3 Gun

[Rumpshot]

Well, maybe not what you are thinking.

1873 Trapdoor Springfield rifle
1884 Trapdoor Springfield carbine
1884 Trapdoor Springfield rifle cut down to carbine length

Went shooting with a couple of fellows today, both have been to RR. Mine is the cut down rifle. The 1873 is for sale, asking $700.00, not mine. The carbine has the grain running the wrong way through the grip and has a couple of nasty cracks.

Shooting Trapdoor Carbine loads: 55 grains, 2F Goex, behind 405 flat nose cast bullets. Out of 14 rounds, there were 3 keyholes. At about 20 yards. Two different guns.

What would cause the keyholes at that short range?

Have not slugged any of the barrels. The bullets were locally commercial cast, sized to .458. Would bore size vs bullet size account for the keyholes?

All of the shots were inside of 14 inches or so.

We were not trying very hard for accuracy.

[First Shirt]

Please bear in mind that these are just guesses:

Undersized or oversized bullets?
Over or undercharged loads, either giving too much spin, or not enough?
Oversized chambers, not allowing enough pressure to build up?

I'd probably start with slugging the bores, then doing a chamber casting.

JMHO, YMMV, IRDDU.

[Flintlock Tom]

How is the rifling?
Maybe you're shooting undersized slugs through a 130 year-old smooth-bore.

My 1884 had barely discernible rifling.

[Kommander]

How is the rifling?
Maybe you're shooting undersized slugs through a 130 year-old smooth-bore.

My 1884 had barely discernible rifling.

I don't know as much as others about this but this was my first guess as well. I recall that some years ago there were some 5.45 rifles that were keyholing because some genius put 5.56 barrels on them, or rather barrels that had been sold to manufactures as 5.45 were actually 5.56.

[Rumpshot]

Well all three guns have 3 land/3 groove rifling. All three are pretty shallow grooves.

I "slugged" my gun this morning. I used a lubed .458 bullet for the process. pushed down the bore from the muzzle. Very obvious difference from the bore to the chamber. Seems the bore tightens from the chamber to the muzzle.

The bullet used was commercially sized and lubed, sold as .458 sized.

The bullet required the use of my rawhide mallet to push it through about 1/2 the barrel length was then able to be pushed into the chamber area by hand with a cleaning rod.

My suspicion, based on comments made in this thread is 3 pronged. First very shallow grooves. Second bullet nearly exactly bore sized. Third low pressure loads that do not cause the bullet to upset any on firing. The last one I can take credit for as I intentionally loaded light, carbine, loads because of the age and design of the trapdoors.

[Vonz90]

To be honest, I don't think I would shoot an original trapdoor Springfield as I am a bit short on replacement eyeballs at the moment.

[Flintlock Tom]

Perfectly safe with BP loads. Never heard of one blowing up.

[First Shirt]

I'd try a .459 bullet (or bigger, if I could find it) over 60-70 gr. of 2F Goex, or the smokeless equivalent.

If that didn't work, then I'd go for the cerrosafe chamber casting.