive. Being a Savage pre fit barrel, im curious if the barrel has ever been removed and reinstalled since the first BTO measurement taken when the barrel was new? If not put back to the same exact position you could change the chamber length to the lands a lot.
No sir, barrel has never been moved since I installed it. I also used the same bullet to check at 601 rounds that I used on the very first round. Kept it in a baggie in the die box. Spoke with barrel manufacturer, they said to pull it and they will take a look to see if there is a problem with it if I want to.
Thanks Bill
 

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