AR-10 Short-stroking With Scope Mounted, Zero Issues Without

[Valkyrior]

Hi all,

Just made this account tonight actually. My first AR-10 build is giving me too much trouble. I've got an ATN X-Sight 4K Pro 5-20x that I bought to use with it, but every time I take it shooting, there's short-stroking. I started out with a Juggernaut Tactical handguard on an Aero Precision M5 upper and lower receiver (I am now aware the JT handguards are incompatible with Aero stuff), and switched to an Aero Precision handguard and barrel nut after having problems with the gun short-stroking then as well. I assumed this would fix it due to the gas tube not going in to the gas port on the upper without some tough loveeven with proper timing on the barrel nut. This problem was fixed after switching handguards, but the short-stroking problem was only fixed when I had the scope off the gun. It feeds just fine! An entire 10rd PMAG shot perfectly without the scope, but every single round short-strokes with the scope on the gun. I've checked to see if the gas block has moved, is not properly aligned, or has even come loose. All three are negative. I'm at my wits' end with this gun and just confused on the whole thing. Is it still a gas issue? Is the weight of the scope just weighing the gun down so much that it's affecting the cycling? Any help at all is appreciated; I'll post my specs below this wall of text.


Specs:
-Aero Precision M5 upper and lower receivers
-Aero Precision handguard
-Aero Precision gas tube (rifle length) and block
-Aero Precision carbine buffer tube kit for .308
-Aero Precision 308 BCG, black nitride
-Bear Creek Arsenal 20" barrel
-ATN X-Sight 4K Pro 5-20x
-Magpul M-Lok bipod

 

[Runnineh]

I'm assuming you used the same ammo with the scope on and off? By short stroking, are you stove piping?

 

[sboone]

Does the optic mount attach or contact the handgaurd somehow? Interfere with charging handle?

 

[Valkyrior]

Using the same ammo, 150gr and 162gr. No stovepiping though. It's ejecting just fine.

 

[Valkyrior]

Using the same ammo, 150gr and 162gr. No stove piping though. It's ejecting just fine.

I'm assuming you used the same ammo with the scope on and off? By short stroking, are you stove piping?

 

[Runnineh]

So then it's not feeding the next round?

 

[Valkyrior]

Does the optic mount attach or contact the handgaurd somehow? Interfere with charging handle?

Doesn't connect with the handguard, and the most it interferes with the handguard is just in terms of it getting in the way when I pull it.

 

[Valkyrior]

So then it's not feeding the next round?

Correct. I suppose this would be more of a failure to feed, but it doesn't lock back on an empty mag either. Leaves scrapes on my bullets, even picks some up but gets them jammed between the grooves on the chamber and the BCG, sometimes leaving dents in the brass.

 

[BuildingConceptsllc]

Using the same ammo, 150gr and 162gr. No stove piping though. It's ejecting just fine.

It's ejecting just fine? Then we can only assume it isn't picking up a round from the mag and that's the issue???

What buffer and spring are you running? AR10 variants can be picky about the buffer set up and the gas too. Need more info

 

[Runnineh]

It sounds to me it's a gas/buffer weight issue. The scope can't have any effect on this, I think it was just coincidence. I had built my own ar10 and there's a lot of growing pains, and doing searches here you'll see the same for a lot of people. My first problem was I didn't have an ar10 specific buffer, which it looks like you covered. I would start with getting an adjustable gas block.

What mags are you using? It could be that, however if it's not locking back, it makes me think it's not getting enough blowback.

 

[BuildingConceptsllc]

Correct. I suppose this would be more of a failure to feed, but it doesn't lock back on an empty mag either. Leaves scrapes on my bullets, even picks some up but gets them jammed between the grooves on the chamber and the BCG, sometimes leaving dents in the brass.

Ok, but if you manually pull the charging handle back, you can get it to lock and to pick up a round?

 

[Valkyrior]

It's ejecting just fine? Then we can only assume it isn't picking up a round from the mag and that's the issue???

What buffer and spring are you running? AR10 variants can be picky about the buffer set up and the gas too. Need more info

I'm using Aero Precision's M5 carbine buffer kit. Not sure what spring they use in that, but the weight and length of the buffer are 2.5" and 3.8oz. Yeah, it just won't pick up rounds from the magazine, instead just scrapes the brass and bullet or gets the bullets stuck between the BCG and chamber, sometimes denting the brass. This only occurs with my scope mounted.

 

[Valkyrior]

Ok, but if you manually pull the charging handle back, you can get it to lock and to pick up a round?

Correct.

 

[Valkyrior]

It sounds to me it's a gas/buffer weight issue. The scope can't have any effect on this, I think it was just coincidence. I had built my own ar10 and there's a lot of growing pains, and doing searches here you'll see the same for a lot of people. My first problem was I didn't have an ar10 specific buffer, which it looks like you covered. I would start with getting an adjustable gas block.

What mags are you using? It could be that, however if it's not locking back, it makes me think it's not getting enough blowback.

I'm using Magpul PMAGS, their 10rd ones. I'll pick up an adjustable has block and see if that fixes my problems. I thought at first it might be my buffer, but truth be told I don't know enough about the nitty-gritty details of it all to make an informed decision on if it was that...

 

[BuildingConceptsllc]

I'm using Aero Precision's M5 carbine buffer kit. Not sure what spring they use in that, but the weight and length of the buffer are 2.5" and 3.8oz. Yeah, it just won't pick up rounds from the magazine, instead just scrapes the brass and bullet or gets the bullets stuck between the BCG and chamber, sometimes denting the brass. This only occurs with my scope mounted.

An adjustable gas block would be my first thing to add. You could also play with the buffer weight and check spring length. The scope thing is weird, but in theory possible IF and only IF you are not securing the weapon into your pocket and the scope weight is causing the weapon to move a little too much and taking some of the force the bolt needs to go all the way back. Again, more gas would likely fix that. Just my thoughts, some others here are waaay better versed in this.

 

[BuildingConceptsllc]

I'm using Magpul PMAGS, their 10rd ones. I'll pick up an adjustable has block and see if that fixes my problems. I thought at first it might be my buffer, but truth be told I don't know enough about the nitty-gritty details of it all to make an informed decision on if it was that...

With AR10's, there's a lot of trial and error, even for gunsmiths. This is why people pay more for factory high end ones than for built high end parts put together. The factory has already debugged it.

 

[Valkyrior]

An adjustable gas block would be my first thing to add. You could also play with the buffer weight and check spring length. The scope thing is weird, but in theory possible IF and only IF you are not securing the weapon into your pocket and the scope weight is causing the weapon to move a little too much and taking some of the force the bolt needs to go all the way back. Again, more gas would likely fix that. Just my thoughts, some others here are waaay better versed in this.

That seems to be the consensus. I'm already looking for an adjustable gas block as we speak, as well as a heavier buffer to see if that fixes anything as well. I appreciate all of your help my friend! This has certainly been a process...and as much as it is annoying, I'm also enjoying it. Just means I'm learning for future builds, y'know?

 

[LonewolfMcQuade]

308AR.com

 

[357Max]

This thread needs pictures!

For starters a pic showing how this optic is mounted. Are you clamping the first pic rail on the hand guard?
Then pull the BCG/charging handle and take a picture showing where the gas tube ends within the upper. Should be middle of the cam pin notch.

The Bear creek barrel is listed as AR-10. Now maybe they're just using that as a generic term, but you've built a DPMS LR/SR 308.

AR-10 = Armalite
DPMS = LR/SR

They use different length gas tubes.

 

[Runnineh]

That's w

I'm using Magpul PMAGS, their 10rd ones. I'll pick up an adjustable has block and see if that fixes my problems. I thought at first it might be my buffer, but truth be told I don't know enough about the nitty-gritty details of it all to make an informed decision on if it was that...

Like BC said, it's a trial and error game with customs. If it doesn't work, don't let it get you down, move on to the next thing. Spring/buffer combo. Welcome to the ar10 life bud

 

[6.5SH]

Are you sure your gas block is aligned? After the first handguard issue did you replace the gas tube?

 

[357Max]

I strongly suspect that the Bear Creek barrel requires the Armalite rifle length gas tube.........meaning yours is to short and it's cutting the gas flow off to soon.

The picture of gas tube termination point in upper will confirm.

 

[Aftermath]

Does the optic mount attach or contact the handgaurd somehow? Interfere with charging handle?

You do realize that the charging handle does not reciprocate, right? And...contact with the hand guard would also have zero to do with cycling, right?

 

[357Max]

This post reaffirms my suspicion!

Bear Creek Arsenal Rifle Length Gas Tube Length

This may be common knowledge, but I couldn’t find it on the old inter web and there was no response from BCA. It was time for me to replace a 243 Win barrel which was shot out. Not needing a 4000 yard 1/4 inch MOA barrel like most, and not wanting to spend $600, I bought this BCA barrel for next ...

forum.308ar.com

 

[Aftermath]

An adjustable gas block would be my first thing to add. You could also play with the buffer weight and check spring length. The scope thing is weird, but in theory possible IF and only IF you are not securing the weapon into your pocket and the scope weight is causing the weapon to move a little too much and taking some of the force the bolt needs to go all the way back. Again, more gas would likely fix that. Just my thoughts, some others here are waaay better versed in this.

Agreed on the gas block but you'd think the added weight of an optic would mean you could hold LESS tight in the shoulder. Honestly, I've never had an AR platform that would not fire even if fired free recoil. Back in the day, we would test fire by holding on the other side of an oak tree, firing into the ground, one handed. Never an issue of cycling from the one hand hold. After a couple of builds, we stopped the around the tree firing.

 

[Valkyrior]

I strongly suspect that the Bear Creek barrel requires the Armalite rifle length gas tube.........meaning yours is to short and it's cutting the gas flow off to soon.

The picture of gas tube termination point in upper will confirm.

 

[BuildingConceptsllc]

Agreed on the gas block but you'd think the added weight of an optic would mean you could hold LESS tight in the shoulder. Honestly, I've never had an AR platform that would not fire even if fired free recoil. Back in the day, we would test fire by holding on the other side of an oak tree, firing into the ground, one handed. Never an issue of cycling from the one hand hold. After a couple of builds, we stopped the around the tree firing.

If the gun weren't right on the edge of not getting enough gas or some buffer issue,it likely wouldn't matter. I guess in theory the weight of the scope is only in play because of not holding the gun tight, therefore the added mass requires a little extra force to move the gun than it would have otherwise, and that extra force is just enough removed from the bolt cycle to not let it go all the way back. It's real easy to get a wrong part in the mix with how many are labeled online these days. It could very well be an issue of crossing patterns with either gas tube, spring, or buffer. If it cycles without the scope just fine every time, it sounds like an "add a little gas situation " and not a gas tube length issue imo, but I would never say never with AR10 Building, especially with how parts are labeled these days.

 

[Valkyrior]

Are you sure your gas block is aligned? After the first handguard issue did you replace the gas tube?

Pretty sure it's aligned. No, I did not replace my gas tube. I wondered if I should have, but wasn't entirely sure if needed to since I didn't see any dents or bends in the tube, nor any cracks for that matter.

 

[357Max]

From the angle of your picture it's hard to tell.

Here is a picture of a Bear Creek AR-10 308 with a std DPMS gas tube (the one Aero sells).

This is to short.

After replacing with an Armalite rifle gas tube.

This is correct.

Bear Creek barrels are also set up for the GI hand guard meaning you need to space the block forward about a credit card width, not slam it up against the step.

Like this. And yes this is a Bear Creek 308

If you have it tight to the step it's probably cutting 1/2 the gas off as can be seen in this photo from the same Bear creek thread.

You can see the outline from when the gas block was tight to the step and cutting off gas vs the forward position shown in the above pic. allowing full flow.

 

[357Max]

Large frame AR's can test your patience.

Ultimately the poor bastard who's pictures I robbed found out he had a defective gas block, in addition to the wrong length gas tube and miss aligned block.

With the tube pinned in the block the whole in the tube was miss aligned with the hole in the block.

Can't stress enough; everything needs to be checked on large frame AR's.

 

[2aBaC̶a̶]

Verify gas block and tube alignment.Taking it off you should see a little carbon residue around the hole. An adjustable gas block wide open wont likely give you more gas than a non-adjustable one wide open.

Try a lighter buffer and or different spring.

And lube it up good.

 

[Valkyrior]

From the angle of your picture it's hard to tell.

Here is a picture of a Bear Creek AR-10 308 with a std DPMS gas tube (the one Aero sells).

This is to short.
View attachment 7607442

After replacing with an Armalite rifle gas tube.

This is correct.
View attachment 7607443

Bear Creek barrels are also set up for the GI hand guard meaning you need to space the block forward about a credit card width, not slam it up against the step.

Like this. And yes this is a Bear Creek 308
View attachment 7607444

If you have it tight to the step it's probably cutting 1/2 the gas off as can be seen in this photo from the same Bear creek thread.

You can see the outline from when the gas block was tight to the step and cutting off gas vs the forward position shown in the above pic. allowing full flow.
View attachment 7607445

Picture of my gas port on my barrel. I see a little bit of the same effect... Gas tube is awfully dirty on the end that inserts into the upper receiver. I feel embarrassed to admit this, but I haven't ever noticed if this is the usual amount of dirty this end gets. There's also a better angle of how far the tube sticks into the upper.

 

[Valkyrior]

Picture of my gas port on my barrel. I see a little bit of the same effect... Gas tube is awfully dirty on the end that inserts into the upper receiver. I feel embarrassed to admit this, but I haven't ever noticed if this is the usual amount of dirty this end gets. There's also a better angle of how far the tube sticks into the upper.

Ah, rats. Double posted some photos... Apologies.

 

[357Max]

Picture of my gas port on my barrel. I see a little bit of the same effect... Gas tube is awfully dirty on the end that inserts into the upper receiver. I feel embarrassed to admit this, but I haven't ever noticed if this is the usual amount of dirty this end gets. There's also a better angle of how far the tube sticks into the upper.

Your gas tube does look to be short & I suspect you had the block slid tight to the step. So if you space it out .060 then it has the affect of making the tube that much shorter.

I'd suggest hunting down the Armalite rifle length gas tube & replacing yours.

Adjustable gas blocks are most helpful when your over gassed & you've got the opposite problem.

Your 3.8oz buffer is already on the light side for a 308.

FWIW I run an 8.5oz buffer in mine with an SLR adjustable gas block set in middle of range. 18" Proof barrel/rifle gas. It's like Mikey it'll eat anything and has run flawless for 600 + and counting.

 

[Valkyrior]

Your gas tube does look to be short & I suspect you had the block slid tight to the step. So if you space it out .060 then it has the affect of making the tube that much shorter.

I'd suggest hunting down the Armalite rifle length gas tube & replacing yours.

Adjustable gas blocks are most helpful when your over gassed & you've got the opposite problem.

Your 3.8oz buffer is already on the light side for a 308.

FWIW I run an 8.5oz buffer in mine with an SLR adjustable gas block set in middle of range. 18" Proof barrel/rifle gas. It's like Mikey it'll eat anything and has run flawless for 600 + and counting.

Went ahead and did that. I'm looking at one from wilson combat which is just a little bit longer than my current one. Current tube (according to Aero's website) is 15.125" while the Wilson Combat tube is 15.5".

 

[357Max]

Make sure that longer tube doesn't bind in the gas key. Sometimes you have to tweak the tube a little to get it riding smothly in the key.

My large frame didn't exactly bolt together and run like a Swiss watch. It had plenty of issues.
If I didn't enjoy the tinkering part I'd have just bought an LMT.

Tons of good trouble shooting info in this thread.
https://www.snipershide.com/shootin...turd-trouble-shooting-with-solutions.7001453/

 

[Valkyrior]

Make sure that longer tube doesn't bind in the gas key. Sometimes you have to tweak the tube a little to get it riding smothly in the key.

My large frame didn't exactly bolt together and run like a Swiss watch. It had plenty of issues.
If I didn't enjoy the tinkering part I'd have just bought an LMT.

Tons of good trouble shooting info in this thread.
https://www.snipershide.com/shootin...turd-trouble-shooting-with-solutions.7001453/

Will do. Thanks, I appreciate all the help! I've got that thread bookmarked.

 

[Valkyrior]

I appreciate everyone's help here!

 

[sboone]

You do realize that the charging handle does not reciprocate, right? And...contact with the hand guard would also have zero to do with cycling, right?

I am well aware, but if theres something screwy going on with the optic mount, not installed correctly or some other reason that it is somehow putting pressure on either of those parts, it would affect the gas tube and possibly be causing an issue that would come up specifically because of the mounted optic. Is it likely? No, but its not impossible. A tweaked charging handle will absolutely dick with how well an AR runs and shoots

 

[Yondering]

An adjustable gas block would be my first thing to add. You could also play with the buffer weight and check spring length. The scope thing is weird, but in theory possible IF and only IF you are not securing the weapon into your pocket and the scope weight is causing the weapon to move a little too much and taking some of the force the bolt needs to go all the way back. Again, more gas would likely fix that. Just my thoughts, some others here are waaay better versed in this.

I hate to rag on a guy who’s just trying to help, but everything in this post is wrong.

Adjustable gas blocks can only restrict gas, they can’t provide more. On a rifle that isn’t getting enough gas, this is completely the wrong solution.

And the rifle weight thing is backwards too - if it was malfunctioning due to free recoil (not holding it solidly into your shoulder) then it’d be worse with less weight; adding a heavy scope would make it better rather than worse.

This post is a good example of times when people here need to stop giving advice about things they don’t fully understand, no matter how bad you want to help. Steering someone new in the wrong direction is never helpful.

357Max on the other hand has given great advice that’ll probably solve the issue.

 

[BuildingConceptsllc]

I hate to rag on a guy who’s just trying to help, but everything in this post is wrong.

Adjustable gas blocks can only restrict gas, they can’t provide more. On a rifle that isn’t getting enough gas, this is completely the wrong solution.

And the rifle weight thing is backwards too - if it was malfunctioning due to free recoil (not holding it solidly into your shoulder) then it’d be worse with less weight; adding a heavy scope would make it better rather than worse.

This post is a good example of times when people here need to stop giving advice about things they don’t fully understand, no matter how bad you want to help. Steering someone new in the wrong direction is never helpful.

357Max on the other hand has given great advice that’ll probably solve the issue.

Reading is hard

 

[Yondering]

Reading is hard

I don’t think you can blame that on not reading thoroughly. You said more gas should fix it, and recommended an adjustable gas block. And you talked about more rifle weight causing it to move more. Both are backwards.

 

[BuildingConceptsllc]

I don’t think you can blame that on not reading thoroughly. You said more gas should fix it, and recommended an adjustable gas block. And you talked about more rifle weight causing it to move more. Both are backwards.

I said "the first thing I would do is put an adjustable gas block on an ar10" and it is. I did not say an adjustable gas block would fix it, I said MORE GAS would fix it. I said it wasn't getting enough gas. Then I said the scope thing was weird (which is a nice way to say "that's not going to be related" and I said "in theory" (this means not in practical reality, in an effort to humor your concern)...but IF blah blah blah, maybe that's possible somehow)

Some folks on here just can't wait to be an internet hero. I'm so glad the record was set straight. Thank goodness this didn't go unaddressed.

 

[2aBaC̶a̶]

I like chimichangas.

 

[LRRPF52]

It sounds like you’re on the edge of getting too much gas to cycle the action.

Once you mount the scope, the added mass of the rifle/optic combo resists being moved as fast, and the cyclic rate is out-running the magazine lift, causing bolt-over-base malfunctions. This is common on guns that are gassed too hard.

Your biggest problem is this:

* Bear Creek Arsenal 20" barrel

Replace that with a real barrel with a correct gas port diameter and chamber dimensions. Your gas block is mounted correctly as the shadow shows coverage of the port.

I would expect to find pretty much every BCA barrel out of acceptable specs in some way, whether it be chamber dims, gas port, bore diameter, gas block journal diameter, thread concentricity, you name it.

 

[Mario1961]

I have the same problem. However I have a Vortex scope on mine. Aero lower and upper is a parts kit with a bull barrel from Delta team tactical. Its short stroking with the case ejecting fine . All cases landing 3 feet to the right and behind me same place. It will fire 2-3 rounds fine ( federal ammo) then the cartridge will not fully enter the chamber... press the trigger... click... nothing. No pin strike or extremely light on the primer. Fired some of my friends reloads ... 5 in a row no problems ... finicky as hell. Sluggish when the bolt goes forward at times. Odd, because sometimes it goes forward as it should. When it does that I know the cartridge has fully entered the chamber and I know its going to fire. I have replaced the spring with a stronger one, really lubed up everything and will replace the buffer with a different weight if the next range session is a bust. Maybe look into a hydraulic buffer one piece unit. Its a process. I have has issues with .556 rifles and have got them running with replacing , springs, buffers, my 300 BLK was fixed with a lighter spring. Just trial and error.

 

[2aBaC̶a̶]

JP LMOS bcg, JP SCS and SLR AGB.

 

[DRT308]

Never had a problem that couldn't be fixed with Lubrication!

 

[Yondering]

I have the same problem. However I have a Vortex scope on mine. Aero lower and upper is a parts kit with a bull barrel from Delta team tactical. Its short stroking with the case ejecting fine . All cases landing 3 feet to the right and behind me same place. It will fire 2-3 rounds fine ( federal ammo) then the cartridge will not fully enter the chamber... press the trigger... click... nothing. No pin strike or extremely light on the primer. Fired some of my friends reloads ... 5 in a row no problems ... finicky as hell. Sluggish when the bolt goes forward at times. Odd, because sometimes it goes forward as it should. When it does that I know the cartridge has fully entered the chamber and I know its going to fire. I have replaced the spring with a stronger one, really lubed up everything and will replace the buffer with a different weight if the next range session is a bust. Maybe look into a hydraulic buffer one piece unit. Its a process. I have has issues with .556 rifles and have got them running with replacing , springs, buffers, my 300 BLK was fixed with a lighter spring. Just trial and error.

Trial and error shouldn’t be the method of fixing one of these, and doesn’t need to be if you take time to understand the system and the effect that each part has.

Band-aid fixes like using a hydraulic buffer to fix a cycling issue is cringeworthy. If the rifle cycles sluggishly, figure out what’s wrong and fix that. These are not finicky rifles if you have the right combination of parts and tune it well.

You might have a short 308 length buffer in a long 308 buffer tube, at a guess. That can cause some weird issues because the buffer doesn’t bottom out in the tube as it should.

 

[Justin Petrovich]

Hi all,

Just made this account tonight actually. My first AR-10 build is giving me too much trouble. I've got an ATN X-Sight 4K Pro 5-20x that I bought to use with it, but every time I take it shooting, there's short-stroking. I started out with a Juggernaut Tactical handguard on an Aero Precision M5 upper and lower receiver (I am now aware the JT handguards are incompatible with Aero stuff), and switched to an Aero Precision handguard and barrel nut after having problems with the gun short-stroking then as well. I assumed this would fix it due to the gas tube not going in to the gas port on the upper without some tough loveeven with proper timing on the barrel nut. This problem was fixed after switching handguards, but the short-stroking problem was only fixed when I had the scope off the gun. It feeds just fine! An entire 10rd PMAG shot perfectly without the scope, but every single round short-strokes with the scope on the gun. I've checked to see if the gas block has moved, is not properly aligned, or has even come loose. All three are negative. I'm at my wits' end with this gun and just confused on the whole thing. Is it still a gas issue? Is the weight of the scope just weighing the gun down so much that it's affecting the cycling? Any help at all is appreciated; I'll post my specs below this wall of text.


Specs:
-Aero Precision M5 upper and lower receivers
-Aero Precision handguard
-Aero Precision gas tube (rifle length) and block
-Aero Precision carbine buffer tube kit for .308
-Aero Precision 308 BCG, black nitride
-Bear Creek Arsenal 20" barrel
-ATN X-Sight 4K Pro 5-20x
-Magpul M-Lok bipod

I hope you figure this out, I just installed the x-sight 5x20 on my Black Rain Fallout-15. I was going to try to get to the range this weekend or next to sight it in.