Home Forums Reloading Big Game Rifles Opinions on bullet size for .45 cal bore with polygonal rifling?

Metford rifling slugs out to 0.457 / 0.453 bore and rifling.

.459 lead cast bullets too big to safely shoot with Trailboss in a Martini action?

I'm going to stand back with a string and make sure, just looking for a sanity check first.

I cannot speak with authority about using Trailboss in a Martini action because I've never done it before.

However, I do know that the Martini-Henry requires bullets in the .463-.466 range for best accuracy if you are not using a patch.

I have used Trail Boss with a 405 water quenched cast bullet that measured 0.4585" in a Buffalo Classic, and it was very accurate. I think it was 12 grains for a whopping 970 ft/sec. It would pick off empty 12 guage hulls at 50 yards all day long. The report was more of a "poof" than a "bang." Loved it. Fun for wives ad kids too.

well, took it to the range today with the 450gr loads, and it wasn't a total disaster. Loads are safe in terms of bullet size / pressure. Its Trailboss, after all. 70% rule translated into 21 grains of TB. Report was a muffled crack, not as loud as I would expect from 4895 or similar rifle powder. Accuracy at 100 yrds was terrible, 18 in groups with some bullets key holing. Frankly, I've seen better with Remington slugs out of my old model 12 pump gun with just a bead on the muzzle.

What am I doing wrong?

Its a Greener sporting rifle based on a Martini action. I think it was made in the 20th century as it has nitro proofs. I dont think the bullets are undersized given how they slugged out. Maybe I should remove the copper bases to get better results with this polygonal rifling? One thing...the bbl is 26" and the rifling looks like it barely makes a turn. Its the 500 / 450 "Express"....maybe I need to use lighter bullets at a higher muzzle velocity?