45/70 Accuracy Issues

[longbow]

I'm betting that you are getting gas cutting at the heavier load. Check the outside of the bottom driving band and I bet you see smooth ripples from gas cutting. You may need a magnifying glass but I bet you see some smooth and shiny uneven ripples on that bottom driving band.

I used to shoot a lot of cast boolits through my converted Siamese Mauser back in the 70's and with the hottest loads (top end Ruger #1 and Siamese Mauser rated) I got just a bit of leading near the muzzle with PB boolits. My solution at the time was to add a .410 fiber wad and that stopped it.

I did not have the leading issue with my 1895 Marlin but of course was using Marlin loads for it so a little less poop.

As mentioned,using a boolit of 0.462" may help if there is some gas cutting. Slightly softer boolits may help too but also as mentioned, even with the thick "skirt" he may be getting some flaring now and even if not could well do with softer boolits. A flat base boolit would be a better choice for heavy smokeless loads... in my opinion anyway.

Longbow

[EDG]

What I found that seems to work in all .45-70s as long as rhe bore is decent. If you have tight spots at sight or magazine hanger dovetails you may have problems with cast bullets. You can have tight places in the bore if a banded fron sight or front sling band was installed too tight..
The following is what has worked for me.
1. Bullet metal is 20 to 1 tin lead = 10 brinell to clip on WW at 13 brinell.
2.bullet is .002 oversize. I have actually shot bullets as large as .004 oversize.
3. Velocity is regulated by the powders in the range of 2400, 5744, SR4759 and 4227. Do not use the similar burn rate H110 or WW296.
4. Powder charge of 5744 and SR4759 IS about 23 to 25 grains with heavy bullets.
5.i use only strong single shots so these loads may not be good for an old antique.
6. Bullet lube is 50-50 alox and beeswax.
7. No gas checks

Check your bore after each shot for unburned powder kernels.
If there are dozens of unburned grains you can increase the powder charge a grain or 2 in a strong rifle. The increased pressure will burn more of the powder. Having your cast bullets run over unburned powder is a good way to degrade accuracy.
Velocity should be somewhere between 1000 fps and 1300 fps.

I get groups near 1" at 100 yards with good bullets using aperture sights on Browning 1885 BPCR rifles in 45-70 using a 500 grain bullet.

I get similar groups using similar 312 bullets with gas checks in a .40-65 Browning.

[a danl]

something i have'nt seen or heard on this forum is something i have been doing for many years. i use a flat base bullet in my trapdoor with a 45cal gas check seated upside down in the case and i seat it with the bullet itself. it will only work in a straightwall case . the inverted gascheck acts as a wheel cylinder cup and expands to seal the hot gases . as i found out trapdoors have a wide variety of bore dia. it should be used as per example with a powder that is bulky like imr3031 that way there isn't much room for it to become lodged. i have never had that problem. doing it this way the bullet just slides out the barrel with absolutely no gas cutting.

[osteodoc08]

Slow it down, soften it up and use a better lube is my suggestion. I use a 405gr FN GC design with the levels of Varget you’ve mentioned and get superb accuracy. My go to is 50gr Varget. I’ve been able to shoot several sub MOA groups with that load if I do my part.

[GregLaROCHE]

My Marlin has always been very forgiving no matter what I feed it. However, I’ve only used solid based boolits. My alloy is pretty hard too. I would try some different boolits. You don’t have to buy a mold. Just buy some different cast boolits. There are lots of different ones for sale on the internet.

[hanleyfan]

what I use is a lead hardness around 12-13 and powder coated 405 boolit with 43 gr. of 4198 get right at 3 in.groups at 100 yards. I have gotten 3 deer with this load all pass through

[WHITETAIL]

+1 on softer boolets
and a flat base
But I also use a wax paper card.
I got a punch out of MID-WAY
and cut cards from milk cartons.

[GregLaROCHE]

+1 on softer boolets
and a flat base
But I also use a wax paper card.
I got a punch out of MID-WAY
and cut cards from milk cartons.

With those cards, are you shooting BP or is this something with smokeless, that I haven’t heard about?

[GregLaROCHE]

Have you verified that those micro grooves are all clean. No lead or copper in or around them?

[huntingsgr8]

It's "Ballard" rifling, not microgroove in this one. And I haven't got it on hand to check, but it grouped well with commercially made bullets, so I don't think fouling is to blame.

[dubber123]

I have the same gun, and it was a chore to get it to shoot well. I ended up with mid range loads, and cast and size large, (.462"). I have since gotten it down to sub 1" at 50 yards using the iron sights. If you get vertical stringing, check the mag tube for tension/binding. Mine had it and would string over 4" vertically until I fixed it. Good luck.

[WHITETAIL]

I shoot a Marlin CB and the load is IMR- 4198 with a wax card
under the cast 405 NOE boolit

[GregLaROCHE]

I have heard that the new .45-70s had issues with the full length tube. The original load tubes were produced with only enough for four. The heavy rounds would have an effect on accuracy as they were used up and affecting the balance and maybe harmonics of the barrel.

Maybe someone else can add to this. It’s just something I remember once reading.