My Uncle's nipples are blowing out

[Murv]

:idunno: My Uncle called me and wanted to know why his nipples blew out of his black powder rifle.
It is a .45 cal. Thompson Hawken.
He is shooting pyrodex.
He said the first time he shot it he loaded it with 60 grains and it blew the nipple out.,
He screwed in the new nipple and said it was tight, he loaded it then with 50 grains and said the same thing happened. He said both nipples blew out and he couldn't find them.
He said the threads where the nipple screws in is fine, and he said the area around the the threads don't look rusty.
Can anybody shed any light on what could be happening?

:idunno:

 

[CaptainKirk]

Damn, I hate it when my nipples blow out! :rotf:

Seriously though; the only reason that would (could) happen is if the threads were damaged, undersized, or the wrong thread (metric vs std)
To my knowledge (don't bet the farm on this!) the only manufacturer using metric threads is Lyman. He should start with a new nipple, threaded correctly for his rifle, then run the correct size thread tap into the "snail", watching for signs of loose-fitting threads. The tap should be fairly snug. If not, he may need to replace the snail with a new one. They are fairly inexpensive.

 

[Zonie]

Murv
The TC Hawkens use a nipple with a 1/4-28 thread. If your Uncle bought some M6-.75 nipples that are commonly used on the Italian reproductions they would be undersize in a 1/4-28 threaded hole.

A M6-.75 thread has a major diameter (the outside diameter of a male thread) that equals .2362.
The thread spacing on these threads is .75mm which, if converted to our thread system of measuring threads per inch would equal 34 which to the naked eye looks pretty close to a 28 threads per inch hole.

A 1/4-28 internal thread has a minor diameter (the smallest diameter of the thread) that equals .2113-.2173.

Notice that this is smaller than the .236 size of the M6 thread. If the M6 nipple is screwed into a 1/4-28 hole it will only be engaged about .022, or eleven thousandths per side. That's about equal to the thickness of 4 pieces of printer paper.

What this can result in is something that can feel like it tightens up but in reality the male nipple threads are just hanging on by a thread (Ho ho ho...I couldn't resist :grin.

Seriously, the metric nipple can screw into the inch sized thread even though the thread pitch isn't the same and it will feel like it has tightened up but because the threads are just barely engaged the results is there is no strength there. Almost any heavy force can cause the nipple to blow out.

Tell your Uncle to buy some nipples with 1/4-28 threads on them and the problem should go away.

 

[ebiggs1]

He can order them directly from Thompson Center and be sure he has the correct one. I suspect he got some Lyman nipples at Cabela's or other sporting goods store that sells Lyman products.

 

[hoochiepapa]

OUCH!! :haha:

 

[ohio ramrod]

If he used undersized nipples and blew them out the origional threads are probably damaged. Dixie and log cabin both stock over sized 1/4 28 nipples and taps if needed. :hmm: