Short cycling problem when switching between upper

More
15 years 10 months ago #993 by THREEDFLYER
Short cycling problem when switching between upper was created by THREEDFLYER
So here's the situation:
I am shooting a Noveske/Armalite AR10 with the Vltor Carbine AR10 Buffer tube/stock.
I have two complete uppers both Armalite/Noveske....one is the 16" Noveske barrel, the other is the 24" match Armalite barrel.
Was at the range today doing my barrel break-in.

Shot approx 30 rounds of 5 different ammo versions through the 16" upper and I had one short cycle with some Lithuanian surplus.
Shot about the same ammount through my 24" match barreled upper and had several (80%) more short cycle's.
Again, using the same lower/mag, etc.

I have checked for gas tube leaks and see nothing apparently out of the ordinarly.
I have a completely seperate BCG for both uppers, not using the same upper.

Ideas of why my 24" upper is short cycling?

Thanks in advance,
Tom

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago #994 by crux
Replied by crux on topic Re:Short cycling problem when switching between upper
In Armalite's Tech Note 50 (2002) suggests fouling as the primary cause of short cycle. They recommend checking all these: Fouling or corrosion on rifle chambers, ejector spring, extractor, extractor spring, Gas tube etc.

I presume you were cleaning frequently during breakin, so I raise my eyebrow at the problem. Some mil surplus is reputed to be dirty, any chance any of the components they mention are fouled?

If everything is clean and lubricated, I'd probably send them a note describing the trouble shooting done, and ask for further suggestions.
The following user(s) said Thank You: jtallen83

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago #998 by THREEDFLYER
Replied by THREEDFLYER on topic Re:Short cycling problem when switching between upper
Yes, I was cleaning the rifle between shots during breaking thouroughly and had no fouling issues for sure.
In fact, the short cycling happened on the first and second shots.
I plan to call both Noveske and Armalite in the morning to get their feedback.

Thanks for your thoughts! Others are welcome to chime in.

Tom

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago #999 by THREEDFLYER
Replied by THREEDFLYER on topic Re:Short cycling problem when switching between upper
www.calguns.net/calgunforum/showthread.php?p=1636510

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago #1001 by THREEDFLYER
Replied by THREEDFLYER on topic Re:Short cycling problem when switching between upper
From what I am reading, there may be an undersized gas port issue.
I will contact Armalite and get the scoop and report back.

3D

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago #1002 by THREEDFLYER
Replied by THREEDFLYER on topic Re:Short cycling problem when switching between upper
Talked to Tim at Armalite.
My gas port measures .078 and Tim is telling me it should be .084 for this 24" heavy barrel.

I found a couple of numbered drill bits that are close.
The #45 is .082 and the number 44 is .086 so I'll start with the smaller first and check function.

I hope to range test this later today and report back.

3D

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago - 15 years 10 months ago #1004 by THREEDFLYER
Replied by THREEDFLYER on topic Range results are in....
Two words....PROBLEM SOLVED!!

So I used a #45 (.082) drill bit on the gas port and had no issues doing it. Used a small amount of cutting oil and a new bit. Since the barrel is Chrome/Moly, the drilling went smooth.

I re-installed the gas block and made sure it was lined up perfectly with the port. There are no torque specs on the two hex bolts that hold on the gas block, but Tim Rooker of Armalite said to go good and tight.

After setting up at the range, I went through several 5-shot groupings of several types of ammo including Federal premium 168 grain Match, Winchester 147 grain (white box) Austrailian, Lithuanian, South African and English surplus.
I had NO malfunctions of any kind....no short cycling, and the bolt latch engaged every time the mag was emptied.

I am not sure if there are different gas port sizings depending on the barrel length (forgot to ask Tim that) but I do know that using the .082 on mine solved all of my issues.

So...if you have an Eagle Arms 24" Match Upper, and are having issues...this is the fix that worked for me.

3D
Last edit: 15 years 10 months ago by THREEDFLYER.
The following user(s) said Thank You: jtallen83

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago #1018 by crux
Replied by crux on topic Re:Short cycling problem when switching between upper
Good to hear the probable root cause was found. Will be interested to hear if that fixed it. Any thoughts on how the rifle might have ended up with wrong size on the gas tube? Was the tube salvaged from a previous build?

Please Log in or Create an account to join the conversation.

More
15 years 10 months ago - 15 years 10 months ago #1020 by THREEDFLYER
Replied by THREEDFLYER on topic Re:Short cycling problem when switching between upper
Crux...

It was NOT the gas tube, it was the gas port that is drilled on the top of the barrel at the location of the gas block.

Yes...drilling out the gas port to .082 fixed the problem.
Apparently there were approx. 100 barrels drilled to the .078 port size...and these were an experiment.
The experiment failed and these barrels were never supposed to be shipped/sold.
BUT...someone in the wharehouse sent them out by mistake.

So, if you have one of these 24" barrels with the .078 port, you can either drill it out to .082 yourself OR send it back to Dave at Armalite. But it's very easy to do if you have the tools.

3D
Last edit: 15 years 10 months ago by THREEDFLYER.
The following user(s) said Thank You: jtallen83

Please Log in or Create an account to join the conversation.