Im with trickymissfit. The few times ive had bullets key hole it was caused by awful lead fouling.
have never owned a 45-70; I'll be first to confess. But do shoot some 45 caliber rounds when I fell it's time for a new round of shoulder abuse<g>! Most 45-70's come with deep cut rifeling (Ballard?), and this is well suited for cast lead bullets. But one needs to remember that your done with lead before the 1700fps mark. A gas check will help a tiny little bit, but then hurts the accuracey (leastwise in my findings). Most guys fail to realize that it really dosn't take a lot of lead build up in the barrel to screw everything up. Specially in the throat.
Now I recommend a long overnight soak with Shooters Choice Lead Remover (plug one end of the barrel and simply fill it up while standing vertical). Use a nylon brush,and a bronze brush as a last resort. I have had to soak barrel as much as three times to get all the lead out. Have a buddy that swears by somekind of an electronic doodad, but can't vouch for it myself. There is a better compound for removing lead, but if not used right can be fatal.
Now back to the 400 grain bullet a second. I highly recommend Speer P/N 2479 over 58 grains of H335 (about 1850 fps). The barrel needs to be squeaky clean. I've been playing around with this bullet in my .450 Marlin. Recoil is not to be taken lightly! Another great powder to try is AA 2015BR and IMR 3031
Lots of excellent advice. Casting and loading for the 45-70 takes a whole lot more knowledge and skill then most modern calibers. Twist rate, bore size, composition of the lead, type of powder, etc. are all factors. This round has been in use for around 140 years. With the exception of the modern commercial rifles built to SAMMI specs, customs, repros, and older rifles have a wide range of twist rates and bore sizes. You find that out when you buy a mould. The OP's buddy's rifle is likely one of them. It can probaly be set up to shoot, but it will take some serious homework and skill to build a shootable cartridge. IMHO.
I used to work with a group of guys that shot BPMC silhouette all the way out to 1000 yards. One of them holds eight world records last ime I heard (Russ Combs). None of them would ever be caught using a jacketed bullet! These guys shoot groups that many centerfire guys would often be envious of.
What the original poster needs to do is to clean the barrel squeaky clean. Then slug it! After slugging it with about four or five lead slugs you will come up with some accurate measurments to base your bullet sizing operation off of. One thousandth of an inch can make a word of difference. Then if the builder simply reworked a factory Siamese Mauser barrel it may not even be to the same spec that a modern blank is machined to. I ran into this with two
38-55's I own. One has a .3775" bore, and the other is .376". I use a .379" cast lead bullet with one and a .3775" with the other.
I need to learn how to cast bullets and size them
Now I recommend a long overnight soak with Shooters Choice Lead Remover (plug one end of the barrel and simply fill it up while standing vertical). Use a nylon brush,and a bronze brush as a last resort. I have had to soak barrel as much as three times to get all the lead out. Have a buddy that swears by somekind of an electronic doodad, but can't vouch for it myself.
I'll vouch for the electronic doodad (outers foul out).
Wouldn't be the first time I saw someone try and use bullets meant for a 45 cal handgun in a 45-70 rifle. Handgun = .451 bullet, 45-70 = .458 bullet. Make sure the mold is for a rifle bullet. My 45-70 Guide Gun loves .459 diameter lead bullets.
The above advice is very sound.
I'll toss something else into the pie here, though. With cast bullet shooting you do not shoot for velocity at all, but for the pressure that gets your bullet to perform properly in your rifle bore. You want full obduration without destroying the alloy and causing leading. The harder the alloy, the faster it can go as it can take more pressure, to a point. You want to go from an extremely mild load and push the load until the accuracy comes in and then goes away. Back the load down until you have accuracy and you have your charge. Do not change your alloy without re-working the load.
You may get as little as 1400 fps accurately with some alloys, and you may get 2000 fps as I do with my 375. I am not quite sure where I am landing yet with my 405 and lead, but I'm aiming for somewhere in the 2000-2200 fps range at 2 moa or less from its blade sights.
As far as the rifle in question, clean it with hoppes and a good bronze brush. Then after making sure your diameters are compatible with the bullet about a .001" bigger than the bore, start from a charge that'll give 1000 fps or so and work up. You may need to work with more than one powder (the preferred powder for cast in my 405 is 4895- my rifle shoots shotgun patterns with it- I had to go to rl7 to get ithe rifle to start grouping). Also, never use a swaged bullet in a rifle; they just aren't tough enough. Hard cast is the way to go unless you are using very mild loads.
I kinda gather that Lefty shoots a lot of cast lead as he seems to be right on with his post. I'll be first to tell you that I'm not all that upto speed with cast lead in a rifle. In a handgun I can get by OK, but rifles are a different animal.
I can say for sure that the Shooters Choice Lead Out works very well, depending of course on just how bad the bore is fouled up. Once you have it to the point that there is little if any lead comming out of the bore from cleaning, then I also recommend cleaning it again with Shooters Choice rifle borecleaner or Montana Mikes. I like to at least start out with a good stiff nylon brush, and then will use a bronze brush only if I can't get there with the nylon brush. Avoid the stainless steel brushes! I've seen badly fouled bores (not mine) that after an all night soak and a nylon brush bring out sliver after sliver of lead.
One poster commented on maybe they were using .452" bullets in a .458 bore. I know of nobody that sells a 400 grain 45 acp bullet yet. But it's quite possible that the guy sizing the cast lead bullets did it with a .453" bushing!! Lastly anyone shooting cast lead bullets would do well to get himself a copy of the Lyman Cast Bullet Manual. There's a ton of information in there, and a huge library of loading data
Yep, sure is possible on the under size bushing .458 to .452" thing. My brother is using a 45 cal. pistol sizer to re-size 400 grain cast for his 460 s&w pistol. They shoot wonderfully out of the pistol; just take roughly enough H110 to shoot two 357's and you are good to go.
I really suspect it's either a bullet diameter issue or the bullet is being driven too hard for the alloy and she's going nutz after the barrel leads a bit.
Is the bullet even getting to the target, or are the bullets bouncing in?? I had that with the 405 with 4895 (and its bad grouping); a few bullets hit low and bounced in causing a keyhole in the target.