Got a gunsmith question. I am replacing the barrel on my old Smith & Wesson M&P .38 revolver because of a split on the bottom of the forcing cone. ( I have a thread titled "Do you see a problem?" on the revolver forum about this). I screwed the new barrel in as far as I could and still line up the sights and cylinder lock. The cylinder gap at this point is .004" to .005". Problem is I still have a gap between the cylinder boss and frame of about .012". Not enough room to make another turn. My question is can I shim the barrel or do I need to cut the boss on my lathe and then will have to cut the barrel gap and re-cut the forcing cone. Is shimming an acceptable method? I have found shims in multiple thicknesses on-line.
Changing a S & W .38 M&P barrel
- Thread starter Hdonly
- Start date
What's a cylinder boss? Do you mean the gas ring?
Your cylinder gap is good. Make sure it is measured with cylinder pushed forward.
-TL
OK you are talking about the barrel shoulder. The proper way is set the shoulder further back so that you can go in another full turn and index up. Certainly you will machines the forcing cone back to keep proper cylinder gap.
But that requires a lathe and machining skill. If you just need the revolver to shoot, shimming is an option. You need the right shim thickness such that you can torque the barrel to index.
-TL
But that requires a lathe and machining skill. If you just need the revolver to shoot, shimming is an option. You need the right shim thickness such that you can torque the barrel to index.
-TL
Right, the barrel shoulder. I knew that, I just couldn't remember that at the time. The gun is old and already a mix of parts that the numbers don't match. The cylinder had been replaced some time ago before I got it. All I want is a shooter. It doesn't have any real collectors value. A shim in there wouldn't bother me at all. I have found a variety of shims available from .003 on up that would fit without sticking out past the shoulder. I don't own the tools to cut the gap and the forcing cone. Don't want to invest more money in tools than the gun is worth and that I would probably never use again. Thanks much for the feedback.
Got the shims. Took .017" of shims to index the barrel properly. Cylinder gap ended up at .004". You can see the shims, but they don't look real bad. Puts the gun back in shooter status. I am happy with the result. The barrel is torqued tighter than it originally was but not overly tight. Barrel pin is back in. I do need to find a pin for the small plunger that locks the end of the ejector rod. I think about 3/64". Pretty small. Then a little cold blue job.Thanks.
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It has a little, but not very much. The only problem I see that I still have is too much movement of the cylinder stop in the frame. The stop looks good.The cutouts in the cylinder look good. The cutout in the frame is where it looks like the problem is. I am a little afraid to ask what the fix is. A little tig welding and reshaping?
Regroup. After getting my magnifying glass and better light, I do see a slight rounding on the edge of one side of the stop. It looks like most of the movement is in the frame though. If I look down the barrel with good light, when I rotate the cylinder back and forth against the stop, going one way, I can just see the edge of the cylinder. Not good I am sure.
How well the chamber and bore line up is called ranging. The gun is good if it passes the ranging test (doesn't need to go to the range and shoot the gun). You will need a range rod for your caliber though.
Endshake is important for the well being of a revolver. It should be no more than 0.002".
-TL
Endshake is important for the well being of a revolver. It should be no more than 0.002".
-TL
Do you know what the diameter of a .357 range rod? I am going to guess that it fits in the barrel and then slides down into the chamber when the gun is cocked in firing position. If it hits the cylinder anywhere then the gun fails the ranging test. I have never used or seen one. As a matter of fact, this is the first I have heard of a range rod. Back to the internet to study some more.
I don't remember the exact diameter. It could be 0.342". But it would be quite easy to figure out if you own a set of pin gauge. Get the biggest gauge that goes into the bore of the barrel. Going down 0.002" would be the diameter of the range rod.
I actually use pin gauge as range rod. Just epoxy a piece of thinner steel rod to the found pin gauge as a handle.
Check all 6 chambers in fired position with trigger held back. The rod should go in on its own weight. No more than 2 "clicks" are allowed. If the test fails, the gun may need to be re-ranged.
-TL
I actually use pin gauge as range rod. Just epoxy a piece of thinner steel rod to the found pin gauge as a handle.
Check all 6 chambers in fired position with trigger held back. The rod should go in on its own weight. No more than 2 "clicks" are allowed. If the test fails, the gun may need to be re-ranged.
-TL