Remington O/U derringer? In .41 rimfire?
Where do you expect to find ammunition?

If it's not really a Remington, please post pictures of your problem.
That will help us solve it.

(What company made it?)

Thanks Steve,
It's a bonafide Remington. Yes; it's the .41 rimfire. I believe it's a model 3. I have a couple of hundred rounds for it and my single shot Remington derringer.
Larry

Wow!
I am in awe!
(Not for the gun, so much, as for the functioning cartridges. Each one might be a valuable collectors' item.)

I'll see if I can get you an answer.

Also, you could PM TedDeBearFrmHell. He's a gunsmith.


Later:
OK, I've got it. See: http://stevespages.com/ipb-remington...derringer.html
(No, I'm not that Steve.)

You may need some sort of clamp, or a third hand.
Remove the hammer and its associated parts. Remove both grips.
Place the mainspring into the grip frame "crosswise," so that it projects out both sides of the grip frame, but the screw holes are close to lining up.
Keeping the spring crosswise, line-up the screw holes and insert the screw. (Here's where you may need a clamp or a third hand.) Tighten it, but allow the spring to "wiggle."
Rotate the spring into the grip frame.
Install the hammer. Maybe you can hook the spring with the hammer stirrup, and still insert the hammer screw; but if you can't, use your clamp on the spring after the hammer is well in place.
Tighten the spring screw. Tighten the hammer screw.

just read this steve and you did exactly what i was gonna have to do.... only seen the pistol, never worked on one

Originally Posted by TedDeBearFrmHell

just read this steve and you did exactly what i was gonna have to do.... only seen the pistol, never worked on one

Thanks guys. I'm working on it now. Now I can't seem to get the hammer/trigger out again. I guess I must be having a bad day. I'll let y'all know how it all turns out.

OK; it's back together again, with the exception of the spring retainer screw. I figured the spring would go into the frame sideways with the hammer/trigger installed, just as well as it would with them out. The spring won't fit sideways into the frame either way. The arch is too tall. I'm right back where I started. Anyone else have any ideas?

You need some sort of spring clamp.
Try padding the jaws of an adjustable locking pliers, so it won't scratch anything.

Originally Posted by Steve M1911A1

You need some sort of spring clamp.
Try padding the jaws of an adjustable locking pliers, so it won't scratch anything.

Thanks Steve; but I had already got it done. It was a two step process, starting with the spring in the frame and hooked into the stirrup. Then levered down on top of the spring with a screw driver to line up the holes, and get the screw started. Then with a needle nose vice grip, and leather pad on the flat of the spring; I was able to get the spring flat tight against the frame, and turn the screw into full tighten. Released the pliers, and then replaced the firing pin ratchet spring, and then the grips. Yahoo!

Nice work!