A thought for you on the "long barrel" idea.
It was quite a few years ago now, but someone writing for the American Rifleman magazine did a test wherein they took a "long" barrelled (24") .22LR rifle and chronographed it for several shots, then cut the barrel back 1" at a time until they got to the legal minimum of 16".
They discovered that the .22LR ctg.s they were using (not sure if they tried different brands, etc.) reached MAXIMUM velocity in an 18" barrel!
Longer than 18" the added friction was actually slowing the bullet down.
Less than 18" and the bullet hadn't accelerated to its maximum velocity.
So, if you're looking for a longer sight radius for iron sights, well that's fine.
However if you're looking for maximum velocity, a "long barrel" might not be the way to go.
