3/8 liner or drum in a 7/8 barrel?

[Roger Fisher]

Ok a question for the Machinist types out there!  What is the opinion of using a 3/8 liner in a 45 cal 7/8 straight barrel , if there is a reason to go to that size as in a sloppy hole for a 5/16th?   Is there enough 'meat' left safety wise? Never saw this question posed here or elsewhere.  

Anyone care to give an educated opinion?

Does the champher under the liner flange tightened up against the sideflat add a substantial amount of strength to it?  

I witnessed one come out of a CVA or TC couple years ago.  Examination showed the barrel threads were burned cut over time and the liner left go in his .54 half stock.  The shooter well known to me and he seldom if ever shot heavy charges!

I'll give you one guess who was on the firing line to his lock side

[oldiemkr]

Of course I'd like to see the barrel but my first nickel would be bet on the fact that the threads were not up to snuff to start with. This would then readily allow hot gases and then dirt and then rust into the threads. That would cause premature failure for sure.

Even the "fine" threads used on liners have a surprising pullout strength even at a 75% thread depth. I often use a slightly smaller tap drill to increase thread depth on tapped holes like this.

The type of metal could also make a difference. Leaded stock taps real well with a good finish BUT sometimes when the tap is backed out you can drag a little off. harder  steel would tap a little different [4000 series} and be more apt to be affected by a dull tap or lack of lube.

I used to have to teach a "student shop" course. Tapping was not something everyone did well. I always go with the smallest liner first.You can always open it up.

[wvmtnman]

If you were afraid of gas leaks, you could always braze the drum in.  make a match line, like on the breech plug/barrel, where the drum should be.  back the drum out a little and heat it.  Allow the solder to begin flowing in the threads then screw in the drum until it meets the match line, all while holding the heat on it.  I did this with a 13/16 barrel I did, as an added measure of protection.  Works well!
                                                                           Brian

[TomK]

If you were afraid of gas leaks, you could always braze the drum in.  make a match line, like on the breech plug/barrel, where the drum should be.  back the drum out a little and heat it.  Allow the solder to begin flowing in the threads then screw in the drum until it meets the match line, all while holding the heat on it.  I did this with a 13/16 barrel I did, as an added measure of protection.  Works well!
                                                                           Brian

Brian, I was wondering what to do with a Vincent 7/8 barrel in 50 cal. Sounds like brazing the drum in is a good "peace-of-mind" idea.
Thanks!

[Roger Fisher]

Actually, we were asking about a vent liner

[Simon]

If the original vent was in the middle of the flat so that you did not have to cut into the flat above, and it left all of the vent on one flat, you should be ok. I have seen vents into the flat above the pan and when it was filed flush it didn't get a good seal. To much chance of leakage in that case in MHO.