SC on Gunbroker

[B. Dudley]

Originally Posted by edgarspencer

Without a top locking lug or cross bolt, cartridge is somewhat restricted to lower velocity/ pressures. As much as I enjoy 45-70, I think a flatter shooting round is more appropriate for this type of gun. As Brian suggested, there's nothing wrong with the old timers like 30-40 (.30 US), .303 British or .300 Savage. For simplicity, I'd stick with the rimmed cartridges, but don't I wish that action could handle .375 FNE.

Edgar,
I did some calculations using Ellis Brown's formulas for building rifles on shotgun actions.

A 12g. shell with max average SAAMI pressures of 11,500psi ends up calculating to 7,086 psi of force against the breech face. That is a safe number given use of any factory 12g. load. Not talking proof loads.

I calculate the .35 Rem to be well under those pressures with force against the breech face being only 5,564 psi.

The 30-40 Krag calculates to 9,326 psi and the .32 Special is 8,441 psi.

So, based on the numbers, the .35 Rem looks like the best option.
I am sure that realistically the others would be plenty fine as well if one were to adjust the 12g calculation upwards to factor in proof pressures. But why push the envelope.

[edgarspencer]

I'm not sure about the pressures of 30-40 Krag vs. 35 Remington. The 35 Rem is a lot hotter than the Krag. I know the 8x54 Krag has a chamber pressure of 42Kpsi, and as I recall, .30US was less than 32Kpsi.

I may be wrong, but I think you're oversimplifying the problems that need to be considered in chossing a cartridge for this action. The distributed force over a smaller area increases the stress significantly. The 12ga forces are distributed over .62 sq in, but the 30US, and most similar 7mm, .30, and 8mm cases are less than .2 sq. in.
Also consider the action type; the center line distance of the SC, above the pivot point (Front lug) is close to 3/4" while most center fire cartridges are in line with a bolt face. The further away the center line deviates from the from the points restraining it, the more important a top locking lug becomes.

I love the 8x68S but I wouldn't subject it's 52,600 psi chamber pressure to an action design to restrain 12kpsi

This also does not take into account the rapid drop of of pressure is a shotshell vs distance from the chamber as opposed to the progressive burning powders where pressures are still increasing away from the chamber.

Do you recall seeing the stalking rifle in the rack at my table in Baltimore? It was a wonderful single shot in 9.3x72, and it had a single locking crossbolt, in addition to two locking underlugs. There must have been a reason for three locking points, above, and below the centerline of the cartridge.