Well I casted some lead in 405 gr weight and ordered my sizing die which came in at .457 which I knew was going to be too small. But I loaded a few anyway before honing my sizer to .458. The rounds at 457 shot terrible at 100 yrds grouping to 15 inches. Then I tried a few at .458 and the groups were noticebly smaller about 9-10 inches . Then at last I had honed my sizer to .459 and 4 inches was about average. I bet they would have been tighter if my shoulder wasnt all beat to hell. The 45-70 is a real beast with the stock rifle butt plate. I dont know if I should stop there or hone to .460 This was using 38 grains of IMR 4198 . Either way my next thing is to figure the drop at 150 and 200 yrds to have some fun with a gong.

You ought to be able to hear that gong really well.

4 inches with iron sights and a tenderized shoulder is pretty good. I think I'd wait for the shoulder to recover a little, then go try some more .459 loads. 4 inches is plenty good enough to take a lot of game, especially .45-70 sized game.

So I can steady my aim a bit more. I was worried some with all the negative stuff guys said about micro groove barrels and lead rounds. Even with the under size rounds I had no leading I could see. The barrel cleaned out nicely mirror bright. When I do cast I use a 1 to 16 mix of lead and tin and the bullets are quenched in cold water in a bucket with a rag at the bottem. They were a bear to size at the original .457 . And I didnt use lube in the grooves. I used Lee Alox tumble lube with 2 coats and the powder through die helped to seat the bullets with out squeezing the lube off as they seated. I finished them off with a factory crimp die as well

Oversized cast bullets are the key for microgroove. I have found that gas checks help too in my 30-30, I can even get away with shooting gas checked .309s with no loss in accuracy. Plain base I stick to .311.

(Note to the reader: Use these loads at your own risk. The loads below are developed from Cast Performance's load data (405 g hard cast) and Hodgdon's (350g jacketed loads) and work well in my gun but may not work so well or safely in yours. Always work up from the minimum published loads and watch for over pressure signs. Please also keep in mind that these loads are developed in a cooler climate - Alaska and will probably be at higher pressures in warmer cliimates)

Disclaimer aside, I also own a Marlin .45-70 gov with a MicroGroove barrel (22 inch) and reload my own ammunition. Up front, I recognize that you are casting your own bullets and do respect that. I have a load worked up with 46.2 grains of IMR 3031 and a 405g hard cast bullet that will easily group inside 2 and a half inches at 100 yards. The bullets are sized at .459. I've run them over the chronograph at 1480 fps on cooler days; 45 degrees and about 100 fps faster on warmer Alaskan days - about 65 to 70 degrees. The IMR 3031 seems a bit temperature sensitive. This is a fun load for smacking the gongs with!

But in terms of what my rifle seems to shoot best with, I really do like the IMR 4198 but I use it with jacketed bullets in the 350g weight range. I think it excels with this bullet weight. At 49.5g of IMR 4198 with the Hornady 350g FP, I have no difficulty clustering 5 shots under two inches at 100 yds. This load is taken from Hodgdon's data and stands at .5 grains less than maximum. The load runs at about 1993 fps average at 65 degrees Fahr. and drops about 40 fps when the temps run down in the low 40's. The bullet drops about 10 inches at 200 yds. I have a similar load for a 350 grain Swift A-Frame at 49.1g of IMR4198. I've noticed pressure spikes when I run any higher than 49.2g of IMR4198 under this bullet so I consider it to be at max load. The bullet appears to have a longer bearing surface than the Hornady 350g bullet, so the pressures are probably higher. It runs a little slower (1972 fps), but it is the hunting load that I carry when in in brown bear country.

BTW - putting a Limb Saver recoil pad on my rifle made extended shooting sessions much more enjoyable. I put 10 of the 350g loads and 18 of the 400 grain loads through the rifle today without aggravating my shoulder at all. It has seriously knocked down any tendency to flinch at the bench for me.

Good morning
Marlins are generally FAT throated.
Measure the throat diameter and size to Throat + .002 and you should get 1.5 " groups at 100 yards with good bullets. I have 3 45-70 Marlins and they all need .461+ to shoot good groups.

I can't vouch for the 45/70 in a Marlin Micro-grove but my 30-30 Marlin Micro-grove shoots cast just as well as jacketed; maybe better. I am shooting a Lee 180 gr gas check bullet at velocities that match factory jacketed ammo (I can't recall the load data right now). Although my range is limited to 50 meters I have no trouble getting 1 to 1.5 inch 5-shot groups with my cast bullet loads using a peep sight. My .357 mag Marlin also shoots cast well. I agree with Missionary; match bullet diameter to throat size and don't worry about what type of rifling you have.

I also am using a 45/70 micro groove. Had a heck of a time working up a load with it but finally found one that works great...34 grns of IMR 4198 under the Lyman 457193 405 grn bullet using WW's. What I found, at least in my rifle was shoot a few rounds through too warm up the barrel and "foul it up a little." Afterwards they flew great downrange. This is a all day shooting load. I also use a Limbsaver recoil pad. I was really loading heavy for awhile but got tired of loosening my teeth. Don't know of too many critters that can walk away from the above load in N. America.

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You'll shoot your eye out kid

The conventional wisdom of the day indicates 1600 fps is where the micro groove will shoot cast bullets well. NEF/H&R have used micro grooved barrels for several years and I seem to have several of them.

My 22" barrel also has a factory recoil pad on the other end, which helps a lot! Since I don't live in bear country, I try to send a 405 gr cast bullet downrange as accurately as possible. This 100 yard target was shot with a Rem 400 gr JSP, but cast will do just as well.



One advantage to using this load is the tremendous reduction in recoil!

Moving a little faster, around 1475 fps, this 300 gr Rem JHP uses 20.0 gr of Blue Dot .



I've shot as much as 25.0 gr of Blue Dot with that 300 gr bullet, but 20.0 gr was much more accurate and recoiled less.

Great information. Thanks, guys. I now have some food for thought. A couple years ago, I tried cast bullets, 405 grain, in my 1895 micro-groove. I loaded down. Accuracy=nil; keyholing; leaded the bore like crazy. Seemed like the bullets were stripping. I think they were .458's. A hard, tight bullet makes sense. Rifle's great with jacketed! They do kick a little, don't they!?

You guys need to try some AA 5744. It shoots really good in 45-70s. I size mine to .460 That seems to work in Marlins and Pedersoli Sharps.