45 70 Trap door..... official SAAMI pressures?

[Spokerider]

What are the *official* 45 70 trap door saami pressures?

It seems that the published maximum varies between 18,000 to 28,000 psi, depending upon the company's reloading data. How did this variation in pressure come to be? Did it start at 28,000 psi and then get bumped down to 18,000 psi with the prospect of a lawsuit in this sue-crazy era? That 10,000 psi could be the difference of 200-300 fps with the same projectile.

Hogden is right around 18,000 psi and Barnes looks to be at 28,000 psi. Then there is this Terminal Ballistics Research site;
http://www.ballisticstudies.com/Knowledgebase/.45-70+U.S+Government.html that states the 28,000 psi.

I'm not looking to load for an old trap door, but rather a 45 70 contender. For a hunting load, I need all the fps I can get from this little carbine without buggering the frame.

[Don McDowell]

Be sure you're not looking at 18000 cup. Cup and psi are not really interchangeable, but they both get to the same spot.

[Chicken Thief]

The original Trap Door is 28000psi
Modern/1895 pressure is 31900psi
And Ruger #1 is stated as beyond 45000psi.

http://www.saami.org/index.cfm

[Larry Gibson]

The variation is from "psi's" determined from C.U.P. and from peizo-transducer/strain gauge measurements. The two "psi's" are not the same and one can not be reliably converted from the other. The 45-70 Gvmt cartridge is one of those rare exceptions where the SAAMI C.U.P. and peizo-transducer MAP (Maximum Average Pressure) is the same; 28,000 psi. Where the afformentioned 18,000 psi comes from is a good question, perhaps Hodgdon can explain? Most BP and smokeless powder "trapdoor" level loads, including factory loads, for the 45-70 run 20,000 - 28,000 psi(M43) as per my own pressure measurements. Interestingly though a recent test of Remington 405 j bullet loads showed a psi of less than 11,000 with a correspondingly low velocity (1038 fps from 24" test barrel). A handload of 28 gr 5744 under a 405 - 415 gr cast will push 28,000 psi from the same test barrel.

Larry Gibson

[Chicken Thief]

I dont know about Trapdoor strength but in a 1867 designed rolling block i would stay under 20000psi for sure!

[Don McDowell]

Not sure where the 18000cup stuff came from? But it's sure not from Hogdons data, they flat out state that max saami is 28000 cup and they show some loads that get right to that line...

[Spokerider]

Not sure where the 18000cup stuff came from? But it's sure not from Hogdons data, they flat out state that max saami is 28000 cup and they show some loads that get right to that line...

My mistake, sorry. I meant to say that Lyman's TD loads are at 18,000 psi, not Hogden's.

[Spokerider]

Larry, thanks for sharing what you have learned about your own pressure testing of factory 45 70 ammo and explaining the differences between C.U.P. and peizo-transducer/strain gauge measurements.

And yep, I too would like to know the origin [ and the justification?] of the published 18,000 psi maximum TD loads.

[Spokerider]

The original Trap Door is 28000psi
Modern/1895 pressure is 31900psi
And Ruger #1 is stated as beyond 45000psi.

http://www.saami.org/index.cfm

Thank you for posting the info.
I'm going to browse the SAAMI site for more info.

[Don McDowell]

The 18000 in Lyman's smokeless data comes from that's the maximum pressure they found with blackpowder. At least that's what the explanation looks like in their cartridge description page in the #48 manual. Altho in the 46th manual they included blackpowder data in the Ruger only chapter and most of that came out around 12000 cup .
But even if you look at the data they posted at a max of 18000 its still pushing the bullets well into the longer cased bp rounds territory, and provides more than enough velocity to do anything needs done with a 45-70.