Moving a chamber forward

[Henryrifle]

Maybe this question isn't a great fit for the gun project subform... I recently rechambered a barrel that had previously been a 7mm Shehane. I cut off 2 1/2", the entire old chamber and the new chamber, a 7-6.5 PRC consumed another 2" of rifling. The round count before rechambering was 560.

After the new chamber was cut, I could not tell by looking with a borescope at the lands and grooves that the barrel was not brand new.

Would you expect this barrel to speed up over the first 100-150 rounds as usual or is that effectively pre-completed given the barrel's history?

Thank you,
Hank

 

[LVLAaron]

This is one of those threads that could end up being 18 pages long.

 

[Bill K]

I would think the bore is already broke in and not much change will occur as to FPS. Your chrony will tell you after you shoot it for those 100-150 rounds.

 

[Henryrifle]

I would think the bore is already broke in and not much change will occur as to FPS. Your chrony will tell you after you shoot it for those 100-150 rounds.

For sure that is true, Bill, and normally I'd be fire forming anyway, making my question all but irrelevant except that this is my second chambering with this reamer and I cut both chambers exactly the same. Would be great to just get on with load development w/o being concerned about what is going to change.

Thank you,
Hank

 

[TylerFromMS]

@Henryrifle I just did this and it did not speed up again- went from 7-6.5 PRC to another 7mm. I didn't even cut 2" off- just the tenon.

 

[jackieschmidt]

I set barrels back on a regular basis and the tune does not change.

 

[Alex Wheeler]

No, because the speed up is caused from the lapped finish breaking in, not the throat. Barrels do break in. And your about to see the proof for yourself. If the throats cut nice you wont see copper either.