Troubleshooting AR FTF problems

[SAN compnerd]

My home build seems to have issues with feeding. I have found that after I pull the BCG and clean the carbon out, it seems to work fine, but sometimes after 30-50 rounds it starts again. It seems even the tiniest amount of carbon build up causes it to FTF.

The upper I got from Marks Armory as a 'blem' and its 18". CD lower and DPMS parts kit. Cheap adjustable stock, don't recall the brand came with the buffer and spring. Last time out shooting I was running Hotshot ammo.

I saw another thread discussing issues with rifle length upper and carbine length buffer/spring, but I am not quite sure how to identify this condition.

Wondering if getting a different BCG would make a difference. How much trouble is it to properly fit a new BCG with proper head spacing, etc?

Thanks.

[falbuff]

The rifle length buffer is longer than a carbine buffer.

[DFence]

Possible incorrect buffer or buffer spring. Have you tried different mags? May be faulty mag follower or spring as well. Lastly, make sure the gun is well lubricated. Might be running a little to dry and after a some rounds go through it, it really dries up.

[b.faust]

Can you explain a bit more about what happens when you get a FTL?
The BCG sticks? Get's hung up on something? Etc....

[thomashoward]

Rifle length buffer and spring in A2 = rifle legnth
Carbine buffer and spring in M4 = carbine
upper's are interchangeable
run it wet

[SAN compnerd]

Possible incorrect buffer or buffer spring. Have you tried different mags? May be faulty mag follower or spring as well. Lastly, make sure the gun is well lubricated. Might be running a little to dry and after a some rounds go through it, it really dries up.

I have tried different mags. I will have to go out again and remember to hit it with break free after every couple of mags.

Can you explain a bit more about what happens when you get a FTL?
The BCG sticks? Get's hung up on something? Etc....

The action does not cycle back far enough (my observation) to eject the previous round and strips the next round from the mag as it goes forward again.

It seems to be very sensitive to the carbon that builds up inside the BCG.

[b.faust]

That sounds more like buffer spring to me.

You also said, you have a rifle 'length' upper, what's the gas system length?

[ar15barrels]

Sounds like a lubrication quality issue.
Either not enough lube and it's burning off quickly, or crappy lube that burns off quickly.
Try some quality oil on the carrier and inside the carrier.
By quality oil, I suggest Slip 2000 EWL or Weaponshield EWL.
Put on enough that when you shake the carrier, some comes off.

If that's not it, there could be an assembly problem that is giving marginal function and the lube is making the difference in if it will run or not.

[SAN compnerd]

That sounds more like buffer spring to me.

You also said, you have a rifle 'length' upper, what's the gas system length?

Ok, not sure how to determine the gas system length.

[ar15barrels]

Ok, not sure how to determine the gas system length.

Meaure from the gas port back to the end of the barrel extension.
Carbine length is about 8"
Pistol is about 5"