cape gun chambering

[45LCshoooter]

I have been planning to build a cape gun from one of the short barreled "coach gun" SxS shotguns for some time. It occured to me that a .577-450 Martini Henry's rim is large enough for a 20 gauge extractor to catch(though not quite as large as 20 gauge rims...I am sure i could get Dave Casey to make some with larger rims if that is an issue). Could a .577-450 MH be done on a 20 gauge shotgun? would the chamber need to be opened on the barrel to be lined so the liner could have significant thickness in the chamber area? Would it be simpler (that is, cheaper) just to have the extractor modified to fit a smaller rim?

[gunnut69]

I would think it much cheaper to simply alter the extractor rather than create a special round just for this weapon.  I am also unsure of the operating pressures of the rounds you've mention.  Be aware that most shotguns use very low pressure rounds and there may be issues there. Still altering an extractor is a fairly simple process considering the alternative.

[45LCshoooter]

I was concerned about pressure too; not that the pressure is high (it is an old black powder cartridge and would be loaded as such) but that the case head is huge (close to the 20) and could possibly raise a bolt thrust issue. Still, my first choice of shotguns is the Baikal and is fairly strong. I think i can get by with BP loads but am not sure. Of course, that is why i am asking around.

I had my dummy case out (got one ordering 500 NE brass from Huntingtons because i am a .45 nut) looking at it and i think rim size is fine on Betram Brass. The case does have a fair amount of taper to it, would there be a risk of the extractor pushing past it.

I may well be better off with a .450 Express loaded nitro-for-black, but that Martini Henry case is kinda charming.

[KSR]

In the long run this would probably be cheaper and it would give the instant
gratifacation of being a ready to shoot gun.

http://www.spartangunworks.com/spr22.htm