Muzzle Attachments

Give a shooter a barrel with threads on the front and he will find something to screw on there. Give him a barrel with no front threads and he will find something to clamp on. The M14 had a flash suppressor screwed on. With the AR-15/M16, Stoner made the choice of front-end devices for us. AR-15 rifles appearing in the early years of Viet Nam were equipped with three prong flash suppressors. That was later replaced by a "birdcage" design with vents all around.

Further along in history when the M16A2 was developed one of the differences between it and its predecessor was that the flash hiders on the newer version had no vents on the bottom which helped deal with the "dust signature" when firing prone in dry environments. All three of these devices work to disperse burning gases, reducing the firing signature, and retaining night vision better in during dim light engagements.

Now that I am retired from the military I am glad that we civilians really don’t need flash suppressors. "Need" notwithstanding, at least 9 out of 10 of my customers want front threads and want something screwed onto them. In fairness, the suppressors do help guard against damage to the crown of the muzzle in case of guns being dropped. While the military has pretty much stuck with the A2 suppressor design, civilians have the choice of a wide array of flash hider varieties.

One of the more popular versions for civilians is the Vortex. Think of the original Stoner design but with four fingers instead of three. Manufacturers of the Vortex claim that it is superior in dealing with flash. Some shooters report tighter groups when replacing stock flash suppressors with a Vortex. Let’s look at some options.

Lessons Learned I am pretty sure that when arms manufacturing plants are first being stood up the upper management lines up all the new hires against a wall, walk the line like a drill sergeant, and pick the burliest of them in charge of flash suppressor installation. Decades back, shooters and gunsmiths posited that excessive torque on flash suppressors was distorting the muzzle and causing fat groups.

They discovered that if they unscrewed these gorilla-torqued units and reinstalled with modest torque the groups improved. I researched the matter on my machine rest and found these claims were valid. Chrome-moly and stainless steel barrels responded best and chrome-lined issue barrels improved to a lesser degree. I suspect that the chrome lining is less elastic and not behaving as favorably. It is still to our advantage to relax the torque on all barrels, however.

In true American fashion quite a few gunsmiths over-reacted early on by installing suppressors only hand tight and relying heavily on red Loctite to hold things in place. A bunch of those units came loose, causing shifts in zero and all sorts of may- S. service rifle, the M14, came equipped with a rather long flash suppressor. hem.

To add insult to injury some barrel makers heard about the flash suppressor issues and applied the "hand tight standard" to barrel extensions, resulting in disaster when barrels began to unscrew. I had it personally happen to me with a barrel I had purchased from a big-name custom maker. Before that, I had a revolver barrel start to unscrew and was able to apply lessons learned to diagnose and correct the rifle issue promptly. Shooters with less experience were puzzled and I ended up fixing their problems.

I don’t know any gunsmiths or barrel makers still installing flash suppressors or barrel extensions hand tight. Military technical manuals recommend 20 foot-pounds of torque for the front end, which is excessive for tight groups. I thoroughly degrease all threads and use lots of red Loctite with three ft-lbs. of measured torque and have never had one come loose. For barrel extensions, 150 ft-lbs. is problem free. The use of peel washers on ARs has declined being replaced with crush washers.

Those devices can result in some really excessive torque settings and the sight of them raises the hackles on the back of my neck. I wrote about them in my "AR-15 Fliers" series in the February through April 2021 issues. My admonition then, and now, is complaints of fliers

or fat groups should begin diagnosis by replacing peel washers and use a lighter torque. Even with improved groups, this will probably cause a zero shift. I covered flash suppressor torque in "Improving Rack-Grade AR-15s" (December 2014) along with other tips to improve battlefieldgrade rifles. Email me at NCC1701@ penn.com and I’ll be happy to help you with this. Next on the flash suppressor learning curve is barrel harmonics.

The first that I heard of barrel harmonics was with Browning hunting rifles equipped with their Ballistic Optimizing Shooting System. The BOSS came in one version without exhaust holes as an accuracy tuning device accomplished by screwing part of the unit in and out. Graduation marks kept track of the settings. The other and more popular version model achieved better accuracy performance as well but also had vent holes to lessen recoil. As a former Pennsylvania Game Warden, I saw this one the most.

In my 28-year career in the woods, I don’t recall encountering a BOSS that didn’t have the gas vent holes. Browning claimed that the vents reduced felt recoil by about 30%. What they may have reduced in terms of recoil they more than made up for with noise. Browning included a chart of recommended settings to dial in for different commercial ammo and various popular bullet weights.

After dialing in the factory recommended setting the owner was free to fine tune the setting by firing groups and comparing them to arrive at the tightest. Some smart hombres in the AR community started to move flash suppressors in and out on the front threads in an effort to tighten groups. I have always assumed that they got the idea from the BOSS but I can’t prove it. I even named the process of using the flash suppressor this way as the "Poor Man’s BOSS".

I was a firing member of the Army Reserve Marksmanship Program at the time and we used issue M16 rifles in Service Conditions events, so being able to improve performance by just changing the suppressor’s position was useful. This entails using an issue, nondirectional flash suppressor; the A2 unit has a solid section that needs to line up at about 6 o’clock and isn’t an option, leaving the A1 suppressor with vents all around. I installed and A1 unit with no peel washers at three ft-lbs.

After a test group, I removed the suppressor and added a peel washer, which area paper-thin 0.004". One washer moves the position of the suppressor about "one hour" from the no-washer 12 o’clock initial setting to about 11 o’clock for another test group. I continue this process while closely watching group size to determine a sweet spot. Group sizes will begin to shrink at some point, and then start getting bigger. This normally happens before adding enough washers for a full revolution back to 12 o’clock again.

While not offering BOSS adjustability, this accomplishes the same thing. Lowering the crushing torque on the suppressor and tuning the suppressor position can be done by shooters on the range with the appropriate tools and time and ammo to test. From those humble beginnings so many decades back I developed other, even more effective tuning techniques for Stoner rifles, documented in "AR-15 Barrel Harmonics" (October 2016).

What I detail in that article requires a greater level of gunsmithing skills and tools in addition to range time. Before we leave the topic of flash hiders there is one bit more of history to discuss. When guys first began to experiment with trying to get greater precision with the AR they copied many tricks that worked with the previous M14. Gunsmiths working on the M14 almost always bored out their flash suppressors a bit but this doesn’t usually do anything with the AR.

It may have to do with keeping the "bore" of the flash hider properly centered. We will discuss this further with regard to the topic of other screw-on devices and problems with their group sizes. For sure, if you area do-it-yourself home hobbyist I would strongly discourage clamping a suppressor in a vise and attacking it with a hand drill! In full disclosure I have to tell you that I have not set up any scientific studies regarding before and after groups with flash hiders subjected to boring.

I figured that gunsmiths decades back discarded the technique for a reason and I have not seen fit to resurrect it. Pre-Ban vs. Post-Ban The Left hates guns, especially handguns and anything resembling an AR- 15. You already knew that. In 1994 they scored a victory over us when then President Bill Clinton signed the "Assault Weapons Ban" into law. To this day, Joe Biden proudly boasts that he wrote a significant portion of that legislation.

It lapsed ten years later but some states adopted similar laws that are, unfortunately, still on the books. Due to that legislation, the terms Pre-Ban and Post-Ban were coined and are still used today. Pre-Ban ARs have bayonet lugs and flash suppressors and Post-Ban guns do not. Gunsmiths can’t use the barrel harmonic tuning as previously described on Post-Ban firearms as they lack threaded muzzle accessories. Clamp-on items are an option to be discussed later.

Pre-Ban ARs universally have flash suppressors and military shooting teams could ignore this. Since I was a member of a military shooting team during that time, my experience with unthreaded barrels was minimal until I started working on civilian guns. The vast majority of my customers today want threaded barrels but I’ve worked on many Post-Ban configurations, such as Bartlein gain twist barrels.

I machine rest test and harmonically tune every gun that I build or rebarrel and haven’t noticed any accuracy difference between Preor Post-Ban but haven’t set up a scientific study to prove it. Other military

shooting team armorers conducting machine rest testing have reported the same. Unfortunately, civilian gunsmiths with more Post-Ban experience usually don’t conduct as much machine rest testing. For now, the available data indicates no advantages either way. The gun community has a small but growing segment that spends more time near air conditioners and keyboards rather than shooting ranges and competitions while remaining all too certain in their assumptions.

Collectively they have beaten this Pre-Ban/Post-Ban accuracy topic to death. Their concern seems to have to do with the significant step down from the 3/4" diameter of the barrel behind the threads to the skinnier 1/2" at the threads. They posit this influences barrel harmonics to the detriment of group size. This might be a more valid concern if AR shooters were shooting with just the bare threads exposed, but when does that realistically happen?

As stated previously, barrel threads will find amounted accessory, which will likely be metal and have a diameter greater than 3/4". For those readers not averse to range testing sessions, don’t take my word for it. Begin tuning with the barrel threads exposed and continue with amounted accessory adjusted as previously detailed to compare groups. Of course, a single experience is a useful start but doesn’t prove a rule.

Also, I suggest spending more time in testing and collaborating with those that do instead of online forums. Screw-On Muzzle Devices We’ll start with recoil reducers. The first I ever experimented with venting for recoil reduction was Mag-naporting (MagNaPort.com, The company uses electrical discharge machining to cut small trapezoidal ports near the top of the barrel on either side of the front sight, claiming this had no negative effect on precision.

I purchased my first new Colt Python in 1972 for the then outrageous sum of $190, including tax. About a year later I bought my first machine rest for pistols and tested my Python, sent it to Mag-naport, and then retested with the same ammo. Group size was the same, as advertised. I’ve since performed this testing with customer firearms showing the same results. The only downside I’ve seen (pardon the obvious pun) with the ports was a bona fied Roman candle display with the muzzle flash!

Guys used to love watching me shoot my Python with full 357 Magnum ammo during night police firearms qualifications. A lot of pistol shooting in the early 1970s was single hand at bullseye targets. Police officers of the era were discovering that this practice was inadequate. Two handed grips and silhouette targets gained more favor. Soon semi-automatic pistols began turning up more often and time limits became shorter.

The ability to shoot fast is hampered by recoil and shooters soon wanted something more effective than Mag-na-porting so compensators on the front end of pistols (mostly 1911s) gained popularity, effectiveness, and numbers. The race was really on. An interesting side note: Recoil pushes the gun back and causes the muzzle to rise. Recoil is not the only factor that hampers the shooter in getting back on target for the next shot. Rotational torque is also important.

As the twist of the rifling is putting a spin on the bullet the firearm is reacting in the opposite direction and trying to twist. Generally speaking, the fatter the bullet the more pronounced this rotational torque. Faster twists also exacerbate the problem. Watch somebody shoot a 45 ACP one handed and see the pistol rise up in the air and twist toward the side.

Gain twist barrels that start out with a slower twist and progressively increase the rate of twist lower rotational torque, allowing shooters to get back on target faster. A fellow member of the Reserve Shooting Team had a 45 ACP 1911 equipped with again twist barrel and won the National Matches at Camp Perry more than once with it. He credits part of his success to the gain twist allowing him to get back on target faster. I cover gain twist in depth in the November and December 2013 issues.

Service rifle shooters really lagged behind in compensator development. The first reason is that National Rifle Association and Civilian Marksmanship rules disallow compensators. Where forward thinking pistol shooters formed the International Practical Shooters Confederation headed up early on by the smartest person I have ever known, Jeff Cooper, pistol compensators found utility, even Far

after creating different equipment divisions putting such use in Open Division. Until rifle shooters began in various 3 Gun and Multigun events, they had no place to go. A second reason was that onerous Assault Weapons Ban stifled innovation and its notion that anything screwed onto the front of ARs was inherently "evil". Finally, it could be that pistol shooters are just inherently smarter. Naw, scratch that! Although rifle shooters came to the compensator dance late, they sure have made up for it.

The latest catalog from Brownells has six pages of items that attach to the front end of AR-15s and that’s a fraction of the total population. I concentrate on building National Match Service Rifles. Occasionally, when time permits, I allow myself to be talked into something different and receive some AR compensators of various makes and models. Sometimes the owners identify the parentage of these devices and sometimes the manufacturers remain anonymous.

The first time this happened I shot the rifle on the machine rest with the device in place and groups were awful! I replaced the compensator with a regular A2 flash hider and groups shrunk to acceptable levels. There was a weight difference between the two items which influenced harmonics. I reattached the compensator and went through my normal harmonic tuning process. Although this improved groups they remained unacceptable.

Since that initial experience this scenario has repeated itself with different compensators. My conclusion is that there is a manufacturing or design flaw on some compensators causing them to shoot fat groups. I have not tested every compensator and suspect there are some good ones and I’ll eventually happen upon some, however, none of these are legal in NRA/CMP Service Rifle matches. The message for gunsmiths: Warn your customers wanting compensators installed this might increase group size.

I’d recommend a standard A2 flash hider, a simple thread protector, or one of the tuner/brakes described below instead. There are other ways to reduce felt recoil that don’t make groups fat. One is to bed a mercury recoil reducer in the hollow portion of standard AR stocks. This adds about 3/4 pound and changes the balance a little but I’ve never found this to be a problem during shooting.

The second option is a shock absorber that replaces the buffer and slows the bolt carrier at the end of its cycle, lowering the jarring impact as it impacts the back of the buffer tube. Brownells carries several models of both. Unlike a screw-on recoil reducer, these are both internal modifications and not in violation of NRA or CMP Service Rifle rules. There are two categories of devices that purport to offer more than one improvement. One attachment is a tuner/brake such as the BOSS.

It’s claimed the porting lessens felt recoil by about 30% while allowing the owner to tune barrel harmonics. Harrell’s Precision (HarrellsPrec.com, offers a similar device with standard 1/2×28 threads. My tests show this works and it is offered in two configurations: one has round holes all around the outside and the other has two large ports at 3 and 9 o’clock. The second configuration gave better groups for me and having no vents at the bottom reduces the dust signature.

While they’re easy to tune, the units don’t include instructions. Numbers with long tick marks are engraved on reading 0, 50, 100, and 150 with shorter tick marks in between. I begin by shooting a group at each of those four long tick marks and identify the best group. From that setting, I shoot a test group a short tick mark above and below it. If either of those two new groups are tighter, I continue following the bread crumbs with additional groups on the next tick mark until groups start getting fat again.

After tuning a bunch of these on barrels of different contours, lengths, and calibers, I usually hit a sweet spot around the lower numbers of 0 or 50 and haven’t a best group around 150. I always use plenty of red Loctite on the barrel threads and lock in the number settings as dependent on whether you plan more testing in the future.

Tuners and brakes are not permitted in NRA or CMP Service Rifle events but the Harrell’s Tuner Brake has a contour similar to A2 flash suppressors with regard to maneuvering in pucker brush. It goes without saying that you should perform the tuning process using the same ammo that the gun is going to fire later in real life. The second category of dualpurpose devices has to do with the mounting of suppressors. In spite of the hurtles of the National Firearms Act to own these devices, they are growing in popularity.

Older models simply screwed onto front barrel threads but some ingenious folks have since invented devices that screw onto those front threads, which serve as flash suppressors on their own, and permit quick attach/detach of compatible silencers. However, there isn’t a universal standard and different company’s units probably aren’t compatible. Also, any large muzzle device gets stuck in pucker brush and none of them are NRA/CMP legal. The main problem with most of these devices is their impact on precision.

Of all of these that I have machine rest tested to date only the OSS Model 1677 produces consistent tight sub-minute groups from across section of ARs. All of the other models from other manufacturers I’ve tested shot fat groups larger than MOA when mounted on the same firearms. Their groups can run from half again the size of groups from the OSS to two or three times as great. This is without the actual silencer being in place.

What about these combination flash suppressor/silencer mounts causes so many of them to shoot really fat groups? Most of these units weigh about double that of a standard A2 flash hider and weight has an influence on barrel harmonics. I have applied tuning techniques to guns outfitted with these combination units and still can’t get decent groups from them. I have also tried tuning the harmonics of ARs equipped with many of the screw-on recoil reducers with the same dismal results.

I am, therefore, inclined to believe that the problem with both of these devices is not just barrel harmonics. Harrell’s Precision is a company I respect. They make tuners and combination tuner/brakes that work and improve groups. They stress that the threads need to be CNC cut on a lathe as opposed to being tapped as this helps get screw-on devices square with the bore of the firearm. It is easy to imagine what would happen if a device was set at an angle to the bore.

Most of us likely don’t have any way to measure this alignment so I can’t say for sure that thread issues are the cause of so many of these screw-on units shooting fat groups. If a customer brings in a firearm with either a screw-on recoil reducer or a combination flash suppressor/silencer quick mount and is complaining of fat groups, this is a good place to start looking. These devices are not Author prefers the model on the right. the only potential cause of precision problems.

I discuss further in my three-part February-April 2021 series. Given a threaded barrel, if a shooter wants a screw-on device removed, install a thread protector. These are available in standard 1/2×28 thread, 3/4" diameter, and match normal AR barrel dimensions to look like a Post-Ban barrel. I use red Loctite if installing a thread protector for a customer with no plans to use a screw-on device; otherwise, I use a knurled thread protector with blue Loctite.

Brownells, Midway USA, and Yankee Hill (among others) offer a variety of these at reasonable prices. Clamp-on Devices With clamp ons, we’ll start with stand alone accuracy (harmonic) tuners. Although some predate the BOSS, they never achieved much popularity on Stoner rifles. My only experience with them has been Harrell’s Precision units for .22 caliber rimfires, which also work with 223 Remington rifles and I’ve seen 30% group reductions. Harrell’s devices have hash marks to use as described above.

This unit is made for any 0.750" barrel, will fit Post-Ban AR- 15s, and work equally well on Pre- Ban configurations because it goes completely over the front threads and hides them. Too easy! I recommend the use of some green Loctite on the surface of the barrel if you are mounting one of these permanently as well as blue Loctite on the threads of the clamp screws. An Internet search will locate other makers offering tuners for larger caliber rifles. Bloop tubes are another clampon device.

For some competitive shooting, match rifles are equipped with expensive (about $1,000 per set) iron sights. In the case of Stoner rifles, the rear sight clamps onto the upper receiver rail section and the front sight clamps onto the front of the barrel which, in most cases, is stepped down to 3/4" diameter. Match Rifles barrels are typically longer than the 20" found in Service Rifles, with 26" being common and increasing the sight radius for improved alignment and scores.

Some shooters wanted the advantage of an even longer sight radius without going to the significant expense and added weight of replacing existing barrels with longer ones. The first bloop tubes were born of this need and began appearing on bolt gun Match Rifles and Smallbore rifles. Imagine apiece of hollow pipe with an inside diameter to perfectly match the outside diameter of the barrel.

That piece of pipe has a clamp on the end that fits over the barrel and could be of most any length depending on the desired sight radius. Some of this bloop tube tech has found its way onto match grade Stoner rifles. Imagine a normal 20" barreled Service Rifle upper equipped with a 10" bloop tube resulting in the same sight radius as a Match Rifle with a 30" barrel. Using this bloop tube approach does lengthen sight radius but it does not increase bullet velocity (with its lowered

wind drift improvement) the way a longer barrel would. So, my admonishment to those choosing to use a bloop tube is to couple it with a high ballistic coefficient bullet that will buck wind changes. In the case of most AR-15s that will likely be a 90 grain match boat tail seated longer than magazine length. The Sierra Match King and Berger are two such bullets available and both are very user friendly shooting out of barrels with a 1:6.5" twist.

My customers are split between these two choices, or rather, their particular rifle shows preference to one or the other. Both of these 90s and most all other bullets will perform better out of again twist barrel that has the proper rate of gain, which is to double from the front of the chamber to the muzzle. In the case 20" Service Rifle barrels shooting 90 grain .223 caliber, that will beagain twist of 1:13" increasing to 1:6.5".

Many of you have likely already fast forwarded to a potential issue with bloop tubes: the weight of the tube and front sight has a significant influence on barrel harmonics. Handload development needs to take this into account. Some tubes come with integral harmonic tuners like the tuners previously described. Conclusions I’ve discussed a wide variety of muzzle devices here and most of them do exactly what they were designed to do with no repercussions.

Unfortunately, some recoil reducers and combination flash suppressors/silencer quick mounts negatively influence accuracy. I don’t currently know of anyone else researching these problems and most of my gunsmithing is focused on National Match Course Service Rifles that disallow them completely. I’m limited to testing the occasional customer rifle that has one while the devices on the market seem to be multiplying like rabbits!

Given that so many of them look better suited as a prop in a Mad Max movie instead of being a useful accessory for a good shooting rifle, I question if their makers ever shot a group with them to see what impact they have. Customers see these things on websites or online forums, think they look cool, and buy one without considering potential consequences. Then, a box full of parts arrives at your shop with a customer wanting you to make a silk purse out of a bunch of sows’ ears.

This makes me appreciate why so many auto garages and custom gunsmiths refuse to accept customer supplied parts. It is none of my business to try to tell you how to deal with this conundrum. If I get one of these muzzle attachments that I am in doubt of I contact the customer and let him know that often these parts cause groups to be overly big.

If the customer is going to be shooting in some discipline that requires really fast recovery time but only modest accuracy he may be okay with moving forward; likewise, if he really "needs" quiet shots as opposed to precision, that is his choice. At the very least, I tell the owner that accuracy issues can by fixed by replacing the offending muzzle device with an A2 flash suppressor or a thread protector.

If the customer has made other questionable purchases of major components I have little hesitation to just declining the project, period. For builders of National Match Service Rifles the front end of the barrel is pretty much over looked. It gets either an A2 flash suppressor with lots of red Loctite and modest torque or the barrel choice is for a Post-Ban with no front threads at all. Those are the only options that are legal by NRA/ CMP match rules.

This article points out that you builders of guns for other disciplines have many more options. Hopefully, what you have read will help you make more informed choices. Getting the muzzle device right is only one of many critical decisions involved in building good rifles. Getting the muzzle right along with the other variables will usually result in a stellar gun. Unfortunately, getting the front-end right while making mistakes elsewhere will likely not save you.

You may lessen the impact to precision but that is all. I’m always happy to discuss issues presented in all my articles. Email me at Good luck! AG