1/2 x 20 Breech Plug

[44-henry]

Kind of an odd question, but what are your opinions on a 1/2-20 breechplug thread on a pistol barrel? If the caliber was small, say 32, would a well fitted plug be considered safe if 1/2" deep?

[okawbow]

Yes. A 1/2" breech plug would likely work at 1/4" if fitted properly. That would give you 4 or 5 good threads.  So, at 1/2" long, you would have9-10 good threads. With a 32 cal. You would still have a good shoulder left to seal the plug.

[Bob Roller]

Kind of an odd question, but what are your opinions on a 1/2-20 breechplug thread on a pistol barrel? If the caliber was small, say 32, would a well fitted plug be considered safe if 1/2" deep?

I would have no qualms abut a 1/2x20 thread in a 32 caliber pistol.With loads used in those little calibers I wouldn't be afraid of a 7/16x20.Small bore caplock pistols are common in Germany and use about 10 grains of powder so the chance of a blow up is zero.

Bob Roller

[44-henry]

Thanks for the info, didn't figure it would pose any problems with light loads, I'll definitely proof it if I go that route. I did the calculations on shear area compared to a 9/16 -18 thread and it was substantially different.

Regards,

Alex Johnson

[gunmaker]

A 1/2"-20 tpi is much bigger than a 1/4"-28 vent liner some of those only have 3-4 threads.  Why wouldn't 1/2" work well on a 36 or smaller bore rifle or pistol as a plug ?   Just asking,  if one of the metal eng. knows yes/no--just like to find out ?  ...Tom