Originally Posted by zogger52

Awhile back I did this analysis:

Revolver vs Semi-Automatic Handgun Reliability Using FMECA Approach


Summary of Results:

Modern handguns are extremely reliable. They are capable of firing many thousands of rounds with no malfunctions. In evaluating the difference in reliability between revolvers and semi-automatic handguns, the primary difference is the dependence of the gun on external factors such as user, ammo, and magazine (if a semi-automatic).
The user’s ability to properly manipulate and hold a semi-automatic is a key to semi-automatic reliability. Revolvers have less dependency upon the user than semi-automatics.

After the gun user, a gun system is most dependent upon the ammunition. Since ammunition is used once and an individual bullet can't be tested without "consuming" it, it is not possible to know with absolute certainty if a specific bullet will perform properly in a gun before using it.

Semi-automatics are more dependent than revolvers upon properly functioning ammunition since the stripping the bullet from the magazine, inserting the round into the chamber, discharge of the round, extraction of the used round, ejection of the used round, movement of the slide rearward due to ammunition discharge has significant dependences on the ammunition for properly functionality.

Semi-autos also require that magazines function properly for the gun to operate properly.

Semi-automatics have higher "first shot" reliability assuming a round has been properly inserted in the chamber.

Revolvers generally have slightly higher accuracy repeatability due to the barrel and sights being mechanically fixed.

Semi-automatics are generally less susceptible to fouling due to gun powder residue than revolvers. Hence semi-automatics generally do not need to be cleaned as often.

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System Description:
The handgun system consists of the following components:
-Gun
-Ammunition
-Magazine for semi-automatics
-User

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Assumptions:
1) The gun is being maintained properly. Proper cleaning, lubrication, tightening of screws, and replacement of parts that wear (like recoil springs) are performed at recommended intervals.
2) Proper ammunition is being used.
3) The magazines used in semi-automatics are compatible with the gun.
4) The gun has been "broken in" by firing the recommended number of rounds of the recommended type.
5) The user is familiar with the gun, ammunition, magazine, etc. and handles it per the instruction manual.
6) Revolver is being shot in Double Action mode

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General Operation:

Revolver: The user opens the cylinder, inserts the rounds, and closes the cylinder. He then points the gun at the target and squeezes the trigger. The action of squeezing the trigger rotates the cylinder to align a round to the barrel and retracts the hammer. Once the trigger has be moved back far enough to release the hammer, the gun discharges the round.

Semi-Automatic: The user loads the magazine with the ammunition and inserts the magazine into the gun. He then cycles the slide to load a round in the chamber which cocks the hammer/firing pin/striker priming the firing mechanism. He then points the gun at the target, releases any safety mechanisms, and squeezes the trigger. The gun discharges the round and then cycles the slide to load another round into the chamber. The cycling of the slide re-cocks the hammer/firing pin/striker re-priming the firing mechanism.

Note that in a semi-automatic that as long as there was a round in the magazine to load into the chamber, the gun is ready to shoot the next round. After discharge in a revolver, the discharged round remains aligned with the barrel hence squeezing of the trigger (or cocking of the hammer in a single action revolver) is needed to move a live round into firing position.

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Definition of Critically Levels:

Low: Round does not discharge and/or exits the barrel but the gun is capable of discharging on next trigger squeeze.

Medium: Round does not discharge and/or exits the barrel. Manual action is required to set the gun for next use.

High: Round does not discharge and/or exits the barrel. Gun system will no longer operate.

Severe: Round does not discharge and/or exits the barrel. Damage occurs to the gun system or injury to user.

Note: Normally a probability is given for each failure mode. However there are little statistics available on these failures, hence no probabilities are used in the analysis.


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A High Level Listing for Credible Failure Modes for Each Component:

The high level credible failures for reach component of the gun system (gun, ammunition, magazine, and user) are detailed.
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Gun:
The high level credible failures for revolvers and semi-automatics are detailed.

Revolver:
-Failure to properly align the cylinder to the barrel.
Results in bullet not discharging or not properly going into the barrel. Possible damage to user and gun.
Criticality: Low to Severe. Low if cylinder aligns properly on next trigger pull. Severe if injury to user or damage to gun.

-Failure to strike the primer with sufficient force to cause it to discharge the round.
Results in bullet not going into the barrel (light primer strikes)
Criticality: Low to High. Low if next rounds discharges when user squeezes the trigger to fire the next round. High if gun will no longer strike primer with enough force.


Semi-Automatic:
-Failure to properly strip a round from the magazine and insert it into the chamber.
Results in a jam.
Criticality: Medium to High. Medium if user can clear the jam and another round can be inserted into the chamber. Severe if jam cannot be cleared.

-Failure to strike the primer with sufficient force to cause it to discharge the round
Results in a non-discharge.
Criticality: Medium to High. Medium if user can cycle the slide to eject the unfired round and insert a new round into the chamber. High if unfired round cannot be cleared and new round inserted.

-Failure to eject the discharged round properly
Results in a jam.
Criticality: Medium to High. Medium if user can clear the jam and another round can be inserted into the chamber. High if jam cannot be cleared.

-Failure to prime the firing mechanism for the next shot.
Results in a jam.
Criticality: Medium to High. Medium if after user manually cycling the slide, the next rounds discharges when user squeezes the trigger to fire the next round. High if gun will no longer strike primer with enough force (light primer strikes)

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Ammunition
The high level failures of ammunition and its effect on each type of gun are detailed.

-Failure of the primer to discharge even when the primer is struck with sufficient force (dud)

Revolver: Same as a light primer strike.
Criticality: Low to High. Low if next rounds discharges when user squeezes the trigger to fire the next round. High if all subsequent rounds also do not discharge.

Semi-Automatic: Same as a light primer strike.
Criticality: Medium to High. Low if after the user manually cycles the slide, the next rounds discharges when user squeezes the trigger to fire the next round. High if all subsequent rounds also do not discharge.

-Failure of the bullet to travel fully out of the barrel due to insufficient force (squib)
Revolver: Results in cartridge discharging with bullet entering the barrel but does not exit.
Criticality: Low to Severe. Low if user does not fire next round or bullet is lightly
lodged and will exit if next round pushed it through the barrel. Severe if bullet is tightly lodged and next bullet causes barrel to explode.

Semi-Automatic: Results in cartridge discharging with bullet entering the barrel but does not exit.
Criticality: Low to Severe. Low if user does not fire next round or bullet is lightly lodged and will exit if next round pushed it through the barrel. Severe if bullet is tightly lodged and next bullet causes barrel to explode.

-Failure of the primer to discharge immediately (hang fire)
Revolver: Bullet still in shell casing
Criticality: Low to Severe. Low if user does not fire next round. Possible severe if user squeezes trigger for subsequent round and round discharges when cylinder is not aligned to the barrel causing injury to user or damage to gun.

Semi-Automatic: Bullet still in shell casing
Criticality: Medium if after user manually cycling the slide, the hang fire round is ejected, new round is inserted into the chamber properly, and the gun is ready for next use.

-Backing Out of Bullet from Shell Casing
Revolver: Can cause cylinder not to rotate
Criticality: Low to Severe. Low if bullet back out des not interfere with cylinder rotation. Possible severe if bullet backs out far enough to stop cylinder from rotating.

Semi-Automatic: Bullet stuck in magazine
Note: All most not possible because of the way the rounds are held in the magazine.
Criticality: Low to Severe. Low as long as there is not issue with feeding the backed out round. Severe if the next round cannot be fed from the magazine.

-Failure to present the round properly so it can be stripped off and inserted into the chamber.
Revolver: Not applicable
Criticality: None

Semi-Automatic: Results in a jam.
Criticality: Medium to High. Medium if user can clear the jam and another round can be inserted into the chamber. High if jam cannot be cleared.

-Not allowing the slide to lock back after the last round in the magazine has been fired.
Revolver: Not applicable
Criticality: None

Semi-Automatic: No Impact
Criticality: Low as user can eject magazine, insert a new one, and manually cycle the slide.

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User
The high level failures of due to the user and its effect on each type of gun are detailed.

-Not properly holding the gun so as to inhibit semi-automatic from recycling properly (limp wrist)
Revolver: No Impact
Criticality: None

Semi-Automatic: Gun fires but does not cycle the slide properly causing a jam.
Criticality: Medium after user manually cycles the slide.

-Not properly loading rounds into a magazine
Revolver: No Impact
Criticality: None

Semi-Automatic: Results in a jam.
Criticality: Medium to High. Medium if user can clear the jam and another round can be inserted into the chamber. High if user must eject magazine, insert a new one, and manually cycle the slide.

-”Short Stroking” trigger (not pulling the trigger all the way)
Revolver: Gun does not fire but the cylinder rotates.
Criticality: Low as gun fires on next trigger pull

Semi-Automatic: Gun does not fire nor does the slide cycle.
Criticality: Low as gun fires on next trigger pull

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Other Factors to Consider:

"First shot" Reliability
A semi-automatic has an advantage over a revolver when firing its first shot (or subsequent shots if the gun has cycled properly after firing a round). The advantage for the semi-automatic is that to discharge a round, only the trigger release mechanism and the round have to function properly for the gun to discharge. This is because a round is in the chamber and the firing mechanism is "primed". In a revolver, the cylinder must cycle to align a fresh round to the barrel in order for the gun to function properly. If a revolver is being fired in “single action” mode, then this factor is negated.

Accuracy Repeatability
Assuming a gun is sighted in properly and the ammunition is consistent with what was used to sight in, there can be different point of impact based on the gun design.
Revolver: In most revolvers the sights (front and back) are structurally lined to the barrel. However the cylinder chambers are moved to alight with the forcing cone and the barrel. The alignment of the cylinder chamber to barrel varies with each chamber in the cylinder. This difference in alignment can affect the accuracy.

Semi-Automatic: Except for designs that have the barrel fixed to the frame, barrels on semi-automatics move after each shot and return to position for the next shot. Since the barrel and sights are not structurally fixed together, there can be variability from shot to shot with the barrel to sight alignment. However since the bullet is inserted snugly into the chamber which is part of the barrel, the bullet to barrel alignment is consistent from shot to shot.

Effect of gun powder residue on functionality (fouling)

When the cartridge is discharged, residue from the gun powder is propelled forward and out of the shell casing. This residue adheres to various parts of the gun mechanisms. The effect of the residue is different on a revolver versus a semi-automatic. Different ammunition produces different amount of gun powder residue. So the amount and effects of residue varies considerably between different ammunition.

Revolver:
In a revolver, the bullet is housed in the cylinder where it is discharged. The bullet and any gun powder residue are propelled forward thru the front of the cylinder, across the gap between the cylinder and the forcing cone, and into the barrel. Gunpowder residue is built up in the inside of the front of the cylinder starting at the top of the shell casing, on the front of the cylinder, on the forcing cone, around the forcing cone (and frame) and in the barrel. The effect can result in the inability to eject shell casing from the cylinder, inability to insert new bullets into the cylinder, opening of the cylinder, and the cylinder not rotating properly. This effect can be observed when firing a revolver that can use both .357 Magnum and 38 Special ammunition. Since the 38 Special bullet is shorter than the .357 Magnum, if it is shot before the .357 Magnum and causes built up inside the cylinder, then issues can occur when .357 Magnum ammunition is inserted into the cylinder-it may not go all the way into the cylinder. Hence the functionality of a revolver is significantly more affected by gun powder residueand more frequent cleaning is needed.

Semi-Automatic:
Since the bullet is discharged in the chamber which is part of the barrel in a semi-automatic, the majority of the gunpowder residue goes down the barrel and ejects out the gun. Some residue comes back into the slide, magazine, and frame. Some also comes out of the barrel and adheres to the front of the barrel plus the front and sides of the slide. The amount of gunpowder residue that adheres to critical parts of a semi-automatic is significantly less than in a revolver. Hence the functionality of a semi-automatic is significantly less affected and it can function reliability for more rounds before cleaning is needed.