Here's a recent thread on Arfcom with a lot of great info on the new USAF Modernized M4 / "IMR BLUE" program.
The best info is from GS5414, who was directly involved in the testing program.
Below are the highlights of his comments:
In regards to any hopes of a "M4A2":
"Will never happen. US Army G8 has, and I quote, "No interest in M4A1+ [or similar modifications]". They want to sit around until NGSW-Carbine becomes a thing, which is pretty damn criminal and lazy, seeing as how it'll sit there as vaporware for years until they downgrade requirements until industry can actually do it.
It's sad, but soldiers in the conventional Army truly do not have any voice, nor do their proponents."
In regards to any hope the Marines will see the light and develop a "M4A2" instead of the M27:
"Negative. M4MR test got diluted once FMID took operational control of it, results were not compartmentalized per component, results were briefed in a twisted manner, test report was sealed and placed on limited distro (FMID basically killed the USMC URG-I effort) waiver from LOGCOM CG, IG, all the way up to SECDEF was approved for the M27. That rifle is all the Marine Corps will get for the future, no further improvements are to be had. There is a DUNS for an improved rail to resist rail deflection during lasing aiming use, but some NSFs take the intellectually lazy path out and place lasers right over the barrel nut to reduce the effect.
A slight win for the Marine on the ground, but not nearly as much as he could have had. The little guy will pay for lazy and culpable intermediate level leadership.
Will the M27 receive improvements in the future:
"They could, but they won't. When I'm telling you there is no desire to PIP or mod anything, I am not kidding. Until you fire the Colonel at SYSCOM, Marines will never get anything better in the way of rifles.
You need to understand, that place is job security for people. It isn't designed truly to get the right thing out the door, for the right guy, in the right time (case studies - PRC117G, MTV vest, IMTV vest, LWH, M40A6). If it was, it would be called USASOC CDD/G8.
ETA - Add to that list how they didn't want the capabilities in the PVS31B, because "Marine's didn't need it"... and instead wanted to default to PVS31As. Institutional, intellectual LAZINESS"
Who will be getting the IMR-BLUE:
It is intended for most USAF SecFor (around 30,000 in number), the Battlefield Airman community (CCTs, PJs, etc), and some other users.
In regards to how the airforce got a 20 moa figure for the stock M4A1's accuracy:
Yes, but it is an aggregate (shooter, weapon, ammunition) metric. It factors in ammunition, in this case being M855A1 and using 30-shot composite groups, and adding it to the unpredicatble cone of fire created from using a non-floated system in many different positions and means of support.
Floating the AR is the singular best performance improvement you can do to it.
Precisely predicting POI shift with a non floated system with various means of support is impossible.
On why an improved M4 is necessary:
19" is a worthless accuracy standard. The target isn't 19". An Echo target is 19". The actual target is about 6".
That equates to a 2 MOA target, firing ammunition (AB57) with an SD of 6.8 MOA. Now, rest the handguard or barrel on a barricade, bipod, grip pod, or pack, and try to hit the same target. Watch that 6.8 MOA cone of fire shift an undetermined distance and direction, very easily over 5 MOA.
Basically, you can't guarantee a hit anymore. Float the gun? Your cone of fire can yield you about 90-95% hits on that 19" Echo target. The other IMR improvements? Hitting that 6" target becomes easy.
Using URG-Is, Hodge or similar rifles with 1-8s, I routinely train on NRA B8 targets out to 300M with various means of support.
The equipment truly does have more of an effect than folks realize.
On how the Air Force ended up with a more advanced rifle then either the Army or Marines:
It makes perfect sense.
As a branch tasked with air dominance (air interdiction, strategic bombing, and close air support), a huge amount of emphasis is placed on the aviation community, but the ground combat elements within the USAF generally go unnoticed.
When you're unnoticed, and weapons programs are laughable in terms of cost when compared to the cost of aircraft, you can get a whole lot done.
In regards to the Geissele High Speed selector I advocated for the M4A2:
In my testing and tweaking design of it, it was great for some things but there is no free lunch. If one rides the selector too hard, the weapon can recoil and result in the thumb inadvertently bumping the selector lever to auto. Adding more of a detent helped a little bit. Then, you're asking the selector drum to accomplish a lot with less travel. Simple receiver pin hole variations meant that sometimes there would be issues with releasing the auto sear. Tolerances came down to thousandths at times.
In regards to the Picatinny Durable Sold Lubricant coating for bolts:
DSL isn't ready for primetime. I got briefed on this at the inaugural USAF symposium in 2017 by Picatinny. The problem was that to get a part coated, you had to run electrical current through it, but it resulted in the part being heated near 1000 degrees F. In the Marine tests, and another Govt. test, DSL coated 9310 (more sensitive to heat treat issues than C158, but it wouldn't have mattered) bolts shattered within 4000 rounds, often at the cam pin hole.
In regards to improving bolt life on the M4:
Your current bolts (Colt, anyways) go about 13,000 rounds worth of M855A1 before losing a lug. By that time it's about time for a new barrel anyways, and you've lost 100 FPS velocity and about 1 MOA of precision.
The solution is to have a 15,000 workup cycle (UTM and live), rebarrel with a new bolt right before deployment, and go hunt bad dudes.
One could use the JP bolts, which I honestly consider to be the best of the breed of backwards compatible bolts. DLC is about the best coating you can get for it right now (nitride is a no go. Look at the application temperature, then reference the temper temperature of the base metal...), they can actually produce them, their heat treatment is bang on, and they have fantastic lug root geometry.
I despise proof testing every bolt. I even have a paper/presentation Picatinny made on the topic. It literally induces micro fissures in the bolt and reduces usable bolt life.
Keeping bolts lubricated more than once every 600 rounds (on an aggressive cycle) goes a long way to maximizing life.
In regards to the LMT Enhanced Bolt vs the JP design:
I like elements of both. I love the dual extractor springs of both the LMT and KAC (a long spring is a happy spring), and I love the lug root geometry of both.
The LMT carrier cam pin slot being elongated is outstanding, something I wish JP would do, but I prefer JPs carrier and bolt surface treatment and polishing (both on carrier rails and in carrier bore) over standard phosphating/chroming.
Many good features in both!
In regards to DLC/Diamond Like Coating for bolts:
I have used DLC on BCM carriers. It really does make a difference when things get super dry at high round counts and minimal lube. Carrier speeds stay closer to where it started out clean.
I have shot an ungodly amount of rounds through a JP carrier, and have also had phenomenal results (nitrided and polished).
Bolts I prefer DLC due to low application temperatures, high durability, and unlike phosphating application isn't an acidic process (does not help with bolt life, either).
In regards to the "constant recoil" Jim Sullivan developed Surefire Optimized Bolt Carrier advocated for in the M4A2:
The OBC, I did actually test them out, and they do have some redeeming features. Cyclic rate is hugely reduced, dwell time is excellent. In full auto they are a dream, but in semi its actually possible to hit a rate of fire that has the counterweight slam forwards right as you're trying to fire the next round. This can result in REALLY low hits. Just something to be aware of.
Its a good solution for 10" guns, for sure. I got a video somewhere of a mag dump with a 10.3" M4 and a G Mk4 rail. The thing ran flat and wonderful.
On Cold Hammer Forged / CHF barrels vs the Army standard button rifled barrel:
CHF of various brands have been outlasting button rifled barrels. Problem is, who is judging what is acceptable dispersion? US Army standard is an abysmal 7 inches.
I’m reality? That’s a garbage standard. You need a 2 MOA or better gun.
Anyways, yes, CHF has been better. There’s a well known vendor on this site that thinks otherwise, but I won’t mention the name or there will be a forum war. To that I say that live fire testing always proves reality. Simulation and theory does not. Reality sees even the lightweight DD CHF barrels holding velocity, precision, and longevity better and longer than button rifled equivalents - by a long shot.
-The Army is stuck on NGSAR, the Marines are stuck on the M27
-Only the Airforce and SOCOM will have "state of the art" M4A2's for the forseable future, despite the serious flaws in the existing M4A1
-Free floating the handguard is the #1 improvement for M4 performance, but a number of other small tweaks can also improve performance.