Breach plug thread size

[Walks with fire]

I have a Green Mountain drop in percussion barrel in 1/70 twist .54 caliber that I want to have converted to flint. What concerns me is what thread size to get the flint plug in. I don't want to remove it until I am sure it can be done. Has anyone removed the percussion plug on one of these barrel or know what size threads they are?

 

[Herb]

Should be 3/4 x 16.

 

[MSW]

Walks with Fire,

[disclaimer] my terminology may mis- name things, or confuse nomenclature; i apologise in advance...

you have undertaken a more challenging than usual project vis-a-vis the timing of the plug. usually, you must get the shoulder of the plug (by this i mean where the outside of the plug hits the very end of the barrel), the base of the plug (i mean here where the bottom of the plug meets the ends of the threads and the flat spot inside the barrel), and one of the flats (here's where one of the flats of the plug comes into alignment with any of the flats on the barrel) to meet at the same time.

since you have a 'drop in' assembly, you will have to get the shoulder of the plug and the base of the plug must do all of the above, yet have one specific flat meet its opposite number on the barrel, so that the hooked portion of the breech (which is part of the breech plug) will correctly align with the touch hole, sights, under rib, and other good stuff which you would otherwise apply after you timed the plug.

i have managed this trick, and it requires either a lot of skill or a good bit of snarling, cursing, and dumb luck... lacking the former, i relied upon the latter. inasmuch as i have yet to blow myself to bits, i believe that i managed to get it right.

best of luck with your project... remember that patience is a ^&*%ing virtue, and as always,

make good smoke! :grin:

 

[Walks with fire]

Well my intent is to call Bob Hoyt and see if he can do this job but the only flint plug I have is a 5/8" x 18 so I would have to order the proper thread size if I can get one. I don't know if Bob can or will do it yet. I know it's not something I want to attempt and not even sure if it's worth the risk of ruining a good barrel in the attempt.

I was hoping to at least find out what size it was before I called him. I do know that the 15/16" .54 barrel blanks Green Mountain currently sells are 5/8 x 18 but don't know if the drop-in's are the same. Not an easy job by any means but a good smith like Bob may be able to do it.

 

[Herb]

You did not say 15/16 barrel size, but the Green Mtn web site does say 5/8 x 18. The more common 1" .54 barrel has a 3/4 x 16 thread.

 

[necchi]

I do know that the 15/16" .54 barrel blanks Green Mountain currently sells are 5/8 x 18 but don't know if the drop-in's are the same.

There is/was no reason for GM to change up their barrels,
They are the same.

 

[Walks with fire]

Yes; I believe that it would be 5/8 x 18 and sent an email to GM as someone suggested. I would think that if the plug can be bottomed out when aligned properly the smith could use a wedding band to fill any gap between the barrel and the end of plug. That might look pretty good anyway.

 

[Walks with fire]

I received an email reply from a Mr. Mike Hagar at GM today and he wanted some additional information on the barrel such as the serial # and whether it was purchased as a GM made drop-in and not an assembled from parts by someone else.

He provided no conformation on the thread size as of yet but am certain he will reply shortly.

Very good customer service in my opinion. I originally purchased it intending to have a Mr. McCandless do the conversion but he fell ill before I got it sent to him. The project will move on and I hope Mr. Hoyt will accept the project.

 

[Walks with fire]

Posting this for anyone considering conversion of Green Mountain drop-in barrels. They were all made with 11/16-20 breech plugs according to Mr. Hagar from GM.

 

[necchi]

Now that's just plain weird.
I believe you,, but I wonder why they did that?

 

[Walks with fire]

Not a clue why. The first email requested the serial # on the barrel and wanted to be sure that it was manufactured at the GM factory. I assured him it was a genuine GM drop in barrel an supplied the serial #. Track does offer a flint plug 11/16-20 in 15/16" and I have not been able to reach Mr. Hoyt yet.

When I clicked on the plug on Tracks site it also said for TC and Green Mountain drop-in's

GM would not do the conversion.

 

[necchi]

Well I'll be darned, I'm glad you came back to correct my erroneous presumption. :redface:
I'll try to file away that info about the drop-ins.

 

[Walks with fire]

Yes; I would be logical to think it would be 5/8-18 and that's what I believed it would be. Glad I found out though. Wouldn't do much good to send the wrong plug now would it.

Getting Bob Hoyt on the phone is quite an job in itself. I am sure he is very busy and I am the very patient type. I hope he will do the project for me. I think I could do it myself but for what it would cost it's better to have a gunsmith do it.