What kind of gun? Many Picatinny rails are made for firearms that don't come with a rail, like a Marlin lever, misc shotguns, or an H&R single shot rifle. Just google Picatinny rail, then click images to get ideas. A springer receiver is round so I'd check out H&R rails which are shaped to match the round chamber of an H&R. I doubt it will be a perfect match but it should work, and if you like you can sand the rail to a better fit.
A springer typically has a receiver of ~2mm thick which is enough for screws imo, but I'd add more screws since a springer is hard on them. I suppose one screw in each groove would work, or maybe two in every other groove. A springer typically can't have the the screws protruding thru the receiver so once set and tightened you can simply grind off the excess. You can also drill countersunk holds on the inside, then thread up into the mount which is no doubt stronger but more work. Either way 3mm screws would be easier but 4mm would be much stronger. Or similar US threads like
If not a springer then maybe check out the Marlin rails, many of which are flat on the bottom, and if not a springer them no need for additional screws. Tell us what gun and post a px of the area you want it please...
I suppose JB Weld could be an option too, which is super strong and I'd assume it would hold on most springers but no personal experience with that. Also, springers vary drastically on how abusive they are to mounts so it depends on which one you have. Lastly; screws and JB Weld would likely hold anything.
Telecopes are not ideal, should probably use a rifle scope
