Need Advice on Fitting Breech Plug

[cjbrown_2000]

This is what I'm working with: Colerain .58 cal straight octagon barrel. L&R flint patent breech plug. .75 x 16 threads.

I fitted the plug to seal with the shoulder inside the barrel. The plug is indexed so bottom flat is on bottom. Problem is that I have a 1/32 to 1/64 gap between barrel and plug (plug face is not square with threads). Doing the math, I see only two solutions...

1) File the plug to seal and index to the nearest flat that will index with no gap. This will likely put the bottom flat directly on top.

2) File the plug and barrel so that I am indexed with the bottom flat on bottom. Problem is I'll need to take 1/32 off barrel. Barrel came from Colerain (via TOTW) with only 0.52 thread length. That means I will only be left with 0.49 thread length.

Any suggestions?

Also, the plug face is not square with threads. Is this normal? Do I file the plug face to be square with barrel?

Thanks!

 

[poker]

Losing the 30 thou is the route I would go. I highly doubt that would affect barrel integrity, but call the barrel maker and get their opinion.
And yes the plug face needs to be square to the barrel.
Im assuming you are doing this in a vice with a file? It may be good to visit a machinist and use a lathe. He could deepen the cavity in the barrel so you need not lose thread length if that concerns you. Also he would be able to easily get everything squared up properly. Should not take much time at all.

 

[M. De Land]

Both the internal and external shoulders need to be square with and simultaneously meet their respective seats so if the threaded area is not coaxial (in line) with the bore it needs to be set back and redone. It should be done in a lathe but if by hand then an alignment jig/guide needs to be made to keep the tap straight with the bore.

 

[Herb]

The plug thread is 16 per inch. Turning the plug one revolution moves it 1/16" or .0625 inch. If you have that gap on the bottom, you need to thread the plug into the barrel one revolution. This means filing that much off the plug face (end of the plug inside the bore, which you already have contacting) (which is a lot to file, a Dremel carbide disc cuts faster, followed by filing. Leave it long for final smoke-fitting, or use black Magic marker). You also smoke up the plug where it contacts the back of the barrel, and the end of the barrel. File or carefully grind the high spot off the plug to allow it to turn in. Don't file the end of the barrel. The plug should be square to the threads, the face of the threaded plug and the end of the bore. You can do this by hand, I have done it 50 or more times.

 

[SDSmlf]

The plug thread is 16 per inch. Turning the plug one revolution moves it 1/16" or .0625 inch. If you have that gap on the bottom, you need to thread the plug into the barrel one revolution. This means filing that much off the plug face (end of the plug inside the bore, which you already have contacting) (which is a lot to file, a Dremel carbide disc cuts faster, followed by filing. Leave it long for final smoke-fitting, or use black Magic marker). You also smoke up the plug where it contacts the back of the barrel, and the end of the barrel. File or carefully grind the high spot off the plug to allow it to turn in. Don't file the end of the barrel. The plug should be square to the threads, the face of the threaded plug and the end of the bore. You can do this by hand, I have done it 50 or more times.

Herb has got it spot on. Personally have only fitted about half a dozen, but no big deal as long as you move slow. With a octagon breech plug and a four jaw chuck it goes pretty quick in a lathe, but so does just using a file (I resist the urge to use a Dremel for this type of work). I use Prussian Blue (a $5-$6 tube from an auto parts store will last forever) for marking, but that is just personal preference.

An important point that Herb made that I believe needs to be emphasized is DONOT file or modify the end of the barrel. As a general rule, always modify the less expensive of two parts when fitting, whether it be a breech plug or sight for example, modify the breech plug or the sight to fit, not the barrel you are fitting it to.

Another option is to let TOW fit your breech plug for you. Only $25 as long as you haven’t modified the breech area of the barrel or removed too much from the plug, in which case the cost could go up.
https://www.trackofthewolf.com/Categories/PartDetail.aspx/1012/1/LABOR-BP