For questions relating to specific aspects of the 76 / 760 please go to the appropriate pages.
For GENERAL QUESTIONS, please go to our FAQ page:
76 / 760 FAQ.
For MAGAZINE PROBLEMS, please go to our magazine page:
76 / 760 Magazine Problems.
For INSPECTION & EXAMINATION, please go to our inspection page:
76 / 760 Inspection.
A blow-back submachine gun such as the Smith 76 / MK 760 is simple machine. None the less, each and every
component must be in its proper position and in proper working condition for the machine to operate as it
should. Get one item out of position or out of specification and improper functioning results.
The following Troubleshooting Guide is intended as an aid in diagnosing the most common problems with the
Smith 76 / MK 760. It provides a place to start and gives the most likely cause of and fix for these problems.
Keep in mind that isolated malfunctions can and do happen. Frequent malfunctions are symptoms of something
being "not right" and the final underlying cause(s) may require further digging beyond what is listed here.
It is divided into sections dealing with specific types of problems.
FEEDING PROBLEMS
| Problem: |
Cause: |
What's Happening & Why: |
Correction: |
|
Bolt catches round in the middle:
|
Magazine is too low in the receiver.
Magazine feed lip(s) bent inward. |
The left magazine lip should be about 1/16" +/- (about the thickness of a
dime) below the ejector. Any lower and the bolt can miss the round,
any higher and the bolt may strike the back of the right magazine lip.
Bent lips position the cartridges too low to make the transition up the feed ramp and into the chamber.
|
Replace magazine catch.
Replace magazine latch plate.
Straighten and reshape feed lip(s)
Replace magazine |
| Round "nose dives" into feed ramp:
|
Magazine is too loose in mag well.
Magazine is too low in the receiver.
|
Magazine has too much fore and aft play and is pivoting on the magazine catch as the off hand pulls backward
on the magazine to counter muzzle rise when firing. Thus points the nose of the round downward.
See above.
|
Thicker front pad on magazine.
Shim front of mag well.
See above.
|
| Cartidge rim catches under firing pin:
|
Lower feed lip on bolt is heavily worn, badly damaged or missing.
|
The lower feed lip keeps the head of the cartridge away from the firing pin until the round is seated in
the chamber lining it up with the recess in the bolt face. Heavy wear or damage to the lower feed lip
allows the rim to catch under the firing pin and stop the round from feeding.
|
Repair or replace bolt. |
EXTRACTION & EJECTION PROBLEMS
| Problem: |
Cause: |
What's Happening & Why: |
Correction: |
|
Fired cases "stove pipe":
|
Extractor hook is worn or broken.
Extractor spring is weak.
Crud in extractor slot.
Weak ammo.
|
Gas pressure will blow the case from the chamber, but a good extractor is needed to hold the case so
the ejector can kick it out of the ejection port.
Springs have a finite life and weaken with use. A weak spring allows the spent case to slip away from the
extractor hook.
Powder residue collects in extractor slot.
Bolt not moving back far enough for the ejector to provide a good 'smack' to the case head. The fired case
doesn't have time to get out of the ejection port before the bolt catches it.
|
Replace extractor.
Replace extractor spring.
Remove extractor, clean slot in bolt.
Try hotter ammo or lighter recoil spring.
|
| Case drops in receiver:
|
See above.
Case not getting a good smack from ejector.
|
Usually runs fine for a burst, but the last fired case of the burst drops in the feedway.
Ejector worn or damaged.
Bolt movement slowed or impeded by kinked recoil spring
or recoil spring feeding over a damaged spring guide.
|
See above.
Repair or replace ejector.
Replace recoil spring and / or guide.
|
TRIGGER GROUP PROBLEMS
| Problem: |
Cause: |
What's Happening & Why: |
Correction: |
|
Fires SEMI when set on FULL:
|
Wear / tolerance stacking on trigger bar, sear & safety.
Nose of trigger bar improperly shaped.
|
There is no positive disconnect in the 76 /760 trigger mechanism. SEMI fire requires the trigger bar
to drop free of the sear from forward movement. FULL auto fire occurrs when the trigger bar is prevented
from dropping free of the sear. Wear on the trigger bar and / or safety allows the trigger bar to drop
free when it shouldn't.
|
Repair or replace trigger bar.
|
| Keeps firing when trigger is released:
|
Wear on bolt cocking shoulder.
Sear nose worn or improperly shaped.
Weak sear spring.
Weak ammo.
|
After many many rounds the cocking shoulder in the bolt will burr and its angle will change.
The engaging surface on the sear will also wear allowing the bolt to overide the sear.
Springs have a finite life and weaken with use.
Bolt not moving back far enough to engage sear.
|
Repair or replace bolt and / or sear.
Replace sear spring.
Try hotter ammo or lighter recoil spring.
|
| Doubles when set on SEMI:
|
Design of the trigger mechanism.
|
There is no positive disconnect in the 76 /760 trigger mechanism. SEMI fire requires the trigger bar
to drop free of the sear from forward movement alone. FULL auto fire occurrs when the trigger bar is prevented
from dropping free of the sear. This can happen from a "short" pull on the trigger.
|
A long firm pull all the way back is needed.
|