Cycle of operation:
Feeding
Chambering
Locking
Firing
Unlocking
Extracting
Ejecting
Cocking
Trigger pin/FCG holes are .155” if mil-spec.
Colt large pins are .170”
Mil spec receiver extension (buffer tube) diameter is 1.14”
Commercial is 1.17”
Gas port location 0.295” (shoulder to center of port)
FSB’s:
Original is shorter than models on flattop models. Models made for use on a flattop are marked with an F.
1.98”: flattop
1.94”: original
Colt is no longer marking their FSB’s because they are no longer making rifles that use the original FSB.
Malfunctions:
Double feed: caused by bad mag
Stovepipe: caused by weak ejector
Failure to extract: weak or improper extractor/spring or chamber too tight
Short stroking: failure of gas system. Check gas rings, carrier key and screws, gas tube/roll pin, and gas block. Possibly ammo, as well.
Failure to feed: Mag seated? Did rounds feeds from mag?
Failure to Chamber/Lock: chamber obstruction, operator induced (riding charging handle), weak or damaged action spring.
Hammer pin come out: J spring inside hammer is worn. Hammer must be replaced.
Trigger Pin comes out: Hammer spring is broken or is improperly assembled
Failure to lock after last round: Bad mag follower or the bolt lock/release is damaged. Also short stroking
Trigger reset/Double fire: check disconnector and disconnector spring
Buffers (Standard/Vltor)
Carbine buffer 2.9oz A5 H0 3.8oz
H buffer 3.8oz A5 H1 4.56oz
H2 buffer 4.6-4.7oz A5 H2 5.33oz
H3 buffer 5.4-5.5oz A5 H3 6.08oz
Rifle buffer 5.1-5.3oz A5 H4 6.83oz
Vltor A5 H2 is the “default setting”. Will generally run in a gun from 10.5”-20”
As you shorten the barrel, you must increase the size of the gas port, and increase the weight of the buffer.
Operating systems:
Pistol: 7.5”
Carbine: 9.75”
Mid length: 11.75”
Intermediate (KAC): Just over 13.16”
Intermediate (Noveske): Just over 13.5”
Rifle: 15.125”
Torque values:
Bolt carrier key screws: 58in/lbs
Lower receiver extension carbine: 38-42ft/lbs
Barrel nut USGI: 30-80ft/lbs
Buffer spring measurements:
Carbine: 10 1/16” - 11 1/4”
Rifle: 11 3/4” - 13 1/2”
Standards:
Colt M16A2/A4: 20” + rifle buffer + .093 gas port
Colt M4 Carbine: 16” + (H)H2 buffer + .062 gas port
Crane MK18: 10.3” + H2 buffer + .071 gas port (Crane)
Crane MK12 (SPR): 18” + rifle buffer + .0995 gas port
Gas port sizes:
14.5” w/ carbine gas .062-064"
16” w/ carbine gas .062-064"
14.5” w/ midlength gas .076-.0785"
16” w/ midlength gas .076-.0785"
10.3/10.5” w/ carbine gas .071 (Crane)"
11.5” w/ carbine gas .076"
12.5” w/ carbine gas .078"
18” SPR .0995"
20R” .0935"
Feeding
Chambering
Locking
Firing
Unlocking
Extracting
Ejecting
Cocking
Trigger pin/FCG holes are .155” if mil-spec.
Colt large pins are .170”
Mil spec receiver extension (buffer tube) diameter is 1.14”
Commercial is 1.17”
Gas port location 0.295” (shoulder to center of port)
FSB’s:
Original is shorter than models on flattop models. Models made for use on a flattop are marked with an F.
1.98”: flattop
1.94”: original
Colt is no longer marking their FSB’s because they are no longer making rifles that use the original FSB.
Malfunctions:
Double feed: caused by bad mag
Stovepipe: caused by weak ejector
Failure to extract: weak or improper extractor/spring or chamber too tight
Short stroking: failure of gas system. Check gas rings, carrier key and screws, gas tube/roll pin, and gas block. Possibly ammo, as well.
Failure to feed: Mag seated? Did rounds feeds from mag?
Failure to Chamber/Lock: chamber obstruction, operator induced (riding charging handle), weak or damaged action spring.
Hammer pin come out: J spring inside hammer is worn. Hammer must be replaced.
Trigger Pin comes out: Hammer spring is broken or is improperly assembled
Failure to lock after last round: Bad mag follower or the bolt lock/release is damaged. Also short stroking
Trigger reset/Double fire: check disconnector and disconnector spring
Buffers (Standard/Vltor)
Carbine buffer 2.9oz A5 H0 3.8oz
H buffer 3.8oz A5 H1 4.56oz
H2 buffer 4.6-4.7oz A5 H2 5.33oz
H3 buffer 5.4-5.5oz A5 H3 6.08oz
Rifle buffer 5.1-5.3oz A5 H4 6.83oz
Vltor A5 H2 is the “default setting”. Will generally run in a gun from 10.5”-20”
As you shorten the barrel, you must increase the size of the gas port, and increase the weight of the buffer.
Operating systems:
Pistol: 7.5”
Carbine: 9.75”
Mid length: 11.75”
Intermediate (KAC): Just over 13.16”
Intermediate (Noveske): Just over 13.5”
Rifle: 15.125”
Torque values:
Bolt carrier key screws: 58in/lbs
Lower receiver extension carbine: 38-42ft/lbs
Barrel nut USGI: 30-80ft/lbs
Buffer spring measurements:
Carbine: 10 1/16” - 11 1/4”
Rifle: 11 3/4” - 13 1/2”
Standards:
Colt M16A2/A4: 20” + rifle buffer + .093 gas port
Colt M4 Carbine: 16” + (H)H2 buffer + .062 gas port
Crane MK18: 10.3” + H2 buffer + .071 gas port (Crane)
Crane MK12 (SPR): 18” + rifle buffer + .0995 gas port
Gas port sizes:
14.5” w/ carbine gas .062-064"
16” w/ carbine gas .062-064"
14.5” w/ midlength gas .076-.0785"
16” w/ midlength gas .076-.0785"
10.3/10.5” w/ carbine gas .071 (Crane)"
11.5” w/ carbine gas .076"
12.5” w/ carbine gas .078"
18” SPR .0995"
20R” .0935"