Question for the AR guys

[john 800]

I brought a couple new ars to the range today and had some issues. It is. A midway ar stoner upper in 6.5 grendel with a home assembled lower if it matters. One leaves the round locked in the chamber without the bolt rotating and the upper needs to come off and have a good bit of pressure on the bolt carrier group to open the chamber.
The other is a bca upper also in 6.5 grendel. The second one doesn’t always eject the empty case and it ends up wedged against the round going in or wedged against the front of the ejection port.
Any advice? Do I need a particular buffer or buffer spring matched to ammo?
I was shooting 95gr druid hill armory amax ammo

 

[Walt Krafft]

What bolt and extractor? Does the bolt face have enough clearance to the case head? Is the extractor binding things up?

 

[john 800]

What bolt and extractor? Does the bolt face have enough clearance to the case head? Is the extractor binding things up?

They came assembled, one is a bear creek arsenal one is an ar stoner, which I have heard is made by bear creek. Anything I should look for on the bolts? I am mot sure how to check clearance or what I am looking for, but I will check to see if anything looks suspicious

 

[john 800]

Update:
The bolt says MPI on it, and feels very slightly sticky when unlocking by hand compared to a different ar that is functioning correctly with a few rounds through it. I guess I will dig into disassembling it and cleaning it.

 

[topclass2017]

sounds like disassembly, thorough cleaning and lubrication, followed by break-in usage should solve most of the problem. that has been my experience with new AR's. prior to re-assembly check for burrs and/or any other rough spots and treat accordingly.

 

[Coyotefurharvester]

Has the lower you assembled functioned with any upper?

 

[TIMO]

Not trying to start anything but, I have never had or heard that an AR needed any type of break-in, factory or home built. Failure to eject may be a dirty chamber or too large gas port just to name a few items as well as the extractor stated above. The other AR sounds like it is binding between the bolt & carrier or the barrel extension. May be as simple as the gas tube is not aligned with the gas key. Inspection and proper cleaning and lube will help in the diagnosis.

Just my .02
Tim

 

[john 800]

Has the lower you assembled functioned with any upper?

No, both were new and I did not have another one with me at the range

 

[Twdmar]

sounds like disassembly, thorough cleaning and lubrication, followed by break-in usage should solve most of the problem. that has been my experience with new AR's. prior to re-assembly check for burrs and/or any other rough spots and treat accordingly.

This is what I would do. Pull it apart, hose it down with brake cleaner. Then oil it well and cycle it by hand a bunch.

Not trying to start anything but, I have never had or heard that an AR needed any type of break-in, factory or home built. Failure to eject may be a dirty chamber or too large gas port just to name a few items as well as the extractor stated above. The other AR sounds like it is binding between the bolt & carrier or the barrel extension. May be as simple as the gas tube is not aligned with the gas key. Inspection and proper cleaning and lube will help in the diagnosis.

Just my .02
Tim

Some ARs are junk.

 

[Herzo]

I had a 5.56 that would not extract, it turned out to be an oversized gas port. The bolt was attempting to begin the extraction cycle before the case had relaxed it's "grip" on the chamber. An adjustable gas block could rectify the situation.

A misaligned gas port may be the answer to the second situation, too little gas can cause the bolt to not fully move to the rear. If it has a free floating barrel, it may require a 0.040" spacer between the shoulder on the barrel and the gas block.

 

[john 800]

I had a 5.56 that would not extract, it turned out to be an oversized gas port. The bolt was attempting to begin the extraction cycle before the case had relaxed it's "grip" on the chamber. An adjustable gas block could rectify the situation.

With that instance, after the round had been fired would it extract by pulling the charging handle? Is the adjustable gas block how you fixed yours?

 

[Herzo]

With that instance, after the round had been fired would it extract by pulling the charging handle? Is the adjustable gas block how you fixed yours?

I could sometimes cycle the action using the charging handle, but frequently I would need to use a wooden block to drive the bolt open. This was before adjustable gas blocks were available so l carefully drilled and tapped the barrel (being certain not to drill into the bore), inserted a stainless screw and then drilled the hole to the proper size. The 16" barrel came with an 0.093" gas port which would be proper for a 20", I redrilled it to 0.070" I'm not certain what the proper gas port size would be for your situation.

 

[Walt Krafft]

WOW!!! I want to see that drill that makes an 0.093 hole a 0.070 hole.

 

[Herzo]

WOW!!! I want to see that drill that makes an 0.093 hole a 0.070 hole.

I have the world's only supply.

 

[Coyotefurharvester]

Op is saying 2 commercially manufactured complete uppers don't function on a lower he assembled? I know where I would start.

 

[Herzo]

Op is saying 2 commercially manufactured complete uppers don't function on a lower he assembled? I know where I would start.

Different problems do not necessarily correlate to the same instigating cause. My situation was with a commercially manufactured upper.

 

[jelenko]

I'm with finding a known good lower. I find it's a lot easier to have at least one part that's known to work.

If the new uppers don't work with a known good lower, I'd call the vendor for help. They know them best.

 

[Herzo]

Are both uppers the same barrel length? If not, what are they and which exhibits which problem?

 

[Forum Boss]

Lube the contact surfaces on the bolt carrier. Check the gas rings on the bolt — the gaps should not be lined up (I liked the one piece spiral rings, but I know many folks don’t understand them ).

Make sure the fitting for the gas on top of the bolt is clear.

Look for any binding of the spring and buffer.

 

[john 800]

Op is saying 2 commercially manufactured complete uppers don't function on a lower he assembled? I know where I would start.

Correct but it was on 2 different home assembled lowers. I have another lower I will try tomorrow. One question I have that nobody has really said much about is the buffers and springs, I dont know if a 6.5 grendel needs anything other than a standard buffer and spring or not. Maybe I will call bca tomorrow.