I showed some of this to my pal Bish and he said i should do a post so I guess we'll give this a shot. I'm building the old Airfix 1/24th scale Bf 109E-3 and the guns that come with the kit are pretty horrible. The barrels aren't round, they have horrible mold lines and of course they're solid styrene so the muzzles have to be opened. I can get a nice set of MG17 barrels for the nose guns from Master Model, but I couldn't find any MGFF barrels for the wings. I have them in 1/32nd scale, but couldn't find them in 24th so I decided to make my own. The top gun in this shot is from the kit, just primed flat black.
Here are the tools I used
In the foreground you can see the piece of 1/16th steel tubing I got at the local hobby shop. I also have the same size in copper tubing and styrene rod, which would also work OK but I decided to go with the steel. The 1/16th inch matched the 24th scale gun barrels pretty well, but you could use other sizes for other scales. I used a pair of model railroad rail nippers to cut a piece of tubing longer than I needed and chucked it up in a variable speed drill. If you have a drill with a trigger lock or a vise you can gently grab the drill with that would work even better but I have niether of those so I had to hold the drill and the tools at the same time. A little more difficult but not too bad.
I used a flat file and just held it against the tubing at an angle to get the front of the muzzle
It turned down fairly quickly and after a little practice I was able to get a convincing muzzel cone. Then for the groove behind the muzzel cone I gently applied a thin razor saw blade until I had the depth right. And I only had to start over once because i went too far and cut off the whole tip. Also be sure to check the teeth on your saw so you can spin the drill in the right direction. My saw cuts on the backstroke so I had to run the drill in reverse to get a bite.
I used a number 11 blade gently inserted into the muzzel to get the cone shape there. Once again, as with all of this stuff, a little experimentation and practice was required before I got the hang of it, but I think they came out all right.
I then cut the barrel off one of the kit guns and drilled a hole in the body, and trimmed the barrel a little bit at a time until it matched the kit length. Cutting the gun barrel and drilling the hole was just the same as it would be for most aftermarket gun barrels. Only cut one gun at a time so you can use the other for a guide. Then I colored them and they're ready to install. Later I'll post a pic of them in the 109, just in case anyone is interested. I'm sure others have done this before, but maybe it will help someone out a little.
And if there's anyone out there that has built this particular kit I'd really like to hear about it.