Loading data IMR for 45-70 trapdoor

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gfol70

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This may be obvious but is the reason for the difference in IMF website start load for cast bullet FN and the Sierra HP in 300g is so different (approx 30gr and 40 gr give or take) because one is flat and the other... pointed? Or is it to do w how cast and jacketed bullets behave. Just wondering.

Also does reloading cast billets require any special attention or just follow data for cast and go through the same steps (as per loading manual) as standard jacketed bullets?

Guy
 
Cast bullets have a speed limit before they fail. Copper is significantly harder than lead and they started jacketing bullets to increase velocities and pressures. If the pressure is too high you can get gas cutting where the gas shoots up the rifling grooves around the bullet and cut into it leaving chunks of lead in your bore. A gas check (copper or aluminum disk) crimped to the base of the bullet can help prevent this. If you push the bullet too fast it can again leave chunks of lead in your barrel. Some say this is due to the bullet stripping itself against the rifling and others say that isn't physically possible; neither side has confirmed with laboratory data. In both cases your accuracy will go out the window and you will have chunks of lead stuck to the inside of your barrel that you need to scrub out. You may also get tumbling bullets that keyhole on the target instead of hitting straight. Softer lead bullets also have a speed limit in the air before the air resistance will actually start to deform the bullet in flight and cause it to tumble. That is around 1700fps with pure lead if I remember correctly but as hardness goes up, max velocity goes up as the bullet can better resist deformation.

One major concern with cast bullets is to make sure you flare the case neck quite a bit. You want to be able to start the base of the bullet maybe 1/16" to 1/8" into the case with your fingers or else the brass can shave the outside of the bullet as it's seated in the die.
Another significant concern is matching bullet diameter to barrel diameter. If you shoot a .457" jacketed bullet through a barrel that measures .4575" in the grooves you wont have a problem. If you did that with a cast you could have some leading issues. Generally you want the bullet to be .001" to .002" larger than groove diameter in your specific rifle. Easiest way to find your groove diameter is to slug the bore (gently hammer a soft lead ball through the bore and measure it with a micrometer when it comes out). So if your barrel is .4575" you will want a bullet around .459" as a general rule. I've gone as much as .003" over groove diameter without problems.

Some rifles and bullet combinations will cause leading at different velocities. Really rough bores tend to lead at much lower velocities than nice crisp bores in my experience. Barrels with shallow rifling (like Marlin Micro Groove barrels) can be very picky and erratic with cast bullets. One can work flawlessly with cast and another that is identical in every way leads horribly even at low velocities.
 
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Thanks for the detailed response. I had a general sense of these considerations but your explanation brings it together. I have been putting off slugging my two 45s for two reasons 1. Not sure where to get lead ball / can I use a fishing weight?
2nd - concerned about damaging rifle. Also I see some doing it in one direction and others the opposite. Which is best? I would think going towards end of barrel would be best - follows trajectory of bullet.
 
I slugged my Uberti Hi Wall with a wheel weight cast bullet (405 gr). Bought a 7/16" dowel at the local hardware store, cut off about 2" from one end to use as a starter & using a hard plastic hammer started the bullet into the rifling from the muzzle end. With the 2" dowel, tapped the bullet in until this short piece is flush. Then remove it & using the rest of the dowel tapped it on through to the chamber end & out.

Oil up the bullet or grease it before & it was rather easy to do once you get the bullet started. Mine measured at .4575". I was using bullets that were .358", but if using slightly larger bullets would probably be a little harder to start. Also a softer lead bullet would be easier to work with too if you can get some. Sinkers should work too...

I did buy a .458" sizer to see how this works, but if accuracy isn't satisfactory, I will get one in .459"!

Oh & a caution,..... don't hit the dowel too hard when using the long piece of dowel, as splitting/breaking it could cause you an injury & please wear your glasses....

Good luck & let us know how it works out for you, & happy shooting.....:)
 
You just need one that is at least .460" though I'd want to go a little bigger. You could try to get a couple .505" pure lead round balls for muzzle loaders. They will probably get shaved a little going in but will still work. They are often $15/100 or something if you want to get a whole box but a friendly local muzzle loader may be able to help. Talk to the sidelock guys who use real black powder as in-line rifles generally don't shoot patched round balls.

Slugging .30 to .32 cal is easy as you can use 00 buckshot which is usually .330". The bigger ones are never as easy. With my 44 mag I used a .435" cast bullet meant for a .44-40 black powder cartridge. I had some .460" round balls a while ago I used to slug my 45-70's but haven't had to do one in a while.
 
The regular pointed bullets are not for lever actions(unless they're Hornady Leverevolution bullets), but other than that loading a cast bullet is no different than a jacketed, except they must be lubed. Just follow your manual and you'll be fine.
Difference in manuals and sites is about velocity. If you try to drive a cast bullet too fast, it'll lead your barrel.
.458" cast bullets will do, but if you want to slug your barrel anyway, use one of your cast bullets. Can't imagine you'd ever find a sinker big enough. Mind you, I quit fishing long ago and never used a hunk of lead that big for fishing.
 
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