2 more Krag 30-40 questions

[Battis]

I loaded ten rounds .30-40, using a .308 150 gr FMJ bullet, 32 grs H4895. I full length sized the cases before loading. Every round chambered and fired perfectly. After firing, each case had blackened necks (no cracks). Is this because the bullet is too small? Would a gas check help?
(I have searched for this answer). I'm having a hard time getting a good bore/groove measurement.

2nd question - I have some .309 cast bullets (170 grs) that slip right into the fired case mouth. Now, if I resize the cases (full or neck), I'd have to use an expander die to get these cast bullets to fit. Should I just load the cast bullets without sizing the case, and crimp them? (this is kinda like the question I asked a few days go).

[Outpost75]

The Krag rifles have a large throat and long ball seat which is dimensioned for the 220-grain service bullet.

It is very likely that with the shorter 150-grain bullets and your 170-grain cast ones the bullet base is actually clearing the case mouth before the bearing surface of the bullet begins to engrave. Therefore the rounds don't develop normal pressure and accuracy will be poor because of poor bullet alignment and gas leakage past the bullet in the throat.

You should start by casting your chamber to determine the diameter of the ball seat, or unrifled portion of the chamber ahead of the case mouth, before the rifling starts. In typical Krag rifles this cylindrical freebore section is .312" diameter or larger, and the unrifled portion is longer than its diameter.

Best results will be had using longer and heavier cast bullets of 200 grains or more and .313" diameter. The #314299 is a good choice, and a charge of 15-16 grains of #2400 is a fairly standard plinking load. For a heavier hunting load try 28 grs. of 4198 or 30 grs. of RL7, which are both full charge loads around 2000 fps.

#311284 was the standard cast bullet for the Krag, but most of the Lyman molds produced since WW2 are too small in the forepart and the bore-riding nose receives no guidance from the rifling. You can check fit by taking a bullet with your fingers, inserting it into the muzzle nose-first and observing whether the forepart enters the bore easily with no resistance, or is a tight fit. Ideally it should require firm thumb pressure to force the bullet nose into the muzzle and upon removing it the nose should be visibly marked by the lands. If the bullet enters easily all the way to the front driving band without engraving, accuracy will be poor, like throwing rocks.

[Battis]

Good info. Thanks.