1876 Pressure?

[KenH]

Hello ya'll, and a Happy New Year to all. 

Does anybody have info on the safe chamber pressure for the 1876 rifle?  It seems like I've read an original Sharps in good condition should safely handle up to 25K psi, with a trapdoor only 18K psi range.  For the few rounds I've shot thru my 1876 I've held pressures (calculated pressures) below 12K psi, and mostly below 10K psi.  I loaded 30 grains of 3031 which calculated to around 1300 fps and 8575 psi chamber pressure, but only 50% of powder burnt.  I saw some grains in open action after firing.  Yea, I know 3031 is too slow but had the powder on hand.  I've got some Lil'Gun that looks pretty good.

Thanks to all for any shared knowledge.

Ken H>

[King Medallion]

I don't have a direct answer to your question, but smokeless powder wise, for MY Uberti 45/75, IMR 4198 worked best, and Shooters World Buffalo Rifle and Trail Boss did very well. I know different caliber's, you should give them a try.

[Coal Creek Griff]

The 49th edition of the Lyman Reloading Handbook includes an article about hand loading for 1876 replicas. The author used Chaparral guns, but I imagine that it translates to Uberti guns as well.  In the article, he states that the rifles "feature improved steels and are capable of safely handling smokeless powder loads with pressures up to 28,000 cup".

Keep in mind that this is for modern replicas.

[KenH]

Based on some graphs I've seen for 45-70 pressure curves 62 grain of GOEX FFFg w/500 grain bullet gives around 25K psi chamber pressure for "around 1100 to 1200 fps.  PSI not CUP units, they are different.  Sometimes CUP will be close to psi, other times they can vary a good bit.  SR4759 powder gives same velocity range at less pressure, seems like remember it's in the 16k psi range for the same fps range.  Looks like the old rifles where shooting in the 25k to 28k pressure range.

My question about safe pressure for the 1876 is based on the concern about strength of the toggle link system.  Is it as strong as a Rolling Block or Falling Block action?

[greyhawk]

Based on some graphs I've seen for 45-70 pressure curves 62 grain of GOEX FFFg w/500 grain bullet gives around 25K psi chamber pressure for "around 1100 to 1200 fps.  PSI not CUP units, they are different.  Sometimes CUP will be close to psi, other times they can vary a good bit.  SR4759 powder gives same velocity range at less pressure, seems like remember it's in the 16k psi range for the same fps range.  Looks like the old rifles where shooting in the 25k to 28k pressure range.

My question about safe pressure for the 1876 is based on the concern about strength of the toggle link system.  Is it as strong as a Rolling Block or Falling Block action?

KenH
Winchester did a writeup on the 76 ---- what it took to blow it up (that part - how much it took - I struggle to believe - it was after all the era of the snake oil salesmen!)

however the interesting bit was when the gun blew the toggles held and the barrel ruptured underneath the chamber (where its thinner to accomodate the magazine tube)

modern day there was a story about "Shrapnel" (maybe he is still on one of these forums) blowing a 76 - more or less the same - the back end held while the barrel ruptured under the chamber

maybe the toggle system is stronger than we think? if the links, action and bolt are machined and fit correctly its not the pins taking the thrust but rather the shoulders cut into the bolt and action body and the outside curve of the links............................

Ages ago DT posted details of a load winchester made for single loading in the 45/75 ....450 grain PP / 90 grains of powder ....thats a stoutish load - you would reckon they would not have done that if there was any chance the rifle would not take it.

[dusty texian]

Yep what Greyhawk said , I believe  the 76 is stronger than some think . ,,,,DT

[Cap'n Redneck]

I read somewhere (maybe on this forum?) a statement going something like this:
"The 1876 Winchester is stronger than you think, but not as strong as you would like."

(I for one will not be hot-rodding my Uberti 1876.  I'd rather get a Win 1886 or some Marlin for that.)

I would rate the Falling Block (Sharps / High-Wall) as the strongest.  The Rolling Block falls somewhere in the middle.  Then the Toggle-link Winchester. 

[KenH]

Thanks for the comments folks.  It sounds like the 1876 (with properly fitting toggle links) should be fully safe with 18,000 psi loads, and perhaps even up to the 25K loads.  Don't worry, I'm in no way considering any "stout" loads.  Those days are waaaaay behind me by many years.  I can get all the velocity I want from loads well less than 10K psi and they punch holes in paper and ring steel just fine.

[Trailrider]

In theory, the strength of the toggle-link action depends on the backthrust on the bolt. Properly fitted, the ends of the links should bear on the cutouts on the bolt and receiver. The force is the pressure times the area of the cartridge head. The force is linear between the ends of the links. Some guns may not have the ends of the links bearing on the cutouts, in which case the force is on the pivot pins, which are in shear.  In that case (NOT correctly made), the shear strength of the pins would constitute the weakness. If there is any sign of the pins bending, then the fit is incorrect and the pins should be replaced with stronger ones (using hardened drill rod, for example).
I haven't compared the sizes of links between Winchester '73's and '76's, but the size of the heads between .44-40 and .45-60 or .45-75 is different, so the '76 will have more backthrust. The best thing when using smokeless powder is to use the slowest powder that will burn most efficiently and keep the MV the same as the original BP loads. IMR4198 is probably better than 3031, but the latter will probably do, although, as reported, there will be a lot of unburned or partially-burned particles.

[dusty texian]

In theory, the strength of the toggle-link action depends on the backthrust on the bolt. Properly fitted, the ends of the links should bear on the cutouts on the bolt and receiver. The force is the pressure times the area of the cartridge head. The force is linear between the ends of the links. Some guns may not have the ends of the links bearing on the cutouts, in which case the force is on the pivot pins, which are in shear.  In that case (NOT correctly made), the shear strength of the pins would constitute the weakness. If there is any sign of the pins bending, then the fit is incorrect and the pins should be replaced with stronger ones (using hardened drill rod, for example).
I haven't compared the sizes of links between Winchester '73's and '76's, but the size of the heads between .44-40 and .45-60 or .45-75 is different, so the '76 will have more backthrust. The best thing when using smokeless powder is to use the slowest powder that will burn most efficiently and keep the MV the same as the original BP loads. IMR4198 is probably better than 3031, but the latter will probably do, although, as reported, there will be a lot of unburned or partially-burned particles.

I agree with you Trailrider on all but  the advice to Beef up the pins as a fix. If pins are damaged from bolt thrust because the toggles are not long enough or ill fitted  (rigid) when in battery . The proper fix would be toggle replacement or repair .  The toggle pins purpose are only to link the toggles together and not designed to absorb the bolt thrust  and if they are having to absorb the bolt thrust ,the toggles are the problem and must be fixed . I realize you know this and only say it for those that may not . ,,,,DT

[Slamfire]

 Ditto, DT & others ,, .002 -.003 thnds. on the toggle links is a loooong way ( ask me ).



   coffee's ready ,, Hootmix.