13 replies to this topic

[Penguin]

Hi there!

I am very new to the world of AR 15's and would love the input of the boffins here on the board.

Every now and then my Rifle will choke and not chamber a round. It is very random in occurance, sometimes it happens twice in the same mag, then does not occur at all...

It seems as thought the round gets "stovepiped" against the feed ramps of the gun and the bolt does not go into battery. Note that I am using magpul p mags and PMC ammo.

Here is a picture of the round after clearing the jam


Seems that the bolt is riding over the top of the cartridge, and then digging into the shoulder of the casing.

I am thinking this could be
1. Magazine related
2. Related to the gas tuning of the rifle?

Thanks for your input!
3. Ammo related

[Biloxi23]

Replace either your mag springs and followers, or try magpul P-mags. I think that will solve your problems.

[open17]

Does the gun lock back on an ampty mag? Every time??
If not, it could be a gas problem. Possible a loose
gas key, bad rings on the bolt, loose or mis-aligned
gas block, partially plugged gas system.

It looks like it's short cycling. Bolt comes back far enough to
kick out the empty, but not far enough to pick up the next round
100% of the time.

Does it do it with all of your magazines??

[StealthyBlagga]

Good advice above. I'd lean towards a gas problem.

[assaulter]

Check the gas rings in the bolt and gas key on the carrier first.

[Penguin]

Thanks so much everyone! I will give these a try and report back...

[grouse]

What kind of buffer are you using?

[Merlin Orr]

M4 feed ramps - yes?

[Penguin]

The rifle is a JP Enterprise SCR 11, brand new, straight from the factory, with the LMOS and Silent Spring system.
It is an amazing rifle.
I do not for 1 second believe this is the rifle's fault - this is driver error for sure - driver needs to become more familiar with the rifle...

Edited by Penguin, 17 September 2012 - 10:52 AM.

[Sleepswithdogs]

Perhaps you just need to open up your gas block a little.

Tar

[carbon9]

Perhaps you just need to open up your gas block a little.

Tar

+1. Although, if the gas block is wide open try some different ammo. PMC is a little weak in my opinion. I was having the same issue with a new rifle and PMC, switched to Fiocchi and Federal and the problem went away. PMC wouldn't lock the bolt back, Fiocchi and Federal would. After a few hundred rounds of break in the PMC ran no problem but I haven't bought any since.

[DocMedic]

When I got my new JP barrel, I had issues to feed because the lugs inside the barrel were to sharp and they would catch a bullet as it left the feed ramp every-once in a while. Affected ammo looked like yours. My Buddy took a jewelers file and "soften" up the two lugs that the rounds feed through. As of now the rifle runs 100%. The jams my rifle was doing can be seen in my SM3G video.



It happens at 06:30 several times

Edited by DocMedic, 17 September 2012 - 02:55 PM.

[saibot]

Those marks are from the bolt hitting side of the cartridge rather than the bottom of the case.
If it's happened with more than one magazine it's a gas system problem.
What's happening is that the bolt carrier group isn't going back far enough so it never gets a chance to get behind the cartridge.
New AR's often need more gas than they will once they've broken in and loosen up. If you haven't already, open up your gas port. Check it again after 1000 rounds.
Also be sure you're properly lube'd.

[doubleaay78]

Perhaps you just need to open up your gas block a little.

Tar

+1