S&W cylinder contacting forcing cone


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springfield30-06
April 1, 2010, 09:34 PM
I just noticed today when cleaning my S&W 10-5 that when the cylinder slightly contacts the forcing cone on the lower left side of the forcing cone. Once the cylinder is locked in place there is no contact. What is causing this and how can it be fixed?

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Confederate
April 2, 2010, 01:59 AM
The best way is to file a little off the forcing cone until you have about a .004-.006-inch gap.

.

Oro
April 2, 2010, 02:21 AM
First, let's start with the fact on a 10-5 and similar period build S&W's, this is not uncommon. And they run fine and shoot straight regardless of it.

It's likely a slightly uneven forcing cone combined with a healthy amount of endshake. If it's not doing it at lock-up, it's really not a problem. You need endshake so you can keep the gun running when it's had 50 rounds through it. With residue build-up, you need the gun to be able to easily give a little on the cylinder end to work past it and not seize-up.

With the gun in the locked position, take some feeler gauges and measure the b/c gap top and bottom, left and right. Take four distinct readings. What you'll likely find is that one corner or side is .002 or more off the rest. There are more precise gunsmith tools to square the throat, but if you are careful a file like Confederate said will work. But honestly, I'd do a lot of measuring and firing before I decided it was actually a problem.

Guillermo
April 2, 2010, 09:40 AM
here is the gist of Oro's comment

If it's not doing it at lock-up, it's really not a problem

springfield30-06
April 2, 2010, 09:53 AM
If it's not doing it at lock-up, it's really not a problem

Ok, I won't even worry about it then. Thanks to everyone for your info!

gbw
April 2, 2010, 11:04 AM
Just one opinion, but if it's contacting the barrel during rotation it may interfere with the double action pull.

I had a Smith 66 that did this. Double action pull was very uneven.

The frame area immediately below the slot cut for the hand was not flat with the rest of the area where the lugs rotate. Lugs were rubbing as they passed over this area and forced the cylinder forward into the barrel (which also accelerated end-shake wear).

The more you use the gun or the dirtier it gets, the worse it is likely to become.

I'd find out where and why it's rubbing and fix it or get it fixed. Usually not too hard to do. It is out of spec and not ok.

springfield30-06
April 2, 2010, 01:17 PM
It does not happen at all after the cylinder is fully closed or when trigger is pulled, just when closing the cylinder. It seems that when the ball detent (not sure of the actual name for it) on the extractor star is being depressed it pushes the cylinder face against the forcing cone slightly. Once everything is locked into place it functions normally when pulling the trigger and lock up.

springfield30-06
April 2, 2010, 03:35 PM
I read on another thread about these cylinder bearings http://www.brownells.com/.aspx/pid=9858/Product/CYLINDER_BEARINGS

Is this an option or does a gunsmith need to work on my issue?

unspellable
April 2, 2010, 09:09 PM
If it contacts the barrel, I'd say it has a problem. However, and this is a BIG however, make sure the head space and end shake are as they should be before you mess with the barrel breech.

When checking end shake, check not only the usual cylinder end shake but the crane end shake as well. I had a S&W with this problem due to end shake, not in the cylinder itself but in the crane relative to the frame. If you don't have the crane located, there's no point in worrying about the cylinder end shake.

Once you are sure all is well for end shake, then measure the cylinder gap and see what you have.

Steve C
April 2, 2010, 09:56 PM
Often on revolver after shooting lead ammo for a while you can get lead build up on the face of the forcing cone, enough to contact the cylinder and even stop the revolver from working. I had this happen to my first Ruger Security six. The gunsmith I took it to put it in his vise and ran a flat file across the face of the forcing cone and checked with a set of feeler gauges to set the proper gap.

springfield30-06
April 3, 2010, 10:02 PM
I tried to measure the end shake and it is not consistent throughout the each rotation. Is this normal? For most of the measurements I wasn't able to get the smallest feeler gauge (.0015) in between the cylinder face and forcing cone while pushing the cylinder forward (but I can see a gap when holding it to a light), and got .007 for 5 of the measurements when pushing the cylinder backwards. For one of the measurements I got .0015 and .006, meaning that the end shake for this measurement is .0045 correct?

What is considered normal for a S&W revolver for end shake, cylinder gap & head space?

springfield30-06
April 3, 2010, 10:04 PM
I had a S&W with this problem due to end shake, not in the cylinder itself but in the crane relative to the frame. If you don't have the crane located, there's no point in worrying about the cylinder end shake.

How do I tell if the crane is the problem?

Stainz
April 3, 2010, 10:33 PM
Call S&W's 800# with your s/n - they'll send you a pickup label - ship it to them. If it costs anything, they'll let you know. The crane could be 'sprung' - maybe from a 'Hollywood Rap' or two - or too many hard closures - maybe too many +P rounds. They have the jigs, fixtures, special tools, and parts - and, if they charge you, it will be reasonable - and more importantly, it'll be right. Don't 'file' the forcing cone!

Stainz

rmfnla
April 4, 2010, 01:46 AM
"Slightly" is probably not a problem.

Whatever you do, do NOT start filing on your gun! (Shame on you, Confederate!).

If you really think there is a problem take it to a qualified gunsmith or send it to S&W, but unless it's exhibiting a real malfunction don't worry about it.

Oro
April 4, 2010, 02:00 AM
How do I tell if the crane is the problem?

Open the yoke, and set the gun firmly on a table top or similar. Spin the cylinder and watch for wobble of both the cylinder and the ejector rod. Basically, using your eyes as a coarse run-out gauge.

Take the cylinder out of the yoke (if you can, it's a little tricky but not awful) and close the yoke. Examine the mating joints to the frame along all visible edges.

Also, you can take feeler gauges and measure the b/c gap top/bottom, left and right on each cylinder bore. See if there is a measurable difference on one side or on a pair of cylinders, indicating the cylinder as a whole is not square to the forcing cone.

You also need to make sure it's not the forcing cone being uneven - this is not unheard of.

unspellable
April 4, 2010, 11:59 AM
The check above is for a warped yoke or bent ejector rod, not end shake in the yoke.

This can usually be detected with the cylinder in place, but is surer without the cylinder. Close the crane and while it is closed look for some play in the crane in the fore and aft direction. It should be almost non-existent. End shake or play in the cylinder itself should be 0.0005 minimum, 0.001 nominal, and 0.002 maximum. The crane should have less. With the cylinder in place, see if you can increase the apparent cylinder gap by pushing the crane, not the cylinder, to the rear. I've only seen one N frame S&W with this problem, so it's probably not common. (I'm getting sloppy, it's a yoke on a S&W and a crane on a Colt.)

Confederate
April 4, 2010, 04:27 PM
Whatever you do, do NOT start filing on your gun! (Shame on you, Confederate!).
Believe me, with the small amounts of space we're talking about, it doesn't matter. Opening B/C gaps a little is easy and harmless. If the gun is firing reliably and accurately, it's not even really necessary, but this is something I'd do with my own gun.

Now the only other thing worth noting is that in every case of tight B/C gaps, headspace (gap between case head and revolver frame) also needs to be checked. I had a revolver with excess B/C gap years ago and I took it to Interarms and dropped it off. When it was returned, the gap was normal, but headspace had increased to .013 (normal is .004-.009). It still fired reliably, but I sold the gun because all they were doing was moving the cylinder fore and aft in the cylinder well. By reducing one you increase the other, and I just didn't want to play that game.

Fixing a tight B/C gap with a file is far easier than fixing excess B/C gap; and if the forcing cone is not true, a little light filing can make it so. Such filing cannot change the angle of the forcing cone throat in the least, neither can it affect headspace by a jot.

But headspace should be checked on all revolvers with forcing cone abnormalities. Endshake is not desirable at all on heavy recoiling gun -- that is, when it's not within tolerances.

Just my view!

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