.45-70 BFR pressure limit? Why?

[eldon519]

I have read from Magnum Research's FAQs that they recommend using the lever-action level loads as a pressure ceiling for the .45-70 BFR. I am curious why that is. Since it is chambered in .500S&W which has a max 60kpsi and a larger base diameter/casehead diameter, it seems like the .45-70 should be able to handle 60kpsi just fine. Do they use different steels?

I'm not really interested in owning one of these guns, just curious why that is.

 

[ArchAngelCD]

From what I was told, just because the frame is the same doesn't mean the entire build is the same. The space between charge holes will be different and possibly the heat treating will be to a different level too. There are so many variables we don't see. It's also possible the length of the cylinder alters the strength but that is just speculation on my part.

When in doubt ask the source. Write Magnum Research and ask them. Please remember to post their answer here...

 

[eldon519]

Well that was to some degree what I was getting at, with a smaller base diameter, the .45-70 has more meat in the cylinder walls. It also has a smaller casehead so it should have less thrust, but it does taper, so perhaps that makes up for the smaller casehead. They use the same length cyclinder.

The only differences I can think of are if different steel or heat treatment is used or if the taper of the .45-70 causes too much thrust. Maybe a .45-70 loaded to 60kpsi puts too much stress on the gun from recoil. I don't know.

 

[cal44mag]

I wonder what they mean by lever-action level.

In Buffalo Bore's line of high power 45-70 loads the highest of all are called "Lever Gun Rifle Ammo".

Muzzle energy above 3500 lbs.

 

[Varminterror]

Called MR directly - (508) 635-4273

The tech service rep cited they use the same steel in the 45-70 as the 460's and 500's, specifically referenced the 60kpsi limit, and said "that must be a typo on our website," and claimed it would eat any ammo available on the market. He cited also their stance on reloads/handloads - no go if you want to exercise your warranty, so you're really limited to whatever you can find on the shelf.

 

[CraigC]

Probably has more to do with the availability of load data for anything heavier than loads suitable for the Marlin 1895 and recoil. The .45-70 loaded to 60,000psi would be EXTREMELY nasty. It should have no problem with the limited Ruger No. 1 data available.

 

[Varminterror]

[The BFR] should have no problem with the limited Ruger No. 1 data available.

I'd agree with this. But in the context of MR's FAQ's page, they disapprove the use of handloads, and I don't think anyone (BB, Garrett, etc) is making factory loads labeled specifically for the single shots (?), so it's right for them to put some kind of "it can take hot loads" disclaimer on their page.

I was very interested to see Garett claims their 540grn BFR load is under 28,000psi, that's pretty impressive - pushing a 540grn pill at 1200fps AND being under 28kpsi is quite the load. It's BFR only because the bullet is seated long - to look at them, there must only be a teeny bit of bullet crimped in that case!

 

[highlander 5]

I've fired a T/C Contender in a factory barrel with a brake and 300 gr factor ammo and quite frankly that's about as much recoil I care to subject myself to. Can't imagine what a load like Garrett would be like.

 

[CraigC]

What manufacturer's claim in the vein of liability with regards to the use of handloads is irrelevant.

I'm not at all surprised by that. It's basically an original blackpowder equivalent load. The .500Linebaugh flings a 525gr at 1200fps and is under 36,000psi but has nowhere near the .45-70's case capacity.

 

[CraigC]

I've fired a T/C Contender in a factory barrel with a brake and 300 gr factor ammo and quite frankly that's about as much recoil I care to subject myself to. Can't imagine what a load like Garrett would be like.

It would probably be more comfortable as single action revolvers have a higher bore centerline and transmit more recoil upwards as muzzle rise.

 

[bobinoregon]

Looking at my 45/70 BFR the cylinder walls look surprisingly thin. I take the manufacturers word for its capabilities and I have loaded and fired quite a few upper end Marlin loads through it with no issues. Girlfriend loves to shoot the pistol,the hotter the load the better. Reloading manuals have three levels for 45/70; trapdoor, Marlin and modern rifle, and Ruger #1 or equivalent

 

[ArchAngelCD]

I wonder what they mean by lever-action level.

In Buffalo Bore's line of high power 45-70 loads the highest of all are called "Lever Gun Rifle Ammo".

Muzzle energy above 3500 lbs.

When handloading for the 45-70 there is load data that limits the pressures to 3 different levels.

The first is suitable for Springfield Trapdoor rifles, the second is suitable for stronger actions like Leverguns and the third and highest pressure ammo should be shot only in modern rifles like the Ruger #1and #3 rifles. Different data sources differ slightly but Trapdoor pressures to out around 18,000 CUP, Levergun pressures top out around 28,000 CUP and modern rifle loads @40,000 CUP. (according to Lyman)

Now, if the ammo shot in a really strong rifle like the Ruger #1 tops out @40,000 CUP I don't see any revolver topping that number.

 

[eldon519]

Hodgdon data goes up to 40,000CUP for leverguns and 50,000CUP for modern rifles. But again, keep in mind the .500 S&W goes to 60kpsi. If I recall correctly, 50kCUP and 60kpsi are relatively similar in value.

 

[ArchAngelCD]

Hodgdon data goes up to 40,000CUP for leverguns and 50,000CUP for modern rifles. But again, keep in mind the .500 S&W goes to 60kpsi. If I recall correctly, 50kCUP and 60kpsi are relatively similar in value.

Much of the Hodgdon data is in PSI, not CUP and they are not convertible.

I did say different data sources will show slightly different limits. While I trust Hodgdon I trust Lyman even more with my over 130 year old Trapdoor rifle.

 

[eldon519]

Huh? What does it matter if Hodgson has data in both psi and CUP? Hodgdon data has max loads listed for exactly 40,000CUP under leverguns and exactly 50,000CUP for modern guns, whether or not other loads in those categories are in PSI. And in neither case should you stick either into a trapdoor, regardless of whether it is from Lyman or Hodgdon.

I am just pointing out that there is data going higher than the 40,000CUP Lyman data. And you cannot conveniently convert CUP to PSI, but that does not mean that they do not have equivalents. Afterall, they both measure pressure. For instance I also reload .35 Whelen, and data is found for both 52,000CUP and 62,000PSI, so you can assume 50,000CUP and 60,000psi are relatively close in value.

 

[ArchAngelCD]

I already mentioned there are different limits from different sources well before you did.

Why are you arguing with me, I didn't compile the data?

I hope you find what you're looking for, I'm done here.

 

[dh1633pm]

Not sure I would want to load a 45-70 Round to Ruger No 1 levels and then shoot it out of a pistol. Call me a Sissy, but my cousin did just that and he never shot it again.

 

[eldon519]

I already mentioned there are different limits from different sources well before you did.

Why are you arguing with me, I didn't compile the data?

I hope you find what you're looking for, I'm done here.

Perhaps I just don't understand what you are trying to say or what your intentions are. Maybe I am simply misinterpretting things, but several of your comments just seem non sequitur to me, and I am confused by them.

Specifically you said you don't see any revolver topping a 40,000CUP Ruger #1 load after we've established that the same gun already fires the 60kpsi .500 in a fatter round. I just don't follow. I was pointing out that the Ruger rounds in Hodgdon's data can go to 50kCUP which is roughly the same thing.

Anyway, thanks for participating. I imagine we're just miscommunicating.

 

[MaxP]

I don't think there is any sane load data that will be detrimental to the big BFR. That said, top end loads (despite having lower pressures than top end .500 S&W) can be pretty lively. The .45-70 case is pretty big and holds quite a bit of powder and subsequently burns a lot of powder, affecting recoil. I've shot a bit of that Garrett BFR-specific ammo and it will get your attention no doubt.

 

[Steve Cover]

I have read from Magnum Research's FAQs that they recommend using the lever-action level loads as a pressure ceiling for the .45-70 BFR. I am curious why that is. Since it is chambered in .500S&W which has a max 60kpsi and a larger base diameter/casehead diameter, it seems like the .45-70 should be able to handle 60kpsi just fine. Do they use different steels?

I'm not really interested in owning one of these guns, just curious why that is.

45-70 is a longer cartridge.
Pressure is exerted over a larger area.

Steve

 

[eldon519]

That shouldn't matter. Length doesn't play into calculating hoop stress or casehead thrust that I am aware of.

 

[25-20 WCF]

It is a common misconception that it is the case rim size which determines the case thrust against the breach. Rim size has nothing to do with it, it is the area which the pressure acts upon which matters. On most straight wall cartridges that is close to the bullet diameter.

So at equal pressure there is less case thrust in the .45-70 than in the .500. Thicker cylinder walls also go in the .45-70s favor. I think that by now the OP's original question has been answered. He was never interested in owning or shooting a revolver so chambered.


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