A hun­dred ways to repli­cate a mil-spec M4 car­bine from scratch

In re­cent years, repli­cat­ing ser­vice ri­fles has be­come one of the hottest trends for both mil­i­tary col­lec­tors and firearms en­thu­si­asts alike. Some wish to recre­ate the weapon that they were is­sued while serv­ing in the mil­i­tary while oth­ers sim­ply want to clone a fa­vorite ri­fle vari­a­tion that they’ve seen used by our na­tion’s armed forces. Re­gard­less of the rea­son, choos­ing which ri­fle to repli­cate is the first step.

Fans of the AR-15 plat­form have more than a few choices as far as which di­rec­tion to go. Be­ing Amer­ica’s front­line weapon for go­ing on five decades, the Ar-type ri­fle has been mod­i­fied by the mil­i­tary ev­ery which way to serve a va­ri­ety of pur­poses. From the length­ened and ac­cur­ized Navy Mk12 to the com­pact and ag­ile CQBR, each dif­fer­ent type of Ar-style weapon has a fas­ci­nat­ing his­tory.

One of the most widely used carbines in the U.S. mil­i­tary is the M4. De­vel­oped over years but fi­nally of­fi­cially adopted by the U.S. mil­i­tary in 1994, the M4 is essen­tially a short­ened ver­sion of the M16. Tread­ing the mid­dle ground be­tween the per­for­mance of a longer ri­fle and the ag­ile com­pact­ness of a close-quar­ters bat­tle sub gun, the M4, with its 14.5-inch bar­rel and col­lapsi­ble stock, be­came the do-all car­bine of choice. Since it first went into ser­vice, the M4 it­self has it­self given birth to many a vari­ant.

Clone Build­ing

Be­fore we delve any deeper, let us clar­ify that when we use the term “clone,” what we mean is to repli­cate, within rea­son, the de­tails, at­tach­ments, accessories and com­po­nents of a ser­vice weapon that was used by the mil­i­tary at a par­tic­u­lar point in time. Just how ac­cu­rate you want to get is up to your bud­get and parts pro­cure­ment skills.

Some clone builders are stick­lers for the fine de­tails, and to them we tip our hats. We, on the other hand, are more for­giv­ing and will make do with what we can get that’s within

our bud­get and ca­pa­bil­ity. How­ever, there’s a cer­tain sat­is­fac­tion about get­ting the de­tails just right or luck­ing out and find­ing an old out-of-pro­duc­tion part to com­plete your build.

M4 and Vari­ants

The M4 is cham­bered to ac­cept 5.56x45mm NATO cal­iber rounds and features a 14.5-inch bar­rel with a 1/7 twist rate. The most com­mon round it em­ploys is the 62-grain M855. Orig­i­nally de­vel­oped and man­u­fac­tured by Colt for the mil­i­tary, it is has a col­lapsi­ble butt­stock and its most ba­sic ver­sions fea­ture a flat-top, Pi­catinny-railed re­ceiver and a de­tach­able carry han­dle as well as a plas­tic hand­guard. Nearly a decade into the 2000s, the U.S. Army fi­nally took over own­er­ship of the de­sign and em­braced other com­pa­nies such as FN Her­stal to sup­ply the M4 as well. The M4 features a semi-auto fir­ing mech­a­nism that can also be switched to fire three­r­ound bursts. An M4A1 vari­ant has also been used since 1994, ini­tially mainly with special op­er­a­tion units. In­stead of a three-round burst op­tion, it has a full-auto-ca­pa­ble trig­ger. Other dif­fer­ences over the orig­i­nal M4 com­pared to an up­dated M4A1 in­clude a heav­ier pro­file bar­rel and a heav­ier H2 buf­fer. Other M4 vari­ants ex­ist, but for the pur­pose of this ar­ti­cle, we’ll fo­cus on th­ese two.

Accessories found on an M4 may vary widely and de­pend on fac­tors such as the time pe­riod in which it was is­sued, the mil­i­tary branch and unit it was is­sued by, and the in­di­vid­ual end user’s per­sonal setup. For th­ese rea­sons, M4s can dif­fer from one an­other, even those is­sued at the same time and in the same unit. That said, M4 clones and their accessories would nat­u­rally dif­fer as well. That fact might drive some purists nuts, but for oth­ers, it’s this lee­way that makes build­ing an M4 more en­gag­ing. Be­ing able to set up an M4 how you want it within the con­fines of what was is­sued is an in­ter­est­ing prospect.


U.S. Special Op­er­a­tions Com­mand added more M4 vari­ants when they de­vel­oped an en­hanced kit for use with Special Forces units. Com­monly called SOPMOD, which stands for Special Op­er­a­tions Pe­cu­liar Mod­i­fi­ca­tion, the kit is based on an M4A1 car­bine and adds to it a se­lec­tion of accessories that in­cludes a Knights Ar­ma­ment Com­pany (KAC) Rail In­ter­face Sys­tem (RIS) railed fore­arm, an M68 Close Com­bat Op­tic (which is mil­i­tary speak for an Aim­point Compm2 red dot op­tic com­monly seen mounted in a Wil­cox M68 30mm op­tic mount), a KAC 300m back-up iron sight, KAC NT4 sound sup­pres­sor, a Tri­ji­con ACOG TA-01NSN 4x op­tic, an In­sight Tech­nolo­gies AN/PEQ-2A laser des­ig­na­tor, and an op­tional 9-inch-bar­rel M203 grenade launcher.

The SOPMOD pro­gram was de­vel­oped to al­low Special Op­er­a­tions warfight­ers to con­fig­ure their weapons to suit their in­di­vid­ual needs as well as par­tic­u­lar mis­sion re­quire­ments. The afore­men­tioned kit has since been up­dated and is now known as the SOPMOD Block I kit.

As SOPMOD kits fur­ther de­vel­oped over time and newer accessories were in­cluded, Block I

“how ac­cu­rate you want to get is up to your bud­get and parts pro­cure­ment skills.”

kits were up­dated on the fly, re­sult­ing in what some peo­ple call “Block 1.5” kits. This run­ning up­date phased in Daniel De­fense M4A1 RIS II and RIS II FSP, full-length railed hand­guards, a low-pro­file gas block, an Eotech 553 HWS op­tic, and more. A fi­nal­ized SOPMOD Block II kit was even­tu­ally de­vel­oped and gives users the op­tion of us­ing an El­can Spec­terdr 1-4x Scope, AN/PEQ-15 Ad­vanced Tar­get Pointer Il­lu­mi­na­tor Aim­ing Laser (ATPIAL), and other accessories.

“the M4 be­came the do-all car­bine of choice.”

Get­ting Started

Colt, be­ing the orig­i­nal man­u­fac­turer of the M4, has an ad­van­tage over other com­pa­nies that also of­fer M4-style ri­fles or up­per re­ceiver as­sem­blies. It is said that Colt’s LE6921 Law En­force­ment Car­bine is as close as you can get to buy­ing an M4 di­rect from the com­pany—the major dif­fer­ence be­ing that it has a semi-auto trig­ger group and that its bar­rel isn’t the ex­act same pro­file as that of the M4.

FN Her­stal also of­fers a com­plete M4-style ri­fle un­der their Mil­i­tary Col­lec­tor se­ries. If you’re look­ing to build your own M4gery from the ground up, com­pa­nies such as BCM and Mid­way USA’S AR Stoner also of­fer M4-style up­pers at a con­sid­er­able sav­ings. Just use a forged lower of your choos­ing and get build­ing. Is­sued M4s com­monly use a full-auto bolt car­rier group, stan­dard A2 pis­tol grip, Mil­spec buf­fer tube ex­ten­sion and M4 col­lapsi­ble stock. The rest is up to your in­ter­pre­ta­tion.

A quick word about bar­rel se­lec­tion: To many, M4 clones must be as­sem­bled with 14.5-inch bar­rels. To oth­ers, it doesn’t mat­ter much and a 16-inch bar­rel will suf­fice. That’s a call you’ll need to make when you build your car­bine. When pos­si­ble, we rec­om­mend choos­ing a qual­ity M4-pro­file bar­rel with a 1/7 twist that’s

It’s also good to re­mem­ber that 14.5-inch length bar­rels like the one that comes with the LE6921 should be pinned and welded with a muz­zle de­vice that’s long enough to bring it to an over­all length of at least 16 inches to be in com­pli­ance with the National Firearms Act (Nfa)—un­less you plan to SBR it, that is.

The Forg­eries

We took the lib­erty of build­ing sev­eral dif­fer­ent M4 replica builds based on our re­search of mil­i­tary-is­sued ver­sions. As you can see, they each dif­fer from one an­other. The parts for th­ese builds were sourced both from what is currently avail­able at stores as well as what we found on­line from scour­ing the sec­ond-hand mar­ket.

As you may have no­ticed, many M4s are fit­ted with Kac-railed hand­guards. It’s worth not­ing that al­though th­ese rails mostly look the same, there are two dif­fer­ent ver­sions: the RIS and the Rail Adapter Sys­tem (RAS). The RIS is the older ver­sion of the two and due to how it is mounted is known to ro­tate ever so slightly when torqued is ap­plied. Un­like the newer RAS, it can fit heavy pro­file bar­rels. The RAS on the other hand, also due to how it’s mounted, is much more sturdy and will not ro­tate. It can­not ac­com­mo­date heavy bar­rels how­ever. We went with the RAS ver­sions. The equip­ment ex­change on on­line fo­rums such as Ar15.com and M4­car­bine.net, as well as auc­tions on Gun­bro­ker.com, were great re­sources for us to find parts for our builds. But as with all sec­ondary mar­ket pur­chases, re­mem­ber that it’s a buyer be­ware sit­u­a­tion. Our two cents is be care­ful of “too good to be true” deals.

Worth the Ef­fort

Soon after we com­pleted our M4gery builds, we headed to the range to have some fun with them. The process took plenty of re­search and parts gath­er­ing, but we feel that it was well worth the time and ef­fort. The only prob­lem we have now is that since com­plet­ing our M4geries, the clone-build­ing bug has re­ally bit us hard. Lucky for us, there are plenty more vari­ants out there… which one’s next?

M4 clones come in many dif­fer­ent vari­a­tions. The two M4 look-a-likes shown above ac­tu­ally use 16-inch AR Stoner bar­rels, which are tech­ni­cally in­cor­rect since real M4s use 14.5-inch bar­rels.

Above: This M4 clone re­flects many of the mod­i­fi­ca­tions im­ple­mented with SOPMOD Block I kits.

Right: A col­lapsi­ble M4 stock and Mat­ech rear flip-up back up iron sight are com­mon to find on real M4s and their repli­cas.

The SOPMOD pro­gram calls this red dot the M68 Close Com­bat Op­tic. The M68 is an Aim­point Compm2 red dot that is com­monly mounted in a Wil­cox M68 30mm op­tic mount.

An M4 pro­file bar­rel has a re­cessed con­tour that fits the mount for an M203 grenade launcher. Note the ex­tended A2-style flash hider per­ma­nently at­tached to the 14.5-inch bar­rel to keep the gun NFA com­pli­ant.

The LMT M203 launcher seen be­low features a 37mm, 12-inch bar­rel. Au­then­tic M203-equipped M4s com­monly uti­lized a shorter 9-inch bar­rel in­stead.

been mag­netic par­ti­cle tested and chrome lined for best per­for­mance re­sults. Mis­sion adapt­able accessories for SOPMOD kit M4s in­clude mul­ti­ple choices of op­tics, lights, lasers and grenade launch­ers. This al­lows clone builders a wide va­ri­ety of...

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