I am working up some loads for my 45/70 guide gun, the load I have been working on is a home cast bullet (lyman mould 457193) this is a 405 grain plain base bullet, with 40.7 grains of 3031 this load is incredibly accurate, like all bullet holes touching at 50 yards, problem I am having is every once in awhile one will keyhole, does anyone have any idea why? what can I do to stop it?? The only time I have ever seen this before was with my 50 cal muzzle loader useing a 495 conicial with pyrodex pellets, with regular triple 7 the same load shot fine. In my 45/70 loads with the 40.7 grains of 3031 the case is not full, could this be the problem?? Thanks for any help, I need this gun soon as I am going out to the bush next week.
I'm not a self caster or a 45/70 guy but key holing is generally caused by poor stability. Your bullets may be a touch long for your rate of twist.
If your velocity and or twist rate are at the minimum then the occasional slow shot will key hole. Try to step up the velocity by 0.5gr of charge and see if your issues go away, that is of course if your not at max load now.
A couple of quick reactions. That 405 should be ideal length for your 45-70, so I think you can rule out bullet length.
So lets look at the bullets. What's your alloy? Are you getting some leading? Those are stout loads for a plain based bullet unless it's really hard. Could be all sorts of base damage if they're too soft. See if you can recover any and look at the condition of the base. Not likely if you're not getting some leading, but base damage is a definite possibility.
Other possibility is an error in your casting. That's a base-pour bullet isn't it? If you're not getting a good sized puddle on your sprue plate, then letting that harden till the little dimple forms in the middle there's every chance that you've got some of the bullets coming out with a void in the base, whether you can see it or not. Weigh a bunch of them and see if you can find some that are unusually light, load those, and see if they aren't your keyholing culprits.
I'm thinking slag at the base also.
Brownbear is leading really apparent? my alloy tests 10 brinell with my saceo tester. I actually did recover one of the keyholed bullets today, it went through the tree I had as a backstop and was stuck just in the bark on the outside, what should the base look like?? I will try and have my wife help get a picture of the recovered bullet if that will help. Do you have any loads for that bullet? Yes it is a base pour mold. In the cast bullet handbook it lists that load, at 1600 fps, but doubt im getting that with my guide gun. Its to bad as the load is mild recoiling and extremely accurate. Thanks guys for all your help, there is more gun savvy guys on here than anywhere.
BHN 10 in a plainbase lead rifle bullet is quite soft, especially with a faster twisting barrel (relative to bp twist)
If you can get tire wheel weights, they make a fine bullet alloy, typically they test bhn 13 when air cooled, or you can drop them into a 5 gallon pail of water direct from the mold and they'll test bhn 18-20.
Leading takes on many forms, and there are many causes. Leading can be caused by an undersized bullet which will allow the hot powder gases to blow by the base of the bullet and vaporize the bullet onto the barrel. Bullet lubricants can fail which will cause leading. And if the forces of ingraving the rifling are too severe for the bullet, the rifling will literally tear the bullet. The lead tearing is more severe on plainbase bullets.
My advise would be go to a harder alloy, make sure the bullet is sized 0.001" over the bore dia, and use a good lube. Many commercial lubes are too hard and work poorly. Melting beeswax and adding equal parts moly lithium axle grease makes a great lube.
If all else fails, consider going to a gas check bullet design. Gas checks make many things less critical in regards to shooting cast rifle bullets.
PORTED guide Gun?
Hunted moose, unsuccessfuly , I must add , in your great wilderness with a guide gun this sept. 300 grain hard cast GAS CHECKED shot great . couldn't get any plain base bullet to shoot nearly as well, even with modest loads. The 300 is loaded to "burn, blind, and deafen" with 53 grains Rx 7. Found a pretty fair amount of lead coming out the ports after shooting the last time, at south Cushman range in Faibanks. The gas ckecked bullets still shoot great, just wodering if the gun is the ported barrel model and if you're seeing lead in the ports. Gas check may be the answer.
Beautriz66 no my gun does not have ports. Who did you hunt with?? I guide for Ceaser Lk. here is some of our moose this year.
I'm glad some casters and 45/70 shooters tuned in to help. Good luck with your issues.
+1 for gas checks
+1 for a harder alloy