Bushmaster ACR Review

Bushmaster ACR review by Dave@rifleshooter.com

Picked up the T&E Ban Compliant ACR yesterday.  Today I began a test of the weapon.
After field stripping it at the shop, I was impressed with the fit and function of the parts.  Obvious thought and testing prior to release went into the production of this carbine.  It is a short-stroke piston-driven operating system, combined with the multi-lug rotating bolt idea of the AR15.
A gas port in a similar location to the AR allows gas from the fired cartridge to flow into the cylinder directly above, within which is contained the head of a single spring-loaded piston.  The gas pressure forces the piston rearward, where is impels against a very substantial bolt carrier, driving it and the rotating bolt head rearward.  By rotating within a cam slot in the carrier, the bolt unlocks and carries rearward with the carrier, taking the fired case along for the ride until it clears the ejection port and is forced out by the spring-loaded bolt-face ejector.  The bolt carrier stops at the end of its travel inside the receiver only (and not inside the buttstock as in the AR), and is pushed forward by a guide and spring, striping the next round from the magazine and chambering it.
The fire control system appears to use AR-compatible parts in the hammer, trigger disconnector and springs, with the exception of the hammer spring which as an angle turn on one leg to retain the firecontrol system-retaining lever.
More details on the internals will be forthcoming in later installments of this review.
Construction is polymer for the handguards, lower receiver, buttstock, “iron” sights and some parts.  Upper receiver including the integral full-length top rail is an aluminium forging with stainless bolt carrier guides. Screwed into place.  Rest of the weapon including major fire control parts, bolt and carrier, barrel and gas system is steel.
Despite the extensive use of polymer, the carbine has a substantial feel and heft.  It is obviously heavier than an equivalent AR, and feels “bulkier” as well.  However it is not ponderous, and the balance point of an unloaded weapon is exactly at the midpoint under the front lower receiver hinge.
Once loaded with a 30 round magazine, the weapon becomes noticeably hefty, so much so that firing accurately one-handed in an emergency would be problematic without artificial support.  Two-handed firing balances very well, again between the hands.
Ergonomically the controls are well placed and all in all the weapon is faster to manipulate than an AR.  With the exception of the cocking handle it is completely ambidextrous (mag release, bolt release/catch, selector), and why they did not include that I don’t know, it would have been simple.  The bolt catch in particular is very slick and well –positioned design.
As factory configured, the cocking handle position suits no one.  Although it is in the right spot, the handle is angled downward; presumably to avoid interference with gear and/or forward mounted optics.  Sorry, forward mounting your EOTurd or Aimpoint is for barfcom or m4crapbinet nerds; actual operators but them back over the receiver, not the barrel.  The downward sloping handle will catch your support thumb badly when the bolt is released after manually retracting, and is poorly angled for fast racking.  It is reversible, and mounted on the left side of the barrel it is angled upward, much better for the lefthander, but awkward for the righty.  It can be mounted on a proper upward angle on the left side for right handers, but the cocking surface is backwards.  At the shop, we drove out the roll pin holding the cocking pad to the handle, and reversed the pad and reinserted the pin, making the whole piece exactly right.  Not sure who is advising Shrubmaster on these things but they need a new consultant.
On to the first shooting impressions.  I fired 3 rounds into the barrel at the shop as a test.  The cocking handle does NOT reciprocate with the bolt while firing.  This has confused some people because the cocking handle does not appear to disconnect from the bolt carrier when manually cycled or manipulated.  But indeed, it does NOT reciprocate when firing.
At the range I decided to try three sighting systems.  First the issue Magpul BUIS sights.  These are certainly serviceable enough as a backup but I would not use them as first line sights as they are plastic.  Durable enough as a backup, but lacking in the precision lockup, durability and sense of gravitas you would want in a primary sight.
Second, I used a Trijicon ACOG TA-33 3x optic with amber triangle reticle.  The triangle reticle is very versatile, and largely undervalued in the USA.
Finally, in allusion to the Hebrew underpinnings of the original Masada design, I opted for a Mepro 21 unmagnified optic, again with amber triangle reticle.  This is a self-powered sight used heavily by the Israelis, featuring tritium and fiber optic illumination.  As a sight it works well, but it is rather heavy and has a huge white fiber optic front face which is not particularly low-profile or camouflage friendly.
I only had time for 70 rounds on the first session.  At 25 yards I spent 20 rounds zeroing, using an unsupported kneeling position.  I first zeroed the BUIS.  From the factory it was dead nuts on for windage… but also dead nuts on for the target’s nuts!  Very low, must be some sort of mechanical zero.  I adjusted to 1.75” low for a 50 yard zero.
Next up I installed the TA-33 on LaRue mount (yes he’s a blowhard but he makes good mounts) on the upper receiver rail, and optimized the eye relief for my preference.  This zeroed 2” low at 25 yards to account for the higher mounting.  The carbine features an adjustable comb – two positions only and rather stiff in operation – for higher mounted optics.  It was not totally necessary for the TA-33, but did make for a better stock weld in the up position.  As a bonus, the BUIS and low-mount dot optics are still very usable with the comb in the high position, something that CANNOT be said for most AR adjustable combs.
Finally, I removed the TA-33 and installed the Mepro 21 in it’s integral mount and zeroed up 1.75” low.  The factory BUIS co-witnesses in the lower third with this and made zero easy.
No attempt at measuring groups was made – on this large target precision was not the goal today; basic zero and function/ergo check was.
Next up, I chronographed today’s ammo choice, the 5.56mm Winchester 55 grain JSP NT, which features a tin core projectile with a copper jacket.  This round has caused feeding problems in many ARs without M4 feedramps in exact spec, due to its long bullet and blunt nose.  The ACR digested it without any problem or malfunction.  This round went 3046 fps with SD 26.
I finished up with 50 rounds an M4 Qualification Course, which is shot from 50 yards up through 7 yards, where it ends with 2-shot double taps in 2 seconds.  To add to the challenge, I shot the latter from the very low Entry Ready and On Safe, and took head shots.  To test the on/off zero of the optics, I removed the Mepro 21, and reinstalled the TA-33 onto the rifle.  A Shrubmaster failure in this regard was the lack of any “T numbers” on the top rail for indexing purposes – for over $2K you would expect they could add some stenciled numbers on there.
I suspect his will be a recurring observation – for over $2k you expect more than what is being offered, other than arrogance.
I shot the 50 yard stage of the M4 Qual with the TA-33, then switched back again to the Mepro 21 for 25 yards and in.  Results were a perfect score of 100-46X, partially a testament to an in-spec rail and optics mounts.
Obviously, it is more than combat accurate.  After only 20 rounds of fam fire while zeroing, I turned in a respectable target.
Whatever finish in being applied to the metal is quite tough, as the carbine took a few spills onto the sand and the concrete range surface, and was none worse for the wear!
Recoil sensation is milder than the AR.  Yes I said milder, despite the piston system, which by its nature is a harder kicker than direct impingement.  This Ban Compliant carbine has a swedged on Y-Comp style brake.  Whether this affected the recoil sensation I cannot know without comparison to a non-comp model.  The ACR is also heavier than the AR.  Finally, the bolt carrier is MASSIVE and appears to contain tungsten powder inside a cavity to control bolt bounce.  The piston ARs all use the same AR bolt carrier, which is no match for the ACR carrier in mass.  All three factors resulted in a soft-shooting rifle.
The ACR is more forgiving to shoot than the AR.  Hold the AR loosely and accuracy goes south fast.  The ACR benefits from a tight hold as well, but does not suffer greatly if you get lazy either.  When shooting from awkward or unconventional positions, this would be a plus for the ACR.
Trigger feel – better than a stock Colt AR, not as good as a NM Rock River, no comparison to a Geissele.  I used both the fingerpad and joint techniques, and cannot yet say which one is superior in the ACR.  Zeroing was challenging as the trigger is nowhere as light as the RRA NM triggers I use in my ARs.  When I get to the hardcore accuracy work, I will start concentrating on trigger manipulation and measure the groups.  Certainly, it is a combat-adequate trigger, and safe for SD use.
The fixed buttstock is just about perfect in length, size and overall handling.  No need for a collapsible on this one unless you are built like a freak.  The LOP works without armor in the traditional stance, and with armor in the tactical stance.  It is very adaptable and one of the best features of the rifle.
The pistol grip has been complained about for not being modular – it does not need to be.  It is well-shaped for all users, well-stippled, uses the standard Magpul MIAD grip core inserts and features a large trigger guard for use with gloves.  Indeed, the grip is much closer to the bore line than an AR, which makes for a much faster and positive pointing weapon!  It also leads to a problem….
A few bugaboos became apparent after only 70 rounds, and Shrubby needs to address them or have a substandard rifle.  The selector pad is poorly designed, and combined with the high pistol grip location, interferes with shooting.  It is difficult to use in the prone position, and in any fire position the ambi side pad digs into my trigger finger.  I have piano fingers, not dyke plugs, and the selector is in the way.  I was able to discover how to remove the selector (and trigger group), and while it will function with the ambi side removed, doing so exposes the trigger group to entry of foreign matter.  The whole assembly needs to be revised as right now it is ASS SQUARED.
There are copious sling attachments on the carbine, which is good, but they left one off at the front of the handguard, which is bad.  Not everyone wants 2 feet of rifle hanging past the front swivel of their sling.  Major oversight.
Not only that, but the neat-o QD sling mounts they have on BOTH sides of the carbine have no swivels stops built in, so your sling rotates around and twists itself up during handling.  The rear swivel mount location in particular allows that end of sling to bind up and get caught between the butt and your shoulder, making for a slow presentation and poor shouldering.  This should have been addressed in testing.  As a counter example the excellent Daniel Defense Omega rail for the M4 has built-in swivel mounts, AND they contain rotational stops.  They did their homework; Shrubby apparently read a few gun rags to get ideas – and one erroneous idea is that they make everything on the weapon appeal to lefties.
Finally, I used a 20 rd Pmag and two 30 rd Lancer L4s.  The ACR was designed around the Pmag.  While there were no shooting malfunctions, the Lancer mag was used on the qual course and twice I over-inserted during reloading.  The mag ran past the catch and the bolt forward travel was impeded.  The first time I pulled the magazine down until it latched and the round chambered without anything else.  The second time I  used the cocking handle – with it’s direct connection to the carrier – to cycle the carrier, which caused the Lancer mag to drop down slightly and lock.   Disturbing to say the least.  I was able to replicate this problem later off the range with an empty magazine. I’ll try more tomorrow and see.  If the ACR only works with Pmags, why bother with a Ban Compliant model?
But taken together, the first two sessions with the ACR were a pleasant surprise.  It zeroed well, was 100% reliable with an often problematic 5.56mm ammunition, shot a combat qual course with outstanding accuracy, and showed some outstanding ergonomic touches.  Disassembly is easy and access to parts is excellent.
I have not yet cleaned to lubricated it in any way.
On the down side, it also produced some head scratching on a few design features, and was heavier than it appeared.  Next up will be some accuracy work, and heavy drills.
I had some unexpected time today and decided to move into Part 2 of ACR T&E.
Before the bore became too fouled, I wanted to check 100-200 yard accuracy with a few different rounds available.  Unfortunately, I was not able to get the bench rest set up and shot prone unsupported instead, using the Trijicon TA-33.
Point impact was somewhat higher than the expected 2” at 100 yards, although certainly still a center-of-mass hit.   This illustrates the need to check your 50 yard zero at longer range if you intend on shooting at distance.  Factors of rifling twist, bullet velocity and ballistic coefficient, and height of sights above bore are not always predictable in a linear fashion from a basic 50 yard zero.  If you are using the NYPD 25 yard zero, you are even worse off.
As usual, the Winchester 60 grain Nosler Partition load was the least consistent, although the terminal ballistics of this round is awesome.  I adjusted the group size to reflect a bad shot on my part while getting used to the trigger.

Bushmaster ACR Ban Compliant, 1-9”, Trijicon TA-33, 5 shot group, unsupported prone

Federal 223GM, 69 grain BTHP                    2.65”
Hornady 75 grain BTHP TAP                                    3.34”
Winchester 60 grain Nosler Partition              3.12”
Federal 223A 55 grain FMJ                            3.46”
Winchester M855 62 grain FMJ-AP               2.65”
Shooting a 3x wide-angle scope with large illuminated reticle for precision at 100 yards is hard enough;  add a trigger which I measured at 7.25-7.5 lbs and unsupported prone on a concrete deck, and it becomes challenging.  I intend to repeat the test from sandbags in a later installment.
Note the 1-in-9” twist rate did not seem to bother the 69 grain and 75 grain loads.  The perceived lack of a 1-in-7” twist barrel is just more internet whining.
For longer range testing, I made a sight adjustment to conform the zero load (not tested above due to my senility) to the intended 200 yard zero.  Once zeroed, all of the loads tested above easily kept a bowling pin bouncing at 200 metres.   The ACR is plenty accurate for combat use at the prime effective range of the 5.56mm.  It will not be a tackdriver with a nearly 8 lb trigger.  The trigger feels lighter than that, but the scale does not lie.  It was initially more abrupt at the break point, but after a total of 200 rounds, is now smoothing out nicely, so much so that I had a few bad shots due to the surprise.
I had intended to conduct a comparative test of two trigger pull techniques, but the bad bugaboo of the lousy selector shape prevented it.  After about 20 rounds shooting with the first finger joint method, I was getting a welt raised on my trigger finger from the embedded contact with the right-side ambi lever.  While not immediately injurious, further firing was ready to tear skin and degrade shooting performance.  The poor design noted yesterday, was having consequences today.  As a result, most of the firing was done using the first pad of the trigger finger.
Speaking of the selector, its shape is so poor that it is actually more positive to place the selector on “safe” using the trigger finger than the traditional dominant thumb.  Perhaps this was intentional so that noobs would have their finger off the trigger when safeing the weapon.  It is impossible to move to the “fire” position in prone without breaking one’s firing grip.
Despite this hindrance, the carbine as tested stays right on target through recoil, firing in both prone and kneeling positions.  Spotting your own hits is easy, and the minimal recoil comes straight back.  There is hardly any muzzle rise, unlike the bounciness associated with firing an AR.  This is a strong point for the ACR.
But now, for the really BAD news…
The rifle is advertised as being “optimized” for use with the Magpul Pmag.  If you call overrunning the magazine catch when inserting the magazine “optimized”, I’d like to see what a non-optimized non-spec magazine would do.
Upon loading the rifle for first time, I used a current generation 20 round Pmag.  After inserting the magazine, I released the bolt using the bolt catch lever, and the magazine promptly dumped the Pmag from the weapon, and the bolt went forward without chambering a round.  Doing a re-enactment, I saw that the magazine had overridden the magazine catch, and the act of releasing the bolt caused the magazine to fall from the weapon – bypassing the catch on the way down – and the bolt went forward over the dropping magazine.
I attempted this a third time, but the bolt would not move forward on actuating the bolt catch lever:
I removed the magazine and examined it, and it appeared normal.  It is the current generation and I have used it in a couple of ARs without issues.  I was not using extreme force to seat the magazine, nothing more than a firm insertion.  When inserted with deliberate gentility, the Pmag did not override the magazine catch.
These photos illustrate an overrode magazine, and a normally seated one:
Thinking that magazine was odd, I picked up a 30 round 3rd Gen Pmag and tried it. It overrode the mag catch with ease:
This time I attempted to load it using the charging handle.  No go, the bolt would not move forward (but at least the Pmag stayed in the rifle):
Maybe it didn’t really like Pmags.  What about good ‘ole USGI?  Hellooooo, Federale:
Lancer L5 30 round magazine, 1st generation with large flange molded in for the bottom of an AR magwell?  No, sorry.  Pmag 2d generation?  Nope.
All these mags easily overrode the magazine catch, and either failed to feed or fell from the weapon after the bolt was released.  In no case of an override, did a round chamber and the magazine lock itself in place.  After being loaded gently, all these magazines worked.
That’s bad news.  I have never had a mag catch override in an AR with a functioning magazine.  During the stress of a combat engagement, a magazine could be forcefully inserted in the weapon, causing a malfunction that does not occur in an AR.  And in this case, I did not use close to stress-level force.
I removed the lower receiver and examined its function with an unloaded magazine.  Using my war wagon M4 as a comparative sample, the problem became apparent.  The bolt catch on the AR is physically limited in its arc of travel, so that when the magazine engages it, the bolt catch it blocks a magazine from overriding the mag catch.  Once blocked, the bolt catch spring has a heavier tension than the corresponding magazine spring, and therefore forces the magazine away from the bolt catch and into the magazine catch, which also has a heavy spring.  In the event of a slightly out-of-spec magazine, the heavy spring tension and catch design limits the amount of override, and forces the magazine back down from the bolt catch and into the magazine catch.  Of course, these are steel parts.
In the ACR, the bolt catch is able to rise farther than the minimum needed to lock the bolt open, so therefore does not provide a sufficient mag catch override stop.  In addition, the bolt catch spring is weaker than the magazine follower spring, and cannot force the magazine back down to the magazine catch.  Also, the magazine catch spring appears too weak – and possibly the catch itself too small – as several times the magazine fell from the weapon after an override and bypassed the magazine catch, falling to the ground.
This is a major flaw in a combat weapon.  The bolt catch, bolt catch spring, magazine catch and spring all need a redesign or re-spec to be considered reliable as a combat arm.
After this major disappointment, I wanted to end the test, but I gave it another chance and continued to the basic drill portion.  I used my standard 60 round 5-Circle Carbine Operator Drill as a benchmark for testing the handling and speed of the ACR.  All drills start with the selector on safe.

50 Yards

  1. 5 rds prone no time limit center circle iron sights (zero check)
  2. 5 rds prone no time limit center circle CQB optic (zero check)

15 Yards

  1. 1 rd from High Ready upper left circle in 2.5 seconds x 5
  2. 1 rd from High Ready upper left circle and 1 dryfire shot in 3 seconds x 5
  3. 2 rds from Entry Ready upper right circle in 2.5 seconds
  4. 1 rd @ from Low Ready lower left and circles in 2 seconds x 2
  5. 2 rds @ from Low Ready lower left and right circles in 2.5 seconds x 2
  6. 1-2-1 rds @ from Low Ready lower left and right circles in 3 seconds x 2
  7. 1 rd on Target, lock back reload, 1 rd in 4 seconds x 5
As you can see, zero return was excellent for a combat arm with the removal and refitting of the Mepro21.  On the reloading drill, all times were under the par 4 seconds (shot to shot), averaging 3.74 seconds and best time of 3.27 seconds.  This is outstanding performance from a weapon system that I was using for only the second time.  With practice, sub-3 second reloads might be possible.
Moreover, the magazine in every instance did NOT override the bolt.  I attribute this to the fact that I was using a CQB shouldered method of reloading, which in addition to saving time shouldering and re-shouldering the weapon, serves to physically limit the amount of upward force that can be applied to the magazine.  Reloaded from an alternate position, such as the military or waist-level methods, a bolt override would be quite possible, and deleterious in a gunfight.
The ACR is a bit slower onto the target from a position of readiness than an M4, due to its bulkier profile, heavier weight and lack of forward mounted VFG.  However, the excellent shooting characteristics noted earlier played well for speed and accuracy once engaged, as can be seen in the targets, and the “A” level operator par time numbers were all met.
The selector – once again – proved to be a hindrance, this time in speed drills.  The ambi side interfered with my trigger finger, and I could not obtain a firing grip AND move the selector to “fire” at the same time.  Towards the end of the 130 rounds fired today, I was wanting to stop due to the annoyance to my trigger finger.  Moreover, much more concentration and specific technique was needed to move the selector quickly to fire.  Since these times are already obtainable by an “A” operator with an M4, the ACR to be an improvement at $2K+ needed to be better.  It cannot with that selector lever.
On a positive note, by reducing the amount of “clutter” on the Blue Force Gear Vickers Tactical sling at the buttstock end, I was able to eliminate the twisting and bunching of the sling on my firing shoulder pocket.  Whoever designed the sling added too much extraneous buckles and clasps at the butt end.  The ACR is not immune, it has happened on ARs as well with that sling.  But the lack of a handguard forward sling swivel stud proved annoying again today, especially when moving in and out of prone, and doing lock-back reloading drills.  In the former case, there is too much rifle out past the forward swivel and it hits the deck frequently, and in the latter the sling hangs right in front of the “action”: area of the weapon when reloading, especially the magazine well.
How much fouling in the ACR after 200 total rounds?
Bolt carrier and Bolt – Cleaner than an AR!
Piston and Spring – Cleaned up in seconds with MP Pro 7.
Gas Cylinder Plug – What You Lookin’ At?
I still have not cleaned or lubricated the carbine, and the bolt carrier is pretty dry.  I don’t recommend this practice.
Closeup of the adjustable comb:
The handguard needs to be removed to release the piston for cleaning.  It is a tight fit and does not fall out of the gas cylinder after the plug is removed.  Fortunately, the handguard is easily removed and reinstalled.
Finally, no stoppages in another 130 rounds, for a total of 200 out of the box without any cleaning or lubrication.  I had the misfortune of firing a round without hearing protection.  The muzzle brake is loud.
At this point, given the selector lever and magazine catch override issues, I would not purchase the ACR as a combat rifle.  These two items are in need of a re-design.
I was intending to continue the firing drills, conduct a night fire session, and do a head-to-head ACR Vs M4 comparison, but given the issues noted above, I don’t believe it is worth the effort, despite the many positive attributes of the ACR.  It only takes a couple of farts to stink up the party.  A shame, really.

1 Comment to Bushmaster ACR Review

  1. Kiepskie // August 6, 2011 at 5:43 pm //

    Excellent post. I was checking constantly this blog and I’m impressed! Extremely helpful information specially the last part 🙂 I care for such information much. I was looking for this particular info for a long time. Thank you and good luck.

1 Trackbacks & Pingbacks

  1. Rifleshooter.com Reviews the FN SCAR: A Shootist’s Odyssey: SCARd For Life

Comments are closed.