Trouble with new AR upper

[qwertee123]

UPDATED: 04/11/2015; still having issues; see latest post.

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I recently bought a DPMS AR-15 A3 upper assembly to swap onto my functioning AR15 carbine but I got a FTF on almost every round; the bolt would catch on the side of the new round and jam, leaving the round stuck out of battery.

I thought the buffer spring might be a problem so I replaced it with a CS flat spring and the problem continued.

Am I obviously missing something to remedy this problem?

Exact upper info is: Midway USA Product #: 810366, DPMS #: FTBL-LR-20 Fluted 1x9

 

[mopar92]

Have you tried different mags?

 

[l730dc]

Clean it.. work the extractor (sometimes they need it)

 

[qwertee123]

Have you tried different mags?

I was using two new Magpul 10-round polymer magazines but have not tried other magazines. I'll add my PMAGs to the range bag next time.

 

[qwertee123]

Clean it.. work the extractor (sometimes they need it)

New bolt in the upper; fired, extracted & ejected the first round fine but jammed afterwards. Hadn't thought it could be the mags as suggested above, but I will investigate

 

[INMY01TA]

Gas keys staked and tight?

 

[qwertee123]

Gas keys staked and tight?

I thought so, but will inspect. Thx for suggestion

 

[mopar92]

Generally failure to feed, eject, extract and double feeds can be caused by magazines (typically primary reason)
Does it feed fine manually as in racking charging handle?
Does it eject both manually and operationally (live fire) in a consistent pattern?
Is the chamber rough? Use a low power flashlight shown in crown end and look for anything that isn't smooth.
What lube?
Does the upper charge fine by its lonesome?
Remove the follower and spring from one of the mags and see if you can feel excessive drag when cycling.

 

[outrider58]

M4 feed ramps cut in the receiver?

 

[Boom Boom]

Generally failure to feed, eject, extract and double feeds can be caused by magazines (typically primary reason)

... or running the action too dry.

Another possibility is feed ramps. Check for burrs and rough surfaces.

 

[fidelity]

If you have 223 snap caps, you can do some diagnoses at home cycling the action yourself. Try switching to mags that you've used before, but also try your prior BCG/bolt in case it's not feeding the round correctly. Finally as Boom Boom said, pull off the upper, get a flashlight, and run the nib of a ball point pen up the path of the feed ramps. See if it catches or snags.

Hmm, wondering where I picked up this newfound knowledge from.

 

[inkd]

I was using two new Magpul 10-round polymer magazines but have not tried other magazines. I'll add my PMAGs to the range bag next time.

I had problems with 10 round Pmags before. Scott, from Scotts gunsmithing built me up a kick ass SBR upper that I had problems with. Sent it back up and I got a call saying "I don't know what your problem is, but this thing runs just fine!!!"

When I went to pick it up I brought everything I used that day I had problems and asked him to run it again. Lo and behold, that damn 10rd mag was the issue the entire time.

 

[clandestine]

Current production 10 and 20 round mags are often junk as inkd elaborated on.

 

[rico903]

M4 feed ramps cut in the receiver?

M16's and AR's ran for 30+ years w/o M4 feed ramps.

 

[clandestine]

M16's and AR's ran for 30+ years w/o M4 feed ramps.

That is 100% correct, but in the civilian world there is a hundred mag choices and a thousand ammo choices. The military has but a couple of magazines and a handful of ammo choices.

The M4 ramps make the civilian AR feed hollow point, soft point, ballistic tip, and some ammo with different ogives feed more reliably than just military ammunition.

The downside is M4 ramps can cause more feeding problems if they don't match and transition properly.

 

[GTOGUNNER]

That is 100% correct, but in the civilian world there is a hundred mag choices and a thousand ammo choices. The military has but a couple of magazines and a handful of ammo choices.

The M4 ramps make the civilian AR feed hollow point, soft point, ballistic tip, and some ammo with different ogives feed more reliably than just military ammunition.

The downside is M4 ramps can cause more feeding problems if they don't match and transition properly.

Exactly. Friend has a brand new upper and the ramps don't come close to matching.. I doubt that it would chamber a round. Only found this out by taking Chads class. http://www.schooloftheamericanrifle.com/

 

[outrider58]

Exactly. Friend has a brand new upper and the ramps don't come close to matching.. I doubt that it would chamber a round. Only found this out by taking Chads class. http://www.schooloftheamericanrifle.com/

Nothing that a Dremmel can't take care of

 

[clandestine]

Nothing that a Dremmel can't take care of

Absolutely correct, but many do the Dremeling with the Barrel Assembly installed in the Upper Receiver.

Its not possible to get the right Feed Ramp transition with the Barrel Assembly attached to the Upper Receiver because the Barrel Extension Ramp have to be cut forward the M4 Ramps built into the Upper. If you dont remove the Barrel Assembly you will end up removing the Anodizing on the M4 Ramps which is bad, and you wont get the proper forward profile necessary for reliable function.

Removing the Anodizing on M4 Ramps will lead to accelerated Ramp wear because the underlying Aluminum is much softer then the Anodized top coating.

 

[GTOGUNNER]

Absolutely correct, but many do the Dremeling with the Barrel Assembly installed in the Upper Receiver.

Its not possible to get the right Feed Ramp transition with the Barrel Assembly attached to the Upper Receiver because the Barrel Extension Ramp have to be cut forward the M4 Ramps built into the Upper. If you dont remove the Barrel Assembly you will end up removing the Anodizing on the M4 Ramps which is bad, and you wont get the proper forward profile necessary for reliable function.

Removing the Anodizing on M4 Ramps will lead to accelerated Ramp wear because the underlying Aluminum is much softer then the Anodized top coating.

As is this case. Clandestine will be seeing this upper again!

 

[outrider58]

That is 100% correct, but in the civilian world there is a hundred mag choices and a thousand ammo choices. The military has but a couple of magazines and a handful of ammo choices.

The M4 ramps make the civilian AR feed hollow point, soft point, ballistic tip, and some ammo with different ogives feed more reliably than just military ammunition.

The downside is M4 ramps can cause more feeding problems if they don't match and transition properly.

And besides, it's a lot easier to cut the ramps with the bbl. not affixed.