WARNING: Any modification to a firearm can be dangerous. If you are unsure of anything in this or any other posting seek the help of a qualified gunsmith before attempting any changes.
Setting the Cylinder Gap on any Colt’s pattern percussion pistol is basically done in the same manner regardless of the manufacturer, the primary difference being whether or not a spacer has to be added to the end of the arbor as is necessary with the Uberti pistols.
Follow with me because it sounds complicated but it’s easily accomplished if we are careful and understand a few things.
In a perfectly fit and assembled pistol the arbor will bottom out in the hole of the barrel lug, while at the same time the barrel lug will be fully flush with the frame. This is held together by the wedge which pushes the barrel back against the arbor face and the frame front face by engaging the wedge taper against the front edge of the arbor slot and the rear edges of the barrel slot. All of this takes place with the wedge being inserted to a consistent depth and the cylinder gap being .008”-.010”.
This “could” be a tall order because several things have to be fit almost exactly for all of this to come about. But it can be accomplished and even the confusing statement above can be fully understood and explained to others.
In the 19th century Colt’s individually fit each pistol before it left the factory and the cylinder gap was set with the arbor. Even a very worn original Colt’s pistol will usually have a decent cylinder gap running between .006” and .012” which is testimony to the fitting and the design. The exception to this will be when the arbor has become loose in the threads where it attaches to the frame. If it wobbles a bit the gap will usually be affected. Sometimes the wobble isn’t apparent until the barrel is removed because the multiple contact lock-up stabilizes the barrel.
The original design intent after evaluating the Colt’s design is not what some have written about or has become “common wisdom” among percussion pistol shooters in the 20th and 21st centuries. The Wedge is not primarily an “ADJUSTMENT” device. It is a LOCKING device which was commonly used in firearms in the 17th through 19th century firearms. One can look at many flintlock and percussion rifles with the mortise and tenon joints holding the barrels in location and the wedges (tenons) sometimes with retaining springs just like the Colt’s pistols to understand how they were used and to what primary purpose the taper on the wedge served. It is true the taper will allow a worn component to continue to fit longer than a straight sided part, but the primary purpose of the taper was to lock (“wedge”) the piece in place.
It is obvious pistols will work to some degree without this perfect balance of dimensions and two extremes of fit can be seen looking just at the Uberti and the Pietta pistols. Pietta pistols have arbor fits that are usually closer to being ideal. (Don't assume from this I prefer Pietta Colt's reproductions, I actually find the Uberti pistols to be more authentic and better made, the arbor is the only exception.)
Uberti Pistols have arbors which are always too short from the factory. Uberti accomplishes their cylinder gap by making use of the taper on the wedge to open or close the gap. The problem with this approach is that it isn’t as repeatable in the field and isn’t as stable as a correctly fit pistol. This method has also led to some of the misconception modern shooters have about the correct method of setting the cylinder gap and what it should actually be set to.
Because Pietta attempts to mass produce an arbor to the correct length with minimal factory fitting we sometimes see an arbor which is too long and a cylinder gap which cannot be closed to the ideal maximum opening of .010”. The barrel will bottom out on the arbor and no amount of force from the wedge will close the gap. On these pistols it is common to see a small gap where the barrel lug meets the frame once again because the barrel is bottoming out prematurely on the arbor.
Fortunately there is a better way to assure intimate contact with all four surfaces ( arbor, arbor hole, barrel lug and frame front face) using the natural elasticity of the steel to accomplish not only an intimate contact, but a spring locked fit as well. This fit will last for many years, it may relieve itself of the elastic “interference,” but it will then settle into an intimate surface to surface fit that won’t change unless damaged.
We will first deal with pistols such as the Piettas and others including the originals that have arbors of correct or near correct length.
First we will set the dimensions so the barrel lug contacts the frame leaving a .010”-.012” gap at the cylinder. Then upon insertion of the wedge the barrel will be pulled down into hard contact with the end of the arbor which had a .001”-.002” gap before the wedge insertion. The cylinder gap will close to .008”-.010” which is the ideal gap. The assembly will be very tight and the wedge will not move because the barrel is slightly sprung to close the end of the arbor gap.
To measure and modify the pistol first fully strip it down to the Frame, Cylinder and Barrel. For most of the measurements a wedge is not needed and the “wedging action” is definitely not desired. PLEASE NOTE, a wedge can be used only if it is carefully partially inserted to keep the components in place, but extreme care must be taken not to insert the wedge beyond initial contact with the front of the Arbor slot and the rear of the barrel slot. In other words don’t let the tapered wedge act as a “spreader” and move the barrel back.
First place the cylinder on the frame and insert the barrel as show in Fig. 1
[FONT="]
[/FONT] Use a feeler gage to determine the gap. Without the internal components the cylinder will fully move to the rear. Assure that the lug is fully butted against the frame for this measurement. You may wish to insert the wedge into the slot just enough to take up any slack but do not insert it any deeper than necessary, do not let the taper on the wedge push the barrel back. If you can’t easily pull the wedge out with your fingers it is in too deep.
If you use a wedge you should double check your measurements with the wedge removed. To do that hold the pistol with the barrel pointed up then insert the gage, it should fit, but not lift the barrel away from the frame.
Record this measurement, ideally it will be .009”-.012”. It will close down once we insert the wedge (this will be explained later).
Now measure the gap with the barrel rotated as shown in Fig. 2 and Fig 3, keep the barrel lug from engaging the frame.
The barrel must be bottomed out on the arbor for this measurement to be accurate. If there isn’t any gap then see the explanation in the post about the Uberti pistols to create a spacer. Record this dimension. Ideally it will be .008”-.010”, which will be our final gap at assembly.
Record this dimension, keep in mind when finished it needs to always be .001”-.002” smaller than the first dimension recorded. If it is larger than the dimension recorded in Fig. 1 then we know the barrel will balance on the end of the arbor and not correctly contact the frame at the lug face.
If the dimension in Fig. 3 is greater than .010” then we will adjust it by removing material from the arbor as shown in Fig. 4.
[FONT="]
[/FONT] Removal will be a one to one relationship. If the gap measures in Fig. 3 was .013” then removing .004” from the end face will close the gap to .009”. The arbor can be shortened with either a file or machined in a mill. Keep the end square and perpendicular to the axis of the arbor.
If the gap measured in Fig. 3 was less than .008” but only by a few thousands of an inch (I wouldn’t hesitate doing this if it were .005” or less) the gap can be increased by removing material from the barrel face at the forcing cone as shown in Fig. 5.
Once you have determined the gap now measures .008”-.010” when measured as shown in Fig. 3 put the barrel back on as shown in Fig. 6 and re-measure.
We will now adjust the barrel lug to make this dimension .009”-.011”. It is important to remember this dimension needs to be .001”-.002” greater than your new dimension just measured above.
If the dimension is greater than the .001”-.002” difference you are looking for then remove material from the lug as shown in Fig. 7. You may use a file or a milling machine.
In the case of a barrel that doesn’t have a through full clearance like the ’60, ’61 and ’62 Police models a step can be machined in the lug as shown in Fig. 8.
If it is carefully cut it won’t even be apparent when it butts up to the frame. As shown in Fig 9.
Your fits should now be as shown in Fig. 10.
Personally I like the wedge to fit as shown in Fig. 11
Where the hook on the wedge spring just clears the barrel as it exits slot. This allows an easy visual reference for the correct insertion and in the event of wear will allow the wedge to be inserted deeper to take up any difference. If the wedge is deeper it will work fine, this is just my preference for a fresh pistol at initial set-up.
In a future post I will show a bit different spacer for the Uberti frames. The Uberti frames are set in a manner just like the instructions above, the only difference is that there must be a spacer added to the end of the arbor before you set the gap. Failure to add a spacer puts you at the mercy of the wedge taper
~Mako
I like the idea of taking the material off of the frame like you did. There's probably no evidence that the gap job was ever done. If that is a Pietta I'm surprised you didn't have to take a bit off the end of the arbor.
