Barrel proofing question

I'm currently building a medieval handgonne. I had a machine shop drill the bore and mill the octagon on the barrel, to match an original piece. I've got a question I need answered on that. It has a powder chamber, like a howitzer so it has a fixed powder charge. Can't be smaller than X charge size, but I think having a charge that goes outside the powder chamber into the thinner bore area could also be potentially bad. To proof it, I decided the best way to proof the gonne is to find the hottest BP substitute I can think of, like white hot or triple seven, and load it with a charge of that and two round balls for a projectile. Can I get some thoughts on that idea? Maybe affirm my idea or tell me what I should do?

I've build one of tannenberg.You can forget the bore in 2 steps.You can drill and ream 18 mm during 205 mm.
the reason is if your load dont fill in completly the 12 mm you can destroy the barrel (the void is very not goood). but the first step,what's the steel is used for the barrel ? in belgium,for this caliber,the proof load is 20 grams(320grains) with one bullet 30grams (480 grains).don't forget the vent 1.6mm ( 1/16 ").Have fun and you post a pict with a barrel ...

voltigeur said:

I've build one of tannenberg.You can forget the bore in 2 steps.You can drill and ream 18 mm during 205 mm.
the reason is if your load dont fill in completly the 12 mm you can destroy the barrel (the void is very not goood). but the first step,what's the steel is used for the barrel ? in belgium,for this caliber,the proof load is 20 grams(320grains) with one bullet 30grams (480 grains).don't forget the vent 1.6mm ( 1/16 ").Have fun and you post a pict with a barrel ...

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The stepped chamber is necessary. I intend to eventually use historically correct serpentine powder, and its purpose was to prevent overcompression of the charge. Not to mention already being made like that

make sure you fill the stepped chamber completely to avoid having a gap between it and the bullet.

I preferred to make it with a single bore to avoid this problem. with an actual steel (4140), no problem with a wall of 6 mm (+/- .25").In brass,it's better to do it with a stepped chamber.

On the other hand, on the wood side, I made it conical.

Have fun

voltigeur said:

make sure you fill the stepped chamber completely to avoid having a gap between it and the bullet.

I preferred to make it with a single bore to avoid this problem. with an actual steel (4140), no problem with a wall of 6 mm (+/- .25").In brass,it's better to do it with a stepped chamber.

On the other hand, on the wood side, I made it conical.

Have fun

Click to expand...

I'm gonna make some sort of measure for it that completely fills the chamber with no overflow