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 10 Rechamber to 45-70 (Read 5162 times)
csumpter
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Rechamber to 45-70
Jan 7th, 2019 at 3:26pm
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I have a M1899 US Krag receiver and cut barrel. I am looking to rechamber to 45-70, for low pressure, rimmed cartridge, large bore, and put a 16-20" threaded barrel to shoot suppressed subsonic, 500gr ammo. A real thumper. In theory, if you cut off the rim, created a small channel on the bolt body for the extractor to rotate on that is only if the rim could not be thinned enough to fit the 45-70, tweeked the extractor hook up to accommodate the larger rim, only .0315" higher and lower, as the rim is only .063" larger on 45-70, and kept the magazine box by either shaving down the floor plate and raising the bottom of the action .0315" to fit the rim or alternatively creating a small channel to feed the larger rim as the rim of the 30-40 is still .04" larger than the body of the 45-70. Can anyone fact check this in theory, I have no money into the action, which is in amazing shape btw, so I would be willing to spend some money on making this a unique piece
  
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csumpter
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Re: Rechamber to 45-70
Reply #1 - Jan 7th, 2019 at 3:56pm
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In theory, final product would be krag action with functional magazine, thumbhole compact stock, 16-20" fluted barrel with threads for muzzle break or silencer co hybrid suppressor to shoot 100 or less yards with different loads but mostly high grain, 500gr? subsonic loads. Pressure wise, as long as not +P 45-70, 30-40 krag is still much hotter pressure wise. Additionally I already have a sporter M1896 in 30-40 with leupold 1.5-4x scout scope with original barrel. So I do not need another 30-40. Thanks for your thoughts and help.
  
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FredC
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Re: Rechamber to 45-70
Reply #2 - Jan 7th, 2019 at 4:35pm
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My son has a 45/70 barrel for his NEF single shot. I will compare the 45/70 to the 30/40 case and see if it looks like it would have a chance of working. Have you thought of going 40/40 opening the bore to what ever would make the case straight and reloading 30/40 cases? With 40 or 41 slugs would could use heavy pistol bullets and get good expansion at moderate velocities. I think you would have a better chance of feeding from the magazine also. In times past reaming 30/40 barrels to 35 was done fairly often when the original barrel was shot out. I did a sporter a couple of years ago and chose 35 because of the better probability of feeding with no modifications to the receiver or side plate. It does feed with no issues now.

There was a long discussion about big bore Krags here:
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The OP seemed to decide to go the 35/40 route but I do not know that he ever finished the project. The discussion was what spurred me on my project.
There are some knowledgeable characters that frequent this site and they site perhaps they can help also.
  
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csumpter
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Re: Rechamber to 45-70
Reply #3 - Jan 7th, 2019 at 5:01pm
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A big selling point to me on the idea of 45-70 is widely available factory ammo, cases and bullets, I know there are any more wildcat handloading options, but my experience is limited and I do not have a good set up, also I am in college and my small apartment is not an easy place to handload along with my spare time being limited. 35 wheelen was also a thought but the pressure is much too high for the US krag action. But any research is much appreciated.
  
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FredC
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Re: Rechamber to 45-70
Reply #4 - Jan 7th, 2019 at 7:23pm
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Turning off the rim on loaded factory ammo is better than hand loading? I could do it on my tool room lathe, but I do not know if you could do it on the 9x20 lathe that would fit in an apartment.
I will look later for some 45/70 ammo at the house.

I did add both drawings to this post, what you are asking does not look easy. Even if you can modify the rims to fit a Krag bolt I am fairly certain they will not feed without extensive modifications to the side plate and perhaps the receiver.
Here is a link to the SAAMI drawings you can look at them or print them and I do not have to worry about copyright infringement.
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« Last Edit: Jan 7th, 2019 at 9:51pm by FredC »  
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csumpter
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Re: Rechamber to 45-70
Reply #5 - Jan 7th, 2019 at 9:09pm
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Sorry I believe you misunderstood. Should it be able to be 45-70, I would not shave the rim off of the ammo. But either thin the rim on the bolt face or shave it off entirely as to fit the larger rim of the 45-70. Both 30-40 and 45-70 are rimmed so just the extractor should just need to be tweeted slightly higher as to fit over the 45-70. I believe the  box can fit and feed 45-70 if enough space is created to fit the larger rim of the 45-70. Such as either creating a small deeper channel just for the rim. Or shaving it enough overall.
  
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FredC
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Re: Rechamber to 45-70
Reply #6 - Jan 7th, 2019 at 9:40pm
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Pretty ambitious to get the 45/70 rim through the box magazine. I do not have a receiver in hand to see how much would be needed to remove. Going by the SAAMI drawing the case head diameter is .618 and can be .012 larger, that is now larger than the bolt diameter (.625). So the rim would have to come off the bolt. Not sure if the extractor could be made to work either. The rim is shaped to let aid the extractor to ride over the rim on the 30/40, the bevel helps to prevent jams in case the they are accidentally loaded out of echelon. We had a discussion on this recently. Do get your ducks in a row before making any modifications that can not be undone. Please print the drawings as I will remove them shorty.
Also watch for clearance between the extractor and internal threads in the receiver. As the extractor rides over the rim it may be close to the threads.
  
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csumpter
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Re: Rechamber to 45-70
Reply #7 - Jan 7th, 2019 at 9:51pm
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So my thinking was that with the bolt face rim gone and the extractor now unable turn on the rim. You could create a small channel farther back on the bolt body and move the extractor lip back so it would be able to still rotate as if it was original but farther back on a channel rather than a rim. And since only half of the extra size of the rim would effect the extractor. Has it still have to lay even with the firing pin. You could mill the small cut out for the extractor that difference and heat and slightly bend the extractor tip up so it still fits in the cut out. Grips over the 45-70 rim, and extractor guide can ride on a channel on the body
  
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FredC
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Re: Rechamber to 45-70
Reply #8 - Jan 7th, 2019 at 10:13pm
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Just looked at the original rifle from my dad, not sure why taking the material off the front of the bolt will effect the rotation of the extractor. It seems to me it would act the same as an original bolt.
  The extractor comes no where near the threads but there is a groove on the top of the receiver that it fits into, watch your clearance there.
On the magazine box there is a guide riveted into the beginning, I suppose the rivet could be removed and that guide modified for rim clearance.
I will see if I can find any loaded cartridges and see if I can be any further help, if not I am at my limit here without a stripped receiver and cartridges in hand.
Winchester came out with "big bore" 94 cartridges (maybe 375) a couple of years ago, I wonder if they would fit in a Krag receiver with a spacer attached to the back of the magazine box. Pressure would be about right if they could be fired in a 94 action.
  
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csumpter
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Re: Rechamber to 45-70
Reply #9 - Jan 7th, 2019 at 10:40pm
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Any help or advice is appreciated. I am an expert by no means but enjoy messing around with the old rifles. Thanks
  
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Re: Rechamber to 45-70
Reply #10 - Jan 8th, 2019 at 12:46am
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I would offer a suggestion, have you thought about using a .444 Marlin case for your build. Rim is .514, .063 thick, base is .4706. Might be a closer fit to the .30-40 and the .444 would certainly qualify as a thumper.
  
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csumpter
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Re: Rechamber to 45-70
Reply #11 - Jan 8th, 2019 at 12:59am
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I have. 444 marlin is definitely an easy fit, still within pressure limits, my biggest concern is finding quality barrel blanks, needing to hand load to get subsonic and the choices for bullets are limited. Also factory ammo is more expensive and harder to come by. No factory subsonic loads plus biggest I saw was 350gr I believe, whereas 45-70 is common cheap and 500gr subsonic is available through factory.
  
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FredC
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Re: Rechamber to 45-70
Reply #12 - Jan 8th, 2019 at 3:07pm
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I Got a couple of empty cases and played with them on my sporter and it does not look possible. The rim is the same size as the bolt channel. The rim can get all the way to the bolt with no modifications, but the  front of the magazine will be a problem and MUCH metal will need to be removed to get the opening into the bolt channel to feed. There may be no modification that will even make this work and I could see ruining a pile of receivers finding this out (this would be sacrilege around here). So unless you find one already done and that could be copied I would find another way to go.
Recommend you buy a couple of cases and play with them to verify my opinion.
I have heard of Japanese Arisakas and Siamese Mausers modified to fire 45/70 from the magazine. I think I would research them instead.
Using my son's NEF on pigs with 300 grain flat point bullets was a pleasant experience. Shooting them at night using a spot light you really hear the bullet connect and they went right down.
  
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Re: Rechamber to 45-70
Reply #13 - Jan 8th, 2019 at 4:29pm
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FWIW - The .38-55 cartridge would be neat in a Krag sporting rifle, if it could be adapted to feed.

I have heard of and seen photos of a Krag being re-barreled and the action altered to use .30-30 Winchester ammo.

Still, there is no getting around that the .30-40 is a wonderful and versatile cartridge and that the action was specifically engineered to feed it wonderfully! 

IMHO - This all smacks of 'teaching a dog to walk on his hind legs'.
  
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csumpter
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Re: Rechamber to 45-70
Reply #14 - Jan 8th, 2019 at 7:59pm
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You are right 30-40 is a great cartridge, I have another spotter m96 that shoots it, and with hand loads and factory barrel got 1 moa. But should 45-70 not work, 444 marlin might be the option. With the Siamese Mauser I saw one and actually was going to make it 325 wsm but it was original and no available optics without modifying the gun.
  
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