I have a Stainless Steel M6 and I've added a Red/Green Dot Sight that is really great. It's a 1X and requires a 2032 Flat button battery, but I always keep several on hand anyhow. Mine is the 22LR/410 Shotgun combination and it's really light by my standards. I've tested many different rounds in the 22LR and have found that the Hyper Velocity rounds like the Stinger, Yellow Jacket that are really light bullets, the shotgun barrel has better grouping with slugs and buckshot.
I settled down to the 40 grainers and have discovered in the Stainless Steel weapon the 40 grain is the best to stay with. With that said, I have benched this weapon at 25 yards with the Aguilla and the CCI Velocitor rounds. I was surprised with these for I was grouping about .5 to .9 of an inch. then I tried just your standard 40 grainers, CCI Green Tag, Federal Lightning, Winchester T-22, etc. and have discovered that as long as it was a 40 grain bullet speed didn't matter that much. I had 1.0 inch groups with the Standard 40 grainers and .5 to .9 with the Hyper Velocity 40 grainers.
A friend of mine, who came with me with his M6, tried the others that I didn't get a good grouping with and his performed very well. But, his is the Parkarized Model and it seemed to like all of them just as well. So, I guess the weapon and material it's made from is the deciding factor.
I hope this has been of help for I'm new to this and I'm disabled, so I don't get out to the range like I'd like to. But I enjoy the sport for I can take a brick of 22's and a target and have all kinds of fun. One item I failed to mention is that I've added a 9 round shell holder to the stock of this weapon. I pop-riveted it to the stock and this way I have an extra 9 rounds of 410 ammo on hand. Think about it, 13 rounds of 410 ammo and 15 rounds of 22's. For survival situation I think I could survive for a while. 22's don't weight that much and I've got a pack that holds five bricks, no problem.