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View Full Version : Help! bullets tumbling in my Cowboy 45-70



Roosterbob
09-26-2013, 11:13 PM
Today I loaded up some 405 grain cast from a Lyman mold for my Marlin Cowboy. Trailboss powder, WLR primers in Remington brass. Planning to use it on close range pigs and was going to re-sight the rifle for the load.

Range was 40yds from a standing rest. Fired two, made a sight adjustment, fired one and adjusted again and the next two were 6-8in right and keyholed!
Fired another six with no problem and a nice tidy group.

Bullets were cast from same mix, sized and lubed at one time and weighed before loading. Rifle bore shows no evidence of leading or other problems. I have studied, scratched my head, and went over years of old reloading notes and I can't figure a reason for the two key hole shots.

Any ideas??

Thanks,
Roosterbob

MtGun44
09-26-2013, 11:33 PM
Undersized almost certainly. Possible that you got a few cast smaller than the others. Perhaps
you are just on the edge of being too small and these "fell over the edge".

Have you slugged the barrel? You need to be shooting boolits that are .002 to .003 larger than
groove diameter in most rifles to get good results. Tumbling, inaccuracy and keyholing are
caused by undersized boolits. You will have to think it through to figure out exactly HOW you
got a few undersized, but you did.

Bill

Gunlaker
09-27-2013, 10:25 AM
I agree. They are likely undersized.

Chris.

Sensai
09-27-2013, 11:07 AM
Is your Lyman mold a new one or an old one? I got a new Lyman mold to "upgrade" from my Lee. The new mold cast a full .002" smaller than the Lee, and too small for my '95CB. There's nothing wrong with the mold. It's in spec, but just won't work for my application. Guess I'll continue to use the Lee, if it ain't broke, don't fix it. Slug your barrel and mic the boolits (unsized). You'll probably find that your in the same boat. If it's borderline, you may be able to get away with using a harder alloy. The more antimony the harder and larger the boolit, generally speaking.

Full Mold Jack
09-27-2013, 11:25 AM
I was thinking void in the casts but then you did say you weighed them.

Just throwing it out there.

williamwaco
09-27-2013, 11:44 AM
In my experience, keyholes are always caused by undersized OR by being loaded too slow.

Since this is a hunting load, I assume they are not too slow.

Re-read Mtgun44.

NVScouter
09-27-2013, 12:41 PM
Junk rifle. Send it to me for scrap......

Try some hollow bases with that powderpuff load. It may like it better

pls1911
09-27-2013, 01:50 PM
Harder alloy, gas check and size to .460. Lube with grease of choice, and again with 50-50 lla/jpw.
I cast soft then heat treat hard, though water drop may do as well.

Works very well to 2000fps without leading in my Marlins, Pedersolis, TC, Rugers and Brownings.

fouronesix
09-27-2013, 07:53 PM
Roosterbob,
First, likely your bullets aren't tumbling- but yawing around their axis thus leaving the keyholes in the target.

Even with just a few doing it- one thing or several things wrong. You can try something that usually works. Get the RCBS 300 gr RNFP GC mold (usually the bullet will end up about 320 gr). Use 12-14 BHN alloy. Size to .458-9. Lube with soft lube. Use a more suitable powder than Trailboss. Try about 30 gr of 5744. Don't over crimp- a light crimp with a Lee FCD is all that's needed or wanted. Clean the bore of all copper, lead and other fouling- even though you said it showed no lead.

Roosterbob
09-27-2013, 08:47 PM
Thanks for all the replys. These were cast from an old Lyman 405gr mold that I have used for years. All were sized in a .458 die. How I got undersized bullets I can't imagine, though that is the only thought that makes any sense. Yawed or keyholed I won't say, but one hit so profiled that you can almost see the grease grooves in the target.
The barrel had been properly cleaned when I got it out of the safe, no copper or fouling to create a problem. And yes, it is a powder puff load but it has worked well in the past on smaller feral hogs out to 50-60 yards. This gun and this year is the first time for me to use Trail Boss- I was gifted a large quantity of it and have been playing with it a bit. Haven't run them through the crono but they are mild. While not the newest powder on the block, I have always used 3031 for my heavier loads and Unique for the "play" stuff.
Lastly, no I have not slugged the bore. It shot so well from the start with the bullets I had on hand that I never made the effort. Will remedy that!
Thanks again all,
Roosterbob

TXGunNut
09-27-2013, 10:35 PM
Slug it to be sure roosterbob but I think your Marlin will be happier with a .460 boolit. 45-70 doesn't have to be cast or pushed terribly hard but I think I'd pick up the pace to around 1600 or better and try ACWW or heat-treated 50/50 with a touch of lead.

Driver man
09-27-2013, 10:49 PM
If the only difference from previous shoots is the powder then that is what i would suspect is the problem.

fouronesix
09-28-2013, 12:38 AM
Well, Trailboss is a good powder for smaller high expansion ratio cartridges like the straight wall pistols- but it is a very fast powder for lower velocity loads and if you're using a plain base bullet everything will have to work just right. That Lyman 405 plain base bullet would be much better as a BPCR bullet, cast of an alloy of BHN 7-8 or so with a card wad over a full case of blackpowder.

If you feel you need a 400 gr type bullet, want to use smokeless, then go with RCBS 300 RNFP GC or its big brother the RCBS 405 RNFP GC. Again over a better powder like 5744. I'd still only size to .458-9. No matter, because most regular molds from Lyman or RCBS are going to cast to about that size anyway. If you think you have to go with a .460 size then you'll have to use one by one of the other mold companies. I've never had any problem getting a .458-9 sized gas checked bullet to shoot well in a whole bunch of different rifles including several original 1886s. The only exception being a couple of trapdoors and they are notorious for having fat groove diameters. You have a modern rifle and there is no reason to suspect a groove diameter larger than about .458. Those recommendations have been proven to work over and over. But, I have an idea you are going to do what you want to do anyway.

MtGun44
09-28-2013, 07:46 PM
You may have been shooting undersized for a long time but getting just enough bump up
from your hotter loads to make it work. Now you dropped to a lower pressure load and
(I think) a lower pressure rise rate powder and may not be getting the bump up that you
were getting.

Bill

knifemaker
09-30-2013, 03:28 AM
If your mold will throw large enough, try sizing to .460. My Marlin 1895 loves that size dia. for best accuracy. Most other owners of Marlin 1895s that I have talked too also said that .460 was the size that gave them best accuracy in their rifles. If you slug the barrel, I am willing to bet your groove dia. will be around .4585 to .459.

Janoosh
09-30-2013, 06:33 PM
What has not been mentioned is "Crimp Sizing" the boolits. If all the boolits were sized , and the gun previously shot well, with those same boolits, perhaps when crimping the shell, you are sizing the boolit down smaller, inadvertantly. Also, look at a fired shell to see if the crimp has opened or has the boolit been squirted out into the bore. It's worth a look.

bigted
10-02-2013, 04:44 AM
Well, Trailboss is a good powder for smaller high expansion ratio cartridges like the straight wall pistols- but it is a very fast powder for lower velocity loads and if you're using a plain base bullet everything will have to work just right. That Lyman 405 plain base bullet would be much better as a BPCR bullet, cast of an alloy of BHN 7-8 or so with a card wad over a full case of blackpowder.

If you feel you need a 400 gr type bullet, want to use smokeless, then go with RCBS 300 RNFP GC or its big brother the RCBS 405 RNFP GC. Again over a better powder like 5744. I'd still only size to .458-9. No matter, because most regular molds from Lyman or RCBS are going to cast to about that size anyway. If you think you have to go with a .460 size then you'll have to use one by one of the other mold companies. I've never had any problem getting a .458-9 sized gas checked bullet to shoot well in a whole bunch of different rifles including several original 1886s. The only exception being a couple of trapdoors and they are notorious for having fat groove diameters. You have a modern rifle and there is no reason to suspect a groove diameter larger than about .458. Those recommendations have been proven to work over and over. But, I have an idea you are going to do what you want to do anyway.

well seems like a great time to take a breath. the true Marlins ... not the remlin ... have all liked the .460 diameter boolits. all my marlins have all liked the large .460 inch boolits. everybody I talk to with experience with the marlin's know that they like the .460 inch boolits as well.

they also perform very well ... just loaded some 350's this year for a guide friend of mine and he did a finishing shot at a very large grizz for his client while shooting his marlin 45-70 rifle. that .460 inch 350 grain boolit did its job very well. going thru the bear and mushrooming perfectly to come to a halt under the hide on the far side of the huge grizzly bear. this running around 1800 FPS shooting a fairly soft [muddy creek Sam's] lead alloy. however it wernt shooting that "trail boss" powder... instead the ol standby IMR 3031.

Suo Gan
10-04-2013, 07:12 PM
Make sure it is up to size...push it faster...get a smaller grain boolit.