Queston on breachplug threads

[Bill Hall]

Many years ago, I built my first rifle, a .54 plains, but didn't know where to turn for questions (early 80's so no internet help like MLF), so I just winged it as I went along. The barrel was a tru-bore brand, and was already threaded for a 3/4-16 breachplug, but I ordered a blank breachplug and I didn't own a 3/4-16 die. So I ended up cutting off the factory thread and cutting a 5/8-18 thread directly into the bore, as the minor diameter of a 5/8-18 thread is only slightly larger than the .54 bore. Then I whittled down the breachplug to fit the corresponding die. When it was finished, I had a 1" barrel with a .54 bore, and a 5/8-18 plug, and it seemed to work fine. It remained my hunting rifle for about ten years and withstood some really heavy charges (cuz back then I didn't know any better). The breach end of the barrel and breachplug shoulder mated up very tightly and it never leaked gas or otherwise showed any signs of problems. I have built a few .54 rifles since then and have either used the manufacture's cut 3/4-16 thread, or had a machinist recess the barrel so I could cut the proper thread.

My question is, structually speaking, is there anything wrong with using a bore sized breachplug like the example described above? Is a smaller thread inherently weaker than the standard thread in any given barrel? I may be wrong, but I think CVA plugs their barrels with a bore sized plug, the same as my first rifle, with the exception of a drum threaded through the side of it. Is that internal shoulder really that important? I appreciate any thoughts and answers. Bill

 

[Birddog6]

Getz Barrel company does them every day that way & have told me they have never had a problem with it. :hmm: Personally I don't like it cause I like a shoulder for the breechplug to but against. So if I use a Getz barrel

Keith Lisle

 

[Bill Hall]

Thanks Birddog, I was just wondering if I was playing with fire back then. Sounds like it was ok, but not the best.

I've since cannibalized that rifle and that was the barrel I had a coworker recut and then I threaded it to 3/4-16. Bill

 

[Birddog6]

That is what I do. By the time you get a .54 cal. bore in & then the rifling cut, you have no shoulder at all for the breechplug. I have them redrilled & retapped to 3/4" plug. Even a .50 cal bore & a 5/8 plug, by the time you do the rifling the shoulder is so small you can barely see it.

Keith Lisle