tek4260
08-09-2011, 04:52 PM
With all the questions about cylinder fitting, I thought I'd share some of my measurements and what is involved.
I have an older NM 45 convertable with a nickel plated 45 Colt cylinder. It has been a project gun from the start. First the front sight was too short. That was fixed with a piece of 1/8 keystock being pinned and soldered on top of the front sight. Next, the bore had ridges in both the lands and grooves, almost like it was threaded with a fine tooth tap. Firelapping took care of that. The next problem is the .455 throats. There isn't much I can do other than replace the cylinder, which is what I am in the process of doing. The ideal solution would be to have an OM Super cylinder rechambered to minimum spec 45 with .4525 throats. That way I would end up with tight chambers, unfluted cylinder, and recessed case heads. These attributes are the way I think they should be built by the way.
Since I am doing all this at home, that idea is out. So I am doing the next best thing which is fitting a Bisley cylinder and removing the roll mark. The factory cylinder measures:
1.948 OAL
.152 ratchet
.092 bushing
1.702 cylinder only
The replacement Bisley
1.979 OAL
.153 ratchet
.124 bushing
1.703 cylinder only
Looking at the measurements, I can shorten the bushing to ~.092 and it should drop in. That extra .001 in the bushing and the .001 in the cylinder should close my b/c gap by .002, to around .002(which is good) and only cost me .001 in firing pin contact. I "think" this will be okay considering I have a #26 mainspring.
The extreme difference in length in my case is due to the fact that the 45 is an early New Model. Parts from like vintage revolvers are a lot closer to the same.
In the spirit of home hack job, I will be filing the bushing by hand rather that using a lathe or a 90 deg facing cutter. It is easy enough to keep things true if you know how to use a file and take your time and .032 isn't much.
A lot to do is made about adjusting timing when people answer the questions others have about fitting cylinders, which is usually adding an ACP/9mm cylinder. The response is to let a gunsmith adjust the timing. "IF" you are adding a cylinder, get a range rod and check it. If it is out of time, the correction to the revolver will cause the original to be out of time. The smith isn't going to go and adjust the ratchet teeth or weld and recut the bolt notches. Excluding Murphy(or my luck), everything is pre timed. Slack in the notches/latch plus the forcing cone make up for tiny differences in the individual frames and cylinders. All of this was said to say, I know the timing won't be an issue in this swap.
Hopefully in the next few days I'll be able to complete this and get some decent groups without leading. I just have to stare, think, and measure it a few more times and then I can get started.
I have an older NM 45 convertable with a nickel plated 45 Colt cylinder. It has been a project gun from the start. First the front sight was too short. That was fixed with a piece of 1/8 keystock being pinned and soldered on top of the front sight. Next, the bore had ridges in both the lands and grooves, almost like it was threaded with a fine tooth tap. Firelapping took care of that. The next problem is the .455 throats. There isn't much I can do other than replace the cylinder, which is what I am in the process of doing. The ideal solution would be to have an OM Super cylinder rechambered to minimum spec 45 with .4525 throats. That way I would end up with tight chambers, unfluted cylinder, and recessed case heads. These attributes are the way I think they should be built by the way.
Since I am doing all this at home, that idea is out. So I am doing the next best thing which is fitting a Bisley cylinder and removing the roll mark. The factory cylinder measures:
1.948 OAL
.152 ratchet
.092 bushing
1.702 cylinder only
The replacement Bisley
1.979 OAL
.153 ratchet
.124 bushing
1.703 cylinder only
Looking at the measurements, I can shorten the bushing to ~.092 and it should drop in. That extra .001 in the bushing and the .001 in the cylinder should close my b/c gap by .002, to around .002(which is good) and only cost me .001 in firing pin contact. I "think" this will be okay considering I have a #26 mainspring.
The extreme difference in length in my case is due to the fact that the 45 is an early New Model. Parts from like vintage revolvers are a lot closer to the same.
In the spirit of home hack job, I will be filing the bushing by hand rather that using a lathe or a 90 deg facing cutter. It is easy enough to keep things true if you know how to use a file and take your time and .032 isn't much.
A lot to do is made about adjusting timing when people answer the questions others have about fitting cylinders, which is usually adding an ACP/9mm cylinder. The response is to let a gunsmith adjust the timing. "IF" you are adding a cylinder, get a range rod and check it. If it is out of time, the correction to the revolver will cause the original to be out of time. The smith isn't going to go and adjust the ratchet teeth or weld and recut the bolt notches. Excluding Murphy(or my luck), everything is pre timed. Slack in the notches/latch plus the forcing cone make up for tiny differences in the individual frames and cylinders. All of this was said to say, I know the timing won't be an issue in this swap.
Hopefully in the next few days I'll be able to complete this and get some decent groups without leading. I just have to stare, think, and measure it a few more times and then I can get started.