S&W 1917 .45 ACP / Colt interchangeability

[Texas Pride]

I have seen a lot of posts on THR addressing converting .45LC revolvers into .45 ACP by changing out the cylinders, but can it be done in reverse? I have a family heirloom S&W 1917 that has a messed up cylinder. The barrel is from a Thompson SMG (.45 ACP, obviously).

Since I have to replace the cylinder anyway, is it safe to replace it with a .45LC? I see disagreements about the exact measurement of that round, but most call it a .452 diameter, compared to .451 ACP. Is this true? Does 1/1000th of an inch mean it's a no-go?

With all its modification, this 90 year old gun is probably worth its weight in dirt, but it has strong sentimental value so I really want to get it up and running.

Thanks for the help.

 

[jim in Anchorage]

I can't help you with the technical question's,but someone put a thompson barrel on a 1917 S&W? I thought I had seen everything.

 

[Oro]

I don't think there's anyway a TSMG barrel could be threaded into a 1917 frame, so I think something else is going on.

Upto WWII, .45LC was bored for .454 lead bullets. .45 acp was .452 (.451 for lead bullets). After that time, most guns made in .45LC are on the .452 standard. Since you have a pre-WWII gun, it will work best with .452 sized lead bullets down the barrel. You would need a post-WWII sized .45LC cylinder to go into the frame.

This is NOT a simple proceedure (and we also don't know what barrel is on your gun). Either way, the real answer is the gunsmithing costs are going to be really high - you'd be better off to get a gun in the caliber you want to start with.

If you really want to keep the gun running for sentimental reasons, get a 1917 cylinder fit to it and shoot .45acp in it.

Pictures would help. There are enough knowledgable people here so that if you post several good photos of the gun - both sides, frame with the cylinder open, front/rear views of the cylinder, etc., you can get a lot of knowledgeable and helpful responses instead of suggestions or guesses.

 

[Texas Pride]

I was told by family that my great uncle had used a Thompson barrel. I don't own a Thompson, and don't particularly know what their barrels look like.

Pictures (They're a little big, didn't have time to resize):

Thanks for all your help.

 

[230RN]

I have a family heirloom S&W 1917 that has a messed up cylinder. The barrel is from a Thompson SMG (.45 ACP, obviously).

What's "messed up" with the cylider?

What are the chances of repairing/replacing it with another .45ACP cylinder and keeping the gun otherwise "as is?"

I realize you "want" to go to .45 Colt, but you might be better off with this gun as a fairly collectible piece and buying another revolver already chambered in .45 Colt.

IIRC, my 1917 cylinder looked pretty thin in some places, and I wonder if you've examined the strength of materials involved in a conversion project. With a .45 Colt chambering, you've got a more "bearing surface" for .45 Colt pressures to work on. Force = pressure times area.

(Wish I'd kept that gun, dang it!)

 

[rcmodel]

There is nothing wrong with converting a 1917 to .45 Colt. SAAMI pressure for the .45 Colt is 14,000 PSI.

SAAMI spec for the .45 ACP is 21,000 & 23,000 for +P.

The problem you will run into is the cylinder stop stud on the frame is in a different location for the 1917 .45 ACP cylinder then it would be for a .45 Colt due to the relief for half-moon clips.

The .45 ACP cylinder is shorter on the back, so the stop stud is further forward to make up the differance. WIthout modifing the stop stud, a .45 Colt cylinder will not be able to open all the way.

Now, the other thing is, the gun in your picture is not a S&W 1917.
Judging from the frame scollop just above the trigger guard, and ejector rod shape, it is a Colt.
Maybe a 1917 Colt, but I can't tell from the picture.

rc

 

[230RN]

There is nothing wrong with converting a 1917 to .45 Colt. SAAMI pressure for the .45 Colt is 14,000 PSI.

SAAMI spec for the .45 ACP is 21,000 & 23,000 for +P.

Ah, thanks for that info. Glad I brought up the subject, though.

 

[Texas Pride]

230:
What's messed up with the cylinder is that my great uncle was in the middle of boring it out to fit .45LC. He was an old retired gunsmith and liked trying out weird ideas. He died while still working on this gun (hence its great sentimental value). That's part of why I wanted the .45LC cylinder, because it's what he was trying to do, but I don't mind at all just sticking with .45 ACP. Either way I'll never sell it, and only fire it occasionally. I think it deserves to be brought back to life though. It's my only non-functioning firearm in the collection, and I think it's high time to fix it.

RC:
It may well be a Colt. I did a google search back when I first inherited it a year ago and based on it serial, it said S&W. However, with the mad-scientist gunsmithing stuff my great uncle was up to, it might be a weird concoction of Colt, S&W, and Mosin-Nagant for all I know. Or my search may have simply been wrong. I really wish I knew more about 1917's, and his work on this one. As long as I can get a cylinder I trust, I'm not really picky about the caliber so long as its safe in that barrel. I do really like the design of this revolver, and will probably buy a modern one eventually.

 

[rcmodel]

Post a better picture of the left or right side (or both) of the guns frame, as well as a partial serial number off the butt. (123XXX)

Some of us can I.D. it for you.
But I'm 100% sure already it is not a S&W.
It is a Colt.

Re-chambering a .45 ACP cylinder to .45 Colt would not be possible.

Again, because of the half-moon clip clearance at the rear of the cylinder.

A .45 Colt round would have very excessive headspace in a re-chambered .45 ACP cylinder.

rc

 

[Texas Pride]

I'll post new pics when I get home today (around 6pm). I'm on campus, and people get surprisingly jumpy and law-concious when I whip out revolvers and start taking pictures of them. I don't understand why.

I'm glad you're able to tell that it's a Colt. That way I can start giving out accurate info on it. I'm looking for a replacement cylinder, and have been calling it a S&W. Thanks for the help so far.

 

[Jim Watson]

1. The illustrated revolver is a Colt, very likely a 1917, maybe a New Service the 1917 was based on.
2. It sure looks like it has the muzzle end of a Thompson M1 submachine gun barrel installed. This was not just a matter of screwing it on, it took a fair amount of lathe work to shorten it at least enough to remove the chamber, turn the breech end to the right size and thread it. Sight has been changed, too.
3. Numrich ( www.e-gunparts.com ) says cylinders are not in stock. When they have them, they are $146 in either .45 ACP or .45 Colt.
4. Installation of a revolver cylinder is seldom just a matter of taking the old one out and putting the new one in. Knowledgeable fitting is usually required. (I did have a couple of guns with interchangeable cylinders, but you could not count on that.) Colts are more complicated to work on than Smiths. It won't be cheap.
5. Colt has not made the New Service family of large frame revolvers in 60 years or more. You won't find a new one of the sort.

 

[Texas Pride]

I wouldn't put it past my Uncle Thiddo to be able to do something with a gun that should be impossible. Of course, since he never finished and I was about 5 when he died, I can't say with true certainty what that something was supposed to be. But he got that Thompson barrel on there, somehow, and no one who has ever seen this thing has seen anything else like it.

Additional photos, as requested. Also, the bottom of the grip reads (and is spaced as shown):
U.S.
Army
Model
1917

No
8
29* (I only wanted to * one number because there are so few to work with)

Any additional info regarding its type is appreciated, as I'm a big fan of historical pieces. This isn't my oldest gun, but it's close.

After finding the elusive cylinder, and a gunsmith willing to do the work, how much money are we talking to get it fitted? I'm expecting anywhere between $75 to $150 on the hardware, but what's the smith going to charge? $100? More?

Also, to reiterate my first point, assuming that someone has a .45LC cylinder and a .45 ACP cylinder for sale, is there any reason that the Colt chambering would be unsafe in this Thompson barrel? Diameter, pressure, etc.?

 

[Texas Pride]

I just got off the phone with my father, and he provided me with this account of my 1917's history.

My Great Uncle Thiddo was a machinist by trade, and gunsmith by hobby. So he had a good set of skills for making things fit. He did a ton of modifications on this gun. Besides the barrel, he worked on the cylinder and firing pin. This next part is going to sound impossible, but my father swears it's true.

My dad says that he, personally, has shot BOTH .45 ACP (w/ moon clips) and .45 Colt through it. He said the problem is that after each shot, the casing has expanded and backed out of the cylinder enough to interfere with the rotation of the cylinder. This problem is apparently much worse with the Colt rounds than the ACP ones. He shot it with my Uncle Thiddo while it was still a work in progress. Uncle Thiddo admitted he had "overbored" the cylinder, and that it was ruined for firing the Colt rounds well. His opinion was that if the cylinder was honed out to a smooth finish, it could probably still fire the ACPs reliably. He gave it to my dad, but passed away before he ever got around to this minor work.

Knowing this, I plan to ask a gunsmith to polish it out for me before trying to find a replacement cylinder. But I wanted to put this info up here, because now this gun is impossible for two reasons (barrel + dual chambering).

If anyone knows where I can find cylinders for it though, I'm still looking in case the gunsmith can't fix it.

Included below are photos of .45 ACP rounds (no clip) sitting inside the cylinder. They've sunk down considerably, but won't pass through.

 

[rbernie]

I cannot contribute anything useful to this thread, but I have to comment on how much I think that barrel just looks NEAT.

 

[Badger Arms]

The barrel, from what I can see, looks like it was done right. Despite what was said... though you cannot just 'slap' a Thompson SMG barrel on a 1917 revolver, you CAN cut it down, thread it, and headspace it properly. That looks like it was probably done right in your case.

As for the cylinder.... WOW... that's all I have to say. I would seriously consider hanging this on a wall. If you chose to have it worked on, I believe your cylinder is ruined for anything. I would not shoot the gun with .45 Colt, that's for sure. You can have a new cylinder fit, maybe. You might be able to safely fire .45 ACP through it with clips. Maybe .45 Auto Rim.

 

[Texas Pride]

thanks Bernie, I think so too. It's definitely distinctive. It's possible that it's never been done before, and is truly one of a kind. All the more reason to get it working again.

Badger, why is it a worse idea to fire the Colt rounds than the ACP's? I thought ACP had higher pressure, and therefore more risk. In any case, I only plan on using ACPs (or maybe Autorim, as you suggested). I wouldn't use the "self-defense" max SAAMI pressure loads. I'd rather use the cheap target lower-pressure loads, just to be safe with my 90 year old relic.

Can anyone tell me anything about its history based on the serial number listed above?

 

[Badger Arms]

Badger, why is it a worse idea to fire the Colt rounds than the ACP's? I thought ACP had higher pressure, and therefore more risk.

Well, the .45 Colt cartridge headspaces on the rim. The rim of the Colt cartridge is not as thick as the gap between the face of the cylinder and the recoil plate. IIRC, the .45 Auto Rim has a .090" rim whereas the .45 Colt has a .060" rim. That extra .030" means erratic ignition, blown primers, separated case heads, blowouts, explosions, sparks, fireworks, injuries, Democratic presidents, holocosts, and bunny mutilations. Don't do it!

For the record, 14K PSI when exposed to the atmosphere can move stuff pretty quickly. Older .45 Colt brass was "Folded Head" or "Baloon Head". That means that it was not as thick in front of the rim as modern "Solid Head" cartridges. One shot with an old-style cartridge could be bad.

So, NO... DON'T DO IT!

Oh, and as far as bore diameter, Ruger sells a convertible that fires both .45 Colt and .45 ACP from the same barrel, different cylinders. It's perfectly safe to have one barrel fire two cartridges so long as the cartridges and cylinders are compatible. Reaming out the cylinders as was done in your case means taking out the 'ridge' in there where the mouth of the .45 ACP would normally headspace or rest its rim on at least while the moon clip handled the headspace. If it's too wide in the rear of the cylinder, you could have split cases on .45 ACP shells.

After I left home for the Air Force decades ago, my father's S&W 1917 was stolen from my mother's house. It had a cracked cylinder. No problem, just load 5-rounds in the moon clip! I wonder if the gang-banger that ended up with the gun blew it up? Hmmm, maybe he shot .45 colt out of it!? Maybe he tried to shoot .45 ACP in it and couldn't get the shells to extract without a moon clip?! The 1917 was not a revolver for the criminally stupid.

 

[Texas Pride]

Well, I wouldn't want to risk another democratic president... :banghead:

Thanks for the advice. I'll stick to ACP anyway, especially since I've already been told that it has more problems binding up with Colts. I still think it's neat that it CAN fire both, even if it might be best not to.

 

[TEDDY]

wow

there was a time when the front part of thompson barrels were sold for like $5.00.I have one and gramps turned the barrel and theaded it to fit.you can tell by the conture.there could be a way to fire colts but the head space would be bad. you would have to reload.fire the 45 colt with light loads to expand the case in chamber,then reload to 45 acp power.no gunsmith is going to touch that cylinder.and the notchs would not be changed.there would be no reason to in a normal 2 cartridge conversion.it would be the front of cylinder that was changed not the back.actually the gun was made for 45 colt and in WW1 they chambered them in 45 acp.the smiths are different as they sat on the mouths wereas the colt were bored thru.you could sleeve the cylinder to restore it.try sarco they may have cylinders.
restore it to 45 acp.and you could get a colt barrel.there are a number of parts companies Jack frost--bobs gun parts- frindleys.