CMMG multi 4HB semi auto rifle

CMMG; don’t get me started… as when they first hit the UK a few years ago I had a nightmare trying to find out if there was a single importer and despite what people said there was not. CMMG finally admitted they would sell to anyone, so it was pretty much whoever got a gun across my desk first race! The winner back then was North West Custom Parts (NWCP) and despite what I had heard I was less than impressed with the rifle. The build was OK but things like the buffer tube quality, large plastic case deflector and 3⁄4-length ejection port cover made it feel cheap.

Though in its favour it included both working forward assist and automatic last round hold open/manual bolt release functions.

However, neither of these proved ideal and honestly the rifle ran better with them removed as both were drop-in items. Feed was by Black Dog magazines that gave their own ersatz hold open function with the rising follower blocking the bolt. Better than nothing and some other guns also use this system too! CMMG use standard 223 Rem AR15 uppers and lowers and on the rimfire gun they fitted a large case deflector over the rear of the full-length ejection port. To accommodate this they cut the port cover down by 25% and the result does not look good. NWCP did not go ahead with the rifles.

GETTING HEAVY

The other CMMG importer back then was LANTAC and they later sent me a modified version that had been slicked up by them and to its credit it ran much better. It also showed an in-house magazine, the Evolution, which appeared more robust than the original Black Dog unit. Bang up to date is Suffolk Rifle Co. (Neal Parnham) as they have just bought in a load more Mk4 guns in both standard and heavy barrel (Mk4 HT) options, which is what I have on test. I knew in essence what to expect and was told that these newer production rifles were better than the originals; we shall see. Though Neal told me that CMMG hint rifles from the box might need setting up as to certain functions.

The basic build is that of a CAR15/M4 with Rock River Arms-type, 6-position telescopic butt and A2 pistol grip. The upper receiver is a flat-top and no iron sights are included, it also shows the forward assist plunger and case deflector on the rear right of the action as the M16 A2. Operation is by the standard rear- mounted T-handle. Where the HT really differs is its 16” heavy barrel threaded 1⁄2 x 28 UNEF with a rather wicked looking, crenulated protector, the tube is encased by their RKM11 KeyMod hand guard. This is the up and coming thing and as opposed to four, chunky Picatinny rails it has just one at 12 o’clock with sides – 3, 6 and 9 o’clock being plain which makes more sense. The plain sections have tadpole-shaped cut-outs that will accept Q/D rail sections as you think fit. Good idea really as despite the fashion, unless you have lots of lights, grips and lasers to hang off your rifle a 4-way forend does nothing a round float tube cannot. Plus will need rail covers as they are uncomfortable to hold!

PROBLEMS AND SOLUTIONS

The trigger is said to be – ‘Single stage, mil-spec style unit’, so don’t expect miracles, however, like my Smith & Wesson 15-22 it’s best described as heavy but workable! But being a standard AR lower there are plenty of after-market kits to improve things. Of interest is how CMMG has approached the forward assist and bolt hold open; both of which are drop-in systems. The latter as I discovered was a tad more subtle than early tests led me to believe. It consists of a rectangular adaptor that fits inside the mag well with a tail that sits under the standard hold-open lever. The rising magazine platform actuates this to catch the bolt after the last round has fired.

Initial testing showed this to be less than 100% reliable, it was then I discovered that it’s adjustable, with an Allen-headed grub screw that can raise/lower the ‘tail’ as required. With a bit of tweaking it ran as slick as my Smith - Problem 1 solved! In previous tests the forward assist always seemed to be a mixed blessing. Yes it allowed you to pump the action closed if you got a ‘short bolt’ (action not fully closed) but when removed the incidence of short bolts near vanished!

Looking at the build shows a plastic block with slots in the right side that sits behind the bolt assembly. This is the item that is pushed forward by the tooth of the forward assist plunger. It however shows a bit of side float that in certain cases can decelerate the bolt thus causing feed problems; certainly with lower powered ammunition. If it was fixed concentrically I think it would not be a problem, but I would choose to remove it, as it has little useful function; unlike the hold open!

THUMB BUSTER!

The original Evolution magazines were semi-opaque in a waffle pattern; the one supplied was solid black and showed a very odd feature. When you pushed it into the well it would stop short and only a further press of the release button would allow it to go fully home. On a 223 AR the top/side of the mag is bevelled, which as it’s inserted pushes past the mag catch allowing it to fully enter and lock. On this 22 the feed lips are much slimmer and CMMG have addressed this by cutting a small chamfer in the top of the main body of the mag to accomplish the same thing. However, they have not relieved it enough thus causing the double push problem. I sussed this and a bit of judicious plastic removal from the top had them popping in and out as sweet as a nut.

I mentioned this to Neal; he said he would be going though all the guns and checking them for full function and where required adjusting to suit. The impression I get is that CMMG are aware of these short falls and seem prepared to push the guns out and leaving the user to sort out the small print!

TESTING TIMES

With a cross section of 22 LR ammo from subs to high velocity I fitted up my old Leupold VXII 3-9x50 scope in a Sporstmatch 1” Dampa Mount. I had a Third Eye Tactical, reflex, rimfire can! I was also keen to see how the heavy barrel shot as in previous tests on the S&W M&P 15-22 Custom Shop and the SIG 522 Target both of which also have heavier/longer tubes neither showed any really significant accuracy improvements over their standard versions.

Magazines proved hard to fill, as they have no pull-down side buttons as the Smith and Colt Tactical/HKs do. Like the Black Dog units I expected them to smooth up after a few fills; they did but the running-in period was noticeably longer. I checked the springs and they were not overly powerful or long either. It’s just a matter of busting your thumb until they surrender!
The rifle ran well enough with all ammo-types and makes, though subs did not always lock back the action as reliably as the faster stuff. Accuracy was assessed off the bench, supported at 50 yards. In general groups ran between 1⁄2 to 1” with a working average of 3⁄4” being most common. I found best performance with high velocity brands.

With the forward assist block in place I could get up to 250-rounds with a few short bolts and the usual ammo-related issues unavoidable on 22 rimfire semis. With it removed you can add another 100-150 rounds before a good clean is required. So on that score about what you might expect from a SIG or Smith. I think that for an out of the box rifle the Mk4 HT is CMMG’s best yet! Build quality and finish is good and it has potential it’s just annoying that CMMG have not finished the job 100%. The M4T is identical apart from the lighter/M4-profile barrel with flash hider and weight at 6.3 lbs, which I think would be my choice if I was buying.