Disaster strikes drum installation.

[herath]

While drilling hole for drum on straight contour GM barrel ,drill wandered in old drill press toward plug about 1/8".My fault ,this press is old in need of replacement.Elected to notch plug as some old makers did .Is this a good solution or should I cut barrel off and place a new breech plug and reset tennons[I use staples]?

[herath]

I know some old makers did this intentionally to create better ignition in their opinion.However does this create areas that are difficult to clean  area or a weak area where metal is thinner at breech plug threads[barrel thinner here as opposed to further foward where have full barrel thickness to bore. This is a .40 caliber target and small game rifle ,no loads over 60 grains fffg+prb.

[herath]

Reading some previous posts on this topic there is some concern about gas cutting at threads in this situation where plug has some threads on its face hence seal at plug face is gone in this area[notch].Any comments? I may set back barrel and refit plug and recut drum;this looks safest.

[Dave B]

I have done this my self on several of mine and they work just fine. I will pull the beach just to check on it and its never gotten to be a problem with keeping the breach thread clean. My very first rifle I did this on and only after 45 yrs do I finally need to replace the drum due to gas checking. The bigger issue was then I was hand drilling and tapping and my clearances are what led to the checking more than the notching of the plug. The leak is at the point opposite where the nipple is.

[David Rase]

Herath
Even if you had a brand new drill press drill bits can wonder out of the center punch mark if you try and drill the hole with too large a bit.  You must make a pilot hole and then, depending upon the size of the finished diameter, you might need to enlarge the hole in increments.
Sorry that I did not address your initial question but hopefully this advice will keep you from having the same problem again.
Dave

[bluenoser]

Further to David's advise - a centre (center for our southern neighbors  ) drill is a good choice for starting holes.  Their design keeps them from wandering.

Laurie

[Dphariss]

Buy a selection of center drills to start holes with. They are designed not to drift and require no punch mark. Just a pencil or Magic Marker dot will work.
http://www1.mscdirect.com/cgi/NNSRIT2?PMAKA=71031025&PMPXNO=2044161&cm_re=ItemDetail-_-ResultListing-_-SearchResults

Don't order carbide unless removing a broken tap or drilling hardened material.
Dan

[geb324]

Can you go a size higher on the drum thread?
and redrill

[Acer Saccharum]

Center drills are great. I like to run them deep enough to countersink the hole just a hair, I mean hair, bigger than the tap drill size. This gives a sweet entry spot for all your subsequent drills to center.

Just so you know, ALL drills will drill oversize holes, especially if you don't drill smaller pilot holes first.  I work my way up to the tap drill by stages, start with a pilot hole, then one size under the tap drill, then the tap drill. This leaves the proper amount of stock for the threads.

This is actually a combined drill/countersink.

[Dphariss]

Like Acer said.

Dan

[Herb]

Herath, I took a course called "Antique Custom Riflesmithing" at the Green River Rifle Works in Roosevelt, Utah in 1978, taught by the shop foreman, Greg Roberts.  We built .45 caliber (they had a lot of those barrels) Leman Trade Rifles.  Greg told us that original rifles had the breech plug notched, as you have done.  We all made our plugs like that, and I recently pulled my drum to check how well I was cleaning the bore.  There was no problem with the breech plug face or that notch.  So it won't cause any problems, but I would not build a new one like that.

[smylee grouch]

Call Dennis Mc Candless in Los Cruces, NM. He can make your problem go away and still keep your original lock and barrel pin holes.    Smylee

[herath]

Thank you all for the suggestions and advice.I see that my mistake was trying to drill in one step.I'll use the center drill and size below technique from here on.I already sent the barrel for cutting and rethreading;holes for tennons and pins have been filled and all will be refit.