Breaching with little contact

[chrisweller]

Hello I'm starting my first build and just recieved my barrel. Its a colerian 54 calliber, 15/16 straight. The question I have is that the 5/8 threads dont appear to have much of a shoulder to seat the breach plug to. I'm using a fixed flint breech plug if that matters. Any insight would be appreciated.

[JDK]

You're fine as long as the breech plug face is a compression fit with the shoulder that's there.  The shoulder in this case will be small but you don't need much to make a seal and it is more important to have wall thickness around the plug.

You have to consider that .54" is almost 9/16" so your 5/8" plug will not have much shoulder to engage.  It's a trade off as you have a 15/16" barrel and if it were fitted for a plug the next size up, a 3/4" (or 12/16") plug, that would only leave 3/16" of barrel diameter....divided by 2 and you would only have 3/32" or .094" wall at for the plug.  Thin breech for a .54 caliber.

Now, it's late but I hope somebody else is around to grade my math.  Good night.

Enjoy, J.D.

[Dave R]

Chrisweller,

Are you sure your Colerain barrel has a square face for the breechplug to shoulder on? I have used several Colerain barrels including a .54 Colerain that we chucked up in a lathe and squared the shoulder so the breech plug would flush itself against the plug, All ones I have used looked like Colerain ran a drill bin in the breach end then cut the threads and there fore this area would aways collect fowling!! Possibly they have seen the light? How is your .54 made?

[JohnTyg]

Have a 54 cal. Getz sitting around awaiting a project, there is not much of a shoulder, on that caliber, but I consider it very well breached as it is very well sealed all the way around. 

Pictured is a plug that I fit to an older Orion barrel (a strait taper that I hand swamped to a possibly odd profile of 1" at breech, 13/16 at waist, and 14/15 at barrel.  Used blue layout dye to see how well sealed it is.  It was very nicely bottom taped as received. (You can see the "lands and grooves in the layout dye.) Doesn't look as if there is any room for fouling.

John

[Don Getz]

When you breech a 54 cal. barrel with a 5/8 x 18 plug there will be very little to breech against, and it usually will have
an angled cut on the plug, and the bottom of the hole will also have a corresponding angle.  As long as they are scrunched against each other, there should be no problem.  .........Don

[JohnTyg]

Don,

Funny you should post that seconds after I mentioned your excellent breeching!

John

[chrisweller]

Thanks everyone who responded. Dave R it does look very inconsistant, I need to get in better light, but have to clean out some metal shavings left inside to have a better look.

[Acer Saccharum]

Whether there is a shoulder or not depends what the plug dia is compared to the bore. As long as there is sufficient material to get a complete threading, strength is not an issue.

But if there is a gap between plug face and bore shoulder, crud will collect there, and is very difficult to clean. I like to file the back of the barrel to set the plug face farther ahead to close the gap.