Heat distortion and barrel profiling

[Scott-ak]

I am profiling a PCC barrel that started as a 1.0" blank. I'm cutting w/carbide inserts, taking .015 DOC passes, turning about 1000 rpm. I can't recall the feed at the moment, it's fairly aggressive. Not running the coolant. As expected the barrel gets pretty hot. Out of curiosity I disengaged the tail stock and see the muzzle is about .070 out. After letting it cool the muzzle returns to zeroed. This barrel will be 16", I did several shortys back before the rules changed and don't recall seeing this.

Would you be concerned that at some point (reduced diameter) the distortion will become permanent?

 

[Ggmac]

I would be concerned that the barrel poi will walk after the 3-4 shot ( just guessing on shot count before the heat makes the barrel wander )

 

[DShortt]

Stop cutting for a bit when the barrel gets warm enough to be uncomfortable to hold for 20 seconds or more. Resume cutting when it's cooled.

Been working fine for me for a while now. Takes time, yes. But I've got time.

 

[dnellans]

I am profiling a PCC barrel that started as a 1.0" blank. I'm cutting w/carbide inserts, taking .015 DOC passes, turning about 1000 rpm. I can't recall the feed at the moment, it's fairly aggressive. Not running the coolant. As expected the barrel gets pretty hot. Out of curiosity I disengaged the tail stock and see the muzzle is about .070 out. After letting it cool the muzzle returns to zeroed. This barrel will be 16", I did several shortys back before the rules changed and don't recall seeing this.

Would you be concerned that at some point (reduced diameter) the distortion will become permanent?

If the distortion becomes permanent you can zero it out in a scope, so thats not a problem, you're going to crown/chamber on the ID at each end. As mentioned above though, if the barrel is moving significantly from cold to hot, then there is stress in the steel that will cause it to walk in longer strings.

 

[Scott-ak]

I got busy and just getting back to reply to this post. I finished the profiling. I reduced the DOC enough to still get a good finish while maintaining speed and feed. I also took a couple minutes between passes. I left the barrel a little heavier than planned out of concern for it distorting under long strings of fire. Our matches are under 30 rounds a stage and I don't expect any problems. I'll probably run it a year and then remove some more material if it's stable. thanx all for the feedback.