Smith & Wesson 76 / MK 760

We are often asked these questions. Based on our own experiences, the first hand experiences of others and supported by information gleaned from postings on various boards, we offer the following points:

PLEASE, PLEASE DO NOT take any of the following as an indictment of any particular manufacturer!

Guns from all manufacturers can and do function very well. However experience (both our own and that of others) has shown that regardless of manufacturer, some guns do require some TLC to get them up and running properly. Experience has also shown that guns from certain manufacturers and / or made at certain times may require more intense TLC to get them up to par.

We strongly recommend that if at all possible the prospective buyer at least see the gun 'run' and preferably actually fire the gun. We know that this is often not possible but is none the less the "acid test" or "proof of the pudding" and goes for any firearm not just Smiths or MKs.

At the beginning of this section are links to other pages dealing with specific problems related to these guns. They should be reviewed as well since they provide additional information that might not be covered here.

The list presented here is based on our experiences, the first hand experiences of others and on information gleaned from postings on various boards. We see a definite pattern with these guns which relate to the various makers. The list runs in order of preference.

The first and the one that set the standard. In our humble opinion, the best of the breed.

Referred to as "Fruithurst Guns". Guns will be marked "Fruithurst, AL".
Started by Mike Ruplinger and Kenneth Domenick in 1983 after purchasing the manufacturing rights from Smith & Wesson. Used the trade name "MK Arms".

Sometimes referred to as "Panama City Guns". Guns will be marked "Panama City, FL".
Started by Kenneth Domenick in 1984 after splitting with Mike Ruplinger. Used the trade name "Global Weapons". This version of the S&W 76 clone used the model "76A1".

Referred to as "Irvine Guns". Guns will be marked "Irvine, CA".
Mike Ruplinger moved his operation to Irvine, California in 1984. He kept the "MK Arms" name. MK Arms also made semi-auto pistol and carbine versions. The serial number prefixes used were S (smg), C (carbine) and P (pistol). Full auto Irvine guns will be found with all 3 serial number prefixes. These were most likely machine guns made in-house from receivers intended for semi-autos. This was done in order to get as many machine guns registered as possible prior to the 1986 ban taking affect.

For the inspection and examination procedures listed below, we are referring to the guns made by Smith and Wesson ( S & W  )   in Springfield, MA. and the various guns of the MK 760 series made in the locations listed above. While MK Arms of Irvine, CA made semi-auto only carbine and pistol models, this page deals only with the select fire guns.

These checks are especially important as the great majority of 76s / 760s are used (or, if you prefer, pre-owned) guns and are not new-in-the-box.

A gun can receive proper care and still be well worn just as a nearly new one can look rough due to improper care or a total lack of care. While first impressions are important the inspection steps outlined below should be conducted to gain a more thorough idea of the condition of the firearm.

Rifling in the barrel:
Is the rifling sharp at the top of the lands or are the lands starting to round at the corners?

Rounding of the lands at the corners does show use and wear but is not a cause for great concern. Rounding of the whole top surface of the land is a point of concern. Rounded lands indicate many, many rounds have gone through the barrel. If no other problems are noted this barrel is OK for 'blaster' use and should be reserved for informal shooting sessions. For use in matches a new barrel is recommended.

Pitting in the barrel:
Is the bore bright and shiny or dull and rough looking?

Use of corrosive primed ammunition with out prompt and proper cleaning will result in rust pits in the barrel. Light 'salt & pepper' pitting will not affect functioning but it can affect accuracy. A 'salt and pepper' barrel is headed for the 'blaster' category.

Note:
For many, many years all ammunition was corrosive primed.  In the past, shooters understood the effects of corrosive priming and acted appropriately.  While 99% of today's 9mm ammunition is non-corrosive, odd lots of Egyptian military and perhaps some lots of Eastern European ammo do show up on ocassion. There is no great problem in using corrosive primed ammunition PROVIDED the gun in which it is fired is cleaned PROMPTLY and THOROUGHLY!  PROMPTLY means cleaned THE SAME DAY!!   THOROUGHLY means clean ALL PARTS not just the bore!!  THOROUGHLY also means using a bore cleaner formulated to disolve the potassium chloride salt formed by the combustion of corrosive primers. Most commercial bore cleaners available today are great for removing powder foulding but won't do a very good job of dissolving the potassium chloride salt. One of the best is the old reliable hot soapy water. Hot water dissolves the salt and the soap helps the hot water penetrate better. Dry the parts promptly then follow with your normal cleaning routine.

Bulge in the barrel:
Does the barrel slide out of the shroud freely?

A bulged barrel will not slide out freely and must be replaced. When looking down the barrel the bulge will appear as a dark ring inside the barrel. A bulged barrel is a BIG cause for concern. The barrel must be replaced.

If done properly using the right tools and equipment, the shroud can almost always be saved. The barrel is toast.

Barrel Shroud:
Are the serrations on the end of the shroud nut sharp and well defined?

Proper installation of the shroud requires that the shroud latch be depressed and not released until the shroud is fully tightened on the front of the receiver. Installing the shroud without doing this permits the shroud latch to wear against the serrations. Eventually both the latch and serrations become worn to such an extent that they lose their ability to stay in place. Vibration from firing will cause the shroud to unscrew. Functioning will suffer, often to the point of failing to fire because the barrel moves so far forward.

Worn serrations on the shroud indicate a lack of proper care (or perhaps knowledge) in disassembly / reassembly proceedures. This is cause for concern as the shroud and / or shroud latch will need to be replaced at some point.

Note:
The very early Smith & Wesson guns, the so called "Tool Room" guns, used straight knurling on the outer surface of the shroud nut and the shroud latch was a curved piece of spring steel with mating teeth on it. There will not be any serrations on the end of the shroud nut. The same points listed above still apply.

Firing pin in the bolt face:
Is the firing pin in the bolt face smooth, rounded, and symmetrical?

If it is mushroomed or flattened on the underside the bolt has fired many, many rounds and proper functioning may well be impaired. This is a BIG cause for concern as the bolt will need to be repaired or replaced, more likely sooner than later.

Gas erosion ring:
Is there a noticeable erosion ring around the firing pin from gas leaking past the primers?

A bolt with a gas erosion ring has fired a LOT of rounds. While the gas erosion ring in and of itself does not appear to adversely affect functioning it still indicates a great deal of use. Though minor in scale, this is cause for concern.

Bottom feed lip:
Is the bottom feed lip intact?

If so, is there a notch wearing into the feed lip? The feed lip MUST be present and good condition for the gun to function. With out the feed lip you have a single shot machine gun. The only way it will fire is by manually placing rounds into the chamber one at a time. When feeding from a magazine the rim of the cartridge will be caught by the firing pin and will not chamber. A missing or badly damaged feed lip is a BIG cause for concern. The bolt must be repaired or replaced.

Bolt handle:
Is the bolt handle actually a full auto style bolt handle?

The shorter bolt handle on top in the picture is for a semi-auto MK 760. It must be short to permit passage of the semi auto moveable firing pin behind the square end. While a short semi style bolt handle will "work" in a full auto gun, the short handle will wobble excessively and will result in severe scarring of the outside of the receiver where the handle moves back and forth in its slot.

We have seen several MK 760s with semi handles and everyone showed severe wear along the handle slot and eventually developed functioning problems. You are buying a full auto gun. It should have full auto parts.

Sear notch:
Is the sear notch battered and / or peened?

The sear notch MUST have the correct angle for proper and SAFE operation. After many, many rounds the notch will start to batter and peen and the angle will change. In severe cases the notch angle will change enough to permit the forward moving bolt to cam the sear down resulting in a run away gun. Excessive radius on the sear nose compounds the problem. See the section below on inspecting the sear.

A battered / peened sear notch, especially when coupled with an excessively rounded sear nose is a BIG cause for concern as it indicates a potential run away gun. The bolt (and possibly the sear) will need to be repaired or replaced.

Note:
The sear notch is located at the rear of the wide flattened underside of the bolt and just in front of the hole for the bolt handle. The notch at the rear of the bolt is merely a clearance cut for the sear to rise into with the bolt closed and is there to keep tension off of the sear spring. It allows the sear to come to a rest position so that the safety can be applied with the bolt closed thus preventing movement from the closed position.

Wash Boarding:
Does the wide flattened underside of the bolt have a rippled appearance?

This is caused by the sear nose rubbing on the underside of the bolt after the trigger is released in full auto fire or after the trigger bar has disconnected from the sear in semi auto fire. Since the sear is harder than the bolt, a minute (very minute) amount of metal is scraped away by the sear as it is in contact with the underside of the bolt waiting to intercept the bolt to end a firing cycle.

While wash boarding indicates that the gun has been fired a lot, it is only a minor cause for concern. Often, in ill-advised attempts to eliminate wash boarding, owners will round the sear nose - quite often to excess - which in turn leads to a run away gun. The sear nose should have a VERY small radius, just enough to remove any sharp edge at the sear nose, BUT NO MORE! See the section below on inspecting the sear for functional checks.

Note:
The bolt shown in the photo is still fully functional but definitely has more rounds behind it than ahead of it. This bolt came out of a gun that was in overall good plus / very good minus condition. There is no way to tell if this was the bolt originally installed in the gun when it left the factory. It does serve as an example of how bad a bolt can get and still work.

Is the hook on the extractor straight and sharp or showing heavy wear?

Proper extractor hook shape and condition is vital for proper functioning in the 76 / 760. If the extractor hook is not sharp and well defined the extractor will need to be replaced.

Does the extractor move freely in its slot?  Often the extractor slot and the coils in the extractor spring become gummed up with firing residue which impedes free movement of the extractor. In severe cases enough gunk can build up in the slot that the extractor is held in an elevated position and can't grip the case rim properly.

Note:
The extractor, extractor spring and extractor pin are wear parts. As such they will need to be replaced periodically.

Is it straight or does it have a kink?

While we have seen lightly kinked recoil springs function just fine keep in mind that once a spring kinks, it will not straighten out. Kinked springs are not like fine wine. They do not get better with age. The spring must be straight for proper operation. If the recoil spring is kinked we recommend replacing it or at least having a spare available.

Note:
The recoil spring is a wear part. It will need to be replaced periodically.

Is the front end smooth and evenly tapered / rounded or is it distorted?

A distorted guide will not permit the coils of the recoil spring to feed smoothly over it. Functioning will be impaired. In severe cases the gun will not function at all. If the recoil spring guide is not smoothly rounded / tapered it will need to be replaced. This is definite cause for concern.

Note:
The recoil spring guide is a wear part. It will need to be replaced periodically.

Is the back angled edge of the ejector still flat on top or is it wearing down where the flat left underside of the bolt rides up over it?

Wear in this area is usually a minor cause for concern unless it reaches the point that the wear approaches a quarter to a third of the thickness of the ejector. Wear here does serve to show that the gun has been fired a lot.

Is the front inside corner of the ejector square and sharp or is there a notch there?

EVERY original 76 / 760 we have examined has a notch in the front inside corner of the ejector. The very point that must firmly contact the case head to flip the fired case out of the gun. NO ONE, repeat, NO ONE has ever been able to give us a viable, sound engineering reason for the ejector to have that notch. The notch has the effect of delaying ejection. By welding up the notch as shown in the photo ejection actually starts sooner thus giving more time for the spent case to clear the ejection port. The shop gun as received ran about 85% +/- due to ejection issues. By welding up the notch, problems with ejection were significantly reduced and the gun is now in the 98% - 99% range.

Obviously there are 76s and 760s that run just fine with the notch in the ejector. Is the notch a cause for concern? Only if it causes ejection problems. The only way to be sure is to test fire the gun.

None the less, we would very much like to meet and talk to someone, anyone, who can tell us why that notch is there in the first place and be able to CONCLUSIVELY demostrate that it is necessary for proper functioning.

Note:
The ejector is welded into the left side of the receiver and is not a user serviceable part.

Do the levers click into place firmly?
Move the selector through its arc. You should feel the detents click into and out of the dimples in the trigger housing.

Does the shaft turn freely but not wobble in its hole?
Move the selector through its arc. You should be able to easily turn the selector but the tolerances of the shaft holes in the trigger housing should be such that the shaft does not wobble or wiggle in any direction.

Does the SAFE position prevent bolt movement in both open and closed positions?
Put the selector on SAFE. If the bolt is closed, it should not cock. If cocked, it should not close. Some trigger movement is OK but in no case should the trigger movement be more than just a tiny fraction of an inch.

Does the SEMI position produce semi-automatic fire?
Put the selector on SEMI. While controlling the bolt so that it eases forward but doesn't slam, pull the trigger and hold it back. You should hear and feel the trigger bar drop out of it's notch in the sear and hear / feel the sear rotate upward to intercept the bolt. Carefully ease the bolt fully forward then pull it back. The sear should catch and hold the bolt. Releasing the trigger will reset the mechanism and you can repeat the process. You should repeat this action several times.

Does the FULL position permit full auto fire?
Put the selector on FULL. While controlling the bolt so that it doesn't slam forward, pull the trigger and hold it back. There should be NO sound / feel of the trigger bar disengaging from the sear. Ease the bolt forward then pull it back. The bolt should remain under spring tension and should run freely back and forth until the trigger is released. You should repeat this action several times.

Does the trigger "TICK"?
While performing the FULL auto check there should be NO contact between the moving bolt and sear as long as the trigger is held back in the fire position. If the sear is not being depressed fully enough, even with the trigger all the way back a 'tick' or slight pulse will be felt in the trigger as the bolt moves forward and cams the sear down.

Failure of ANY of the above checks is a BIG cause for concern and indicates the trigger group needs attention and/or repair. More likely sooner than later.

Place the selector in SEMI. Use one hand to hold the gun by the magazine well. With the other hand pull the bolt ALL the way back and release it. The sear should intercept the bolt and keep it from running forward. Repeat the test several times.

Place the selector in FULL. Again, with one hand holding the gun by the magazine well, use the other hand to pull the bolt ALL the way back and release it. Once again, the sear should intercept the bolt and keep it from running forward. Repeat the test several times.

These tests replicate the impact between the sear notch on the bolt and the sear during actual firing. If the sear doesn't catch the bolt properly a run away gun will result. While a run away can be an exhilarating experience it is NEVER recommended and is ALWAYS DANGEROUS!

FAILURE OF THE SEAR TO INTERCEPT THE BOLT IS A HUGE CAUSE FOR CONCERN!

DO NOT LIVE FIRE THIS FIREARM UNTIL REPAIRS HAVE BEEN MADE AND INSPECTION CHECKS PASSED!

Failure of the sear to intercept the bolt can be caused by excessive radius on the sear nose, improper angle of the sear nose, a badly worn sear notch on the bolt, or a weak / broken / missing sear spring or a combination of these factors. Improper geometry of the sear nose permits the sear notch on the bolt to cam the sear down and over ride the sear resulting in a run away gun.

Dose the sear have (a) excessive radius, (b) improper angle of the sear nose? The nose of the sear should be square with the bottom of the sear and the upper point should have only a tiny bevel or radius just sufficient to remove any sharp edge BUT NO MORE. Improper geometry of the sear nose permits the sear notch on the bolt to cam the sear down and over ride the sear resulting in a run away gun.

Does the nose of the trigger bar have the proper shape or is it excessively radiused?

As explained above, excessive radius on either the trigger bar nose or sear nose are BIG causes for concern and if present, the gun will most likely have already failed the checks outlined above.

Are the holes for the receiver plug pin round and and without peening?

The vertical receiver plug pin is the only thing that keeps the bolt, recoil spring, spring guide, and receiver plug in the gun. This pin takes all the force of the bolt at the end of its rearward stroke. Excessive force, particularly for an extended period of time will result in the pin holes becoming egg shaped. A raised burr will start to from on the rear edge of the holes.

Slightly oval shaped, very lightly peened plug pin holes show that the gun has most likely fired either a LOT of rounds, been fed a steady diet of hot ammo, or used with a weakened recoil spring. Perhaps a combination of these causes are at fault here. A large number of rounds coupled with hot ammo and a recoil spring weakened by use and age presents a reason for concern.

If careful examination under magnification shows only very slight elongation and / or peening of the holes and DOES NOT reveal any cracking of the receiver tube between the holes and the end of the receiver, then concern should be minimal.

If ANY fracture lines are seen this is a HUGE CAUSE FOR CONCERN!

DO NOT FIRE THIS WEAPON UNTIL THE RECEIVER HAS BEEN PROPERLY REPAIRED!

Normally you will only get one magazine with your gun. Should you be fortunate enough to get more, you will still need to verify that all of them latch properly in the magazine well and do not move excessively once latched in position. Proper magazine fit is a field unto itself. Please refer to the magazine page 76 / 760 Magazines for a more detailed discussion of this topic.

The stock wobbles. No need to even ask the question. For an explanation of why the stock wobbles and the reasons that not much can be done about it please go to the stock section on our 76 / 760 FAQ page.

The Smith & Wesson 76 / MK 760 submachine guns are simple weapons. None the less, each and every component must be in its proper position and in proper working condition for the gun to operate as it should. Get one part out of position or out of specification and improper functioning results. Sometimes this is simply aggravating. Other times it is decidedly DANGEROUS!

While you may be lucky enough to find a New-In-The-Box 'Safe Queen' the great majority of the 76s / 760s out there have been used. Some of them gently used and cared for properly. Others may not have been so lucky. They may have been WELL used and not given even modest care. Unless you personally know the current owner (and all of the previous owners) you really have no way of knowing the history of the gun you are inspecting. By performing the checks outlined above one can get a good idea of the mechanical condition of the gun undergoing inspection.

All of the deficiencies listed above are repairable either by replacing parts or by having welding and machine work done by a competent gunsmith. Should deficiencies noted above have an impact on the selling price? In our humble opinion, yes. Keep in mind that the Class 3 market operates on a fixed inventory. Ultimately you must decide whether a particular gun is worth the asking price plus the cost of repairs.