Home Forums Reloading Big Game Rifles Loading cast bullets for Micro Groove

I have a Marlin Mod. 1895SS 45/70 with Micro-Groove rifling. I want to load some .460 diameter cast 425 Gr. gas check Bear Tooth bullets. I understand there may be some accuracy problems with the Micro Groove bullets. I don't wish to have maximum loads but those in the 1500 to 1600 fps area, mostly for elk hunting. Any one have experience with similar loads?

Thanks in advance for your advise.

ROUNDUP

My dads old 336 .30-30 with a micro groove barrel will only shoot 3/4” groups at 50 yards with properly sized bullets of sufficient hardness. 1.25” at 100 yards. An old 1895 I had would do 1.5” at 100 with the Lyman 457122 and their 405 gr. Bullet. I don’t think you have to worry about the microgroove barrel being inaccurate if the bullets fit it.

Old70

Micro-Groove barrels shoot cast well, just takes a little more work. Load the largest diameter bullet that will chamber without difficulty. In the .45-70, this will usually be .460" or even .461". As for hardness, former gunwriter and cast bullet expert C.E. Harris recommends a hard bullet for Micro-Groove barrels. I've had success with soft bullets of wheelweight alloy, but I never shot them faster than about 1,300 fps. To me,the Marlin is a hard kicker if loaded much beyond that velocity.

Many say that these barrels won't shoot cast bullets well, but I think they got discouraged when they didn't get good results with poor fitting bullets or bullets of the wrong alloy.

Good advice. I've had excellent results with three .30-30s and a .44 Mag. with Micro-Groove barrels. Hardness of alloy (between 12 and 15 BHN) didn't have much affect. .30's were sized .310" and velocity ran over 1900 fps while the .44 at .332" ran a little over 1500 fps.

It's all about that leade, that leade.

I had good results from the 1895 Marlin Microgroove barreled gun with bullets running about 11 on the BHN scale. I sized them at .460". The Marlin has long since gone down the road but I still shoot bullets sized .460" in my Ruger #1S in 45-70.

I do think bullet size is more important in Microgroove barrels. Case in point. I was shooting cast bullets from my Marlin 30-30 as was another gentleman at the range. When the range went cold and we were changing targets he was moaning about how poorly cast bullets shot. I said I was shooting cast and had a nice 1.5" groups, not bad for the velocity I was shooting that day. (1900 FPS hunting load). As we talked I asked what he's sized his bullets too and he said .308 to fit the bore. I looked at his barrel which was nicely leaded and we then spent time getting the lead out. Once the barrel was decently clear of lead I had him shoot 5 of my load. A nice neat 2" group right off the bat. He asked what the difference was in my load from his and I told him to just try sizing the bullets to .310" which was I did.
I saw him a few weeks later at the range shooting his 30-30 and he was getting good groups. He said the changing in bullet sized made all the difference. I've always started working a cast bullet for a new cartridge at .002" over groove diameter and it's worked very well for me for many years.
Paul B.

Don't be afraid of a reamer. Leade is often a problem with Marlins, but many are clueless of such.

Don’t presume you need .460” diameter bullets. Slug your bore first to find your groove diameter. Then, do a “ pound cast” to find your throat diameter. ( do an on-line search for “pound cast”+ “throat”, Veral Smith from LBT molds started it). Try to match the lubed/sized bullet diameter to your throat.

Throats may or may not be same diameter of the groove diameter. Throats can be greater diameter, and that’s what you want to know.

Who knows, you may need a .461-462” diameter bullet. Get the measurements first of your bore, then may bullet selection decision.

You can get essentially a custom diameter cast bullet mold from Arsenal molds for a great price. They have standard molds, but will alter diameter for no charge. Great molds, and fantastic option. Or, work with LBT molds/ Vetal Smith.


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