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yukonjasper wrote:It gets jammed about a quarter to a third of the way forward. I applied some force to the charging handle but not a lot. Didn't want to bend or damage it.

Ok, so you're saying the bolt isn't jamming all the way back when this happens.

Does this happen after the last round in the mag? Is the bolt about in the same position as the one in the attached photo below?

If so, the front of your bolt career is hanging up on the bolt release instead of the face of the bolt where it should.

Make sure there is no debris in the receiver extension intermittently binding the spring and/or buffer...like a blown primer.

Good suggestions those last too. Might be a gas block issue. Could not be getting enough gas to send the bcg full cycle and short cycling. Try shooting one round with none in the mag and see if it locks back fully and correctly.

Holland&Holland wrote:Good suggestions those last too. Might be a gas block issue. Could not be getting enough gas to send the bcg full cycle and short cycling. Try shooting one round with none in the mag and see if it locks back fully and correctly.

Agreed

I’m a big fan of using adjustable gas blocks better fine tuning of the system and also it allows adjustment when adding a suppressor down the road.

This issue sounds eerily familiar to one I had.

Question for YJ: Does your bolt feel like it's binding/dragging when you try to open it with your empty mag inserted?

If so, check the bolt release for unusual wear patterns. I had a problem with an out of spec bolt release which must have road funny when it was pushed up against the bottom of the carrier by the mag.

It sounds to me like you have an out of spec bolt release or possibly an out of spec lower. Both parts are fairly cheap and easy to replace.

I'd also invest in some better quality mags.

Rip Van Winkle wrote:

yukonjasper wrote:It gets jammed about a quarter to a third of the way forward. I applied some force to the charging handle but not a lot. Didn't want to bend or damage it.

Ok, so you're saying the bolt isn't jamming all the way back when this happens.

Does this happen after the last round in the mag? Is the bolt about in the same position as the one in the attached photo below?

If so, the front of your bolt career is hanging up on the bolt release instead of the face of the bolt where it should.

That is about the right position, shown in that photo. Thanks for all the guidance. The bolt cycles normally except when it jams. It even cycled a few times normally between jams. I'll try to look at it tonight.

Thanks again for your help.

Do you have convenient access to a range? If so I would try a few single rounds with Mag in and see how that reacts. If it does not lock back fully and normally then you do not have enough power to overcome the forces resisting it so it is either something catching, dragging, etc or not enough gas.

A while back someone I know had that same bolt jamming problem with a his newly built AR. I just asked him what solved it and he said he started buying 223 instead of 5.56 and has not had a problem since. Make of that what you will I guess. I'm not sure if that means gas problem or buffer spring/weight problem.

grimbeaver wrote:A while back someone I know had that same bolt jamming problem with a his newly built AR. I just asked him what solved it and he said he started buying 223 instead of 5.56 and has not had a problem since. Make of that what you will I guess. I'm not sure if that means gas problem or buffer spring/weight problem.

5.56X45 should not be fired in a 223 Rem chamber as excessive pressures can be generated due to differences in chamber design interfering with projectile design used

OldmanFCSA wrote:5.56X45 should not be fired in a 223 Rem chamber as excessive pressures can be generated due to differences in chamber design interfering with projectile design used

It was a 5.56 chamber. Apparently it liked 223 Rem better though.

grimbeaver wrote:

OldmanFCSA wrote:5.56X45 should not be fired in a 223 Rem chamber as excessive pressures can be generated due to differences in chamber design interfering with projectile design used

It was a 5.56 chamber. Apparently it liked 223 Rem better though.

I would tender it was that particular 5.56 load that it didn't like.

Did you install the gas block? If the ports are not lined up, you won't get enough gas flow to cycle the BCG.

It was a preassembled Grendel upper from Aero Precision.

yukonjasper wrote:It was a preassembled Grendel upper from Aero Precision.

Well there you go. With a Grendel you only need one shot so...

Chamber a round and then drop the mag. Fire the round. Does the bolt cycle?