1873/1878 Trapdoor update and rifling question??

[Tuolumne Lawman]

Just scrubbed the bore of the trapdoor with a bronze 20 gauge brush.  Then I slugged the bore of my Trapdoor, and a .458 was tight, and rifling crisp.  I really had to whack it hard, even with a lubed bullet and oily bore, to get it going. It is three groove, though so I can't figure out the bore!  It looks like the grooves just barely touch the bullet, though the lands are pronounced enough.  Should shoot well enough for me, though I may go to a .460/500 after I shoot these. Are they all three groove, by the way?

The further update is I broke it down completely, They only evidence of rust and pitting was the bottom of the barrel, under the wood like.  I expected that.  I was amazed that even the buttplate had nor rust underneath, and the lock work still had original blue finish inside.  NO rust to be seen anywhere on the "innards".  All screws turned freely and weren't buggered up at all.  

I took the stock and gave it two light coats of boiled Linseed oil outside and every nook and cranny inside , and let it dry in the sun (which made its first appearance in many months! LOL.  All parts liberally oiled in Ballistol while apart.  This will be a nice piece to pass on to the grandkids, along with  my original Inland M1 Carbine, S&W 38 Spcl. Victory Model, and AC44 Walther P38.

[pony express]

The 3 groove rifling is standard on them. I shoot mine with a 405 gr bullet from a lee mold as cast, flat base, not the hollow base. 55gr (by volume) 2F black, 3/8 hard lubed wad from Circle Fly,  then seat the bullet. I just hand lube mine with Crisco, and have never had a problem with it.

[Tuolumne Lawman]

Thanks for the answer.  I checked the bullet I used to slug the barrel.  It is sized .458, and the elevated portion (that was in the grooves, shows the slightest smearing of the lead and lube.  It is fairly hard cast, so it is not obdurating past the bottom driving band from driving it though nose first.  I am guessing the bore in the grooves is right at .458.  As to the crown and muzzle, the first driving bad stops less than  1/8" to 1/4" in the bore.  Some some muzzle wear, but I can live with it.

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[Arizona Trooper]

Unless you have one of the very rare 45-80 Long Range rifles (6 narrow lands), it should be 3 groove, 1 in 22 twist. There are some Bannerman 5 groove barrels out there on parts guns, usually with 1883 dated locks. Most Trapdoor barrels are way bigger than 0.458" groove diameter. 0.461" is pretty typical, and 0.463" is not all that rare. Springfield used 1:20 tin-lead alloy for their 0.458" bullets, which will bump up to fill the grooves with black powder. Go with soft lead when you cast for these. If you shoot smokeless, bullets often won't bump up reliably, so you may need an oversize mold.

Since the lands and grooves are equal width, you can mic your slug at the corners of the grooves and come pretty close to the actual groove diameter. When you pound a slug down the barrel, it tends to spread out and fill the grooves, even with wheelweight lead.

There is a shooter's page over at www.trapdoorcollector.com that has lots of info on making good ammo.

Trapdoors are great rifles, and very underappreciated at the moment. Once you find out what shoots well, I'll wager that you'll really like that rifle! Had my 1876 vintage rifle out last Saturday and it was shooting quite well. A buddy brought his carbine and didn't do badly with it either. 67gr. of Swiss 1 1/2 F exactly duplicates the original rifle load at 1350 fps with the hollow base 405 gr. government bullet.