aero .308 build short stroking

[duuuuuuce]

Hello all,

This is my first post here but have been reading and trying to figure out my problem for a few days. This is the first .308 AR build I have done, but have accomplished multiple 5.56 builds. Anywho, on to whats going on and the details about the rifle. Yesterday on Christmas my uncle and I snuck out before out family dinner to get some range time and see how my fancy new 308 would fare. Not to good. I am use to running general milsurp 5.56 and wasn't aware that these .308's could be as finicky as it has proved to be. 

When we got out there I had some Federal 7.62x51 149gn and was running the rifle relatively dry. I lubed the bolt before I headed out but that was it. After the first shot the spent casing didn't eject. I tried to pull the charging handle back to get it out of the chamber but that was a little harder said than done. Finally got it out and round after round proved to do the same thing. A couple rounds made it halfway out with the case lodged between the bolt and ejection port. I looked at it and figured out that the case seemed a little tight in the barrel chamber. I got my cleaning supplies out and lubed the crap outta the chamber. After the chamber was lubed it started to eject the spent casings but not grab another from the mag (short stroking). All I had was that cheap federal ammo so we decided to call it a day and head over to my grandparents to get some food.

Today I headed out again, but after reading figured I would try all the suggestions that I have read. I had the chamber and bolt dripping with  slide guide. Also I picked up all .308 match grade ammo. 168gn Federal Sirrea Match, 168gn PPU match, and lastly some Horndady 178 Super Match. Also brought an AR-15 buffer spring for shits and giggles. Had puddles of lube in the chamber and excessively on the bolt. Finally the rifle started doing what its supposed to, I had NO short stroking issues today, but the 168 match wouldn't lock the bolt back after the last round was ejected. I used Pmags and CPD metal mags. No luck. I then just loaded a couple round of the Horndady 178gn and finally it did the unthinkable. Last cartridge ejected and bolt locked back. AWESOME. 

Now I don't want a rifle that can only shoot $1.00+ ammo per round. I have read that after they have a few hundred shots through it they start to get broken in and can then eat the lighter grain bullets. I don't really want to shoot 500 rounds of the pricy Horndady though it, but I will if I have to. I am thinking about opening up the gas hole on the barrel just a tad to see if it don't help any but what are your guys thoughts.

The gun is
Aero Precision Lower (built by aero and from the looks of everything, feel of the spring and all the buffer tube components are correct)
Aero Upper
X-Caliber 18' .308 win barrel with rifle length gas system.
Aero Precision Black nitride bolt.
YH low pro gas block (100% sure it is aligned and barrel as detent on bottom to assist in lining it up)
Standard AR-15 rifle gas tube.

After inspecting everything there are no signs of leaks or anything blocking the gas tube. They gas tube appears to be the correct length.

Do you guys think I should open up the gas hole on barrel just a tad or wait till I get a few hundred more rounds though it?

Thanks
-Chris.

Edited December 26, 2015 by duuuuuuce

[shepp]

I don't have any help for you Unfortunetly, but welcome to the forum!

[duuuuuuce]

Thanks! Might as well post a pic of it. Have a 3-9 rifle scope but gonna get all the bugs worked out before it goes on. So just an ACOG I had laying around.

 

 

[392heminut]

If you can, please post a pick of the gas tube end where it protrudes into the charge handle channel in the upper receiver. We have found that some of these barrels need the (approx. 1/4") longer Armalite gas tubes. The short tubes cause the exact problem you're experiencing.

Edited December 27, 2015 by 392heminut

[survivalshop]

Is the Gas tube too short , does it sit in the Upper Receiver , like the one below ?

I generally try to keep excess Lubricants of of the Chamber. Some new builds need to be run wet for a break in period . 

 

  Damn your a faster  typist then me , 392heminut?

Edited December 27, 2015 by survivalshop

[jtallen83]

Most of the time checking the gas port diameter would be way down the list but then I read "X-Caliber". The barrel I got from them was way under-gassed so it might be worth checking to see what size they gave you before you do much else. 3rd page of this thread is where my port size issue details start;

 

[duuuuuuce]

Thanks for replies I'm thinking the barrel is undergassed here are the pics of tube coming into upper from the looks of my 5.56's it looks dead on.

 

 

Edited December 27, 2015 by duuuuuuce

[guruofhotrod]

In addition to the gas tube length as 392heminut and survivalshop mentioned, you may want to double check the length of the buffer and

the relaxed length and coil count of the buffer spring. Will the bolt lock back manually on the blot catch?

Edited December 27, 2015 by guruofhotrod

[duuuuuuce]

I looked through that thread, I'm gonna pull the barrel and take it down to my shop where I gotta a drill press and have at it, that has to be the issue. When you are saying #44 and #45 what is that. if it's something like 7/32's I get the .084/.086 by just dividing the two numbers right? Was never to good at math.  :)

[guruofhotrod]

I think Jtallen83's barrel is a 16" w/ a rifle gas (2" less from the gas port to the end of the barrel than your 18" = less time for the gas to

unlock the bolt and cycle the action. Your 18" barrel may not need quite that big of gas port to function properly since the greater distance from

the gas port to the end of the barrel = more time to unlock the bolt and cycle the action - best to work your way up to the ideal port size.

[duuuuuuce]

Yes and the bolt did lock back with the Hornady 178gnand is very lax to do it manually, has about an inch of play between the catch and it all the way back. The buffer weight is smaller than a normal carbine buffer and spring much stiffer than 5.56 so I'm sure they are correct parts. 

 

I pulled the gas tube and handguard. Here is a pic of the gas hole on barrel. It's even beveled and is much smaller than the opening on the gas block I would say almost half the size. I'm gonna check it and drill it out. I have gone through everything and now that other people have had problems with X- Caliber I'm leaning toward that being the problem. 

If if it was a 600$ top of the line barrel it would be the last thing I would check but I'm thinking what JT said is correct.

 

 

Edited December 27, 2015 by duuuuuuce

[duuuuuuce]

Also the port is beveled like they didn't drill it out all the way or it might is supposed to be like that.

[392heminut]

Your gas tube is fine, the end is right where it should be.

[duuuuuuce]

I think Jtallen83's barrel is a 16" w/ a rifle gas (2" less from the gas port to the end of the barrel than your 18" = less time for the gas to

unlock the bolt and cycle the action. Your 18" barrel may not need quite that big of gas port to function properly since the greater distance from

the gas port to the end of the barrel = more time to unlock the bolt and cycle the action - best to work your way up to the ideal port size.

Sounds like a plan. I figured the length would affect it. I don't think I will have to go up as much as he did as if I lubee the poop outta it will barely eject the 149 grain stuff but won't grab another bullet. The match 168 will eject and grab another bullet just not lock the bolt back. The 178 functions correctly. I'm gonna try to get out to the range tommorrow and will report back. As long as the rain holds off.

[jtallen83]

My barrel was a 16 inch rifle length gas so I had to open it more than one would in an 18 inch rifle length gas. If you can, get a measurement with calipers on the bit that fits the tightest. My bit set was off when it came to the charts so I just forgot what number was on the bit and measured. I'd post up with the port size before drilling, people here with a ton more experience than me will be able to tell you if you are already close or undersized.

Having an inch between the bolt face and the catch doesn't sound right. I had something around a strong 1/4 inch and members here advised me to put quarters in the bottom of the buffer tube till I got close, like 1/8 inch, an inch would be a big stack of quarters, better check and make sure you have the correct buffer. I also had to notch the extension tube for the detent so I could get one more turn on it, sounded like it was a common issue with Aero but then I was matching in to a different brand receiver. If your BCG has a full inch before it hits the catch it will be awful hard on it.

Give these guys your port size and they will have a good idea if that may be the issue, I just assumed due to the X-caliber reference and my own experience.

[duuuuuuce]

My mistake by the feel of it it's closer to 1/4 of an inch.

Edited December 27, 2015 by duuuuuuce

[Heretic]

I had the same problem with a 6.8SPC.  After the gunsmith was able to get the rifle to reliable cycle with combat loads but i couldn't get it to cycle with any other factory loads, I pulled everything and measured/weighed everything.  My buffer spring was too long.  I received a rifle stock spring in the carbine stock kit I bought.  Never thought to check it.  Also I went up to an H2 buffer.  Just more food for thought.

[duuuuuuce]

The lower was built by Aero, so you would think all that would be right and by looking at the buffer compared to a carbine buffer, the .308 one is shorter. The spring has to be right because there is a BIG difference on the amount of force needed compared to a AR-15

[duuuuuuce]

I will measure it with drill bits and report back tomorrow. I could prob get pin gauges from my friend who does allot of machining but that will be the last resort. 

 

Generally speaking i shoild be looking looking for a .084-.086  hole on a 18" with a rifle system. Correct?

[shepp]

The lower was built by Aero, so you would think all that would be right and by looking at the buffer compared to a carbine buffer, the .308 one is shorter. The spring has to be right because there is a BIG difference on the amount of force needed compared to a AR-15

the way I read your first post I assumed you had bought it as a complete build from the manufacture, is that correct?

[duuuuuuce]

the way I read your first post I assumed you had bought it as a complete build from the manufacture, is that correct?

Negative I bought the complete lower and pieced everything else together. From what I have read there are many variations in .308 LPK so wanted to make sure it was correct.

Edited December 27, 2015 by duuuuuuce

[shepp]

I would check your buffer and spring too. I don't remember specs but I know that's been an issue in the past. Does your bolt lock with and empty mag in when you pull back the charging handle?

[washguy]

I will measure it with drill bits and report back tomorrow. I could prob get pin gauges from my friend who does allot of machining but that will be the last resort. 

 

Generally speaking i shoild be looking looking for a .084-.086  hole on a 18" with a rifle system. Correct?

Duuuuce  its simply the gas port hole size being too small....the dunderheads at x caliber didnt have a clue on JTs barrel gas port size.....open it up

I have all of my middy lengths at .086......start there for sure.....everything else looks good....dont be changing more than one thing at a time up

if you got it to lock back with the pricey ammo you are close....always one round in the mag till she locks back everytime....gotta get that particular function taken care of first        Wash

[unforgiven]

I pickedup a Aero M5 lower that was assembled.Then added a Aero M5 upper 16" FDE keymod with Nickel boron BCG.The BCG would not lock up,was very tight.Had FTE.One of the guys had similar issues and changed the recoil system to an Armalite system.I did the same thing.Armalite extention tube was longer.Put Armalite spring EA1095 [which was about 1 1/2" longer],and Armalite buffer that was longer and heavier.Ran after that.Other problem was trigger had to be push forward a touch to go to reset.After about 75 rds. it worked it self outJust my 2 mags.

[survivalshop]

I'm with them , have to check the Buffing system before I would ream out the Gas Port in the Barrel .

 There has been a lot on the Areo Buffer system & most do as said above & changed out to a Armalite 308 Spring & Buffer. Its not just the Receiver Extension , I think they made their Receivers to different spec's or they had an issue with some sets.Hard to tell .

  I have the measurements of a DPMS 308 Springs , it may help you identify what you have . Are there any Marks on the Threaded portion inside the Lower receiver , from the BCG touching or hitting it ? 

Edited December 27, 2015 by survivalshop