Building a barrel, Need some input

[Ricci Price]

I'm not a gunsmith but do know a little about machine work ,I work at a papermill in NE Fl. one of my good buddies is a machinist here at the mill (onlyone on site) We have been thinking about building a smokeless muzzleloader barrel for a NEF H&R sb2 frame.There is a company building them now for this same frame. We are wanting to make 40 caliber that shoots about a 180-200 grain bullet .First question is what twist should I use ?#2  Can I shoot cast bullets? Any help would be appreciated. We are going to try to make a broach to cut the rifling in barrel(actually we already made test broach worked pretty good)

[gunnut69]

A smokeless muzzle loader?  I assume lead bullets only as engraving jacketed bullets at the muzzle would be interesting.  Paper patched bullets might work but they usually require a false muzzle.  Smokeless powder generates a lot more pressure than black so things can get dicey.. expecially with prssure bleeding back thru the flash hole.  Savage makes such a beast but the local shop refuses to sell them as he 'doesn't want to be included in the ensueing lawsuit.  200 grain bullets would be fairly light for those bullet weights as a 45 caliber round ball weighs in the 170 grain neighborhood.  The barrel makers websights can give you a better picture of twist rates versus caliber and bullet weight..  Try Greenmountain.. I would guess about 1 in 20-28 inches for a general use twist while the lighter bullets such as those you suggested may well work with slower twist rates.  Check the Savage rifle for ideas on dealing with the high pressures at the primer...

[Ricci Price]

thanks gunnut, I'm also a avid reloader of 20 years that being said I fully understand barrel pressures and barrel design (using 4340 for barrel material).I also meant to say .400 to lets say .410 in bullet diameter where as 180-200 grain I think would be about the ideal weight for that caliber(10mm).Also thinking about a gas checked bullet or a electroplated bullet. As far as priming goes was thinking about a empty primed pistol case.If you look at the current design of smokeless muzzleloaders they are using a .030 hole to send a spark through I guess this one way they deal with the pressure.I'm not trying to build a gun that will hit the moon, just an accurate shooter ,of at least 40 caliber, that is muzzle loaded , that is what is legal in my state.

[gunnut69]

I'm sure you know the limits of even gass checked bullets and electro plated bullets are little better.  Your looking at 2000 fps or so, which can be reached with pyrodex and way less pressure than smokeless.  If you interested in building your own smokeless muzzle loader a sabot is likely necessary..  As I said before loading a bullet that can use the extra velocity of smokeless into a muzzle loader won't work well.  Paper patching perhaps with a false muzzle...  but the gain of pyrodex and a sabot is small...  If you build a 45 and use sabot's you may well gain some velocity over pyrodex..  but recoil will quickly become painful.  It's like varmit hunting with a 375 H&H.  The pasture poodles will definetely die but there are a lot better tools to ease their passage to the after life.  A 38-55 usually generates about all the velocity a lead bullet can stand and they operate at roughly the same velocity as a pyrodex powered sabot shooter will generate..  Also the weights you are proposing are pistol weight bullets.  This bore size using lead bullets will likely want 350-425 grain bullets..   At 2000+ fps those will certainly let you know when the rifle fires..