September 24, 2010
How to deal with John Browning's unique design.
Of the various repairs I've made on the 1911 over the years, a significant number dealt with the grips. I know it's hard to imagine having a problem with 1911 grips. After all, there's not much to 'em. They're just slabs of wood or plastic held to the frame by a couple of screws. Well, there's a bit more to it than that.
In designing the 1911, John Browning didn't allow the grip screws to thread directly into the frame. Instead, the grip screws are threaded into thin bushings that are in turn threaded into the frame. These tiny bushings are both a marvel and a machinist's nightmare in the days before computer-controlled lathes.
My guess is that Browning had several reasons for using grip screw bushings on the 1911. The frame under the grips is very thin, only about 0.1 inch thick, which doesn't allow for much in the way of thread depth. By using a larger diameter bushing with a fine thread, Browning was able to get greater support in this thin material.
The thread on the bushing for the frame is extremely fine. It's .2360-60, meaning that it has a diameter of .236 inch with 60 threads per inch. In contrast, the typical scope base screw on a hunting rifle has a 6-48 thread. At 48 threads per inch it's much coarser with 20 percent fewer threads. While the fine thread does offer advantages in terms of holding strength, it's a bit more vulnerable to stripping.
Another reason for using bushings is to help prevent the possibility of the grip screws being run in too far and interfering with the magazine, and the bushings also provide more support or contact area for the grip panels. Rather than just depending on the small diameter of the grip screws, the bushings are much larger in diameter. These bushings furnish significantly more support to prevent the side-to-side or back-and-forth movement of the grips.
One of the most common situations I've encountered is having the bushing detach from the frame. The owner would turn the grip screws out, remove his grips for normal cleaning, and one or more of the bushings would come out of the frame as well.
This is a relatively easy problem to resolve, although it generally necessitates the sacrifice of the bushing. Before getting into details of the repair, let's take a look at just how a bushing is fitted to the frame.
The bushing holes are first drilled and then threaded with a special .2360 — 60 threads-per-inch tap. As far as I know this odd sized tap is not used for anything else and is unique to the 1911. The only place I know where you can get one is Brownells Inc. (brownells.com, 800-741-0015).
Once the frame has been threaded, the bushings are screwed into place. The top of each bushing is slotted for a screwdriver blade. However, the slot weakens the tiny bushing and they can be damaged easily if you use too much force or don't use the proper tool. Again, Brownells comes to the rescue with a special tip for its Magna-Tip screwdriver that combines a proper sized slotted screwdriver blade with a steel reinforcing sleeve to go around the outside of the bushing.
With this cutaway frame, supplied by Numrich Gun Parts corp., you can easily see how the frame is threaded for the bushing.
Note the slot in the top of this bushing. This allows it to be screwed into the threaded frame.
To help secure the bushing in the frame, a staking tool is used to spread the inside rim of the bushing. Another way of looking at this is to think of it as riveting the bushing in place. The staking tool is placed inside the grip frame and centered in the bushing after the bushing has been fully seated.
A punch, extending through the bushing on the opposite side of the frame, is placed on the staking tool and struck with a hammer. This flares the inside end of the bushing. Generally it works quite well, and the bushings stay firmly in place.
Most bushings never come loose and are held quite securely by normal staking. However, if you ever have to replace or reseat a bushing you can make a minor modification that will make it very unlikely that it will ever come loose. All you need to do is cut or grind a very slight taper on the inside of the grip screw bushing hole in the frame. This taper, which doesn't have to be very large at all, will allow the skirt of the bushing to flare out a bit more when it's staked.
For the taper I use either a half-inch diameter round grinding stone with my Dremel or a quarter-inch diameter round carbide cutter in a pin vise. The stone or cutter are inserted through the magazine well opening and positioned in the bushing frame hole. A few turns with the cutter or just touch with the Dremel stone will do the trick.
You don't want to remove much. As soon as you can see a taper all the way around the inside of the bushing hole, stop. Now just install the bushing and stake it in place as you normally would. A drop of Loctite on the threads will also make it even more secure.
Earlier I mentioned that the bushings have a very fine thread, 60 threads per inch. These fine threads can be stripped with just a modest amount of pressure. Years ago when this happened, gunsmiths would generally solder the bushing into the stripped frame hole. That could be messy and often lead to rusting of the frame from the acid in the flux.
Brownells offers an oversize .255-60 tap to rethread the frame as well as bushings with a matching oversize thread. All you need to do is just turn in the special oversize tap and bingo--your stripped bushing hole is now rethreaded and repaired. Follow this up with installation of the oversize bushing, which looks just like a standard bushing, and the repair is completed.
Another problem that I ran into from time to time was damage to the stock bushing. Generally this came about when the owner took the grips off and spotted the slot on the top of the bushing. If it's slotted, that must mean that you can screw it out, right? Wrong. That slot is needed to seat the bushing in the frame.
But the owner would put his screwdriver in the slot, give it a good twist and mo
re often than not just peel away part of the top of the bushing. Now he was in trouble. The stock screw threads in the bushing were often damaged as well as the end of the bushing.
The inside edge of the bushing hole is chamfered or beveled to allow the skirt of the bushing to expand for a more secure attachment to the frame. It doesn't take much; just a bit of chamfer will allow the bushing skirt to expand, securing it to the frame.
The 1/8-inch punch fits into a matching hole in the head of the staking tool. A couple of moderate strikes with a hammer are all it takes to flare the bushing skirt.
But the owner would put his screwdriver in the slot, give it a good twist and more often than not just peel away part of the top of the bushing. Now he was in trouble. The stock screw threads in the bushing were often damaged as well as the end of the bushing.
On rare occasions I could run a tap inside the bushing and clean up the stock screw threads. The stock screw has a .150-50 tpi thread. Yep, it's another odd thread used only in the 1911. And, yes, the only place I know to get a tap for this thread is Brownells.
If the bushing was damaged so badly that it couldn't be saved, it would have to be removed. I found the best way to do this with the least amount of risk to damaging the frame was to use the Brownell grip bushing Magna-Tip bit. With 360 degrees of support all around the top of the bushing in addition to the screwdriver blade to fit the slot, you have the maximum possible amount of support and engagement. Even if half the top of the bushing is torn away, this bit will still support the remaining portion and allow the bushing to be turned.
A trick to make removal of a severely damaged bushing easier is to first use either that round grinding stone or the carbide cutter to chamfer the inside of the bushing skirt in the frame. By grinding or cutting away the steel in the skirt and thinning it, you'll weaken its attachment to the frame. Once this has been done, it will be much, much easier to unscrew from the frame.
Normally these are about the only problems you'll run into with grip bushings. With a bit of patience and a few specialized tools, you can handle just about all of 'em.