I have an original Hepburn Match A in 40-70 Sharps straight. Have a box of brass and dies coming. I have never had a .40 anything.

I just slugged the bore, which is excellent,and starting from muzzle the slug went in and after an inch I pushed it through with almost no resistance. So the bore is choked. Slug measured .4095”-.4100”

Is this bore Grossly oversize?
Any tips for slugging from the breech end or do you guys do a chamber cast to get your measurements from that end?

Thank you for your advice.

Thanks Marlinguy. I should do a chambercast anyway I suppose.

Marlin, 
Next you make a mess like that……and Ive done it several times(all taking a shortcut) slowly pour a teapot full of boiling water on it. It will melt and flow with no damage to any metal. The metal will dry almost instantly.

I think that the next step would be to find a few bullets for the 405 Winchester sized .412 and fire a few.  Then see what diameter your fired brass is and pick a bullet mould that casts that diameter so that you can finger seat the bullets.  A custom neck expander from Buffalo Arms is probably in the works if you need to expand the brass to allow the cast bullet to seat without shaving.  If you will be shooting blackpowder I highly recommend the compression die that Shiloh Sharps makes as it uses the end of the case to set the compression finished depth.  I mostly shoot at 50 and 100 yards with my Hepburn in 40-70 SS as my eyes don't like the 200 yard target at all.  My favorite breech seated load with a 330 grain bullet is a peasley 21 grains of IMR 4227 as it has no recoil and shoots great.  25 to 27 grains of #5744 works good for fixed loads with bullets from 330 to 400 grains.  I have some stout loads for hunting with V133 powder ( I had a bunch and decided to try it) and with IMR 4064 I have a 330 grain paper patched bullet shooting 2150 fps in my 1875 Sharps 40-70 SS.  It lets you know you pulled the trigger!  The biggest problem that I think most people have when starting with a 40-70 SS is to find brass with the correct rim thickness.  The problem I have with my Hepburn is that the primer backs out sometimes and you have to pull back the hammer and fire on the empty case to reseat the primer so that the action will open.  I have mostly cured that by using the CCI 34 primers made for simiauto rifles as they have a tough cup.  My Hepburn firing pin hits very very very hard!  It is my favorite rifle to shoot at the bench and I hope you enjoy yours.  Tom

I use 4198 and 23.0 grains with my lighter 300 and 350 grain bullets. That's under 19,000 psi chamber pressure and safe for older rifles.

You might want to check the barrel twist. If it's slower than 1 in 16 bullets longer than about 1.2 inches long will give you fits if you shoot past 300 yards, and especially so if there's any type of crosswind.

rifleman wrote on May 7^th, 2024 at 1:13pm:


I use gauge pins as the bore diameters can vary slightly. But back many decades ago Bill Brophy told me factory records stated the bores on all .40 caliber barrels were .397"
I honestly never really cared what the bore diameter is, as groove diameter dictates what bullet I'll use.