Our cover gun this is­sue was born from a mis­com­mu­ni­ca­tion. Al­legedly. Ac­cord­ing to com­pany lore, a SIG rep­re­sen­ta­tive, on a busi­ness trip to the place where Great Bri­tain used to be, was asked by a cer­tain Army unit what the short­est-bar­rel op­tion was for the MCX, as they wanted some­thing small enough to fit inside the glove­box

of a BMW, while still cham­bered in a ri­fle cal­iber. Due to a com­bi­na­tion of jet­lag, a strong Bri­tish ac­cent, and, no doubt, the

Brit mil­i­tary propen­sity for at­tempt­ing to drink every­one un­der the ta­ble, the rep be­lieved his in­ter­locu­tor to have re­ferred to the 9mm MPX, which he said can in­deed ship with a 4.5-inch tube in its most trun­cated form. “Al­righty then!” pro­claimed our transat­lantic brother. “We’ll take a bunch of them. Oh, and it’s your round.” It wasn’t un­til his re­turn to New Hamp­shire that the mis­un­der­stand­ing was re­al­ized, but by that time the engi­neer­ing team had al­ready ac­cepted the chal­lenge of mak­ing the world’s small­est se­lect fire ri­fle.

Now, the pre­ced­ing ac­count may or may not be true, but why let the truth stand in the way of a good story? We’ll let you be the judge of its like­li­hood, but there’s not much point in in­cur­ring the de­vel­op­ment costs in­volved in chop­ping down the al­ready pe­tite

MCX, un­less there’s a real op­er­a­tional need from a le­git end user. Go­ing from a 9-inch to a 5.5-inch bar­rel re­quires more than just bust­ing out the an­gle grinder and hack­saw.

We at­tended the launch of the civil­ian ver­sion of the Rattler last year, but we’ve in­sti­tuted an ed­i­to­rial pol­icy that no gun from a ma­jor man­u­fac­turer will be eval­u­ated un­til it’s in fi­nal pro­duc­tion for­mat. There are al­ways prob­lems in go­ing from the lim­ited run, hand­made guns you’ll find at a me­dia event to the ver­sion that ends up on the shelves of your lo­cal gun store. While we ap­pre­ci­ate the op­por­tu­nity to get hands on as early as pos­si­ble, it’s un­usual for there not to be changes made

be­tween first show­ing and re­tail. You’ll find cov­er­age of new prod­uct launches at Re­ and RECOILtv, but we’ll re­serve full re­views in print for the fin­ished prod­uct.

In its cur­rent for­mat, the Rattler is of­fered in two con­fig­u­ra­tions, namely a fac­tory SBR with folding stock and a pis­tol with a col­lapsi­ble brace, both cham­bered in 300 Black­out. We re­quested the pis­tol ver­sion, as it’s trans­fer­able as a Ti­tle 1 firearm and can be car­ried across state lines with­out a, “Mother May I?” let­ter from the BATFE.

At last year’s launch event, SIG per­son­nel in­di­cated that the ver­sion spec’d across the pond would also be avail­able, but thank­fully, san­ity has pre­vailed for the US mar­ket, and the 5.56 op­tion is not cur­rently cat­a­loged. We can’t think of a prac­ti­cal ap­pli­ca­tion of a 5.5-inch bar­reled 5.56 gun, un­less the idea is to si­mul­ta­ne­ously deafen your op­po­nent while set­ting him on fire. Then again, we’ve run a 12inch .308 in three-gun competition this year, so per­haps they’re onto some­thing.


The Rattler is a short-stroke, pis­ton­driven semi­auto, feed­ing from fa­mil­iar STANAG-pat­tern box mag­a­zines. De­signed to of­fer bet­ter bal­lis­tic per­for­mance than a sub­ma­chine gun, but from a smaller pack­age, it fea­tures a two-po­si­tion gas reg­u­la­tor for use with a sup­pres­sor, full-length M1919 top rail, and free-float­ing hand­guard.

The MCX plat­form on which the Rattler is based went through some pretty sig­nif­i­cant changes last year in or­der to reach a 20,000 round ser­vice life, and the tiny ri­fle ben­e­fited from

most of them. Tak­ing cues from Knight’s Ar­ma­ment and their E3 bolt, the SIG part now has rounded, ta­pered lugs, rather than the orig­i­nal Stoner-pat­tern square num­bers. This elim­i­nates stress ris­ers and largely pre­vents the fa­mil­iar AR-15 fail­ure point at the lugs clos­est to the ex­trac­tor. There’s an ad­di­tional safety fea­ture as well, in the form of a fir­ing pin block ac­tu­ated by the ham­mer, so if you’re in the habit of drop­ping your ri­fle muz­zle down it’ll go clunk, rather than bang.

An­other sig­nif­i­cant ad­vance was the adop­tion of a two-stage trig­ger, which felt very much like the ex­cel­lent Geis­sele SSA. Un­for­tu­nately, this has not been car­ried over to the Rattler. Our test gun has one of the worst GI-style bang switches we’ve en­coun­tered in the past few years; gritty, notchy, and break­ing at around 9 pounds. It’s a real let­down on a gun that’s sup­posed to re­tail for al­most 3 grand.

The Rattler does, how­ever, re­tain its par­ent’s anti-wear fea­tures, such as re­place­able, hard­ened steel cam track re­in­force­ment and feed ramps, as well as steel pins where the charg­ing han­dle latches make con­tact on the up­per re­ceiver. The bar­rel is re­place­able at the user level, re­tained by two Torx-headed cross bolts. Com­pared to an AR-15, there’s a def­i­nite feel­ing of so­lid­ity and longevity to the MCX up­per, like it’s de­signed to last a cou­ple of life­time’s worth of hard use. Which it should, given the price dif­fer­ence.

The Rattler’s hand­guard locks into the up­per by means of two grooves cut into the sides, be­low the Pic rail, and is se­cured in place by a lug

cap­tured by the front take­down pin. It’s a neat sys­tem lend­ing it­self to swap­ping out com­po­nents at will, if you’re pre­pared to live with a large gap in front of the gas block — other MCX hand­guards are de­signed around sen­si­ble-leng th bar­rels.

One as­pect of the hand­guard’s con­struc­tion we didn’t much care for, how­ever, was its in­abil­ity to ac­cept most non-SIG sup­pres­sors. Its inside di­men­sions are just a hair smaller than the 1.5-inch out­side di­am­e­ter of many di­rect-thread cans, while the po­si­tion of the bar­rel’s ta­pered shoul­der means the sup­pres­sor has to en­ter the hand­guard in or­der to tighten. One can we found to be a half­way de­cent op­tion for those want­ing to run subsonic ammo only was Si­lencerCo’s Osprey 45K, which when turned up­side down looks like it was made for just this ap­pli­ca­tion. While it’s hear­ing safe, it doesn’t have the kind of Hol­ly­wood-quiet lev­els of sup­pres­sion you might ex­pect from a 300 BLK, as the bore is sized for wider pro­jec­tiles.


The ques­tion fore­most in our mind when we headed to the range was what sort of per­for­mance com­pro­mise did we have to make in or­der to use this ridicu­lously small pack­age. Although 300 BLK was de­vel­oped with short bar­rels in mind, the AR-15 wasn’t, and our per­cep­tion of tiny ri­fles pre­tend­ing to be pis­tols has been col­ored by ex­pe­ri­ence with them. While it’s en­tirely pos­si­ble

to get 7.5-inch bar­reled di­rect im­pinge­ment guns to work, it’s a case of not much, not of­ten. Short-stroke pis­ton op­er­a­tion is an­other mat­ter, and as SIG man­aged to get the 9mm MPX to run re­li­ably us­ing this sys­tem, we were hop­ing their engi­neer­ing mojo had car­ried over to its big brother.

Bot­tom line up front: This isn’t a be­gin­ner’s gun.

There are cer­tainly some firearms that the owner can shoot as a novice and will never out­grow. A sup­pressed 22LR, for ex­am­ple. Hell, for that mat­ter, a good 22, whether it has a can or not. But there are oth­ers passed off as ideal for the new gun owner by idiots who have no busi­ness dis­pens­ing ad­vice. A good ex­am­ple of this would be any­one rec­om­mend­ing a J-frame Smith to a novice fe­male CCW can­di­date, a prac­tice that reeks of con­de­scen­sion in the worst way.

The Rattler falls into the lat­ter cat­e­gory — it’s a spe­cial­ist weapon de­vel­oped for spe­cific cir­cum­stances for a set of dudes who spend a lot time prac­tic­ing to shoot bad guys in the face at close range. If you want a semi­auto to serve in as many dif­fer­ent sce­nar­ios as pos­si­ble — the kind of gun that will al­ways be a solid choice no mat­ter if the job en­tails de­fend­ing home and hearth, putting meat in the freezer, or go­ing up against your bud­dies in a friendly competition at the range, then a 16-inch-bar­reled black ri­fle of what­ever’s your fa­vorite fla­vor will never be a bad choice.

The Rattler is not that gun. That said, if you trust your­self not to place your sup­port hand any­where other than on the very lim­ited amount of sur­face area im­me­di­ately in front of the mag­well, it’s a frickin’ riot. You too can ben­e­fit from the engi­neer­ing prow­ess of a ma­jor firearms man­u­fac­turer that was tasked with cre­at­ing the small­est pos­si­ble ri­fle for a tiny group whose lives de­pended on it. If you have a ten­dency to go full Costa on any long gun you shoul­der, well that would be a self­cor­rect­ing prob­lem. There’s quite lit­er­ally no room for er­ror, and should you make the mis­take of grab­bing the fore end just a teensy bit north of where you should, at min­i­mum es­cap­ing gasses will tear meat from bone; oth­er­wise, you’ll get that ben­e­fit, plus a .30 cal­iber hole where it shouldn’t be.

Now that we’ve been all pa­ter­nal and re­spon­si­ble — oh, and get a hand stop, kids — how does it ac­tu­ally per­form? Recoil is sur­pris­ingly soft. Ejec­tion is to the 3 o’clock po­si­tion when shoot­ing su­per­sonic rounds with­out a sup­pres­sor, and the low re­cip­ro­cat­ing mass doesn’t dis­turb the sight pic­ture as much as you’d ex­pect from a short-bar­reled AR.

One of the met­rics we use when as­sess­ing reli­a­bil­ity in this cal­iber is whether the gun will run when un­sup­pressed and fed subsonic am­mu­ni­tion. With­out back­pres­sure from a can, there’s usu­ally in­suf­fi­cient gas vol­ume and pressure to cy­cle the ac­tion, but in this case it seemed to work just fine. We did en­counter a cou­ple of fail­ures to lock back the bolt on an empty mag­a­zine, but no fail­ures to feed or eject were ap­par­ent. It’s no­table that de­spite the re­duc­tion in ve­loc­ity from the short bar­rel, subsonic bul­lets were ad­e­quately sta­bi­lized. Go­ing to a 1-in-5 twist bar­rel (no, that’s not a mis­print) spins the lanky heavy­weights fast enough to keep them point­ing the right way. Ac­cu­racy hov­ers around 3 MOA with fac­tory ammo, a num­ber we think could be im­proved upon, were it not for that god-aw­ful trig­ger.

As a home-de­fense weapon, the Rattler with a short, 300 BLK sup­pres­sor would be hard to beat. It’s short enough to eas­ily ma­neu­ver around fur­ni­ture, won’t blow out your eardrums should you have to use it indoors, has 30 prob­lem solvers on hand, and de­liv­ers enough on-tar­get en­ergy to en­sure prob­lems stay solved. It’s also a great op­tion in its in­tended role that of a com­pact, “get the f*ck off me” gun for ve­hi­cle pas­sen­gers in low-vis op­er­a­tions. It’ll never re­place a 16-inch bar­reled car­bine as a do-all ri­fle, but it’s sur­pris­ingly ca­pa­ble, de­spite the spe­cial­ized niche for which it was de­signed.

The Rattler would be even more com­pact with a side folder, which would be our pref­er­ence.

With the third in­ter­pre­ta­tion of the ATF’s po­si­tion re­gard­ing arm braces still in ef fect, we won­der why any­one would go to the trou­ble of fil­ing a Form 1. Thank­fully, SIG steered clear of the temp­ta­tion to thread the Rattler’s muz­zle in some...

Two po­si­tion gas pis­ton throt­tles back car­rier speed when deal­ing with a can. This Gemtech al­most fits, but needs a shim set to avoid bot­tom­ing out on the hand­guard.

Legacy MCX car­rier group top, Rattler be­low. Note shor tened car­rier ex­ten­sion due to gas pis­ton lo­ca­tion and ramped bolt lock­ing sur faces.

Pic rail and MLOK make the most out of lim­ited ac­ces­sor y space.

Field strip­ping is ver y straight­for ward and should be sec­ond na­ture to any­one who’s ever main­tained an AR. No need to strip BCG to this level for rou­tine clean­ing, as pis­ton op­er­a­tion keeps it fairly clean.

See that sling loop pok­ing out? It’s an­noy­ing as [email protected] and should be the first tar­get of your trusty Dremel.

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