Keyhole 45-70
I just shot my first box of ammunition (hand loaded)through a used NEF 45-70 (single shot break action) rifle I recently picked up and got really bad results. I used new star line brass, 15g of Trail Boss powder, and cast 385g bullets. I had previously shot one round of full powered 45-70 in someone else's rifle. It knocked me back two inches on the bench (ouch), so I decided to be a wimp going with this rifle and use Trail Boss for a much lighter load (the NEF rifle only weighs 6.5 Lbs). I started sighting in at 50 yds, but didn't place a round anywhere on the target. I kept moving the target forward until it was only 15 yds away before I could figure out what was going on.
About 70 percent of the hits were keyholes and were scattered all over the place. The 30 percent that punched nice round holes actually grouped a little. The first round I fired surprised me. Instead of a resounding boom and a kick in the shoulder I got a pop and a recoil somewhere between a 233 and a 22lr. At first I thought the powder failed to ignite and expected to find the bullet lodged in the barrel. The barrel was clear, there was no unburned powder in the barrel, and no soot on the outside of the case. The bullet had gone somewhere (not to the target). It turns out that the rounds were firing and the charge was burning just fine.
I haven’t run additional experiments with the load yet and would like others insights before chasing down my own wild guesses.
Why are the bullets so unstable to instantly start tumbling and what can I do with the loads to fix this problem?
Thanks guys.
Background Information: The NEF rifle has a 22 inch barrel with a 20:1 twist rate and weighs 6.5 Lbs. I used new Starline brass, 15g of Trail Boss powder, and cast 385g bullets (from a Lyman mold I think). I do not know the MV but I expect it is very low as the recoil and report were both very low. According to IMR load chart, I should be getting a MV somewhere around 1100 fps. I used a Lee factory crimp die, but only enough to remove the bell on the brass. The bullets were not heavilly crimped. I figured there was no need as the rifle is single feed (no tubular magazine). I gave the muzzle crown a good looking at and it appears brand new. The bore of looks practically new as well (eye balling it - no bore scope (I wish I had one)). I made a dummy round (no primer or powder) with the bullet set very long to determine how long the throat of the barrel was. It is very short and barely clears the 385g RN bullet when fully seated. Looking into the breach using my bare eye, it sort of looks like the chamber was cut to head space off the case mouth. There is a very abrupt lip transition from the chamber diameter to the bore. The beginning of the lands look like they were cut off vertical (no ramp). This could all be an optical effect since I am looking in from the breach, though I must say I can see the land ramps on my 45 ACP pistol barrel when looking in from the breach.
