M4 Tactical Carbine System

By Steve Baughman

The author was recently invited to evaluate a unique tactical carbine system under consideration for law enforcement deployment. The “system” consisted of a standard M4 version of the M-16 carbine equipped with iron sights, along with an additional scoped, suppressed flattop for mid-range precision work. We tested the gun over a period of several weeks with help from tactical team members at our local Sheriff’s Office...

The reality of some of the major criminal events in the last couple of years has changed the way law enforcement looks at the rifle - again. The infamous North Hollywood bank robbery and shootout could have ended much quicker if a rifle or carbine had been utilized to end the fray with a single body or head shot. The brave men and women who responded to this monumental event displayed a remarkable devotion to duty. I remember the scenes from the newscast showing officers running into a gun shop to obtain rifles and ammunition. They obviously knew they needed a better tool for their predicament. One item learned from this event was that patrol officers should have small caliber rifle capability. With the proper training and equipment, agencies should be allowed to respond to such emergencies with the proper tools. If an officer is asked by duty to engage criminal elements willing to fight to the death, the use of deadly force to stop the fight is certainly justified.

Previously outfitted with handguns and sometimes shotguns, the trend is well underway to outfit many law enforcement (LE) units with some type of shoulder fired rifle or carbine. Several types of long arms are being deployed. Due to the advantages of having ammunition commonality, many LE units are using carbines chambered in 9mm, 40 S&W, and 45ACP. This combination increases the effective range of common pistol caliber ammunition out to 100 yards. Although the pistol calibers are better suited for the urban environment, some reports of finicky functioning and inaccuracy have questioned the reliability of such carbines. The “tactical” carbine, usually an AR-15 or M-16 seems to be dominating this arena.
There is no argument that the overwhelming majority of SWAT teams have adopted the .308 as their precision rifle caliber. When deployed in the counter-sniper role, the .308 wins over the .223 hands down. Among its many advantages, a 168-grain .308 can punch through heavy glass with a much better probability of success than any .223 loading. Selected marksmen which are deployed with .308 bolt guns might not always be available for backing up the patrol officer, and as was demonstrated in the Hollywood shootout, there are situations where the carbine would obviously help fill the gap. Not meant to take away from the traditional sniper role, the use of the carbine can help fill the niche between the engagement ranges of the pistol, shotgun, and precision rifle. Last time I checked, the national average for LE sniper shots was around 75 yards.

The tactical carbine can be defined as a short-range weapon that exhibits both short and long-range accuracy potential. Its 5.56x45mm cartridge delivers excellent hit probability from muzzle to around 300 yards. With the selection of the correct ammunition, over-penetration issues that have arisen in past thinking are subsiding. Modern .223 hollowpoint ammunition can demonstrate a remarkable amount of expansion that will keep the high velocity projectile from traveling very far after impact with both soft and hard objects. This is something varmint hunters, particularly prairie dog hunters have known and demonstrated for years. Interestingly, this is not a new concept. The carbine or rifle has had its roots planted in rural American law enforcement for a long time. The riot-type shotgun replaced its popularity over the years, but the liability issues related to controlling the launching of several projectiles, over a single one, have changed the thinking of administrators. The concern over the probability of an innocent bystander being injured or killed by an errant projectile, as well as the fear of liability has pushed this decision.

Carbine System Considerations:

Many configurations of the tactical carbine exist. Typically, a single carbine is deployed with a tactical light as an added modification. When equipped with various optics, usually some type of emergency iron sights should be available for backup in case optics fail. The folks at Quality Parts Corporation, better known as Bushmaster Firearms, Inc manufactured the heart of the dual-use system we evaluated. The concept revolves around having two available options depending upon the tactical scenario. The standard, or “primary” upper is equipped with iron sights, and the “secondary” upper utilizes specialized optics and suppressor.

We evaluated both units to determine accuracy potential for tactical LE uses. The suppressed and shorter barreled concept provides an interesting platform to support the carbine equipped rifleman role in law enforcement. The scoped upper can be zeroed in, and removed from the weapon’s lower, as the standard upper would normally be the carry configuration. This dual-use concept provides no loss of zero, and the weapons flexibility is twice enhanced. For example, if called in to assist in a drug raid, the officer can arrive on the scene with the weapon in primary configuration for entry use or perimeter defense. If things don’t go down as planned, and a hostage situation or some other change necessitates it, the officer can fall back and effectively become a stand-off marksman by simply changing out the upper assembly - time permitting. Change out can be accomplished in less than one minute assuming both uppers are equipped with bolt and charging handle. One of the biggest advantages of this dual system concept is the elimination of trigger pull unfamiliarity which would occur if switching to a completely separate firearm. Since the users of such equipment typically don’t swap rifles out between individuals, they can be sure that they will experience the same trigger with the rifle in either configuration.

Both Bushmaster M4 barrels had a twist rate of one turn in nine inches. A Harris bipod was also attached to the suppressed flat top. This helps support the extra weight, and provides a stable platform when shooting from the prone position. It also allows some degree of rotation between the rifle and ground to compensate for uneven conditions. The Harris Series “S” attaches to the bottom of the hand guard via an adapter stud. The #5 adapter stud is required for all AR-15/M-16 hand guards. During our evaluation, the unit performed beautifully, and really made shooting from the prone position a piece of cake. We noted no changes in bullet impact by shooting from either the bipod or sandbags. With large field-of-view optics, the swivel bipod enhances large area scanning capability.

Suppressor Observations:

Besides reducing the muzzle blast sound levels, a suppressed carbine kicks less than an unsuppressed one. Its use in law enforcement may be of little benefit in many situations, but with the reduced recoil, it can allow the shooter to see each shot strike through the scope. Increased practical accuracy, and faster follow-up shots are an added benefit. The suppressor used in our evaluation, the Specop II, is no longer in production. Manufactured by Gemtech, one of the unique features of the design was its two-point mounting system. Besides increasing strength, the two-point mount helps provide the proper alignment between barrel and suppressor. It allows full automatic fire with the M-16 without worrying about misalignment caused by the unit unscrewing from the host weapon. The suppressor is 11.2 inches long, 1.62 inches in diameter, and weighs a hefty 2.5 pounds. Finish is dark gray phosphate, and the degree of sound reduction is rated at approximately 35dB. It is a rugged system - built to withstand the abuse of hi-velocity ammunition and full auto fire. The folks at Gemtech currently offer the M4-96D and Predator models for the tactical carbine. Their new units are shorter, smaller in diameter, weigh less, and can be provided with a quick attach/detach capability. These new configurations may be even more appropriate for deployment in the law enforcement or military role due to their lightweight.

The report of the weapon itself is more like an unsuppressed .22LR, with the major sound being the ballistic crack of the projectile surpassing the speed of sound (approximately 1126 fps @ 68oF). This allows the operator to fire the gun without hearing protection since the report is not overly uncomfortable to the ears. Those involved in the tests made the comment that the sound of the weapon is about like an unsuppressed .22 rifle firing subsonic ammunition. The tactical user can easily train without the use of hearing protection, and most found the extra weight out in front was easy to get used to. I prefer dedicating a suppressor to a particular weapon, and leaving it there. This ensures no shift in bullet impact, which usually changes due to the variables involved in mounting/dismounting.

Configuration Options:

A tactical light was installed on the “carry” upper for target identification in low light conditions. No accessory for the handgun, shotgun, or carbine is more important than a flashlight specifically designed for use with the firearm. The light should be powerful, as they are used to illuminate the target and permit target discrimination to prevent shooting a fellow officer or family member. They also back light the firearms’ sights, and allow the operator to concentrate on the front sight. Serving warrants and searching for potentially armed suspects in the dark tends to elevate ones anxiety levels. Besides a sidearm and a radio, a good quality flashlight is a police officers most important piece of equipment.

SureFire flashlights have come to dominate the field of combat lights, but the new guys on the block are giving them some competition. Diamond Products has a new 30,000-candle power (105.5 lumens) Tactically Advanced Combat Mount (TACM III) light system for the AR-15/M-16. Made of unbreakable Delrin plastic, the mount system is very tough, is not affected by recoil, nor does it interfere with the rifles usual attach points. The mount attaches through one of the lower hand guard vent holes. The TACM III is almost exactly the same size as the SureFire model 6P, which is carried on the belts of many officers. The mount correctly secures the light to the right or left side of the hand guard, as top mounting would illuminate the smoke cloud as a round is fired. The TACM III is a very bright light, and easily lights up a small room. ON/OFF activation is accomplished via a remote pressure switch mated to the firearm via Velcro. Powered by two, three-volt lithium batteries, they provide approximately one hour and 20 minutes of continuous use.

For the flat top, there are many sight options available dependent upon the departments needs. Each agency has its own set of variables and circumstances, which must be addressed, before choosing the correct optics. A compromise must be met which will allow the operator to both adequately identify and hit the target throughout a variety of distances. With the perceived use being the mid-to-long range standoff scenario, a top quality 4 power scope is a good choice. The 4-power scope will do well in both shorter urban situations, and longer rural ranges. Considering that throughout WW I, WW II, and Korea, most sniper scopes were 2-1/2 to 4 power, the 4X seems an adequate compromise for today’s LE uses. The 10 X scopes which dominate sniper rigs are great for long range precision work, but lack a wide field of view. If the majority of engagement distances are 100 yards or less, say from one side of the street to the other, the compact 4 power with a wide field of view is probably the way to go. We tested three different optics on the flat top during the evaluation.

The ACOG (Advanced Combat Optical Gunsite) by Trijicon was first selected for testing on the flat top for the secondary carry configuration. The ACOG is a combat proven optical device, which complements the tactical carbine concept very well. It provides both close-up aiming capability, along with excellent stand-off accuracy potential. The internal reticle is calibrated for bullet drop out to 800 meters. It also increases accuracy in low light conditions much better than other optics due to its illuminated reticle. During daytime use, the reticle uses fiber optics which collect ambient light, and project the reticle as black lines. At night, the reticle glows red due to the internal tritium composition. The tritium lamps are guaranteed to glow for at least seven years from the original purchase date.

At 100 yards, the ACOG field of view is 36.8 feet. This compares to about 10.7 feet with a typical 10x sniper scope. It also can be ordered with an innovative quick-aiming configuration called the Bindon Aiming Concept (BAC). When using the two-eye aiming method and moving the weapon, the image is unmagnified. This permits extremely rapid target acquisition. As soon as the weapons movement is stopped, the targeted image zooms into magnification. The ACOG has no external switches or buttons to fail at the wrong time. The unit is waterproof, and is currently in use by U.S. Special Forces. We also tested two other scopes on the flat top which are discussed below.

With the AR-15/M-16 rifle, the line of sight though the iron sights are about 2.5” above the line of the bore. Roughly speaking, sighting the rifle in at 50 yards allows the projectile to strike around 1.25” low at 25 yards, on target at 50 and 250 yards. Maximum impact will be 3” high at 100 yards. This provides the optimum setting for iron sights in the LE scenario. On our test gun, when zeroing the scope in at 50 yards, the impact was about 1 inch low at 25 yards, and about 3.5 inches high at 100. When zeroed in at 100 yards, the impact was 1 inch low at 50, and about 2 inches low at 25.

Shooting Impressions:

The purpose of our tests was to verify the weapons function, reliability, and accuracy in the hands of a trained LE officer. Precise groupings are a good indication of a rifles inherent accuracy, but are somewhat irrelevant in a combat situation when you’re being shot at. In such encounters, the adrenaline will be pumping, and all you want to do is hit the threat and neutralize it. We took the carbine out to the range with several factory loads from Black Hills, Winchester, and Georgia Arms. We elected to utilize ammunition suited to the practical, real-world scenario. No subsonic .223 rounds were tested. It was the opinion of those on hand that a subsonic .223 round has very limited capability. Although it could be suited for very specialized situations, perhaps the use of a suppressed .22LR would be better.

The weather was not great during our first test outing. Outside air temperatures were around 40 F with winds gusting toward us at 15-20 mph. Nonetheless, we persevered to get a feel as to what the carbine was capable of. The ACOG equipped flat top delivered a 5-shot group average of 1.43 inches as fired from the bench at 100 yards. The best group (.98 inches) was obtained with Black Hills 52gr HP Match loads. From 50 yards out, we fired the standard M4 upper with iron sights to determine practical accuracy from the bench. We then mounted the ACOG to the same upper and retested at 50 yards. The standard upper averaged 5-shot groups less than 2 inches with iron sights, and when the ACOG was installed, the 50 yard groups averaged 0.84 inches.

Measured muzzle velocities were essentially identical with or without the suppressor. The ACOG equipped flat top delivered essentially the same accuracy potential at 100 yards as the iron sighted unit did at 50 yards. Two inch groups at these engagement ranges are more than adequate for the carbine support role in the tactical scenario. At both 50 and 100 yards, the ACOG equipped upper is probably more accurate than the pistol caliber carbines in most cases. Shooting the suppressed flat top is like shooting a rimfire rifle due to the reduced recoil. The shooter can watch through the scope and see the bullet impact the target. Shooting from the prone position, we fired at 50 clay birds positioned on the backstop at 100 yards, hitting approximately 95% with the first shot. The carbine seemed to perform best with the Black Hills 52gr HP Match round.

With the group impressed with the flat top accuracy so far, we decided to try a couple of different optics out on the gun. Just for fun, we mounted a 36x target scope on the flat top to see what the gun was capable of. I used the excellent Bausch & Lomb Elite 4000 scope that frequents me on prairie dog hunts out west. The Elite 4000 is high performance optics on steroids. The B&L 4000 is ideal for benchrest shooting since its field of view at 100 yards is only 3 feet. This is obviously not practical for a law enforcement weapon system, but using a scope of this quality can really help define the weapons full accuracy potential. It definitely limits the tactical carbine to benchrest shooting as it is practically impossible to aim holding the weapon offhand. The suppressed M4 produced an overall five shot group average of 1.12 inches using the 36x scope. The best five shot group produced measured 0.86 inches with the Black Hills 68gr HP Match loads.

One of the Sergeants then suggested we try out a Leupold scope they had on hand which was used on one of their bolt-action sniper rifles. We mounted Leupold’s 4.5-14x50 Long Range Tactical (LRT) on the flat top and retested at 100 yards. The Leupold Tactical is very familiar to police snipers since they are employed on many LE bolt guns. It combines excellent optics and rugged construction. On low power (4.5x), the field of view at 100 yards is 18.9 feet, and on high power (14x), is 5.9 feet. This combination of magnification allows the low power setting for urban scenarios, and the high magnification for long range shooting where precise bullet placement is essential. Groups averaged 1.19 inches, with the smallest group (0.85 inches) being obtained using Black Hills 52gr HP Match Moly loads. The LRT is probably more scope than is required for this type of gun, but I think the team went away salivating with the combination. With the variable scope, they could see the guns potential for quiet and accurate performance for both long and short range scenarios.

Lessons Learned:

Even with a fair trigger, the M4 carbine produced some impressive groups. We did notice that the rifle was prone to throw the first shot slightly, and explains why some of the groups were not as consistent as one would expect. This is probably explained by headspace variance, which results from the difference in speed and force during loading the first round. Past 50 yards, this first shot variance could be disastrous if a surgical strike is required. The user must be aware of this, and compensate accordingly. Our carbine seemed to throw the first shot up and to the right slightly most, but not all of the time. The same ammunition consistently produced sub MOA groups with a Remington PSS bolt action, so I would attribute this phenomenon to the gun and not the ammunition.

The 4 power ACOG allows easy target tracking thanks to the wide field of view. The ability to see the bullets strike the target allow quick follow-up shots with ease and effectiveness. Although the ACOG can be mounted to a removable carry handle with a back up rear sight, I would have preferred mounting it closer to the centerline of the bore. This would be more comfortable to the average shooter utilizing the collapsible buttstock configuration. Obviously the B&L 4000 is too much scope for this carbine. Although it is an excellent piece of optics, it is obviously designed for, and better suited to benchrest shooting. Sight picture is very sharp and crisp, and brings small targets up close and personal. Its adjustable objective is easy to turn and surprisingly accurate for range estimation. It can practically be used for a range-finder since the scope comes into focus precisely at the marked distance on the objective ring. It allows you to determine how accurate your gun is very quickly. A wider field of view would be great to have, but this is the trade-off for clear and precise long-range magnification. The Leupold LRT definitely has its advantages for both the short and long range scenario. The Leupold seemed to have a slight advantage in optics clarity and brightness over the other two scopes. Also, the Leupold had easier focusing adjustments, and seemed to produce less eye strain on the shooters. The side focus adjustment is easy to reach and adjusts for parallax variations. Most other scopes have objective adjustments, which are on the forward part of the unit, further away from the shooter. The LRT also had the most generous eye relief of any of the others tested.

One issue learned related to the use of the suppressed upper is routine maintenance. After cleaning, any cleaning oils which remain within the can, will produce a dramatic smoke plume for several shots. The smoke can obstruct the operators? field of view for several seconds. This may be no big deal for the casual shooter, but is totally unacceptable for LE use. We introduced one short aerosol burst of oil into the chamber, and allowed the oil to drain downward into the can between shooting sessions. Six or seven shots were required to completely eliminate the smoke plume. We checked the suppressor after each series of shots to ensure it remained tightly secured in place. No loosening in the mount was noted throughout the shooting sessions. This also included several full auto bursts utilizing a 100 round Beta C-MAG.

This carbine concept also allows the option of select fire. Tactical use of full auto fire is best kept to two or three shot bursts in the LE scenario. Long bursts do serve such practical purposes as checking the stability of the weapon, and having fun. I’ve never encountered a shooter who would turn down a “go ahead” offer to cut loose with a loaded magazine on full auto. The weapon we tested behaved beautifully in full auto with either configuration, and is especially fun to shoot with a fully loaded C-MAG. With the many early military M-16’s being surplussed to LE departments, the armorer can build upon the option of select fire lowers if the department requires this option.

Maintenance, Carrying, and Storage:

As recommended by Mark White of Sound Technology, a suppressed weapon should be stored with the muzzle pointing down and with the action open to allow venting so internal moisture can evaporate. This is somewhat of a dilemma for the officer who needs to have his carbine system stored in a hard case most of the time. Internal corrosion is the enemy here, and must be addressed. With the tactical user’s main concern being the cold-bore shot, the same maintenance procedures should be established and repeated after each shooting session. This will ensure that the operator knows where the first shot will impact.

Experience has shown that using suppressors which must be disassembled for maintenance is only asking for trouble. Sealed cans are the way to go, and current trends are confirming that point. The use of ultrasonic cleaners in conjunction with solvent soaks is much safer, in that it reduces the potential of improper reassembly. The “depot” level of maintenance would include a complete solvent soak in conjunction with ultrasonic cleaning. After cleaning and reassembly, the weapon would need to have a recheck of zero and adjustments made prior to deployment. With most suppressors on the market being sealed units, the problems associated with disassembling a suppressor for cleaning have gone away. Ultrasonic cleaners and solvent are very effective at breaking up accumulated fouling, and the Specop can also be cleaned by this method.

For protection during daily duty use, a good quality carrying case should be part of the system. This allows both carry and storage of the rifle and extra upper assembly in the same container, ensuring that they are always together. There is however, a danger with a well-sealed case. If moisture is present when the case is closed, it can do severe damage to a firearm’s finish. Some common sense maintenance routines are in order here to keep corrosion at bay.


Many have predicted that the close of the 20th century would be the end of the era for the rifleman. This is no surprise to me. I grew up in the southern United States, and like many living in rural areas, we routinely carried a rifle to obtain food for the home. Developing good rifle skills was a way of life, a necessity to help out the family. It wasn’t until I started my law enforcement career that I had to develop pistol skills, knowing all along the limited range of the standard sidearm as compared to a long gun. Not everyone is suited to being a rifleman. The training and deployment necessary for law enforcement personnel must be carefully thought out. Marksmanship, physical condition, intelligence, personality, and psychological makeup are factors that must be included in the selection process. Those selected for this role should be provided the necessary tools and training to fulfill this duty. Besides the equipment, the proper training will ensure the big three: marksmanship, accuracy, and consistency.

The M-4 “tactical system” provides excellent accuracy and performance within a fairly compact sized package. The suppressed flat top adds significant additional capability to the original carbine. Whether used for law enforcement applications, or for quieter long range target work, the shooter will be impressed with its capabilities. It is a good choice to match requirements for the tactical scenario. The civilian NFA collector/enthusiast will also appreciate its use for various competitions and quiet target shooting. This package certainly turned heads at the shooting range, and all were impressed with the overall concept. It provided more-than-acceptable accuracy for the LE rifleman role. Although not a consistent MOA performer, it delivered some sub-MOA groups with the optimum combination of ammunition and optics.


Bushmaster Firearms
999 Roosevelt Trail, Bldg. #3
PO Box 1479
Windham, ME 04062

Black Hills Ammo
P.O. Box 3090
Rapid City, SD 57709-3090

Georgia Arms
P.O. Box 238
15 Industrial Court
Villa Rica, GA 30180

Winchester/Olin Corporation
East Alton, IL 62024-1174

Diamond Products Mktg., Inc.
2300 Commerce Park Drive #6
Palm Bay, FL 32905

Gemini Technologies, Inc.
P.O. Box 3538
Boise, ID 83703-0538

Sound Technology
Mark White
P.O. Box 391
Pelham, AL 35124

Trijicon, Inc.
49385 Shafer Avenue
Wixom, MI 48393-0059

Harris Bipods
Barlow, Kentucky 42024

B-Square Mounts
P.O. Box 11281
Fort Worth, TX 76110-0281

Bausch & Lomb
9200 Cody
Overland Park, KS 66214

Leupold & Stevens, Inc.
PO Box 688
Beaverton, OR 97075

This article first appeared in Small Arms Review V2N1 (October 1998)
and was posted online on December 16, 2016


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