Shooting my Colt New Service last night--originally .455 Eley but recut to .45ACP--shot a couple cylinders without issue and then it locked up after the first shot on one cylinder. The hammer will not draw all the way back in either DA or SA. The cylinder latch will not pull back far enough to release the cylinder. Pulling the hammer back far enough to drop the bolt, shows the cylinder is free to rotate. The pistol still has 5 live rounds in it and I am a bit on the nervous side here.

Suggestions or ideas are greatly appreciated.

Thank you.

First thing I would do is remove the side plate and see what is going on inside the action. Go from there, carefully. Need I mention to have the FP over the fired cartridge.

I've seen lot of those. You have to get that cylinder out. See if you can put a very slim device in and push the cylinder bolt stop down. Try to take even a little pressure off the cylinder as you do so. Put a piece of wood in the hammer window if possible...just in case.

...thankfully, it was not loaded at the time. It's at Alan Harton's place.

There could be a number of reasons why you can't you can't cock the hammer and rotate the cylinder. I had had this happen a number of times. Most often it is a ammo issue. Check and make certain that a bullet has not jumped the crimp and is tying things up. If it is, work it back into the case...gently.

If it is just dirt, grit, extruded primers etc, hold the latch back and tap on the side of the cylinder with a rawhide mallet or a chunk of wood. Nothing steel or even brass thank you.

I am a bit concerned when you said, you can't hold the cylinder latch back. These old Colts have a fairly complex lockwork and sometimes if the side plate is not down tight, things can jump out of place. If you can't get the cylinder to swing open and the latch won't come back all of the way, it is time to remove the side plate and start looking at and removing internals. The handgun has a V mainspring and one leg powers the hand and the other the hammer. The leg of the spring fits into a narrow shelf in the side of the hand and if the side plate is loose, it can jump out. It is easy to nudge the leg of the spring up and back into the recess in the hand. Much past that things get a little more complex. If you don't know your way around this lockwork, best let somebody that does do the work.

Don't start beating and prying on things and create more problems that you have now.

I was pretty sure it wasn't an ammo issue as, cocking the hammer partially back, allowed the cylinder to turn freely. So, I grabbed a handy leather thong and blocked the firing pin, letting the main spring hold it in place and popped off the side cover. I was able to see that (here we go exposing our ignorance on proper part names again) the hammer block(?) was down preventing the hammer from being drawn back and also keeping the latch from opening. Slid that out of the way and was able to open the cylinder and unload. MAJOR sigh of relief.

One thing noted...my habit in choosing the correct bit for any screw is to take the bit in my fingers and try it for fit before mounting it to the handle. Doing so, revealed the side plate screws were less than finger tight. "Hmmm....", sez I.

The hammer block connects through, as Charles notes, "a complex linkage" to a pin on the right side of the trigger. The linkage itself it thin...perhaps .010" or so thick. A bit of juggling got the linkage reconnected to the pin and all seems well.

My theory is the side plate was loose enough to allow the pin to 'jump ship' vis a vis the linkage. Reassembled and everything works like it did. Time will tell if it was a case of loose screws or wear over the past 98 years. At least I have a bit of an understanding what goes on inside this one.

Thanks to all for the advice!

revolvers were utterly reliable and never jammed? hehehehe, sorry, Hoot, I could NOT resist. Glad you got it sorted out.

I remember posting many years ago about being surprised when I realized my range tool box had lots and lots of Ruger SA parts, a few S&W DA parts, and exactly zero auto parts. After some thought, I realized just how many broken/lost screws and giblets I had replaced in revolvers.

Granted, quite a few were broken ERH screws and lost housings... so I'm not pointing fingers at the manufacturer.

Glad you got it working again. You don't want to horse the screw side plate screws down, but the do need to be quite snug to hold all the guts in place. There was lots of hand fitting in these old Colts and everything has to in the right place for things to work. I think the guy that designed this lockwork must have apprenticed as a clockmaker before working for Colt.

By comparison the Smith and Wesson DA lockwork is simple and rugged. At one time the Colt New Service, Army Special, Official Police, Police Positive and Detective Special were common police issue in America. They were common fare for gunsmiths in America, but those guys have retired or passed on.

I doubt your issue is wear. The wear issue is most often related to the timing lock up and the carry up of the bottom hand. Not a difficult fix, but a problem unique to the old style Colt lockwork. I should think keeping those side plate screws snug will get you "good to go".