HEL 5.56mm Supressor for M16A1

83The Small Arms Review - Vol. 5 No. 8 - May, 2002

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The growing involvement of U.S.armed forces in Vietnam stimulated thedeployment of the new rifle developedby the late Gene Stoner and his col-leagues at ArmaLite as the AR-15, andproduced under license at Colt as theM16 once adopted by the U.S. military.SpecOps personnel soon recognizedthe value of suppressed weapons ingeneral, and suppressors for the littleblack rifle in particular. The U.S.Army’s Human Engineering Labora-tory (HEL) at Aberdeen ProvingGround developed a number of sup-pressors for the M16 rifle from theearly 1960s onward.

The HEL M2 was an experimentalM16 suppressor that used a series ofbaffles coupled with an expansionchamber extending back over the bar-rel to the front sight. The M2 model

HEL 5.56mm Suppressorsfor the M16A1

By Al Paulson and N.R. Parker

for the M16 rifle was 14 inches longand used 24 baffles forward of themuzzle. Following an ENSURE (Ex-pediting Non-Standard Urgent Re-quirement for Equipment) request (DAENSURE Index No. 77) from theUSARV (United States Army, Viet-nam) for silencers for the M16A1 riflein May 1966, HEL designed and testeda noise suppressor designated the HELM4, which was a variant of the M2.

To reduce the bulk and weight ofthe M2 5.56mm suppressor, HELshortened the length to 12 inches, re-duced the number of baffles, andchanged the internal arrangement ofcomponents. The number of baffleswas reduced from 24 to 11, with thefirst baffle being positioned backwards(i.e., so that its apex was toward thefront of the suppressor). Directly in

front of this baffle was a short expan-sion chamber followed by a baffle po-sitioned normally (i.e., with its apextoward the muzzle of the rifle). Thisbaffle had a very large bullet passage,presumably to reduce back pressure.The next 9 baffles were the same de-sign as the first baffle, but were ori-ented normally.

The new can eliminated enough ofthe muzzle blast so that the location ofthe shooter was undetectable to hos-tiles downrange, which greatly im-proved a shooter’s tactical advantageand survivability. Given ideal vegeta-tion and terrain, the muzzle blast froman M16A1 was completely indistin-guishable beyond 50 yards. Only thesonic boom created by the 5.56mmprojectile remained, which soundssomething like the report of a short-

Military Armament Corporation production-modelWerBell silencer featuring both spiral diffusers andfrusto-conical baffles, mounted on an early Colt select-fire AR-15. Al Paulson photo.

These WerBell designed silencers were produced by the Military Armament Corporationand incorporate both frusto-conical baffles as well as WerBell’s spiral diffuser. Thesespecimens saw military usage. Note the top one suffered a bullet exit through the side ofthe can. Al Paulson photo.

84 The Small Arms Review - Vol. 5 No. 8 - May, 2002


barreled .22 rifle. In the absence of amuzzle blast, the mammalian brain in-terprets the origin of the gunshot asperpendicular to the pressure wave ofthe ballistic crack striking the body.Combined with the sound of bullet im-pact, this phenomenon causes individu-als to turn their attention 90 to 180 de-grees away from the shooter. This is a

very good thing during an ambush orwhen a small force equipped with si-lencers must cope with a larger force.

To meet the ENSURE #77 require-ment, the USARV submitted an acqui-sition requirement for 1,080 HEL M4noise suppressors. By December 1967,the first 120 suppressors had been pro-duced, but further production was sus-pended pending a field evaluation by

USARV. Twenty suppressors were sentto USARV for testing.

In March and April 1968, theUSAIB (United States Army InfantryBoard) tested the M4. The USAIB testfound that the M4 had three shortcom-ings. (1) The gas deflector failed to de-flect all of the escaping gases from thefirer’s eyes. (2) The ejection pattern of

the rifle with noise suppressor attachedcaused the spent cartridge case tostrike the cheek of left-handed shoot-ers. And (3) the malfunction rate of thetest rifle was significantly higher thanthe control rifle during automatic fire.The USAB concluded that the HEL M4sound suppressor had military poten-tial but it was not the perfect tool forthe job, so the Board returned the M4

to HEL for correction of these short-comings.

Early development at Aberdeenalso demonstrated that the M4 gener-ated a number of problems with theM16A1 rifle: (1) increased back pres-sure; (2) increased cyclic rate; (3) in-creased rearward bolt velocity, and (4)excessive gas discharge from the ejec-

tion port into the shooter’s face. Themajor problem was the increased backpressure, which actually produced theother problems, such as shearing offthe bolt carrier key. HEL solved thebolt velocity and cyclic rate problemsby adding an additional gas pressurerelief port to the bolt carrier, whichenabled reliable functioning of the riflewhether the selector was set to SEMI

Frankford Arsenal Model FA-XM noisesuppressor for the M16A1.

HEL Model M4 noise suppressor, with pointers showing the front end cap,baffles, barrel connector and rear support.

Early SIONICS MAW-556 rifle suppressor with two-diameter suppressor tube and pressure relief valve. Reprintedwith permission from Volume 2 of Silencer History and Performance.



or AUTO.The only glitch with this solution

was that the rifle would not cycle reli-ably with the modified bolt carrier un-less the suppressor was installed. Thismeant that a rifle fitted with the modi-fied bolt carrier had to be dedicated forsuppressed use only.

Once installed, the suppressor be-came an integral part of the rifle that

could not be removed without swap-ping the bolt carrier as well. This wasnot an ideal situation for special op-erators. Furthermore, the suppressedrifle with modified bolt carrier stilldumped a lot of hot combustion gasinto the shooter’s face, so HEL addeda special gas deflector to the charginghandle of the M16A1 rifle. This deflec-tor was not entirely successful, how-ever.

In April and May 1968, HEL de-veloped a new, shorter suppressor that

eliminated the need for a speciallymodified bolt carrier. Apart from theremoval of 5 baffles from the bafflestack, the new suppressor used thesame arrangement forward of themuzzle of the rifle. This new 9.5 inchmodel was known variously as the HELM4A, or H4A, or E4A which was itsfinal designation. The gas deflectorwas also intended to be used with the

new suppressor, but there is little evi-dence to suggest that it was actuallyused with the E4A suppressors in thefield.

Other developers of noise suppres-sors tried to meet the ENSURE #77 re-quirement, including SIONICS (a com-mercial company that eventuallymerged with the Military ArmamentCorporation) and Frankford Arsenal(FA; which was a government facility).In May 1968, HEL, SIONICS and FAsubmitted a total of seven different

noise suppressors for testing to meetthe ENSURE #77 requirement. TheFrankford Arsenal silencers were 1.25inches in diameter and utilized porousaluminum rather than baffle technol-ogy. These very early SIONICS silenc-ers used WerBell’s spiral diffusers, butdid not incorporate baffles that wouldlater be seen in his patents and produc-tion units. They also featured a flash

hider that screwed onto the front endcap of the SIONICS silencer. The HELM4 and M4A suppressors were testedat Ft. Benning, Georgia, by the USAIBin a Military Potential Test (MPT)against the FA (Frankford Arsenal) FAXM and CM noise suppressors andthree d i f fe ren t vers ions of theSIONICS 5.56mm suppressor (theMAW-A1, A2, and A3 models). Thetest recommendation was that the HELE4A noise suppressor was suitable fora field evaluation in Vietnam.

Extremely early SIONICS M16 suppressor featuring five spiral diffusers and no baffles or pressure relief valve. Thisdesign was patented in 1968 (Patent 3,500,958) and again in 1972 (Patent 3,667,570). Reprinted with permission fromVolume 2 of Silencer History and Performance.

HEL E4A 5.56mm noise suppressor. Ian D. Skennertonphoto. Reprinted with permission from Volume 2, SilencerHistory and Performance.

HEL E4A noise suppressor on M16A1 rifle. Ian D. Skennertonphoto. Reprinted with permission from Vol.2, Silencer Historyand Performance.



The HEL E4A was win-win tech-nology. While it was not as quiet as theM4, it solved all of the reliability anddurability issues plaguing the M4 sup-pressor. Furthermore, it was more com-pact than the HEL M4. While the E4Adid not require a modified bolt carrier(unlike its M4 predecessor), we find itquite interesting that the E4A was con-sidered to be a permanent fixture onceit was fitted to a rifle.

The E4A produced a net sound re-duction of 26 dB (at 12.5 feet downrange and 2 feet to the right of bullettrajectory). That was significantly bet-ter than the SIONICS suppressors (byabout 10-11 dB), but not as good asthe HEL M4 (which produced 35-36dB reduction) or the FA XM (whichproduced 32-36 dB reduction). See theaccompanying sidebar to learn moreabout the sound level measurementprocedures used for these HEL tests.All of the other five suppressors testedby the USAIB had shortcomings. Theperformance of the E4A out-shone theother suppressors, especially with re-gard to the number of malfunctions thatoccurred during cyclic tests. The mal-function rate of the E4A was signifi-cantly lower than all other suppressorstested; during a 1,000-round cyclic ratetest, only 3 malfunctions occurred withthe E4A.

While some shortcomings werenoted with the SIONICS suppressors,SIONICS was well advanced in the useof high-tech materials compared to theother suppressor manufacturers of thetime. SIONICS used a plastic bushingunder the rear retaining collar. Unfor-tunately, this bushing melted during afull-auto testing. A redesigned bush-ing made from Teflon was then submit-ted during the MPT to rectify this prob-lem. Unfortunately, Teflon meltedwhen temperatures reached about

1,000 degrees F, so SIONICS finallysettled upon making the bushings fromnaval bronze.

Another problem was the gas pres-sure relief valve. The springs used inthe relief valve failed during the cy-clic rate testing, so a redesigned springmade from Inconel was submitted inan attempt to rectify this problem.Even resorting to using a high-tem-perature resistant alloy like Inconelproved unsuccessful, so SIONICS de-veloped its third and final design: apassive gas pressure relief valve withno moving parts. Significantly, theMPT found that the pressure reliefvalve had no effect on the operationof the test items, and concluded that itwas an unnecessary part of the suppres-sor. It is also interesting to note thatuse of a gas pressure relief valve withcenter-fire rifle suppressors has notbeen seen since its use in the SIONICSsuppressors, with one exception. Re-cent ly deployed Is rae l i -madecenterfire rifle suppressors for theM16A1 and M14 rifles have featuredthe use of gas pressure relief valves,despite the fact that advances in inter-nal design have clearly eliminated anyneed for pressure relief valves.

Two of the SIONICS suppressorsused titanium spiral suppressor rings,while the third used aluminum spiralsuppressor rings. Following further de-struct tests at Ft. Benning, SIONICSmade significant changes to the con-struction and materials used in the5.56mm suppressors. No internal partswere subsequently made from alumi-num, and stainless steel became thematerial of choice. While the use of ti-tanium has become more widespreadin recent years, it is a little-known factthat SIONICS pioneered the usage oftitanium in firearms sound suppressors,though undoubtedly the cost factor pre-

vented its widespread use during theVietnam years. Despite the advancesin material use, the SIONICS/MilitaryArmament Corporation’s sup-pressors were not as widely used as theHEL E4A in Vietnam.After the MPT report was published inSeptember 1968, final production ofthe outstanding 960 HEL E4A suppres-sors was completed, and these wereshipped to Vietnam in late 1968 andearly 1969 at a cost of $42,000. Thatworks out to less than $46 per unit.According to several sources, the HELE4A suppressor was used in greaternumbers during the Vietnam War thanSIONICS/Military ArmamentCorporation’s suppressors designed forthe M16A1 and CAR-15. Rangers,SEALs and Army Special Forces be-gan using HEL M4 silencers in thesummer of 1968 and then upgraded tothe HEL E4A suppressors, which wereemployed throughout the remainder ofthe Vietnam War. The SEALs, how-ever, eventually used a U.S. Navy-de-veloped 5.56mm suppressor ratherthan the E4A suppressor.

Surprisingly, both the HEL M4 andE4A suppressors were considered to beexpendable items. If they were dam-aged, they were to be destroyed by thecompany armorer rather than repaired.This may explain why the HEL M4 andE4A suppressors are rarely seen todayin collectors’ hands. It is known thatduring the early 1980s, at least onemail-order company was selling partskits for the M4, although this practiceceased when ATF changed the defini-tion of a silencer to include silencerparts. If you ever find a transferableM4 silencer, it’s a rare and importanthistorical artifact from the VietnamWar.

Inside look at an early knurled SIONICS 5.56mm silencer for the M16A1 rifle which features five of WerBell’s spiraldiffusers but no baffles or pressure relief valve.



Industry NewsContinued from page 9

The ruling upholds a December2000 decision by U.S. District judgeBerle M. Schiller of the Eastern Dis-trict of Pennsylvania.

Trying a different approach, GunIndustry Watch, a project of the anti-gun group, Alliance for Justice, hasasked the Federal Trade Commission(FTC) to expand its probe of biologi-cal weapons’ websites to include fire-arms.

At the beginning of the year, theFTC sent e-mails to a number of web-sites claiming to offer protection frombiological and nuclear agents andwarned them that it is illegal to makefalse claims about the health and safetyoffered by their products. The Gun In-dustry Watch letter claimed that gunmanufacturers should be held to thesame standards.

To justify her request, Alliance forJustice president Nam Aron, cited typi-cal anti-gun biased studies in her let-ter to the FTC’s director of consumerprotection, Howard Beales. “By thesestandards, gun manufacturers and re-tailers are in violation of the law anytime they claim that the purchase offirearms will help protect consumers.Scientific data indicates that a gun inthe home is 22 times more likely to beused in a suicide, accidental shooting,or homicide, than in self-defense,”Aron wrote.

Restrictions Reported On.50 Cal Rifle Exports

The Violence Policy Center saysit has been successful in influencingthe U.S. Department of State to restrictthe export of .50 caliber rifles for saleto civilians abroad. The anti-gun groupsays it has been working “closely” withReps. Henry Waxman (D-CA) and RodBlagojevich (D-IL), along with Sen.Dianne Feinstein (D-CA) to get a va-riety of restrictions placed on suchrifles.

Rep. Waxman recently sent a let-ter to U.S. Secretary of State ColinPowell commending Powell on hiswillingness to “offend the gun lobby.”

The letter notes representatives of theState Dept.’s Office of Defense TradeControls met with Waxman’s staff andnotified them that the Department hassuspended indefinitely further ap-proval of applications to export .50caliber rifles to foreign individuals orcommercial resellers in foreign coun-tries in light of the September 11th in-cidents.

Waxman’s letter went on to notethat applications to export seventy-five.50 cal. rifles were approved for ex-port to foreign dealers in 2001. Priorto the decision to suspend, 16 had beenshipped. The State Dept. later sus-pended the export of the remaining 59

rifles.

Banning Youth Guns

Flush with an apparent victory ininfluencing the imposition of export re-strictions on .50 caliber rifles, the Vio-lence Policy Center has issued a 21-page report, “A .22 for Christmas, Howthe Gun Industry Designs and MarketsFirearms for Children and Youth.”

“The gun industry promises that agun in a child’s hand is a shortcut toresponsibility and maturity. In fact, theonly guarantee is one of increased riskof death and injury,” states Martin Lan-gley, a VPC policy analyst and the



study’s author. “The firearms industryis attempting to secure their own sur-vival by endangering that of our chil-dren.”

Taking offense at statements suchas that appearing in the August 2001issue of Handguns magazine that,“Children are our salvation in the fightfor liberty and the preservation of theshooting sports,” the report complainsof the marketing of “an increasingnumber” of youth model firearms.

As “evidence” of the industry’scampaign to attract children to the “gunculture,” the VPC reports mentionsfirearms advertising in youth maga-zines such as Boy’s Life and the NRA’spublication of Insights magazine whichis edited for the younger set; the EddieEagle program which the study’s au-thor calls a “marketing tool disguisedas a safety program; using video gamesto put virtual guns in the hands of po-tential customers; and using publicschool wildlife management lessons todevelop interest in hunting and fire-arms.

The report further complains off i rearms manufacturers’ “open

acknowledgementof their cultivationof the youth mar-ket.” To back this upit uses quotes suchas that of Chr isJohnson, vp, RogueRifle Company, pro-ducer of a diminu-tive single shot .22caliber rifle: “It’s(the Chipmunk bolt-action rifle) a greatfather/son, father/daughter rifle be-cause children can’tcock the r if le bythemselves unt i lt hey ’ re seven o re ight yearsold...Christmas isimportant, but don’tforget about birth-days. Rimfires makegreat gifts all yearlong.”

The repor talso quotes from an“I’m the NRA” ad

featuring pro-gun actor Tom Selleckwhich promised, “Shooting teachesyoung people good things. Because allgood rules for shooting are good rulesfor life.” To counter this, the VPC re-port mentions several instances ofyouths shooting others or getting intohunting accidents. It also mentions therisk to youth of lead poisoning it saysshooting ranges pose.

In conclusion, the report calls forfederal law to be modified to make itillegal for anyone under the age of 18to possess a long gun and for anyoneunder 21 to possess a handgun, appar-ently under any circumstances. Thereport ends with a list of 40 youthmodel firearms produced by 20 manu-facturers “To show the scope of theeffort by the industry to market fire-arms to children.”

Extreme Shock Ammo

Among the most innovative newproducts to hit the market recently isExtreme Shock Ammunition. The lead-free NyTrillium composite product, iscalled “The world’s premier anti-ter-rorist round.”

The result of ten years of R&D ef-fort, the star-shaped composite bulletfragments upon impact and transfersenergy into the target at a faster ratethan conventional hollow-points. En-gineered to expend maximum energyinto soft targets, the bullet mass be-comes an expanding rotational cone ofNyTrillium matrix particles causingneurological collapse to the centralnervous system.

The expended bullet, however,does not fragment into razor sharp



pieces within soft tissue as some otherrounds are known to do, reducing therisks to EMS personnel. The expendedprojectile is typically contained withinsoft tissue targets. The round disinte-grates when it hits hard targets, suchas the interior walls of a dwelling andairplane skins.

For department training use, therounds’ lead-free construction elimi-nates hazardous waste issues and thefrangible characteristics reduce wearand tear on steel targets and lessenricochet hazards. Extreme Shock isavailable in a full range of rifle andhandgun calibers, in both full-powerand subsonic loads. For more informa-tion, call (877) 337-6772 or go to:www.extremeshockusa.com.

The Los Angeles Police Dept. hasselected TASER Int’l’s. ADVANCEDTASER M26 to replace older Tasertronunits. Some 500 units were ordered, toreplace 250 of the older devices. Thetotal expenditure is about $225,000.The units transmit electrical impulsesthat temporarily disrupt the body’s cen-tral nervous system.

“The LAPD was one of the mostsignificant users of earlier generationTASER technology, and probably hasmore field experience with it than anyother U.S. department,” commentedRick Smith, TASER’s CEO. “Their se-lection of our product as a less-lethalweapon platform should further accel-erate the adoption by other agencies.The advanced model is nearly fourtimes more powerful than LAPD’s pre-viously used TASER’s. The M26 hasbuilt-in laser sights and an onboarddata chip to record the time and dateof each firing to backup officers’ use-of-force reports.

In other news, quality handgunmanufacturer Kahr Arms has made theapproximately $20,000 commitmentneeded to join the Sporting arms &Ammunition Manufacturers Institutute(SAAMI). Counting Kahr, SAAMI’smembership now totals 23 producersof firearms, ammunition and propel-lants. SAAMI’s mission is to establishmanufacturing standards for smallarms and ammunition. T h e2001 firearms and ammunition excisetax total dropped to $175,959,000 inFiscal Year 2001 from Fiscal Year

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2000’s total of $197,840,000, accord-ing to the Bureau of Alcohol, Tobacco& Firearms.

Kathleen Townsend Kennedy,Maryland’s lieutenant governor, hasgiven the nod for the launch of ProjectHomeSafe, the firearms safety effort,to begin in her state. The program will

be run in cooperation with police andsheriff’s departments that will hand outfree firearms safety kits including acable-style gun lock and safety bro-chure. Project HomeSafe will sched-ule its “safety tour” truck to make stopsaround the state to provide safety edu-cation at the community level.

HEL 5.56mm Supressor for M16A1

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