This is a question having to do with the strength of a Thompson Center Encore 45-70 barrel.  
Most loading manuals list the 45-70 at three different chamber pressure levels #1 Trapdoor, #2 lever actions, and #3 Ruger #1 and Browning B-78.  Ken Waters in his pet loads book even added a super group three with Siamese Mauser conversions.
My question is in what group would you place the TC Encore with a 45-70 barrel. 
The barrel in question is not a slim factory weight or even the much heavier Catadin weight.  This barrel is a custom build by SSK on the full bull weight which is quite a bit heavier than the Catadin weight because this barrel requires the use of the 12 gauge fore end . I have been using the group two type loads for lever actions but I wonder if I can safely go to group three loads.
The TC Encore is chambered for some very potent magnum cartridges that push pressures to over 60,000 psi but they may perhaps be slimmer than the 45-70 case. On the other hand 
I have another SSK Encore barrel with a more slim contour than the full bull weight chambered for the 458 Win Mag which in the Lyman book shows loads up to about 55,000 cup.
My feeling is that its a green light because group three 45-70 loads dont get near that pressure. That is my feeling but I would like to hear other opinions.  Thanks.

Run it up to the Ruger #1 loads.  I’ve shot heavy loads in the Encore with no ill effects.  That’s advice is worth what you paid for it.

Please explain thrust .

calledflyer wrote yesterday at 9:57am:


Math is right, but inputs off.

Bolt thrust = max pressure x area of the inside diameter of the cartridge. Even if you use outside .5” square is a lot different than  .5” circle. 

.25 x .25 x 3.1416 = .19635 
.19635 x 60,000 = 11,781

If thrust is calculated using the inside diameter of the case then the 45-70 should be about equal to the 458 Win mag. That makes it equal in inside diameter to all cartridges using the standard belted magnum case.
The TC Encore has factory barrels chambered for many belted magnum cases such as 7mm Rem mag , 300 Win mag etc.
It would seem then that the thrust range we are looking at is factory approved no ?  This is just an " I wonder" thing because in any 45-70 when chamber pressures push past 40,000 psi or even reach that level recoil is viciously wicked in the weight of rifles generally chambered to 45-70. That is the reason when I ordered the barrel from SSK I got it in the heaviest contour they offer, the full bull contour. I also had them install one of their artillery type breaks which is needed for this type of loading.

Today I cast a couple hundred of the old Lyman 462560 in a hollow point mold. I just weighed one with a gas check at 550gn.
When staying in the group two range I load those to 1550 fps.
I will now be treading new ground.
   Tomorrow , Lord willing I will be headed up to fire wood camp where there are both black and grizzle bears.  Last week we had a hunter kill a grizz that charged him. Some of you may have heard about it in the news. We get about one mauling per year in this area but this year the bear bit the bullet, so far.
  I will be taking the Encore 45-70 and a favorite Ruger Bisley flat top 44 special.
  I have killed grizz with a Marlin 45-70 and each time it seemed the rifle just didnt feel big enough. My oldest Son still in Alaska now owns my old Marlin and when I replaced it I needed something to test all 45-70 load levels with so got the SSK Encore barrel.

JHand wrote yesterday at 4:01pm:


Keep in mind the loads that are being talked about here are in the 40,000 psi range for the 45-70 The 22-250 still creates more pressure, but it’s not operating any where near 80,000 psi. 

Then back to recoil. The 550 grain bullet at 1550 fps will have close to 4X the recoil of the 22-250 with 50 grain bullet at 4000 fps. in a 10 pound rifle.

I just checked the Lyman 4th edition cast bullet handbook for 45-70 loads.  The heaviest bullet they show is a 540 grain Saeco
They show in their Ruger only section a load with that Saeco bullet with a charge of VV N-135 of 52 grain producing 1737 fps velocity at 37,100 cup
Personally I put that in the group two section for modern Marlin and Winchester laver action rifles.
This does though illustrate the dilemma with trying to take the 45-70 to higher velocities that with powders of the proper burn rate it simply runs out of room if trying to stay with industry standard max cartridge length.
If it weren't true we would likely never  have gotten the 45/2.5" flanged known to more common folk as the 458 Win Mag. I have killed a lot of big critters with max group two loads and never once saw any short fall.

bullshop wrote yesterday at 5:06pm:


Big difference between cup and psi. Might check the VV data for that combination. May not be available in psi, only Mpa. But that converts reasonably well. Cup to psi just doesn’t work.

Quote:

At ~40k they are about the same, in the info I have and separate after that.

My thoughts are 2 fold.  An Encore shouldn't be compared in strength to a Farquharson falling block action like the Ruger No 1, nor the Siamese Mauser action.  I'd feel comfortable using Lever gun data in the Encore, but not No 1, and absolutely not Siamese Mauser data.   
The big issue for me using Ruger data in my No 1 was recoil.  My 8 lb. No 1's recoil with top loads was much worse than my 10 lb. 416 Taylor, closer to a 14 lb. 500 Nitro Express.   
Also,  if I was needing Grizzly medicine I'd want something with more ammo than a SS.

Thank you all for your opinions on this subject.  I appreciate the input.

Those Hornady jacketed bullet loads are too much of a good thing for me.   It has been my experience though that a cast bullet of about the same weight can equal the velocity of its jacketed counterpart at a lower chamber pressure due to the lower coefficient of friction of the lubricated cast bullet.
That is a bonus of using cast bullets that you can equal the velocity of a similar jacketed bullet at a lower pressure or you can load to an equal pressure and get a higher velocity from the cast bullet over the jacketed bullet.  Undoubtedly some will disagree but that has been my experience.