So I just picked up my 1st M1A and I selected the scout. I'm looking to put a optic on the rifle but need help with what mount. I don't know if I want to just get a long eye relief scope and just mount it onto the rifle or go with a mount like the Sadlak.  Any help with the pro's and con's to the mount the rifle comes with or best to suck it up and get a nice receiver mount like the Sadlak. Thanks for any response on helping me out.

I mounted the Sadlak.  It is rock solid.  Definitely adds to the weight of the rifle though.

Bassett Machine Tool mounts are good and a good deal. They can even custom build a mount for an out of spec receiver. Made in Dripping Springs Texas.

Another option is to use a gooseneck mount backwards attached to the existing rail.

I just use the dumb springfield mount.  And I don't even attach it at the rear.  I did that once too though.  But my zero wandered.  It doesn't seem to without attached at the rear.  

I've always kind of wanted a better mount though.  Mine doesn't put the scope exactly over the centerline of the bore.  But it still shoots really well.  I've always gotten good groups with that gun despite the dumb mount.   If you look at pics of genuine M21's in Vietnam, the mount is only attached at the side.  From what I can tell.  

Mine is a loaded model, last range session with it scoped:

Yeah, but that XM3 has a shorter barrel than that, I think.  So it's not like a shorter barrel can't be used for precision.  I forget how far they claimed they were shooting it out to, but I think someone was claiming 1K.

I'm guessing the bolt gun is probably more accurate.  Of course.  But the shorter barrel may even aid in some accuracy on the scout (over a standard, stiffer barrel).  Would be interesting to see how good one could get it to group.

Sadlak is a great mount. Mine is rock solid and I'm very happy with it.

Thanks for the input all.