New '76 pressures? What is the real story?

[yahoody]

Uberti has an article on their web site that quoted 29,000 psi as a max for a new production 1876.  And saw the resulting argument s about how that was unsafe according to the Internet "Experts" eye balling it.  Saw another comment today that Accurate Powders quoted 27,000 PSI.  Although I have not found the actual source yet.   

Then found this today from the editors of HANDLOADER and RIFLE.

http://www.loaddata.com/members/search_detail.cfm?MetallicID=5093

330gr lead @ 1480fps from a 1876 is smokkkkiiiiiinnnng! 

Trap door is listed as 19,000 psi and the '86 as 28,000psi

Not going to ever believe a '76 will take the pressure a '86 will.

But then the '73 is being built on a 44 mag so who knows.  44 mag pressures are listed @ 38,000psi.

Data?  Real data not "insights" ;-)  Love to see it?.  I should know by the end of next week.  But have to wonder right now. 

[yahoody]

Still poking around.  Found this:

"The Model 1876 is the only repeating rifle that had successful, documented use in the northern plains buffalo slaughter. Earlier repeating rifles such as the Henry, Spencer, and Winchester Models of 1866 and 1873 may have seen limited use, but only the Model 1876 was considered by hunters as powerful enough to do the job against the big woolies.

The strength of the Model 1876 rifle and the .45-75 W.C.F. cartridge was tested by Winchester in the late 1870s. The factory conducted tests on the strength and reliability of the action to answer concerns by customers. These tests will astound collectors and shooters who have stated the Model 1876's toggle link action is "weak." In response to a letter sent to the company by Charles Hallock, Esquire, of Forest & Streammagazine, Oliver Winchester responded by telling about the tests the factory accomplished on the 1876 rifle. He indicated that engineers first started the tests by removing one of the toggle links and fired 20 rounds (this was with .45-75 W.C.F. cartridge with 350 grain bullet) with no effect. They restored the missing link then went through 6 more trials starting with a charge of 105 grains of black powder, behind a 700 grain bullet! The comment "worked well" is noted. They then increased the charge of powder to 165 grains behind 3 bullets (1,150 grains) and that "worked well." From there, they increased the powder charge to 203 grains and added more bullets until they reached 1,750 grains of lead (five 350 grain bullets). This also "worked well." Finally, they added one more bullet, bringing the total weight to 2,100 grains, and things began to happen. The comment was, "Breech pin slightly bent. Arm working stiff." The seventh and final test was again 203 grains of powder but this time six Martini bullets weighing 480 grains each (2,880 grains) were used. "The charge bent the breech pin, blew out the side plates, split the frame and otherwise disabled the arm," was the comment. Oliver Winchester noted that in this seventh trial, the shell had burst into fragments and the escape of gas at the breech did the damage."

And that my friends was on an ORIGINAL '76!

Now, how all that was actually accomplished I have yet to figure out.

more here:
http://outlawswinchesters.jouwweb.nl/winchester-1876

[KWK]

Uberti is in Italy, a country which conforms to the pressure standards of the CIP. These standards call for maximum operating pressures of 27.8 ksi for the .40-60 and .45-60, 29.8 ksi for the .25-70, and 30.5 ksi for the .50-95. Proof loads will be another 25% on top of this. (1 ksi = 1000 psi)

While these pressures may seem high, they are realistic for black powder. I think people have gotten used to modern .45-70 ammo, which is loaded down to about 20 ksi. It's actually rated at 28 ksi at SAAMI, but few would want to try that in some of the old, original guns, some of which were poorly designed.

Whelen reported back before WW-I that full power, BP loads for the .45-70 ran around 25 ksi. I think that's why SAAMI and CIP specs are at the levels they are.

The 1886 is far stronger, of course. At the CIP, the .33 WCF is rated to 44.2 ksi and the .348 is 46.4 ksi. One Italian maker of 1886 style guns has loaded the .444, and that's rated at 51.5 ksi by the CIP.

Of course, pressure isn't the only factor. Case diameter determines the area over which this pressure is presented to the breech and thus is a factor in the breech thrust which must be contained. The .45-75 is a fat case, a bit more than the .348 is. The combination is really quite impressive for a toggle link action.

On the other hand, some of the original toggle link actions were known to develop head space woes. This was never a concern with the 1886 -- until smokeless came out and they had to improve the steels a little.

[greyhawk]

Guys  I did no good on the Uberti site - could not find that article - (will try again) - we can kind of get there by deduction - in the manual they say this

"Use only Commercially Loaded cartridges that have been loaded in accordance with SAAMI -CIP standards"

Then we go to CIP Standards for the 45/75 is 30,000  (as KWK writes in his post)

So they are givin us a bit of wiggle room here. 
thanks to all for keeping this alive.
Greyhawk

[Trailrider]

NOTE: I am NOT trying to say that the Uberti M1876 will handle any pressures higher than what they say!  But there are several things to consider when viewing these figures. First, as was posted by KWK, the cartridge case head diameter determines the force generated against the breechbolt, which is, in turn, transmitted to the locking mechanism and the frame. Pressure times area equals the backthrust force on the bolt. In point of fact, straight-sided cases in chambers that are not severly oversized will tend to adhere to the chamber wall, contributing to the reduction of backthrust by the case head. The strength of the brass will affect the amount the case head moves without considering the strength of the action. Years ago, I ran some tests using modern factory .44-40 loads in an original M1873 Winchester from which I removed first one and then both toggle-links. The case actually moved only about half-way out of the chamber!
Second, the pressure measurements done in Europe may differ from the way pressures are measured in the U.S. Another factor is that the quoted pressures are probably the average maximum operating pressure for which the guns are proofed. I would bet that there is a safety factor of at least 1.5 built into the pressures at which damage to the mechanism will result.
Third, modern steels also help improve the safety margins, which is why those '73's can be chambered for .44 Magnum (in addition to the slightly smaller cartridge case).
All this does NOT mean we shoud exceed the recommended maximum pressures, however!

[spacecommander]

Take ALL of this with a "Don't try this at home" attitude. The 44-40 cartridge case has a very thin case wall, it will easily expand and fill my toys at the start load data and the 45LC smokes the case walls at start load data. The only 45-75 PUBLISHED load data for the 45-75 with a 350g bullet comes from Barnes (Cartridges of the world) and smokes the case walls rather badly. The 45LC cartridge case is beefier than the 44-40 and the 45-75 from Jamison has what appears to be a fairly THICK cartridge wall - beefier still than the 45LC. There is a good chance that the force on the action mechanism goes DOWN as the load goes up, then obviously goes UP with increasing powder charges. Huh? Huh^2? If the outer case walls get smoked - the case has not fully expanded to the chamber wall and the coefficient of friction between the case and the wall is pretty close to zero. Therefore all of the chamber pressure acts on the bolt face as the case has not "gripped" the chamber walls. As the load goes up and the case gets sealed against the chamber wall - the case itself helps contain the rearward force, and the load on the bolt face may well be less. I don't have a problem with the 45LC smoked cases as my charges of trail boss are so tiny and the velocity so low that even with a smoked case wall the rearward force on the pistol is negligible. The starting pressures on the 45-75 are a concern, however, and I don't like to see a smoked case wall. Have not ever heard of smoked cases with real black powder - if somebody has seen this please let us know.

Might it be a good idea to work up unknown loads until the cases aren't smoked, assuming the powder charge weight/bullet weight stays within Trapdoor 45-70 equivalents?

(Nomex suit on)

[yahoody]

Space...I agree.

The loads I shoot in my '76 are the cleanest ammo and makes it the cleanest gun I shoot.

[DTS]

Trailrider - very well written.  Some time ago, when I was shooting a .45 3 1/4" Sharps, I perused an Accurate Arms loading manual as they printed data for these guns.  Their data then (RED BOOK) started with a factory-type black powder charge. IIRC, the .45/70 was loaded with 70gr. 2F and a 405gr. Lyman bullet, probably #457141 that developed 22,000PSI on their pezio machine. What is really interesting, is that the .45/90, with it's 300gr. and 90gr. of 2F developed 28,000PSI and the .45 3 1/4" with 120gr. and a 500gr. evened out at 30,000PSI. Thus, they held those pressures with their smokeless loads. the .50 3 1/4 also ran 30,000psi. using 140gr. 2F and a 500gr. bullet.

Lyman's book, the #46th manual also lists pressures for the black powder loads in .45 cal. but did not pressure test their .50 cal loads. Their data closely follows that of Accurate Arms in the long .45, but their .45/70 data is lower, however is CUP, not PSI. further note, they list their .45 3 1/4 loads for use in replica Rolling Block and Sharps rifles. At that time, only the Navy Arms RB and the Shiloh and CSharps Arms Sharps were the rifles referred to.  Their 300gr. data for the noted .45 3 1/4" was loaded to 35,300CUP uisng IMR3031 not psi but CUP.  This pushed a 300gr. Sierra bullet at 2,409fps, yet the next lower pressure using H4895 ran 2,742fps at 34,100CUP.