personaly if i was going to build a grendel IAR i would go more with something more like this
https://www.mgi-military.com/store/index...ategory=11
for quick change barrels like the M249
you could also mate it to a long stoke piston system so you wouldnt have to worry about accidentally bending gas tubes or moving parts attached to each spare barrel
maybe with something like this?
http://primaryweapons.com/firearms/mk1/p...AkZ9fldW9Q
but thats just what I would do
https://www.mgi-military.com/store/index...ategory=11
for quick change barrels like the M249
you could also mate it to a long stoke piston system so you wouldnt have to worry about accidentally bending gas tubes or moving parts attached to each spare barrel
maybe with something like this?
http://primaryweapons.com/firearms/mk1/p...AkZ9fldW9Q
but thats just what I would do

