The tolerance in for example the target master units was .001 and using high velocity ammo the round will not effect the barrel. I recommend taking the gas tube out or tape on it when using for a period of 500 rds or more. Then 5 rds 5.56 to clean rifling should be OK. I shot 3200 CCI stingers through my 16" 1/9 w/O cleaning the conversion or inside the upper receiver or barrel and did not have one problem.
AS far as what unit to go with the Target Master has the best warranty and is designed to work in piston AR-15's by removing the rod.Would recommend the rear YHM take down extended pin just for the ease of breaking down shotgun style in the field if you have a real tight setup or no take down tool. Remington 500 pack of the 32 gr copper jacket HP will not cycle in any conversions, the fps needs to be over 1000 to never have any problems especially ejector issues. I was a distributor For 4 Months so i got to see what they will really do. 60 Rockwell Harding.
