Polygonal Hybrid rifled barrel, crowned at the muzzle
(G19M's hammer-forged 1:9.84 twist barrel is "conventionally" rifled, but is reportedly a "Polygonal Hybrid." Its polygonal barrel has a groove in it, which is supposed to result in better accuracy. Perhaps another reason for the change is to give the agents deploying overseas the option to fire lead bullets if that's the only ammo available. The M model's muzzle is crowned, again for improved accuracy.)
Improved trigger
(The FBI RFP required a trigger weight between 4.5 and 6.0 pounds. The G19M trigger had a short, smooth take-up that broke crisply with no noticeable overtravel. The G19 Gen 4 pistol had longer pre-travel and some creep when it hit sear resistance. Reset was also better on the M model.)
Every part of the trigger system is different from Gen4
Externals and internals coated with NDLC
(Slide and internal parts are coated and "cloaked" with state-of-the-art Nitrogen Doped Diamond-Like Carbon (NDLC). Tennifer, previously used by Glock, is a metal treatment, whereas NDLC is a metal coating.)
Ambidextrous slide releases/stops, both shielded
The absence of the locking block pin
(First and second generation Glocks had triggers with only one pin in the locking block/trigger mechanism. A second pin, the locking block pin, was added to third generation pistols because the trigger pin alone wasn't strong enough to deal with some cartridges [read: .40 cal] and displayed durability issues on high round-count pistols. Now with the fifth generation, the locking block pin has gone. While this change might be a result of Glock improving the strength and design of the trigger bar and locking block components.)
Longer recoil spring assembly
(Internal upgrades consist of a ¼-inch longer dual recoil spring that mates with an improved notch on the barrel's lug for more positive spring base insertion.)
Enhanced firing pin safety and spring
(The firing pin safety has been reshaped from oval to square and is alleged to have been improved.)
Stronger slide lock lever spring
(Three springs essential for pistol operation have been improved and can endure 10,000 rounds before being replaced. Speaking of the slide lock lever, M models and the Gen5 skipped the leaf spring and instead went with a traditional coil spring.)
Stronger trigger safety pin
Enhanced locking block and rails
Enhanced ejector
New striker
New slide cover plate
New extractor
Improved magazine base pads
(Four 15-round magazines with orange followers and larger base pads are issued to each FBI agent, giving them a 61-round carry potential. The larger base pads facilitate stripping and inserting magazines.)
No front-strap finger grooves
Flared magazine well
Cut-out in grip to facilitate easy removal of stuck magazine
"M" guns have the NDLC finish on some internals (at least the trigger bar), Gen 5 guns do not.
"M" guns appear to have an extended mag catch as stock, vs. a normal mag catch for the Gen 5 guns.
Gen 5 are currently available in black. "M" guns are available in several color molded frames.
Black is standard issued to all agents.
BFG is issued to FBI SWAT
FDE is issued to FBI HRT
Gen 5 guns have a "5" rollmark on the top of the barrel. "M" guns have a "5M".