trapdoor springfield problems

[dogmower]

I just purchased an 1873 trapdoor and shot it using both a 405 grain cast bullet and a 500 grain bullet, both sized at .459 and loaded over 28 grains of imr 4198.
the first shot had zero recoil, the bullet hit the ground at 100 yards (was aiming at 300) and lots of unburnt powder in the case and barrel. I cleaned out the bore and action, figured a heavier bullet might seal the case better (a little higher pressure) and tried the 500 grain bullet.
this time, the front of the case ruptured. again, no recoil and the bullet hit way low with low velocity.
the bore measures at .457 at the muzzle. when I loose load a lee 500 grain bullet into a case and cycle it through the action, I get an overall length of 3.14 inches.
is it possible that this is chambered for 45-90? or did I just get a detonated case?
any help is appreciated.
thx,
John

[rancher1913]

still new to trapdoors but it seams they have a wide range of bore sizes. the first thing I did was slug my barrel, it showed .459 and luckily that's the mold I got, picked up a sizer from brassmagnet to size them to .459 and lube, they work really good. best guess is your boolits are to small for your bore. used that same load, 4198 at 28 grains and got a good kick so its not the powder. I was advised against using a filler even though the powder charge left a void in the case and had no trouble with ignition. hopefully some one with more experience will chime in.

[Scharfschuetze]

Hmm. Is it one of the Forager Trapdoors in 20 Gauge or possibly an 1868 or 1870 in 50/70? Just guesses as they would explain the lack of pressure from your loads.

Your load as produced should shoot fine in a properly rifled 45/70 or even 45/90 barrel, although many size their boolits a smidgen larger for original Trapdoors. There were some 45/80 Marksman Trapdoors made for competition, but I don't think any were chambered for the 45/90 round, although perhaps some experimental ones were made. The Marksman Trapdoors are quite rare so an arsenal produced 45/90 must be in the order of a hen's tooth as far as scarcity if there was ever one made.

I might add that your load of 4198 is below the listed starting load for a 405 grain boolit per the Lyman #4 Cast Bullet Manual. Starting load for the 405 grain boolit with 4198 is 31.5 grains. Still, it should be doing better than what you are experiencing.

[rancher1913]

the 3.14 does seem to be long, the specs show the 45-70 should be 2.55 overall, maybe your throat is the problem.

[Mauser48]

Do a chamber cast. That will tell you a lot.

[dogmower]

thx guys. I am going to do a chamber cast, that should explain it. the bore is .457, the pressure leak occurred at the breech. I miked the base of the fired case and it came out at .500, the same as a resized case. the base of the ruptured case also measured .500, so over pressure wasn't an issue. It seems like the end of the case was unsupported and with the low pressure loads, only the heavier bullet generated enough back pressure to rupture the case. that is a chamber issue any way you slice it. will update this after I cast the chamber.

[iron brigade]

I use 34 grains of I 3031 with the Lee 405 HB mould. I have two TD's and both shoot this load well. I have shot sub 1" groups with this load.