Helicoil nipple?

[jbrent]

Good day all. I picked up a nice little 16g a fowler. Something did not look quite right about the nipple - didn't seem to be down tight - so I carefully backed it out to have a look...a small chip of thread came out with the nipple. It would appear that it had been cross treaded at some time then then forced back in. The first 3 of the 6 threads are missing for about 1/4 of the circumference. The bottom 2 threads on the nipple are a little chipped but it can be run in if gentle and very careful to get it straight. A 1/4-28 AN bolt treads into it OK but is a little sloppy so I'm thinking the nipple was oversized - it measures .2625. I don't think there is enough material left to get good threads for a .035 over (.285) nipple so have been considering Helicoil. However, It looks like the outside diameter of the coil will be quite a bit larger than the flange on the nipple. Is this a problem? The fix would be visible - will gas leak through the coil? I would like to hear from someone with first hand experience in repairing nipple threads with helicoil. Thanks...jbrent

 

[Treerat]

Having worked in the Tool and Die tade for thirty two years I feel that helicoils are about the worst thread inserts out there and I certainly would'nt trust my safety or that of bystanders to one in a firearm. I would put on a new drum or if it's a patent breach fit a new breach. Another possibility would be going up to a musket size nipple IF the thread is big enough to completly remove all the old threads and the drum/patent breach is big enough to accept it.
Bill

 

[sc45-70]

If it were mine, I'd contact Track of the Wolf and order an oversize nipple and tap.

SC45-70

 

[Zonie]

This is a "to scale" drawing of a nipple and Heli-coil screw thread insert.

I drew it to explain how spark plugs can still seal when they are installed in a Heli-Coil but percussion nipples may not fully seal.

Although the Heli-coil will probably not seal against powder gas leakage in my opinion, it can be used to repair the threads in a nipple hole if it is bonded in place using a good epoxy.

If you buy a stainless steel Heli-coil it will be stronger than the original threads and it will resist corrosion better than the plain steel type.

Heli-coils come in different lengths. The length is usually a function of the thread diameter and the standard ones are 1D, 1 1/2D, 2D etc long.
You will want the 1D length insert and even this may block off a part of the flame channel hole that connects the nipple hole with the powder chamber.

If you choose to go this route, I suggest that you have a good gunsmith or machine shop tap the hole and install the insert.

 

[bubba.50]

all i can say is- that's a lot of stuff goin' on right next to yer eyes & yer brain-pan to be trustin' to a heli-coil.

my opinion and yer welcome to it. luck to ya & have a good'en friend, bubba.

 

[Treerat]

My point exactly. Keep in mind also that helicoils are supposed to bottom out on the threads in the main piece. If the part is tapped freely through then the insert can move up and down. In years past I have removed many messed up helicoils that came out looking like bent up wires. Our toolroom got away from those things years ago. For the sparkplug diagram that Zonie shows they would probably be great(note the thread bottomed out and a gasket on top) but I would'nt trust my head to one on a gun.
Bill

 

[Treerat]

Just checked. Track has 5/16-18 npples to fit No.11 percusion caps. If you got room for a helicoil you got room for one of those.
Bill

 

[sc45-70]

Since the gun would have to be drilled and tapped for a Helicoil, why not just drill and tap it for a 5/16 nipple?

SC45-70

 

[jbrent]

Thanks guys. Helicoil didn't feel like the right fix - less so now. I got to looking at TOW catalogue last night and also saw their 5/16 #11 nipples. They sell 5/16-18 and 5/16-24. From the charts it looks like there should be enough material left after the old treads are cleaned out to accommodate either. Is there an advantage of using one thread over the other - ease of tapping? strength? other considerations?

Plan "B" - I figure if I mess up on the 5/16, it looks like there may be just enough room to tread in a 3/8 plug and tap it for a std. 1/4-28 nipple.....jbrent

 

[huntinguy]

A 1/4-28 AN bolt treads into it OK but is a little sloppy so I'm thinking the nipple was oversized - it measures .2625.

sounds like a case of someone screwing a SAE into a metric hole. Six mm is close to 1/4.

There are different types of heli coils but, not one would I trust near my face.

Oversize tap and nipple is the best option, IMHO

 

[Birddog6]

I am not a helicoil fan. To me it is a last resort for a unfortunate disaster. I know they used them in lots of situations, however if used in aluminum & etc. the people designing such things know a He// of a lot more about metal than I do & it works. But no way I would chance one on a nipple on a rifle or fowler, as it would forever haunt me of IF I DID IT RIGHT & If it would hold, etc. I say Tap it out larger or replace the drum, fix it correctly...& be done with it is always my thoughts on such. Definitely not a place to experiment.

Keith Lisle

 

[Treerat]

I didn't notice the 5/16-24. I feel that would be better as you get more threads contacting also fine threads seem to stay tight better.
Bill

 

[jbrent]

I don't think it was metric. 6mm = .2262" that is quite a lot tighter than .2625....unless they made some nipples in fractions of mm (.2625" = 6.66mm, 6.5mm = .256"). In any case the threads are boogered now so the repair will be imperial dim. ....jbrent