Hi Gunner,
Yes, the Soderin diopter will fit your m/38. The m/38 and m/96 share the same reciever and same muzzle diameter.

The reasons you'll almost always find diopters on the longer barrel m/96 are because of the longer sight radius and higher velocities you can achieve with the longer barrel.

It looks very tricky to drill and tap (D/T) the rear reciever bridge for a diopter. I have never done it (only bought rifles already D/T). There are plenty of rifles out there that are D/T, you just have to look for them.

Yes, I agree, the new avatar is better, thanks. It's a photo of WWII G.I.s burying their dead at the NORMANDY AMERICAN CEMETERY in Franceicon shortly after the war. A very solomn place. I visited it once. There is also a Germanicon Cemetery near by that is just as solemn (LA CAMBE GERMAN CEMETERY).

American Battle Monuments Commission
La Cambe German Cemetery, Normandy

metzgeri