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Joined:
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VA, USA
Posted: 7/2/2026 6:19:10 PM EDT
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Hello. My barrel extension is sitting short in the upper receiver even when the flange is bottomed out against the receiver face. It is a colt carry handle upper with m4 feeding ramps taken off a 16 inch pencil LE upper. The barrel is a 96 colt m4 barrel. I do not have a barrel nut yet, will torquing it down true the barrel extension to the receiver? Sorry if that is a beginner question, this is only my fourth build. If not, what are my options here. Pictures linked below, any help would be appreciated as I would like to use both these parts as neither is particularly cheap to replace. https://imgur.com/a/RiytzeY |
| I'm not seeing an issue in the pics. If the situation were reversed with the barrel extension protruding past the receiver cuts, there could be a problem. I have and use a receiver honing tool to work back the threaded part so I can orient the handguard. Your pic would be ideal for my builds |
| I have had this happen. Some I left alone if the receiver cuts were close. Some I took a cone Dremel bit to and reshaped carefully to get a smoother transition. It is up to you. |
yin shui si yuan
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Your life is an occasion, rise to it
In time we will be dancing in the streets all night.
Joined:
Dec 2022
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NH, USA
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Double check the upper receiver, but those do not look like true Colt M-4 ramps. Note, look at the upper receiver for the forge markings above the forward assist on the receiver to tell if colt upper oem or not. Colt ramps should look like this as well,  And you want the end of the barrel extension slightly proud of the front face of the upper receiver protruding, so the carrier face will be stopped by the hardened barrel extension, not the softer upper surface instead. So on that note, quick solution would be so set back the upper receiver barrel socket to run that barrel in the upper.   As for the gap in upper to barrel ramps as shown in the first photo, its really not a problem, and lets face it, unless your running Mk262 ammo, upper/barrel feed ramps are not needed in the first place. Hence the mag has inner front tabs in it that will push the round upwards at the correct angle with standard ammo, and its the longer ogive ammo like the 69gr+ bullets that will not have the tip raising fast enough, and why the ramps where added on the M-4 1/7 twist barrel to run that ammo without feed problems. |
Posted By PlaymoreMinds:
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
'Twas not the <cough> sweet and innocent <cough> PlaymoreMinds...
<---skips away in frilly skirts to Candyland, leaving gutters and snorkels FAR behind.
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The barrel extension face should not protrude past the lower flat inside the front of the upper. It should stop between .002" to .018" before reaching it. The carrier will not hit aluminum if the extension is back from the flat face in the range of allowed tolerances. Easy enough to see by dropping a carrier in a stripped upper without the charging handle how deep it travels without hitting anything. Picture looked fine to me. |
Joined:
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NH, USA
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I'm not sure if these are "true" m4 feedramps. The upper is off an old colt ar6520 from the 90s, and the barrel is a 96 m4 barrel. There are feedramps present, but its unclear to me if they are some sort of transitional profile, as the gun was from the era when receiver feedramps were just being rolled out. It seems to feed with no issue, and a toothpick wont catch on them. As for the bolt carrier crashing into the aluminum, correct me if I'm wrong, but I dont believe that should be an issue. Without a charging handle or barrel, the carrier can slide significantly further into the receiver extension bore before contacting any aluminum than the depth of where the extension sits. With a bolt and the barrel seated, it only contacts the extension. If there is something im missing though, please correct me. My primary concern when I made the post was that this would cause an issue with cam path wear in the upperor from the bolt being slightly further forward, but Im also concerned this may cause an issue im simply not aware of. Should I face the receiver for this level of protrusion or just assemble as is? |
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Originally Posted By freemang20: I'm not sure if these are "true" m4 feedramps. The upper is off an old colt ar6520 from the 90s, and the barrel is a 96 m4 barrel. There are feedramps present, but its unclear to me if they are some sort of transitional profile, as the gun was from the era when receiver feedramps were just being rolled out. It seems to feed with no issue, and a toothpick wont catch on them. As for the bolt carrier crashing into the aluminum, correct me if I'm wrong, but I dont believe that should be an issue. Without a charging handle or barrel, the carrier can slide significantly further into the receiver extension bore before contacting any aluminum than the depth of where the extension sits. With a bolt and the barrel seated, it only contacts the extension. If there is something im missing though, please correct me. My primary concern when I made the post was that this would cause an issue with cam path wear in the upperor from the bolt being slightly further forward, but Im also concerned this may cause an issue im simply not aware of. Should I face the receiver for this level of protrusion or just assemble as is? The extension is not supposed to protrude past the upper. Your understanding is correct. Nothing crashes into aluminum on a spec made gun. The GI design magazine even extends over all that upper aluminum and sets about even with the bottom of the barrel's extension. The only reason to face the upper might be if you buy into the it might help accuracy thing being seated better/fully between the uppers face and the barrel extension but still you don't want to do it so much the extension would protrude past the upper. The feed ramp thing is over blown as the bullet normally is above the M4 cut in the upper anyway. The guns worked when it didn't exist. Cam pin wear happens; I'd just make sure the cam pin was made to spec and properly deburred. The final stopping point means little as the wear near the cut out in the upper starts way before the cycle is complete. Where the carrier stops is important in making sure the buffer doesn't crash into the buffer retaining pin but if the all the parts are in the spec'd tolerances that should not happen. |
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