Trapdoor is .357 mag?

[tbx-4]

Aww shucks, you guys are too nice with all the comments!

Here's a little more progress.

I was going to make a tang mounted sight but why reinvent the wheel? Not one of the older folding ladder sights but just a small peep sight. I've used the Skinner sight on my CZ 527 and like it a lot. It's pretty small and streamlined, the size is perfect for the Trapdoor except it needs a little riser.

Skinner sight and a chunk of 1/4" plate for riser. I used my cheap Chinese drill press with my cheap Chinese x-y vice with my cheap Chinese end mill bits to square it up.


Using my cheap Chinese belt sander and cheap Chinese moto-tool and Portuguese made files it turned out ok.




It actually fits flusher than it appears.
Not sure if I'm going to use silver solder or epoxy to get it to stay put.

[woodbutcher]

If you REALLY want it to stay in place,use some Brownells AcraGlas(R).
Good luck.Have fun.Be safe.
Leo

[Larry Gibson]

I wouldn't solder or glue it in place.....not enough recoil to loosen the front screw if Loc-Tite is used. If you do I'd make sure the rear screw is free to move so the windage feature isn't lost.

[tbx-4]

woodbutcher,
I was thinking JB Weld.

Larry,
I was referring to the riser, how to attach it to the tang. Sorry for not being clear. Yes, the sight will be screwed down.

Here's what I got done today

The muzzle of the barrel had a step for setting up in a lathe. I cut that off and crowned the barrel. A 1/4-20 brass stove bolt covered in valve grinding compound spun in a cordless drill motor makes a nice crown.


For the sake of expediency I ended up cold bluing the barrel. Figured while I was at it I might as well re-blue the receiver, breach block and lock.


Putting all together it's looking pretty good.



Next will be setting up the front and rear sights.

[ulav8r]

Looking much better than "pretty good".

[Jedman]

That is really cool ! perfect choice of rebarreling the trapdoor. Like your sight also.

Jedman

[Texas by God]

It looks amazing. Well done sir!

[KCSO]

How are you getting around the pressure problems? A trapdoor won't hold a 22 hornet for long they are rated for 18000 PSI Max and I don't use any hot 32-20 loads.

[vzerone]

How are you getting around the pressure problems? A trapdoor won't hold a 22 hornet for long they are rated for 18000 PSI Max and I don't use any hot 32-20 loads.

KSCO, if I'm correct a modified Springfield Trapdoor was one of the first rifles the 30-40 Krag was tested in. I'd think if that was okay then the cartridges mentioned would be alright. I know the original poster said he figured up breach face thrust for both the 45-70 and 357 Mag if that give you an idea of maybe how he came to the conclusion.

[Moleman-]

If this was done in 9mm no one would question it. 9mm has slightly more bolt thrust than 357Mag and run at a similar pressure. A 22 hornet at 43Kpsi has around 3038 ftlbs of bolt thrust which is less than 45-70, 9mm or 357Mag. I would reduce the size of the firing pin tip and put a bushing in the breach face.

[vzerone]

If this was done in 9mm no one would question it. 9mm has slightly more bolt thrust than 357Mag and run at a similar pressure. A 22 hornet at 43Kpsi has around 3038 ftlbs of bolt thrust which is less than 45-70, 9mm or 357Mag. I would reduce the size of the firing pin tip and put a bushing in the breach face.

Moleman, isn't the cartridge thrust figured by the internal web floor area inside the case, not that cartridge head. Thus I understood it the smaller that area the less the thrust.

Formula

F → b o l t = P m a x ⋅ A i n t e r n a l . {\displaystyle {\vec {F}}_{bolt}=P_{max}\cdot A_{internal}.} {\vec {F}}_{{bolt}}=P_{{max}}\cdot A_{{internal}}. [1]

where:

Fbolt = the amount of bolt thrust
Pmax = the maximum (peak) chamber pressure of the firearms cartridge
Ainternal = the inside area (of the cartridge case head) that the propellant deflagration gas pressure acts against

[Moleman-]

Radius squared times 3.14 times the PSI. Yes, the actual measurement is the widest ID of the case head, but it's easier to go by the base diameter (not the rim) and gives you a slight bit of a safety factor as you are erring on the high side. For the 357 I used .19 x .19 x 3.14 x 35,000= 3967.39 ftlbs. 9mm, .1955 x .1955 x 3.14 x 35,000= 4,200.4 ftlbs (wiki has it at 4012 ftlbs). 22 hornet (above I used .150"), .149 x .149 x 3.14 x 43,000= 2997.6 ftlbs or at 25Kpsi= 1742 ftlbs.

It is important to look at both bolt thrust and chamber pressure when considering a rebarrel.

[tbx-4]

How are you getting around the pressure problems? A trapdoor won't hold a 22 hornet for long they are rated for 18000 PSI Max and I don't use any hot 32-20 loads.

My Lyman reloading manual has the Trapdoor loads rated at 18000 psi too but SAMMI rates 45-70 Gov at 28000 psi. I’ve also seen 25000 psi quoted. Now modern 45-70 Gov. is supposed to be equivalent to the original 45-70-405 load for the Trapdoor... not to mention the long range Trapdoors used 45-80-500 compressed loads with the same receiver and barrel as the standard infantry Trapdoor. (Correction: same steel but tighter twist on the rifling)

But to answer your question “How are you getting around your pressure problems?” Well, so far there’s no indication of any problem.

Please read post #1.

BTW, I’ve shot 70 rounds through the Trapdoor so far with 30 being .357 magnum. Federal 158 grn soft points. Still dialing the sights in. They shoot about 4” higher and to the right compared to .38 sp... But since I don’t own a .357 revolver I’ll be shooting .38 sp mainly and sight in for them. Which is like shooting a .22 rifle, incredibly light recoil and report. Heck, even .38 sp+P wouldn’t be an issue but nice to know that I can shoot .357 mag if I have to.

[tbx-4]

vzeron,
Yes, there were Trapdoors made for 30-40 Krag. They experimented with different barrels but the receivers were not noted for being any different than 45-70. Now, I could be wrong so if anyone knows any better please chime in.
http://www.trapdoorcollector.com/cal30.html

[fivefang]

Tbx 4, as they would say in Chinese DING HOW! ( Very Good) Fivefang

[vzerone]

vzeron,
Yes, there were Trapdoors made for 30-40 Krag. They experimented with different barrels but the receivers were not noted for being any different than 45-70. Now, I could be wrong so if anyone knows any better please chime in.
http://www.trapdoorcollector.com/cal30.html

Yes...thanks for putting up the link.

VZ

[pworley1]

Great job on the conversion. I really enjoyed the read.

[Bill*B]

Bravo! I am in awe. I predict that you will really enjoy this little rife - YOUR rifle!

[Larry Gibson]

tbx-4

"My Lyman reloading manual has the Trapdoor loads rated at 18000 psi too but SAMMI rates 45-70 Gov at 28000 psi."

I've measured the psi of several Lyman loads (they are based on the C.U.P. or L.U.P. method of measurement). They are close (25,400 to 27,600) to the SAAMI MAP using the Transducer method of 28,000 psi.

With the 357 cartridge in your TD I wouldn't worry about the minutia........ I've seen one rebarreled to 44 Magnum and a couple in 45 Colt and they had no problems. TD actions Mostly let go at the front with the soft iron/steel barrel expanding. You've enough quality steel barrel around the chamber that normal 357 loads won't expand it. Consider how thin a revolver cylinder is over the chamber compared to your barrel. As to bolt thrust......not enough to be a concern.

My most used loads in my 45-70 TDs are a 210 gr HB at 950 fps and a 275 gr at 1050 fps. More fun than a guy should be allowed....... your TD should give you lots of pleasure......you do have multi cavity moulds and a progressive press? If not you're gonna need 'em as it's always amazed me how many rounds a fun single shot like yours can devour......

[tbx-4]

Thanks Larry for the clarification on the pressure.
I have a bunch of 158gr cast already to go but only a single stage press... well two single stage presses. I'm making use of what I have on hand. It's all fun.

Further progress.
Had to remove the front sight, it was canted to the left making it shoot to the right. Reinstalled it, now I can hit a 6" steel plate at 60 yards. Didn't have the time to get it dialed in better but its close. I shot Remington .38sp 130gr jacketed flat nose, Magtech .38sp 158gr hard cast and Federal .357 mag 158gr soft point. They all hit the plate. The .357 is high, the Rem 130gr is low and the Magtech 158gr is almost dead center. Made no adjustments, not bad for bore sighting.

I got frustrated at first trying to bore sight with one of those cartridge type lasers. It was all over the place depending how it was rotated in the chamber. This is what caused the canted front sight.
I ended up using a small inspection mirror. With the breach open, insert the inspection mirror and look down the bore at a white board with a 1" black dot 25 yards away. Now try to hold the mirror steady while moving rifle in padded vice till the black dot is centered in bore. Then set front sight on barrel and carefully look through rear sight (already affixed) and align front sight, mark location. I used JB weld epoxy to hold front sight on. Will see how long it lasts. After 25 rounds today it's still holding.

Setting up sights.


Rear sight dwarfed by hammer.


Front sight filed to shape and blued.


Now where's that rear sight?