Quote Originally Posted by ClassIIIGunsmith View Post
so what is the barrel length on this because its can't be 20". A 605 with a suppressor should be reliable because of the back pressure from the suppressor. And what exactly is this model called because it can't be a M16A1 because that is a certain type that isn't this?
They are 20" barrels. The way that the suppressors mounted gave the appearance of shorter barrels. The rifles in the pictures are standard M16A1s and XM16E1s. The only modifications/additions made to them are the suppressors and the optics. This does not change the model designation.

The 605 were not used with suppressors as they were created to be carbines. Colt originally took 603 uppers, milled off the forward assist area and installed a 1/12 M16 barrel (20" cut down to 15"). They then used 604 uppers since they did not require any modification. When Colt cut down the 20" barrels to 15", they gave no consideration to back pressure and gas flow for proper cycling. They made no modification to the gas port size which resulted in a barrage of cycling issues. Additionally, with the FH just in front of the FSB, there was no space to even mount a suppressor.



The suppressors at the time slid over the barrel and were easily attached. The rear collar has a bore just larger than the flare behind the flash hider of a typical M16 pencil barrel, about .010. That allows it to slip freely on the barrel after removing the flash hider. It has a notch on the bottom that engages the web on the top of the bayonet lug, keeping the suppressor from unscrewing after assembly. As the barrel is about .570 diameter in front of the sight base, there is room for gas to escape where it pushes back directly against the front of the front sight base, and not back into your face.

The E4A had enough of a backpressure problem that it also was fitted with a sheet metal deflector that clipped on the charging handle to further stop gas blast to the shooter.