SCAR was a true disappointment to me, as it had so much potential, but got derailed by end user tug of war, and a major failure of the program office to look at integration.
1) Non Reciprocating Charging Handle: This was dreamed up by ideas on OTB (Over The Beach - but really means surf zone operations) where sand etc can get into firearms - and the theory that one can use the NRCH to force the round into the chamber (with the salt and sand etc). I’m not a SEAL, but I still think it was a stupid idea for multiple reasons.
A) Jamming a Cartridge into the chamber that doesn’t want to go is generally a bad idea - the potential for causing bullet setback or cartridge damage is high, which can lead to excessive chamber pressure.
B) The NRCH has a nasty habit of biting the user during the cycle of operations, so you need to ensure hands are clear of the area of the Charging Handle.
C) I’m a firm believer in putting one’s long gun in a dry bag for dive/swim operations, as while EO/IO VAS systems, Lights and MFAL’s are all designed to be somewhat water resistant, Salt Water is the enemy of everything.
2) Suppressors: The SCAR didn’t like being suppressed, partially because FN set the suppressed setting of the Adjustable Gas Block to run unsuppressed, so the carrier velocity is extremely high suppressed so reliability and longevity are significantly impacted when suppressed.
3) Integration/Recoil/Harmonic Wave Resonance: Partially due to being over gassed, with a much higher moving part weight than reasonable, the gun whips like spaghetti noodles during recoil. So it is massively damaging to VAS systems. If your $1,500 gun keeps destroying multi thousand dollar VAS systems, is it really operational? Stuff that does fine on a 7mm REM Mag for recoil was failing inside a few hundred rounds on a Mk17…
All of those issues were solvable, but unfortunately never got really resolved before everyone had had it with the SCAR.
I see a number of related issues that are going to bite the M110A1, and the XM7 because of the urge of some to ignore data and push ahead regardless.