Start with 53 grains of 3031. This is safe with bullets up to 405 grains and will give you about 1800 to 1900 FPS with the 300 grain. You can work up and down from there to determine your best accuracy. Recoil with this load will probably be enough for most shooting situations, too, although you can go higher with a 300 grain bullet!
The Lyman manual suggests casting hard and sizing .001 oversized and to keep vel. to 1600 or less in a Marlin with Micro-groove. I have used lead bullets, both hard cast and swaged, in a Marlin .357 with Micro-groove and had a real hard time getting the lead out of the bore.
As Alleycat noted, Microgroove barrels could be a problem over 1500-1600 FPS. Is your barrel a Microgroove job? I note that today SOME Marlins are coming with Ballard-type rifling rather than the Microgroove stuff.
Oops, heavy varmint!! Sorry, should have re-read your original post!! I see that you do have a Microgroove barrel, which MIGHT NOT handle the 53-grain load with enough accuracy. But, I'd try five rounds, just to see what happens.
I have had good luck with moderate loads of 4895. The extra bulk seems to help. My best load is a 400 gr pure lead swaged paper patch with 47 grains of surplus 4895. I think the pure lead is obturatring to fill the bore and the paper reisists stripping and leading. Heck, you can almost clean your rifle with paper patch bullets. In a microgroove barrel we are talking silver dollar size groups at 75 yards. This is off a bench with good eyes and a peep site. 400 grains of pure lead at 1600 fps will kill anything I care to shoot at, and you can eat right up to the bullet hole!
With your lead gascheck bullets you might even try H4831, a bunch of it. You can't get into pressure trouble with it in a 45-70. You will have a moderate load that is very accurate. This my help with the micro-groove barrel. The slow start will help it to not strip the bullet in the rifling.
"Pet Loads" by Ken Waters, available from Wolf Publishing, has a couple of articals on 45-70s. Bunches of loads too. Many rifles tested. This is a two voume set that no serious reloader should be without.
Scot
[This message has been edited by scot (edited 04-11-2002).]
Posts: 813 | Location: Left Coast | Registered: 02 November 2000
quote:Originally posted by heavy varmint: I need a starting point in working up an accuracy load with the Marlin 45-70 micro-grooved barrel and 300 grain cast.
Your starting point HV is finding out your bore size. Marlin micro's tend to run largish- but will shoot cast very well if properly loaded.
You didn't say if the bullet is checked or not.
Posts: 1529 | Location: Central Wisconsin | Registered: 01 March 2001
