Martini-Henry Rifle- Nepalese Francotte Conversion

[Greenmeance]

Amazing work

[DarkLite]

Now you just need the mutton chops and red jacket.

[tquilha]

Beautiful work CatgutViolin.

[CatgutViolin]

And finally, the promised videos.

 

[Got Wood?]

Incredible. Is it me or is it very loud?

[AG1212]

You have an APS double barrel too??

[renegadecow]

Are those scatter shot shells in the SAA too? And have you tried chronoing the M-H? Curious what all that extra barrel does to APS shells.

[CatgutViolin]

Incredible. Is it me or is it very loud?

 

Oh yeah. CO2 in a narrow pipe will do that.

 

You have an APS double barrel too??

 

It's a Hwa San converted to APS shells using 3D printed parts designed by Blobface.

 

Are those scatter shot shells in the SAA too? And have you tried chronoing the M-H? Curious what all that extra barrel does to APS shells.

 

Yep, homemade six-BB shells made from .357 brass and plastic tubing. As for the M-H, I'm curious too- we couldn't get a chrono reading at the field, but they've approved my other APS shell guns so let it pass. Just from observation it looked like a lower muzzle velocity than the Hwa San, but that could be because my CO2 tank was low and filling gaseous rather than liquid CO2, which would struggle more with the longer barrel. I'm seriously considering ordering a shooting chronograph just to test APS shell loadings.

[CatgutViolin]

Alternative theory to explain worse performance than the Hwa San: Idiot me reinstalled the barrel poorly and left a slight gap between the barrel and the chamber, compromising the gas seal. I just shoved an O-ring in there and it appears to be considerably more powerful now.

[renegadecow]

Might also be the excess barrel. Even in real 12ga it's observed that max velocity is achieved with a 18" barrel. More than that and it begins to drop and the only reason why people go for more is balance. I'm thinking if you can ream out the excess barrel just to have enough blow-by the loss in drag won't be as much.

[CatgutViolin]

I did consider the possibility that the barrel's providing excessive drag. On a real shotgun the powder is designed to burn very quickly, with longer barrels being used to tighten the spread, as opposed to rifle calibers where the powder burns more slowly and you need three feet of barrel to burn it all before the bullet leaves the barrel. But when I fill the shells with liquid CO2, I can see a visible plume erupting from the muzzle, meaning that it's still boiling and expanding even as the wad leaves the barrel. That would imply that a longer barrel would allow more of the CO2 to boil and provide pressure.

 

I initially loaded gaseous CO2 to see what kind of performance it'd get- and that's why I got those squibs in the test video. Granted, that shell was one I had loaded the night before and may have leaked somewhat, but the gaseous CO2 loadings definitely struggle with a long barrel.

 

My airsoft chrono is on its last legs so I've just gone ahead and ordered a proper ballistic chronograph that should be able to measure wads in flight. Hopefully I'll now be able to take some objective measurements of performance with homemade loads.

[CatgutViolin]

Might also be the excess barrel. Even in real 12ga it's observed that max velocity is achieved with a 18" barrel. More than that and it begins to drop and the only reason why people go for more is balance. I'm thinking if you can ream out the excess barrel just to have enough blow-by the loss in drag won't be as much.

 

Having gotten around to setting up my chrono and iterating on my shell loading, I got a load set up that punts 12x 0.2s at 380fps. With 17x 0.25s, it still does 345fps. That's almost 24 joules per shot. I don't think I need to worry much about the barrel.

[renegadecow]

How are you cramming 17 bbs in them shells? So it was just down to unfilled shells in those odd shots?

[renegadecow]

While you were at it, I don't suppose you have any data with really short barrels do you? Planning on making something along 3".

[CatgutViolin]

How are you cramming 17 bbs in them shells? So it was just down to unfilled shells in those odd shots?

 

Unscrew the hull. Take the overshot card and ram it down through the rear of the hull so it sits flush with the front. Drop in five BBs in a star shape, then one in the middle, then another star, then another in the middle, then a third star- 17 total. Ram down an undershot card or gently work a shot cup down around the payload, and compress. Screw the hull back onto the shell base and it's good to go. All the shots in the videos were 17x 0.2s with undershot cards rather than shot cups, the reason there were issues in the first video was that I had filled the shells the night before and some had partially lost pressure, and the lack of a seal was definitely compromising performance.

 

I'll try to get a reading through the Hwa San, but I've generally been finding that with short barrels the physical composition of the load is much less important. You could get away with dumping BBs in the hull and taping it closed and have performance not too far off from my meticulous method.

[Corbeau]

Holy hell man, this is crazy stupid awesome. That gameplay video puts a smile on my face every time I hear the "ka-shink" when you eject a round!