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Re: New to SA Trapdoor
Posted: Wed Dec 13, 2023 10:14 pm
by Dick Hosmer
Tony Beck wrote: ↑Wed Dec 13, 2023 9:37 pm
On the firing load question, the load is taken by the locking cam, not the back face of the breechblock. The base of the cam (attached to the opening lever) rides against a surface machined into the back of the block. You can see it if you remove the cam latch plate and latch assembly from the block. The other end of the cam mates with the cut in the breech screw at the back of the receiver. The pivot points are arranged so that firing loads actually tend to force the cam into the locked position. You will notice that both the cam latch assembly and the breech block pivot are quite loose. This is done on purpose so that only the cam itself takes firing loads. The trapdoor action is intrinsically pretty strong. However, no one understood the importance of headspace, so most Trapdoors have a lot of it, which increases firing loads on the action. Hence low pressure "Trapdoor" ammunition.
Also, to elaborate a bit; because the hole in the block is elongated, the pin (which - understandably - looks like it might be the weak part) is NOT in shear at moment of discharge. The contact point between the rear of the cam and the breech-screw cutout is above bore centerline, which tends to force the block down at the rear. It was actually a rather ingenious design, except for the headspace issue which Tony noted.
Re: New to SA Trapdoor
Posted: Mon Jan 01, 2024 5:25 pm
by 6 Ring
A follow up question:
I read in 1898 manual, and understand the pivot pin hole is loose allowing the breech to move back and transfer the pressure to the back of the receiver.
Now since the breech moves back, does this stretch the case?
Re: New to SA Trapdoor
Posted: Wed Jan 03, 2024 8:53 pm
by Dick Hosmer
I am not a big shooter/reloader. Tony would be the best person to answer that. Even though the movement is quite small, my guess is that the answer would be "yes", at least to some degree. Tony - you have the floor
. . . .
Re: New to SA Trapdoor
Posted: Wed Jan 03, 2024 9:16 pm
by Tom Trevor
I have fired more round than can be counted out of 45-70 Springfields over many years and have found cases do not stretch. The only stretching I have encountered was using Buffalo Arms stretched cases in my long range 45-80 Trapdoor. They take 45-70 cases and stretch them from 2.1 to 2.4. Not a problem any longer as Starline makes very good 2.4 cases now. I am not Tony but Tommy so close enough.
Re: New to SA Trapdoor
Posted: Wed Jan 03, 2024 10:33 pm
by Dick Hosmer
Tom Trevor wrote: ↑Wed Jan 03, 2024 9:16 pm
I have fired more round than can be counted out of 45-70 Springfields over many years and have found cases do not stretch. The only stretching I have encountered was using Buffalo Arms stretched cases in my long range 45-80 Trapdoor. They take 45-70 cases and stretch them from 2.1 to 2.4. Not a problem any longer as Starline makes very good 2.4 cases now. I am not Tony but Tommy so close enough.
I was very remiss in not mentioning you, Tom.
Tony HAS done a lot of shooting, but I suspect YOU are "Mr. .45-70"!!
