Burnishing throats in rimfire

mwezell

mwezell

Mike Ezell
I asked about this sometime back in another thread and didn't get any feedback. What's best for burnishing the throat in a rimfire barrel? I've thought about small ceramic rods. Any thoughts about that? Thanks in advance for the help.--Mike
 
Pack a small RCBS nylon case neck brush(not a thin bristle bore brush) with 320 grit lapping compound and short stroke the throat 10 cycles. Clean the barrel real good to remove all traces of the compound. This will amaze you when observed with a bore scope the difference between as reamed and after lapping. What you thought was a great reamer will change. This will greatly reduce any leading and carbon build up there. This method also eliminates the break in for CF. You can fire 10 max loads right off the bat in a PPC and there will be very little copper fouling. The heck with the one shot and clean method. Don't know if this is the "best" though. Sure is quick.
 
Thanks Jerry. That sounds good.
What I had in mind was to put a ceramic rod in the tool holder on the lathe and to set the compound to match the leade angle, then lap the throat, very lightly, with the barrel spinning in the lathe. Is that even feasible?
 
Sounds dangerous if the throat is not concentric with the spindle axis and I don't think it will do anything for the sharp corners of the lands in the throat.
 
mwezell said:
Thanks Jerry. That sounds good.
What I had in mind was to put a ceramic rod in the tool holder on the lathe and to set the compound to match the leade angle, then lap the throat, very lightly, with the barrel spinning in the lathe. Is that even feasible?
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Hell no, you want the lapping texture to follow the bore centerline, not perpendicular to it, do exactly as Jerry has stated for best results.
 
It's been said here that Calfee(no opinion) uses a hardened steel hob, of some sort, to polish the throat. That's not what gave me this idea, but if true, would seem to give the concept some credence. I understand the lapping finish would be across the bullet path, but would it not be better than what the reamer leaves, considerably? You could always do as Jerry mentioned after this process, but just enough to change direction of the final finish. My thinking is actually, that it would leave a very smooth and more uniform throat, if done properly. Keep in mind, very light pressure and precisely following the exact leade angle. ...polishing if you will. Thanks
 
mwezell said:
It's been said here that Calfee(no opinion) uses a hardened steel hob, of some sort, to polish the throat. That's not what gave me this idea, but if true, would seem to give the concept some credence. I understand the lapping finish would be across the bullet path, but would it not be better than what the reamer leaves, considerably? You could always do as Jerry mentioned after this process, but just enough to change direction of the final finish. My thinking is actually, that it would leave a very smooth and more uniform throat, if done properly. Keep in mind, very light pressure and precisely following the exact leade angle. ...polishing if you will. Thanks
Click to expand...

Probably the most convincing method would be to take a piece of chambered practice barrel stub and try your ceramic rod method, then follow with the brush lapped compound method, borescope and see which produces the best finish.
 
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