A friend has a nearly antique Stevens Nitro Special shotgun. The screw that holds the forearm stock to the barrel had been bent and it would not seat fully. (See the blue arrow for the location of the screw.) He had been to a gunsmith who told him it was not any standard size and would be almost impossible to replace.
(This photo is from gunbroker.com.)
Step 1: The Screw and Its Receiver
If I had known this project would turn out so well, I would have taken photos as I went. The drawing shows a block of steel about 1/2 inch by 1/2 inch square with a tapped hole to receive the forearm screw. My best guess is that the screw was turned partially into this block attached under the barrel of the gun when the gun or the barrel was dropped and the screw absorbed the impact. Anyway, the screw would turn into its receiver only about three turns before it would go no farther. The result was that the forearm stock was loose on the barrel.
Step 2: A Demonstration
Since I did not photograph what I did as I did it, I recreated the process with a common 6 x 32 screw and will demonstrate it here. The three nuts on the screw show that it is straight and the threads work properly. I included my watch to affirm I did not simply take before and after photos of this screw only seconds apart. The original screw from the shotgun appeared to be just a little larger than a #8 screw.
Step 3: I Bent the Demonstration Screw
Here you can see the 6 x 32 screw after I purposely bent it about the same amount as the screw from the shotgun. The nut is turned as far onto the screw as it will go now.
Step 4: Tap With a Hammer
I used a vise for this demonstration. The steel receiver block mounted under the barrel made a vise unnecessary.
As you turn the bent screw into the nut, the head of the screw will swing in an arc off of center. Take notice of which direction the screw is bent by which way the head deviates from the center. Tap against the direction of the bend a couple of times with a hammer. Tap hard enough to return the screw head toward the center just a little. Hitting it too hard could break the screw, depending on the quality of its steel.
Step 5: Turn With a Screwdriver
After tapping, see how far you can turn the screw without forcing it. You might gain a quarter of a turn, or you might gain more. Then repeat the tapping from the last step. Turn again with a screwdriver. Continue this as long as necessary.
Step 6: Success!
Eight minutes after beginning, the screw is straight enough to turn a nut on the full length of the threads again using only my fingertips. The damage to the screw from my friend's shotgun was more complex and required more cycles of tapping and turning before it could go in far enough to pull the forearm stock firmly against the underside of the barrel.
Step 7: Forearm Screw in Place
This is the forearm screw as it should be. Although the photo is not of my friend's gun, the screw seated as well on his gun as on the gun in the photo. Previously it had protruded below the forearm stock surface more than the full thickness of the screw's head. When I was finished, the screw was not quite in factory new condition, but the threads were much more crisp like they had been originally.
Tapping the screw head and turning it down for more tapping is a good method when a replacement screw just is not possible.
(The photo is from gunbroker.com.)