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Mega MATEN cycling issues

sentry1

sentry1

Crayon Eater
Full Member
Minuteman
Jul 7, 2012
1,991
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41
Madison, Alabama
Long story short: My Mega MATEN is having cycling issues. The bolt rarely ever locks back on an empty mag, and most times it will cycle just enough to spit out the empty brass, but not enough to chamber a new round.

I've been playing with the gas block, adjusted it to ensure it was aligned, playing with the gas adjustment screw to see how it works at different settings. Nothing so far has led to reliable functioning.

- With a 16" carbine gas system barrel and low pro gas block on this build, I never had any of these issues.
- LC M80: Rarely ever chambers a new round after firing
- LC M118LR: 30% chance it chambers a new round after firing
- FGMM 175: About the same as the M118LR
- I have tried opening up the gas block all the way for full gas, didn't remedy the issue
- I have used both the heavy carbine spring, and the standard DPMS carbine spring. Both are definitely .308 springs btw, no mixups here.

Option 1: Loc-tite all around the Seekins block to see if it's a leak that's causing the issue.

Option 2: Put the low pro gas block back on and see if that fixes the issue. The Seekins just doesn't work well on this barrel anyway.

Option 3: Throw some things in a fit of rage then find a good AR gunsmith, exchange money for peace of mind and let him fix the problem.

Specs:
Mega MKM MATEN receiver set
Mega 20" .308 barrel, rifle length gas system, .089" gas port
DPMS rifle length gas tube
Seekins adjustable gas block
Carbine buffer tube w/DPMS buffer, DPMS carbine spring & Slash heavy carbine spring (tried both, no good)
DPMS BCG w/ JP enhanced bolt
 
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I'll do my best and say that a carbine needs the right amount of gas/spring/buffer weight. You said you have a heavy spring maybe that is too strong for your buffer and not letting the bcg cycle far enough to strip a new round. My guess is that your set-up is not configured right. Although I can't say that this is the issue but my best guess.

I've never used a carbine system since I like the rifle length better. Hopefully someone can shed some more light on this subject.
 
I bet an AR-10 gas tube will solve your issues.
They are about 1/4" longer than the DPMS and will give your BCG a little more exposure to gas. I read before where a guy was having similar issues to you and thats what solved his.

Thats what I use in my MA-10. I have no problems with gas flow in my 20" barrel, adj. gas block and rifle gas.
 
I have a similar MA TEN Build with no cycling issues.
MA TEN Mono rail
16" Ultra Match Barrel
Syrac adjustable gas block
Slash Heavy Buffer and spring

I would say it is a gas problem ~ check the position of the gas block (not covered)
Try different spring rates or different buffer weights.
 
wareagle700 said:
I bet an AR-10 gas tube will solve your issues.
They are about 1/4" longer than the DPMS and will give your BCG a little more exposure to gas. I read before where a guy was having similar issues to you and thats what solved his.

Thats what I use in my MA-10. I have no problems with gas flow in my 20" barrel, adj. gas block and rifle gas.
Click to expand...

This might be your answer. Despite being DPMS / LR-308 pattern barrels, some manufacturers (including Krieger and Criterion) drill the gas port at AR-10 length, which is 3/8" longer than standard. If that's the case, you might simply need an AR-10 gas tube instead of your DPMS version. (I don't know how your Mega brand barrel is set up.)

An easy way to check is to see how far the gas tube extends into the upper receiver. It should extend at least half way of the cutout for the cam pin.
 
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About a month ago i had the exact same problem with a 18 inch dpms 260 barrel i bought. I tried everything just like you and when taking off another gas block to try i noticed the gas port hole in the barrel was half the size of all of my other barrels. My 308,24 inch 260 and my 243 were all .076 and the 18 inch barrel was around .060 so i had it drilled out to .080 and she runs like a champ. I know that feeling when you want to smash the fucr on a tree but just keep on looking.
 
It seems like your issue is more than the "it just needs to break in issue" that my brother and I had with our builds. Both of ours would cycle fine with 168gr FGMM for 20-30 rounds then begin to fail locking back. Less than 168gr experienced cycling issues a lot sooner. It wasn't until about 300 rounds that the gun reliably cycled (mine was a 16" Noveske barrel and his was a Rainier UltraMatch). FWIW, even after broken in, we could never reliably cycle 147gr ball ammo.

Custom AR308's can be frustrating compared to complete builds by the likes of Larue, POF, LMT etc...
 
xNF_9 said:
I'll do my best and say that a carbine needs the right amount of gas/spring/buffer weight. You said you have a heavy spring maybe that is too strong for your buffer and not letting the bcg cycle far enough to strip a new round. My guess is that your set-up is not configured right. Although I can't say that this is the issue but my best guess.
Click to expand...

Already tried replacing the heavy buffer with a standard DPMS buffer, no improvement.

Rubberdown said:
Sure sounds like you ought to go back to what worked. Why did you switch to the new gas block?
Click to expand...

This barrel never had any other gas block, the previous 16" barrel had the plain gas block, but it had awful groups, even with match ammo. I figured I'd try a fancy new gas block and tune the gas system just right with the new barrel and loads.

wareagle700 said:
I bet an AR-10 gas tube will solve your issues.
They are about 1/4" longer than the DPMS and will give your BCG a little more exposure to gas. I read before where a guy was having similar issues to you and thats what solved his.

Thats what I use in my MA-10. I have no problems with gas flow in my 20" barrel, adj. gas block and rifle gas.
Click to expand...

Hmm, I might try this. But where do I find one that's specifically longer, and will it keep the BCG from going fully into battery?
 
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Just get an AR-10 gas tube from Armalite. They only make one size. Call or order online. I got mine in about 2 days.
As someone said above, some barrels are drilled for AR-10 gas length and not DPMS. My Lilja is an AR-10 length. Your bolt should close on either one.

If you can post a picture of the inside of your receiver with BCG and charging handle removed I can tell you which tube you need.
 
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Well I also have a mega 20" and use a dpms gas tube and it cycles fine but I using a plain rainier arms match gas block that isnt adjustable... so who knows.
 
You probably would have noticed this already if it is the case, but just to be safe... is the gas key on the bolt carrier tight?
 
Ditch the adjustable gas block. Make sure you gas port in the barrel is lined up correctly with the gas block. If the port is covered, even just a little, it could give you issues. Confirm you have the correct hole size with the barrel manufacturer.
 
cfulback32 said:
You probably would have noticed this already if it is the case, but just to be safe... is the gas key on the bolt carrier tight?
Click to expand...
Gas key is nice and tight.

BLDTYLRY said:
Confirm you have a AR 308 Carbine buffer and not a AR15 Carbine buffer.
Click to expand...
Already covered this.

sawman556 said:
Ditch the adjustable gas block. Make sure you gas port in the barrel is lined up correctly with the gas block. If the port is covered, even just a little, it could give you issues. Confirm you have the correct hole size with the barrel manufacturer.
Click to expand...

This was my first thought. Took the gas block off, and I can see the imprint of carbon buildup around the port, where it expands into the hole in the gas block. Looks to be properly lined up. I'll use some drill bits to check the hole size later today.

sawman556 said:
Ditch the adjustable gas block. Make sure you gas port in the barrel is lined up correctly with the gas block. If the port is covered, even just a little, it could give you issues. Confirm you have the correct hole size with the barrel manufacturer.
Click to expand...

Called up Mega, they drill the gas port to .089", and I got .0885" with my calipers, so that seems to be fine.

I was hoping to avoid beating up my fancy match brass with this adjustable gas block, but I think I'm beating it up more with all the jamming issues this block is giving me.

Midway just shipped the plain lo-pro gas block today, so I'll get to that this weekend, hopefully.
 
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So, I talked to Mega Arms today. Their in-house armorer was as helpful as he could be without the rifle in front of him, but basically all he could tell me was to check the gas block alignment, or go to a rifle buttstock/buffer/spring.

So I've got a Rainier Arms barrel dimpling tool on the way, courtesy of a helpful hide member, so the gas block will be as properly aligned as I can get it.

Technically, the current configuration with the carbine stock SHOULD work.

IF some tinkering doesn't fix the issue, and IF the new low pro gas block doesn't help either, can anyone recommend a gunsmith shop that I can send this rifle to? I.E. As a last resort, "Here's my rifle, here's my money, just make it shoot so I can use it."
 
I hope the alignment fixes the problems! What would changing to rifle stock/buffer/spring do? Thats my set up and I am not having issues but I dont get what it would change so that the gun would cycle reliably.
 
cjlane said:
I hope the alignment fixes the problems! What would changing to rifle stock/buffer/spring do? Thats my set up and I am not having issues but I dont get what it would change so that the gun would cycle reliably.
Click to expand...

The A2 spring is not as stiff as the carbine spring, so it should cycle with less gas pressure. However, I checked the gas block alignment, it's right on. My theory is that the Seekins gas block is leaking gas somewhere. We'll see on Friday when my Midway package gets in.

I'm using a Mega Arms barrel, the gas port is 0.089", which is the proper size according to the rep from Mega.

The root issue seems to be that there's not enough gas coming back to fully cycle the bolt. I don't want to go to the expense of purchasing an A2 buffer tube, buffer, spring, and stock unless I absolutely have to. I suppose a Magpul PRS kit would replace the SAPR, but I like my setup as is.
 
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Lock the bolt back with the mag removed. Looking through the magwell, how far does the gas tube extend into the upper receiver in relation to the cutout for the cam pin?
 
Can you post a picture of your buffer and spring? I have two MA-Tens one has a CTR and the other has a PRS, neither have issues.
 
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BLDTYLRY said:
Can you post a picture of your buffer and spring? I have two MA-Tens one has a CTR and the other has a PRS, neither have issues.
Click to expand...

Both buffer and spring are DPMS .308 carbine models, these are the exact items I ordered from Brownells as part of the build. I don't have any other .308 ARs, and the parts went directly from the box into the rifle, so there was no mixup with my .223 AR.

308CS10B 308 CARBINE BUFFER
308-CS-10A 308 CARBINE BUFFER SPRING

Here it is. So, do I need a longer gas tube?

UM1HCshl.jpg
 
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No. That looks good.

Keep at it. You will figure it out. I just went through a similar process with mine ejecting. They are a bit harder to figure out than AR-15's.
 
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I'd replace the buffer spring. I use Tubbs Flatwire AR 308 CS Buffer Spring. They are a little more than the $5 you spent but it should work a lot better.

When you pull the bolt back does it go all the way back with minimal effort?

image.jpg
 

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BLDTYLRY said:
I'd replace the buffer spring. I use Tubbs Flatwire AR 308 CS Buffer Spring. They are a little more than the $5 you spent but it should work a lot better.

When you pull the bolt back does it go all the way back with minimal effort?

View attachment 11835
Click to expand...
Is the Tubbs softer than the standard spring?

Edit: From Tubbs website, he states that his springs are equivalent to 'extra power' springs. Adding MORE resistance to the system seems like the opposite of what I want to do.
 
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sentry1 said:
Is the Tubbs softer than the standard spring?
Click to expand...

Spring rate is about "Normal" but the spring is able to completely compress due to its shape. Nice part is you already have and adjustable gas block so you should be able to dial the gas way down and only require minimal gas to cycle the bolt.

I'm guessing the POS DPMS spring is the issue, it's probably too stiff or has too many coils.
 
sentry1 said:
From Tubbs website, he states that his springs are equivalent to 'extra power' springs. Adding MORE resistance to the system seems like the opposite of what I want to do.
Click to expand...

Good luck figuring this out. All I can tell you is my setup works with the Tubbs Buffer Spring and my Syrac GB is only opened one full turn from closed. I am running a 20" Ultramatch, Young Manufacturing Match 308 Carrier with JP Bolt; so our systems are built fairly close.
 
Your terminology is confusing me. "Completely compressed" just means it's compressed to it's solid length, i.e. all the coils are touching. The DPMS spring is able to completely compress, the Tubbs spring doesn't really give me anything on that basis.

As for the stiffness, the DPMS spring doesn't feel overly stiff either. Depending on what it's solid length is, I may try cutting off a coil or two, but I'm concerned that it won't have enough force on the return stroke to properly lock the bolt in battery if I do that.
 
"At installed height (bolt in battery) the load on the bolt is increased by about 10% compared to our CS round wire spring. This works more energy before the bolt unlocks and provides a flatter recoil impulse. This minimizes the effect of the spring returning the bolt to battery. The CS flat wire spring requires about 6% less force to fully compress than our CS round wire spring. Less energy is bled off to the gun, resulting in reduced rifle (and sight) movement."
 
Everything looks good in the component department. Unless the wrong springs/buffer were shipped. (plausible)
Your rifle looks really dry. Have you tried running it wet? I mean spraying oil in your face when you shoot wet. Just a thought... I had a newly built AR that wouldn't run for shit until it "broke in" with lots of lubrication. Maybe the lug area on the new barrel is a little tighter than the old barrel. BTW did you check headspace? I hope you get it running.
 
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BLDTYLRY said:
"At installed height (bolt in battery) the load on the bolt is increased by about 10% compared to our CS round wire spring. This works more energy before the bolt unlocks and provides a flatter recoil impulse. This minimizes the effect of the spring returning the bolt to battery. The CS flat wire spring requires about 6% less force to fully compress than our CS round wire spring. Less energy is bled off to the gun, resulting in reduced rifle (and sight) movement."
Click to expand...

Are we getting our signals crossed, or am I missing something here? The info above states that the flat wire spring takes more energy to compress than their round spring (irrelevant, since I can't compare it to the spring I have now), but I'm already bleeding off too much energy somewhere in the system, hence the bolt isn't going all the way back. Even if their claims were true, my bolt isn't getting to the point where it would experience their decreased load at full compression.

I want less load on the closed bolt, or more gas.

On a technical note, I'm confused as to their claim that the flat wire spring exerts more force when extended than it does when compressed, relative to the round wire spring. That doesn't sound right, unless the spring constant decreases as it's compressed.

Those figures sound like some marketing mumbo jumbo done up with voodoo math. I've done enough voodoo math on school projects to know! I'd like to see someone weigh in on the specific characteristics of flat wire springs.

Back to the original topic: just checked the tracking on my Midway package, and I should get the new gas block delivered today, so we'll see if the Seekins gas block is the culprit here.
 
biner626 said:
Everything looks good in the component department. Unless the wrong springs/buffer were shipped. (plausible)
Your rifle looks really dry. Have you tried running it wet? I mean spraying oil in your face when you shoot wet. Just a thought... I had a newly built AR that wouldn't run for shit until it "broke in" with lots of lubrication. Maybe the lug area on the new barrel is a little tighter than the old barrel. BTW did you check headspace? I hope you get it running.
Click to expand...

Yup, had the barrel headspaced by someone who knows what he's doing, it came in at 0.002" over the minimum.

You make a good point on the lube... I'm going to hose that sucker down and try running it extra wet.

Note: I tried cycling some rounds through it by hand, and I've noticed that it's real tight sometimes, i.e. chamber a round, and try to eject it by pulling back on the charging handle, and the bolt won't budge. On a few tries, I've had to pull the upper off and use a piece of wood & mallet to smack the bolt out.
 
Travis224 said:
Silly question, how are the gas rings, my AR was doing the same thing and new rings fixed that.
Click to expand...

Gas rings look to be good, I bought a brand new JP enhanced bolt for this build. Hmm... the bolt is a VERY snug fit in the BCG.

Could excessive friction on the bolt be the root cause of my issues?
 
IMO, if shot rings cause bolt to move easily and cause a gun to malfunction, i would venture a guess that the opposite end of that spectrum would cause similar problems. Either oil them or buy a different set. They are cheap so another set just to have on hand might be a good idea.
 
I don't think it's the gas rings impeding movement, I think it's the raised ridge, right behind where the extractor retaining pin goes, that's the issue. I assume that's there to act as a seal against gas?

I think the tolerance between that ridge and the inside diameter of my BCG is a bit too small. If I lube it up, push the bolt in, and then flick the BCG (every Marine knows what I'm talking about, I dunno about you other guys), the bolt only goes about halfway forward.

l_452000111_1.jpg
 
Honestly I think you are running it too dry, way too dry ... My maten with young nm bc and JP bolt was super tight new.... Tolerances were so tight pulling charging handle back to eject round was a pita for about 40 rounds, just like you are experiencing .... Run it super wet and cycle it repeatedly by hand using dummy rounds and I bet it works itself in. It just needs to be broke in....Lube lube lube the bolt, bcg, everything etc.... Run it wet wet wet while breaking in especially... 60-100 rounds with GB fully open.... Don't adjust till after break in. JP has a good article on their website on how AR's should be run wet... To the point they spray lube and that most people don't use near enough lube on a normal basis... Worth a read. If that doesn't solve your issue my guess is your GB has an issue.... I would recommend a Syrac or da7 adjustable gas block.... I run the Syracs, as do many, with no problems and no worries of losing adjustment. I would also make sure you were sent the right spring and buffer.... Mistakes happen.
 
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Well I'm off to Walmart to score a bottle of lube, I'm going to hose this thing down and see if I can't break it in.
 
I'd be truly surprised if that doesn't solve your problem.... Sometimes it's easy to over think things. And it's the easiest place to start.
 
sentry1 said:
Gas rings look to be good, I bought a brand new JP enhanced bolt for this build. Hmm... the bolt is a VERY snug fit in the BCG.

Could excessive friction on the bolt be the root cause of my issues?
Click to expand...

Yes, make sure you lube the crap out of that bolt! I used synthetic ATF to break mine in. Sat the entire bolt in it overnight. Pulled it out shook off the excess lube and ran it. Be mindful to not soak the chamber/barrel. Some will get in there, but, it'll burn off. Put a little grease on the lugs until they mate properly.
 
If you had said it was hard to pull charging handle back to eject a chambered round in your Op I would have chimed in sooner as this is very common from my experience. Lube everything that has any friction being mindful of not to saturate the chamber like already mentioned....Lube inside the upper, charging handle etc, I usually put a light grease like tw25 on the bolt cam pin and lugs.... Reducing any friction will help during break in and the excess lube helps wash away/suspend particles from the wearing in process. After hearing high accolades from some pretty knowledgeable people I'm gonna try fireclean lubricant soon but even if it works as described I'll still run pretty wet.
 
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