Any guidance on proof testing a barrel for a .40 flinter build?

[MiltonBradly]

Hey all,

After a long delay I'm back to working on my .40 flintlock project... I have the stock roughed out, barrel and lock inlet, touch hole liner installed, ram rod hole drilled and I am half way through fabrication a two piece breach plug/tang (for ease of barrel removal).

As it stands I have the barrel at a stage where I could proof test it any time I want. Its a Green Mountain 36" .40cal 13/16" straight octagon barrel with a TOTW white lightning touch hole and a breach plug I have turned/milled from a Grade 8 5/8"-18 bolt. I have no doubt the barrel is sound but I need to proof my instalation job on the touch hole/breach plug...

I can find references to proof tests charges for .45 - .60 cal both single and double loaded and other references to 150% charges but haven't found any specifics for .40 cal barrels and would like some confirmation before I pack in a big charge stopped up with multiple balls and touch it off with a string pull while hiding behind a tree...

Can anyone shed some light on how to establish a "safe" proof load for my application?

Thanks
MB

 

[mooncoon]

I would try using the heaviest charge you are likely to shoot plus another 10 or 20 grains plus a single patched ball. If the breach plug has several threads engaged, I would just hold the rifle at arms length and fire it then check for gas leakage around the plug and around the vent liner.

I would suggest referring to Lyman's Black Powder manual for charges and velocities you are likely to use and pressures that result. If the gun is reasonably put together you should not have to worry about things blowing out and about all your are worrying about would be that the threads are not loose enough to allow gas escapage and therefore eventually gas cutting. I also don't terribly see the point in putting massive charges down the gun to test it

cheers mooncoon

 

[MiltonBradly]

That's kinda the way I'm leaning...

Lymans max charge is 80grns of Goex fffg behind a 92grn RB for 2255fps and 14320 CUP. Goex lists 65grns of fffg behind one 96grn RB for 1960fps as there max.

I'm not intending to be pushing the gun for big power (I wouldn't have gone with a .40 if I wanted a big hitter). I'm more likely to be shooting 35-50grn charges to stretch out a pound of powder while punching paper with an occasional max load for fun...

I'm leaning to an ~90grn one RB proof load then to be sure my vent liner stays where it should be and check for leakage at the breach plug... I'm planning to test the barrel alone bolted to a test bench to keep ant squishy bits (me) away from any pointy/fast moving bits...

 

[mrclean89]

I shoot 80 grains out of my .50 penslyvannia as my hunting load and have gone up as far as 110 grains just to test it.

For target shooting I usually use 50- 60 grains.

One thing I remember mooncoon told me once was for rifle charges you start at the caliber (ie .50 = 50grains) and work up. For pistols its half the caliber then teak it.

McLean

 

[wr.sainsbury]

proofing a barrel

40 cal is a good choice for target. 80 grains would be roughly max load for hunting and -as you plan 35-40 for target. would suggest no more than 100 gr to proof as that would compensate for an accidental overchage under normal use. breech plug in 5/8 x 18 should be good with about 6 threads minimum engaged. did the same on a restored 34 cal original and it works fine. used red lok-tite on the threads and about 60 pounds torque.