All of my Bunker Arms Radial Bore Barrel Bushings have an OD of .701”. The IDs range from .579” to .582” in .001” increments. When you measure your barrel OD to choose a bushing, be sure to have the caliper jaws measuring the forward-most part of the barrel, maybe 1/8” back from the muzzle. The forward-most part of the barrel is typically .003” - .005” larger than the diameter going rearward back to the much larger chamber section. The reduction in diameter is there to reduce friction and allow freetilting of the barrel as the round is fired and the slide flies to the rear.
As to selecting an ID, if you try to order exact dimensions, you are most likely going to have to do some polishing of your barrel OD in the larger forward-most part ¾” to 1” back from the muzzle. If you order your bushing .001" larger than what you measure you should have very little chance of needing to do any fitting between the barrel and bushing.
If you ordered the exact size you measured and the bushing will not go onto the barrel, you can slightly reduce the barrel OD by cutting a strip of emory cloth in the 320-400 grit range and shoe shine polish evenly around the circumference of the muzzle, while holding the rear of the barrel in a padded vise. Polish until you have the barrel sanded and polished until the bushing can be slipped on. I prefer to fit the bushing to the barrel before I try to fit the bushing to the slide for reasons that will become obvious shortly.
The bushings are all .701” OD, so if your slide bore is larger, you won’t have to do much of anything to fit it to the slide bore. If the bushing is too large, you will have to reduce the OD. I use a 6” mill file, fine cut to start with. I hold the bushing between two padded vise jaws with the length of the bushing spanning the vise jaws. Do not grab the OD of the bushing or you will likely ruin it by collapsing or deforming it. Locate the bushing so that part of the OD is above the top edge of the jaws and is all the way to one side of the jaws for access, you will start filing there. Just take a stroke or two around the radius that you can reach with the file, removing the finish, loosen the jaws, index the bushing in the jaws and re-snug the jaws, then stroke the file around the accessable radius, starting just into the first section that you made bare. Continue until you work your way around the circumference. You will have worked all the way around the bushing from the rear edge up to the groove that goes around the bushing that lines up with the rear of the lug. I would shoe shine with a fresh strip of emory cloth and clean up the worst of the file marks. Then test fit the bushing and barrel in the slide and see what you’ve accomplished.
Be sure to always install the barrel and bushing together when you install them in the slide. You may be tempted to tap the bushing in a little, thinking you are closer to being the right diameter than you really are. You can quickly find the bushing stuck in the slide bore and if you don’t have the barrel installed, you’ll have a bad day getting the bushing back out.
If you find yourself stuck, just push the barrel all the way forward with the link swung up against the bottom of the chamber section and the barrel foot centered with the spring tunnel. Then use the barrel as a slide hammer to tap the bushing out until free. If it’s really stuck and slide hammer tapping isn’t doing anything, you can tap against the rear side of the barrel feet with a nylon faced hammer or a piece of wood. Do not beat on it with anything steel!
When you have the first part of the bushing OD so that it will go in the slide bore without a bunch of force, you still have the forward part of the OD to fit. You do it the same way as the rear part, holding it in the vise jaws and filing and sanding while working your way around the circumference. You will have to get clever to file the short section of the OD that’s between the rear of the bushing flange and the front face of the bushing locking lug. You may be able to use the edge of your file or you may have to use a needle file, but you’ve got to make that section of the bushing the same diameter as the rest, or you will have a bushing that is really tight to turn.
Again, test fit the bushing and barrel and try to install it and turn it through it’s arc of travel. Stop if things get too tight, remove the bushing, look at it and find the high spot(s), dress them down and test fit again. Repeat until the bushing to slide bore fit is at a degree of tightness that you are happy with.
You may need to fit the front side of the bushing lug to the slot in the slide that retains the bushing in place when assembled. Pay attention to the first time you try to turn the bushing. If it’s tight, don’t force it. Remove and look for hard scraping contact between the bushing lug’s front face and the groove in the slide. File from the front side of the lug a bit at a time and retest until you have the bushing turning through it’s full range of motion.
Now assemble the barrel and bushing in the slide and move the barrel all the way to the rear and into the top locking grooves. Push against the bottom of the barrel with the slide upside down on a table. Confirm that you do not have any springing of the barrel when you do this. Now assemble the gun with oil as needed and leave out the recoil spring, plug and guide and cycle the slide backwards and forwards noting if there are any tight spots. If none, reinstall the recoil spring and parts and test fire.
