Please excuse me if these have already been addressed, but I couldn't find the answers anywhere.

16" Barrel vs 20" Barrel:
I really like the compactness of the 16" barrel, so what are the advantages of a 20" barrel over a 16".  I really don't ever expect to shoot anything more than 150-200 yrds.  That would be the occasional varmint (coyote, fox, wild dog, etc.).  I'll probably be using Q3131A (I can get by Bass Pro or Galyans easily when it's on sale).  I'm guessing at these distances, both barrels would pretty much perform the same.

A2 Upper vs A4 Upper:
I'm also considering getting an upper with the A4 receiver and a gas block for a removable front sight.  I really like the traditional A2 upper look, but would like to be able to remove the carry handle and front sight and mount a scope.   My question is, once I sight in the removable carry handle and front sight, if I take them off and then reattach them, will they hold zero.

Does any one have any experience with Model 1 Sales uppers?

Thanks

Go 16" if you are not going shoot

- more than 150 yards with M193
- more than 250 yards with Mk262 Mod1

IIRC, 20" gives you about 50 yards more on fragmentation envelope and a little more flatter trajectory, less muzzle blast, gas system being a bit more reliable, et al.

Go flattop - you can choose to use carry handle but if you buy A2 you are STUCK with it.