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Cinders

Short stroke problem

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Hi all!

Criterion 18" barrel w/ rifle length gas tube

Aero M5 carbine buffer kit (standard carbine spring and 3.8 oz buffer)

I'm getting short stroking from the start.  It's not an adjustable gas block, just full open, so that's not an option.

Should I but a lower weight buffer or get a softer spring?  Or any other ideas out there?  

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Also, what is the internal depth of your buffer tube?  Some of Aero's have been known to be a non-standard length.  It should be exactly 7 inches.

Edited by Armed Eye Doc

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1 hour ago, Cinders said:

Hi all!

Criterion 18" barrel w/ rifle length gas tube

Aero M5 carbine buffer kit (standard carbine spring and 3.8 oz buffer)

I'm getting short stroking from the start.  It's not an adjustable gas block, just full open, so that's not an option.

Should I but a lower weight buffer or get a softer spring?  Or any other ideas out there?  

Need aaaalllllloooooooootttt more information here.  You've listed two parts of your system.  The barrel and recoil system parts.  Need to know the rest of the parts that make up this whole gun.

Next, need your definition of "short stroking" - describe exactly what a fired cartridge does - what happens when you fire one round?

Read this thread when you have time - it's important.

Your Criterion barrel will have a 0.095" gas port diameter, if the gas block journal size is 0.750".  That's a given, and that would be the correct gas port size for that barrel configuration.  More than anything, we need to know what you're talking about, with the "short stroke," because that shouldn't be the case here, with your combination of parts. 

Where does your gas tube end, in the upper receiver?  If you read that thread I linked above, you'll know exactly what I'm asking about.

Edited by 98Z5V

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Very important questions here - not like the others weren't important, too - get to those first...   then...

What AMMO are you shooting, that's causing this malfunction?...  How many rounds are through this gun so far?...   How well did you lube it?... :popcorn:

Edited by 98Z5V

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Thanks for the replies so far!  This seems like an easier waterboarding than the one I got in SERE school many moons ago.

Here's what I got:

 

Aero M5 carbine buffer kit

-Buffer is 2.5" and 3.8 oz

-Spring is 11" and copper-colored (standard?)

Buffer tube is 7" deep

Criterion 18" barrel w/ rifle length gas tube

Gas tub length is 15.125" (Aero Precision stainless)

I'll need to get the bolt clearance photos tomorrow.

This was the first batch of rounds I put through it, 3 brands (Winchester, Hornady, and Federal).  I lubed it up with RemOil and disregarded the early issues as the oil working in.  The problem(s) were slightly different with each brand of ammo.  The Federal would stovepipe on extraction.  The Winchester would not extract consistently nor feed the next round.  The Hornady would extract cleanly (mostly) but would not grab the next round.  I could manually rack it and it would grab the next round smoothly (so probably not magazine).

My initial thought was putting a full-length gas tube w/ 18" barrel on a carbine buffer was out of balance, as carbines tend to be over-gassed.  

20200710_155210.jpg

20200710_160558.jpg

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I did wipe it with a dry rag before putting it into vault (didn't full clean it yet, I thought I would go to the range this week), but you might be right that I didn't oil it up enough.  I've never had a new AR, although my experience as infantry thought it was oiled enough at the range... but I only used well-worn systems compared to a bone dry new system.

I'll try giving each carrier piece an oil rub next time and see how it works.

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The large frame ar is unlike its smaller kin. These things need lots of lube during break in. If you think it’s lubed enough lube it some more. If you don’t get some spatter on you when you shoot it probably wasn’t lubed enough. Think dripping wet. Even with that sometimes they take a while to break in. Not like the ar15 that sounds like crap when dry but will still run.

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2 hours ago, Cinders said:

This was the first batch of rounds I put through it, 3 brands (Winchester, Hornady, and Federal).  I lubed it up with RemOil and disregarded the early issues as the oil working in.  The problem(s) were slightly different with each brand of ammo.  The Federal would stovepipe on extraction.  The Winchester would not extract consistently nor feed the next round.  The Hornady would extract cleanly (mostly) but would not grab the next round.  I could manually rack it and it would grab the next round smoothly (so probably not magazine).

My initial thought was putting a full-length gas tube w/ 18" barrel on a carbine buffer was out of balance, as carbines tend to be over-gassed.  

20200710_155210.jpg

 

Your gas tube is perfect - don't mess with it.  Leave it alone.

The "as carbines tend to be overgassed" statement means you're way off track here.  You're running a carbine recoil system, which doesn't have anything to do with the gas system. 

Again, that barrel will have a 0.095" gas port, or close enough within a couple thou.  Gas tube is perfect.  Buffer is WAY too light for the mass of a .308AR BCG, and the power of a .308 Win cartridge.  WAY too light.  It need to be 5.4oz, or as close as you can get to that, and it needs to run a good recoil spring.

So...  You can fix this one of two ways.  You can KEEP your receiver extension - if it's truly 7.000" internal depth, and not 7.100" internal depth (measure closely, and carefully).  If you KEEP that receiver extension, then you need a buffer that's 2.500" long, and damn close to 5.4oz.  KAK makes that beast, and it's 5.3oz - good enough.  It's certainly not 3.8oz.

https://www.kakindustry.com/lr308-carbine-buffer-heavy

Next, you need a spring that's been designed to run a real 2.500" long buffer, made for the weight of a .308AR BCG, and the power of the .308 Win cartridge - you need the Sprinco Orange Spring.  It's in stock here, right now.  That doesn't mean that it will be in stock in 15 minutes, though.  Not in these times.

https://www.primaryarms.com/sprinco-ar10-orange-extra-power-carbine-buffer-spring

Your problem isn't overgassing - you're under-recoiled.  The the weight of this BCG, and the power of the .308 Win round, your BCG is moving too fast, and missing the next round in the mag.  It's also extracting too early - because there's shiit for buffer weight and spring pressure holding it in place, to allow the case to cool - and reliably extract.  There's not enough MASS to control that ASS...  

Looks like overgassing, sure.  The bandaid is an adjustable gas block.  But, that's putting the bandaid on the wrong cut...   You need a reliable recoil system, and not something that's cheap for a manufacturer to pump out.

Second way to fix this, for real, for permanent, forever (the above method will do that, too) - just buy the complete Armalite AR-10 Carbine Recoil System, and be done. The Armalite part # is AR10REKIT01.

https://www.armalite.com/SACItem.aspx?Item=AR10REKIT01&ReturnURL=/Armalite/Product-Category/AR10-Parts-Accessories/Lower-Receiver-Parts&Category=ac614400-ff09-4cdf-9d35-419a654e7201

Both methods work very well. 

 

Reading this thread would have saved you a bunch of time, and you would have figured it out on your own:

 

Edited by 98Z5V

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Thanks 98ZV5!  Appreciate the hard info.  An old USMC buddy built this for me, so rookie mistake on our parts.  Also, thanks for the links, it's hard to find hard info like that in the sea of Google opinions.

I'll report back after getting the armalite.  Thanks to all for the advice!

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Can I get a clarification:

Buddy and I went over the  build in detail to figure out where we went wrong.  On the Aero M5 carbine kit, we found a single line in the description that basically said "for those interested in setting up a carbine gas system."

I realized I've been reading carbine as "short or collapsible stock and shorter barrel," but maybe some companies literally mean "carbine gas system" rather than anything else.  It took a lot of digging to get some hints that the 7" buffer tube is for carbine gas systems and a fixed stock is for longer barrels.  My 18" barrel seems to fall in that gap between short and long.

If anyone has any clarification or knowledge to hit me with, please do!  (Also, I'm awaiting my Armalite buffer kit to test).

 

Thanks!

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14 minutes ago, Cinders said:

  It took a lot of digging to get some hints that the 7" buffer tube is for carbine gas systems and a fixed stock is for longer barrels. 

That's a myth.  Completely.

Gas system and recoil system are completely independent of each other, but there MUST be a balance between the gas system and recoil system for the gun to function as it was designed.

What went wrong was the lightass buffer, at 3.8oz.  These things were designed from the ground up to run a buffer that weighed 5.4oz. 

My .260 Rem runs like a finely tuned F1 racecar.  20" rifle gas barrel, and I experimented with the 7.000" AR15 carbine extension and built my own heavy buffer.  Sprinco Orange spring.  It's a dream, and it's accurate as all hell - and it's rifle gas and carbine recoil.

It works, because I built it adhering to the principles of what it takes to make one of these guns function properly.

https://forum.308ar.com/uploads/monthly_2018_09/image.png.89d707356d99b52eb2bf340e7fb62810.png

 

Did you even read that thread I linked in an earlier post?...:popcorn:   It breaks everything down in excruciating detail...

Edited by 98Z5V

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I did, but I ran across a buffer length/weight chart and it, oddly, pointed to DMPS 7" tubes to use 2.5" and 3.8 oz while Armalite uses 5.8" and a 8" tube.  Why would they even sell a 3.8 oz for a .308?  

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Apples and oranges there. Be careful and read that again. You’re quoting carbine specs on one and some rifle on the other. I’m my own dumbass opinion, I think the reason we see so many barrels with small gas ports is because they are desperately trying to make it run right with a lighter buffer. They think by cutting the gas they can balance it. It’s been proven here. Bunch of times in guns that just won’t run right. Proper gas port opening and the right buffer weight....happy gun. 

Edited by DNP

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In the old days (so I’ve read, I wasn’t really there- plenty of folks on here were though) the long version AR with a fixed stock was a rifle and the shorter one with a collapsible stock was a carbine. Hence the birth of the terminology. Things have changed, but even then you could have run a carbine stock and buffer setup on a rifle platform. We’ve learned to mix and match over the years and when you’re talking carbine or rifle there’s two halves you’re talking about. The gas system, and the recoil seystem/stock. There’s also a bunch of other stuff that’s been thrown in the mix over time. Mid length gas, different stock and buffer setups. As long as you understand them and plan accordingly, you can make a lot of combinations work just fine together. I have noticed they don’t make a mid-length buffer tube....interesting, no?  Not really, two separate halves with two different functions - similar names due to history. 

Edited by DNP

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Solved!  The Armalite buffer and spring fixed the problem.  I am having about 3 out of 10 rounds getting "bit" as the bolt face hits the casing.  Borrowed a slightly softer buffer spring and that seemed to fix the problem.  

 

Thanks again everyone!  It was just a balance of gas vs buffer issue.

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6 minutes ago, Cinders said:

Solved!  The Armalite buffer and spring fixed the problem.  I am having about 3 out of 10 rounds getting "bit" as the bolt face hits the casing.  Borrowed a slightly softer buffer spring and that seemed to fix the problem.  

 

Thanks again everyone!  It was just a balance of gas vs buffer issue.

Awesome news.  Thanks for reporting back.

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