Next Size Breech Threads--Need Advise

[snrub47]

I have a swamped barrel that came with 5/8 breech threads and my plug is 3/4. How can I rebore this barrel without a lathe and square the bottom of the hole in order to make a good seal? I know the logical answer is to use a 5/8 plug, but in this case I am building a hooked breach percussion gun and need to use the 3/4 plug. I considered using an end mill to rebore the hole using my drill press but I am not sure it won't make the hole to large and result in a poor thread fit. Any suggestions??

[jimc2]

bad idea to rebore the barrel.  Your better off getting a new plug   my opinion

[Birddog6]

I would take/send it to someone that has the proper machinery to bore the hole & thread it properly. You can fit the plug to the barrel, but the hole has to be correct & no room for error on this, IMHO.     And I would send the plug with it, so he threads  the plug thread depth correct to get it in. Then all you have to do is fit & index it. 

[flehto]

I would never use an end mill in a drill press....not sturdy enough and it cuts independently of the existing threads. If your DP is tall enough what I've done is put the bbl thru the table center hole and clamp it in a V-block w/ shims on both 45 degree flats so the bbl is perpendicular to the table. When the existing hole and spindle are in line, clamp the V-block/bbl to the table. Use a 11/16" {.6875"} for a tap drill {{75% thread}, drill to depth  and grind a flat bottom on this drill and cut the flat on the bottom of the ctbre to the desired depth. If the 3/4"-16 tap can be chucked, turn the spindle on and then off and while coasting, bring it down into the hole and continue tapping by hand. If the tap can't be chucked, chuck a pointed center and use the hole at the rear of the tap shank and use a wrench to turn. I had to pivot the drill head and table to the side to get away from the DP base for a 42" bbl....Good luck....Fred

[Acer Saccharum]

Never ever try to use an endmill in a drill press in a plunge cut. You will probably ruin the endmill, the end of the barrel, and possibly the drill press spindle.

Take it to a qualified gunsmith.

Tom

[Pete Allan]

The problem with end mills in a drill press or some times even in a lathe is that they want to turn in like a screw. Sure bet to either brake something or hurt someone.

If the plug is one that we make we usually thread them in a number of sizes including 5/8"-18. It would be real easy to trade if it's one of ours. Email me.
Pete

[billd]

Add to Acer's post...and depending on the size of the endmill, possibly a few random body parts.
Bill

[snrub47]

Thanks for all the replies.  Obviously the end mill is a bad idea. My intentions were to use a drill bit (11/16) and just use the end mill to square the bottom of the hole. A 50 cal barrel with a 5/8 plug has very little shoulder for the plug to seal against, almost none where there are rifling groves. It needs the larger plug. I will take or send it to someone that has the equipment and knowledge to do this correctly.  Thanks again for all the replies.

[Acer Saccharum]

I didn't mean to come down hard on you, snrub47, but I was very concerned about the safety of your project...and you!

Regards,
Tom

[J.D.]

The question in my mind is what is the diameter of the breech, across the flats?

Is there enough material to safely thread a 3/4" dia hole?

IMHO, I would go with the 5/8 plug and file it to whatever shape you need.

God bless

[Rootsy]

Lathe that is able to single point and a boring bar minimum IMHO.  An endmill in a lathe will tend to leave chatter on the bottom of the bore.  Any respectable machine shop should be able to perform the work.  At least if you want it indexed off of the flats of the barrel.  If you want it indexed off of the bore... well that requires just a wee bit more time, effort, fixturing and setup... 

[BJH]

The face of the breech plug may be chamfered to the came angle as the drill bit you tap drill the barrel with. Think of the plug and seat of a globe valve.  This is how I have been setting them up for years. Just make sure the face of the plug scrunches into the shoulder of the barrel abit before the outer shoulder of the plug comes into fit. The interior shoulder does not need to be square.

[Acer Saccharum]

The face of the breech plug may be chamfered to the came angle as the drill bit you tap drill the barrel with. Think of the plug and seat of a globe valve.  This is how I have been setting them up for years. Just make sure the face of the plug scrunches into the shoulder of the barrel abit before the outer shoulder of the plug comes into fit. The interior shoulder does not need to be square.

BJ, that is the most practical way. Turn the plug chamfer to match to drill angle. Screw in until you get contact.

I do all the plug machining first, Chamafer, length of thread, shoulder of plug. Then I can try it in the barrel while the barrel is held in the lathe. Then it's easy to time the plug to the barrel: to get the plug to fit the seat, and the shoulder at the same time.

To do the barrel first, you have to take the plug in and out of the lathe to fit it to the barrel, which is darned inconvenient.

[keweenaw]

There is really no reason at all to go with a plug larger than 5/8 for a 50 cal.  Fact is I have a 54 that came from a leading barrel maker with a 5/8" plug in it which is certainly not ideal but it seals just fine with no blow around into the threads.  Sometimes we're all tempted to make things more difficult than they need be.

Tom

[snrub47]

I looked on TOW for a 5/8 English bar lock style breech plug, the one they offer is for a 15/16 barrel, my barrel is 1 1/8th at the breech. It seems I have no choice but to use the larger breech plug. Thanks again for all the replies.