32 20 chamber

[Ruts]

I have a Japanese browning 92 In 32 20. It is in great shape, nearly new condition I bought it a few months ago. It won't shoot straight with 115 grain plated bullets that my uberti 73 in 32 20 shoots well. So I bought some 85 gr. Bullets it won't shoot straight either. I took the bolt out so I could scope the chamber. I found that the end of the case mouth is also the end of the rifling, the rifling is cut off at the chamber mouth at what looks like about a 60 degree angle. I don't think this is right, there is no machining at all ahead of the end of the case mouth cutout. Is not the leade cut with the chamber reamer? Or did they miss a step?

[Tar Heel]

Chambers are cut with two reamers generally. A rough cut and a finishing reamer. Both cut whatever leade is supposed to be there. Sounds like a chamber cast may be a good idea so you can actually measure chamber dimensions in your Miroku rifle although SAAMI specs show almost no leade in these chamber dimensions. Actual cartridge maximum dimensions and chamber minimum dimensions are the same.

Originally introduced in 1882 as a Black Powder cartridge, a longer leade found in more modern smokeless propellant cartridges like the 30-06 was not necessary or desired. I think a little experimenting with propellants may find you a decent load for this wonderful rifle/cartridge combination. I would lean towards one of the faster propellants listed in the loading manuals.

Attachment 292626 Attachment 292627

[Outpost75]

Accuracy with cast is hugely improved by using a common .30 cal. throating creamer to reduce the sharp 25 degrees, Basic transition from case neck to origin of rifling to 6 degrees, Basic (the half-angle per side) or 12 degrees total included angle.

No cylindrical ball seat is needed. Just reduce the angle.

[Nobade]

I found the normal chamber gives very good performance with ammo loaded as intended - a #3118 cast soft loaded over 20 grains of FFFg black powder. But for shooting with smokeless and harder bullets, outpost75 is right on the money. Just kiss the rifling with a throater and it will work much better.