Ask the Gunsmith with Jack Landis

Jack LandisAGI Technical Services Manager, Jack Landis, answers a question
from an AGI customer that many of you will find educational.

Correcting the Barrel/Cylinder Gap on Smith & Wesson Revolvers

Our customer Craig wrote to ask; “I have a S&W Model 29 revolver that has a cylinder to barrel gap of 0.010. Is there an economical way to reduce this gap to about 0.002 to 0.003?”

Dear Craig,
The simple answer to your question is “No”.  This assumes that you do not have access to a lathe.
If you have a lathe (or access to one, or your brother-in-law is a machinist) the barrel shoulder where it bears on the front of the frame needs to be cut back .027” (1 divided by 36tpi = .027777etc.”) and the end of the barrel cut back 0.020” (barrel end moves back 0.027” when the shoulder is cut, cut the barrel 0.020 and the B\C gap is reduced by 0.007”, leaving 0.003 B\C gap). 0.003” is fairly tight if you are at all casual about cleaning the face of the cylinder and the rear of the barrel.  Do not forget to cut the front end of the extractor rod and the center pin by the same .027” you cut the shoulder back.

Before you take the barrel off, don’t forget to make a small witness mark at the bottom of the barrel/frame junction, inside the ejector rod shroud. If your Smith has a pin with the cupped ends through the barrel, Brownells, naturally, has cup tipped pin punches. You can easily make a serviceable revolver frame wrench from two pieces of 1-1/4” wide, 3/8” thick mild steel. One piece should be 6” long and the other 18”. Drill a 3/8” hole 1” from each end of the short piece and 1” and 5” from one end of the long piece. Put the two pieces together, held together by a pair of  3/8” x 2” bolts with washers on each end and a nut and your wrench is built.

Glue two thick pieces of leather to the inside faces between the bolt holes. Place the plates of your wrench directly behind where the barrel comes through the frame. Oh yeah, don’t forget to take the cylinder out, but put the crane (yoke) back in and leave the side plates on.

Tighten the bolts gently so that the top of the jaws are the same width as the top of the frame and the bottom the same width as the bottom of the frame (your jaws will be narrower at the top than at the bottom). Go easy here so you don’t crush or deform the bottom of the frame. Place the barrel vertically, with the muzzle down, in a heavy vise with a ¾” thick block of wood between each jaw and the barrel. Don’t get the front sight between the jaws. The wrench should turn the frame loose from the barrel fairly easily. When you’re ready to put it back on, put some anti-seize on the barrel threads and turn it on smoothly right up to where the witness marks line up.

A GOOD local machine shop could do this for you, but the set-back dimension for the shoulder is critical since the barrel must index correctly to the same place it is now.

Now, the rest of the bad news. To finish this properly, you will need a barrel chamfering gauge (.44, 11¼ — 18¼, from Brownells again, $55) to accurately measure the 11¼ chamfer your machinist will cut in the chamber end of the barrel (Gene says they used to use ½” pipe taper reamers, but you didn’t hear me say that).  Give the machinist the gauge so he can cut the chamfer depth correctly. IF the chamfer was cut correctly at S&W, you can probably get away without cutting it any deeper since you’re only cutting off 0.020, but you won’t know without the gauge. You will have to SLIGHTLY break the sharp new edge at the entry to the barrel.

The other alternative is to buy a barrel set-back fixture (page 148, cat #59) from Brownells, but that will set you back about $150. If you want to gauge, re-cut chamfer and face off all of your or your customer’s revolver barrels, Brownells sells kits to do this.

At this rate, you can see why a gunsmith might get $50 – $100 for the job. To bad it’s just .010, if it were a few thou’s bigger, S&W would fix it under warranty because it would be out of spec.


3 Responses to Ask the Gunsmith with Jack Landis

  1. Thanks for your very informative article.
    I would like to know what is the best B/C gap of an S&W victory model