New Build, Wrong gas tube?

[Rockin308]

Hello, 
New here just built my first LR308. Here is the parts listing. 
Aero Precision M5 Upper and lower receivers with Aero Precision M5 lower receiver kit 
Aero Precision M5 Enhanced Buffer kit complete 
Faxon 18" rifle length gas, with Aero Precision gas block and rifle gas tube, (did notice when assembled the gas tube wasn't in the middle of the cam pin cut out in the upper receiver) 
Strike Industries J2 Comp brake
UTG Pro 15" 308 handguard 
Lantac Mil-spec 308 BCG 
Ambi charging handle (had this laying around not sure of manufacture, will replace asap with either and Aero or Strike Industries) 
MFT Battle link Extreme Minimalist duty stock 

So far on the first range visit the rifle wouldn't cycle correctly, wouldn't hold back after just firing one round in the magazine. This is my first rifle length gas system build in any of the AR/LR 308 platforms, so I think and from what I have read on this wealth of information forum that the gas tube is too short. I don't think it was the gas block in any way I used the Kak dimple jig to put one dimple in the barrel matching up with the gas port. I installed the gas block without the gas tube and used a piece of weed eater cord to see if I had correct alignment and I did. So again, I am thinking it's the gas tube length being too short, the Aero Precision gas tube I got did state rifle length but is only 15.25" in length, I think the Armalite 15.5" is what it needs too properly cycle. 
The buffer system is the Aero Enhanced buffer tubed with their 308-recoil spring and the 3.8 oz buffer, I want to get it functioning with this setup first then try perhaps the orange Springco spring and a Kak 5.3 oz buffer. 
If any of you 308 gurus have any other possible suggestions, please share your knowledge. 

Thank you for the join up on this information superhighway, 
Rockin308

Edited July 8, 2022 by Rockin308

[dpete]

Welcome from WI.  Even with the gas port and gas block perfectly alligned if the port is too small you will never get enough gas through the system to operate properly.  "What is the gas port size" is always right up in the top two or three questions when troubleshooting these.   Reputable manufacturers routinely muck up gas port sizes.  You'll need to measure it.  Numbered drill bits work great, standard drill bits will get in the ballpark.  Once the gas block is removed just insert the non-drilling end into the port until you find one that fits.   Your 3.8 oz buffer is too light and your gas tube is too short.  Those two are for sure.

[jtallen83]

Welcome from Iowa!

2 hours ago, Rockin308 said:

The buffer system is the Aero Enhanced buffer tubed with their 308-recoil spring and the 3.8 oz buffer, I want to get it functioning with this setup first then try perhaps the orange Springco spring and a Kak 5.3 oz buffer. 

You can bandaide that system up with an adjustable gas block and maybe changing port size, hard to know for sure without more info. There is also more of a break-in with these large frames, more surface area to mate, small gas leaks that will seal up with rounds, BUT it will be a much more reliable rifle with the proper spring and buffer weight, years here reading along as people throw money at this issue, myself included, shows me just starting out with the correct stuff is simplest and least expensive. Now I promise the CS at Aero will argue all day long on that...... or just tell you to get a rifle buffer system....which coincidently has the correct weight buffer. 

[shooterrex]

Why waste time and money trying to get the wrong parts to work?

[98Z5V]

18" rifle gas .308 barrels with 0.750" gas block journal diameters need a gas port that's 0.095".

[unforgiven]

Welcome from Indiana brother, what these guys said.

[Rockin308]

measured the gas port size, I got .093" gas port I've been considering drilling it out slightly more but would like to just try the new longer gas tube first. I have a new gas block coming got at Superlative Arms adjustable gas block on it way as well. Thanks for the information I've been reading all the info on buffers and gas port sizes and gas blocks, everything about tuning in your Lr308/Ar10 build. 

 

[Rockin308]

measured the gas port size, I got .093" gas port I've been considering drilling it out slightly more but would like to just try the new longer gas tube first. I have a new gas block coming got at Superlative Arms adjustable gas block on it way as well. Thanks for the information I've been reading all the info on buffers and gas port sizes and gas blocks, everything about tuning in your Lr308/Ar10 build. 

 

Well I just went and done it, remeasured the gas port and I was wrong on my first measurement statement, the .093" was my buddies barrel that I wrote down his gas block measurement, I just thought it was mine, when I remeasured the gas port on my barrel it was .090" I found a drill bit that was .0945" and went with that, since this was the only drill bit in my arsenal of drill bits that came close to the .095" mark. 

 

 

[jtallen83]

57 minutes ago, Rockin308 said:

I have a new gas block coming got at Superlative Arms adjustable gas block on it way as well.

You'll find info here on their use with the 308AR here, if you can get it to function like the instructions say on the by-pass mode let me know, you will be a first to make it happen I have heard of. 

[Rockin308]

Well, 

After drilling the gas port to .0945" and installing a Armalite Rifle length gas tube, it cycles, well kinda. 

I got some strange failures, each time it was like the extractor wouldn't let go of the casing, this happened about 3 times, so I took out the extractor and removed the o'ring donut from the extractor spring, then refired the rifle this time it happened about every 5-8 rounds. 

When inspecting the extractor (will post pics later) could see slight deformation of the extractor claw. Also, discovered that the Lantac M-Spec BCG I got has a one piece gas ring, which I've never had any luck with even on AR 15s. So I'm going to replace it with the standard 3 rings. 

I also replaced the bolt catch it seems to be hanging up on the original bolt catch from the Aero Precision M5 lower receiver kit. I put a bolt catch that looked like an Ar10 type. 

Still need an Orange Springco spring and a 5.3oz buffer. 

Any suggestions on what could have been causing the malfunction, why the extractor wasn't letting go of the casing? Was using Sellier and Bellot 7.62x51 and PMC brass 308 Winchester. 

 

[shooterrex]

Quit changing multiple things at once. How are you going to know what actually solves your problem 

Till you get a proper spring and buffer you are just beating your head against the wall.

The proper recoil system will slow down the cyclic rate. Allowing the brass to shrink down enough to be extracted.

Till your recoil system is correct the rifle will probably not run 100%

[98Z5V]

53 minutes ago, Rockin308 said:

Any suggestions on what could have been causing the malfunction,

You completed half the things necessary for a functional rifle.  You addressed the gas system.  You still have an underpowered recoil system.  That BCG is flying fast as hell, because it doesn't have enough recoil system to keep it under control.

I agree with what Rex stated.  When modifying a gun, you change one thing at a time, and see how it does.  However, we have the recipe down on Large Frame ARs, and if you're gonna fix the gas system, you should fix the recoil system at the same time, before you go test it out. 

[jtallen83]

50 minutes ago, Rockin308 said:

discovered that the Lantac M-Spec BCG I got has a one piece gas ring, which I've never had any luck with even on AR 15s.

Please explain how you can have or not have luck with either? Promise that has nothing to do with your issue. 

 

[Rockin308]

7 hours ago, 98Z5V said:

You completed half the things necessary for a functional rifle.  You addressed the gas system.  You still have an underpowered recoil system.  That BCG is flying fast as hell, because it doesn't have enough recoil system to keep it under control.

I agree with what Rex stated.  When modifying a gun, you change one thing at a time, and see how it does.  However, we have the recipe down on Large Frame ARs, and if you're gonna fix the gas system, you should fix the recoil system at the same time, before you go test it out. 

I am awaiting the Springco Orange spring and 5.3 oz buffer, I just test fired it with the new gas tube to see if it would lock back after a few rounds fired, which it did. 

Now about the gas ring, when preforming a gas ring test, BCG assembled and bolt extended fully it falls down when stood up on the bolt in the carrier. It supposed to not fall under its own weight. This happened after only 40 rounds through the BCG. 

[Rockin308]

I do agree, I beating a dead horse by not test firing with the correct buffer system. 

It's just the condition the Lantac M-Spec BCG is in after only 40 rounds. The gas rings failing the test, I don't like one piece gas rings never had any luck with the on any AR/Lr platform. 

Thank you all for the information this is my go to forum for anything Ar10/Lr308. 

[jtallen83]

8 minutes ago, Rockin308 said:

Now about the gas ring, when preforming a gas ring test, BCG assembled and bolt extended fully it falls down when stood up on the bolt in the carrier. It supposed to not fall under its own weight. This happened after only 40 rounds through the BCG. 

It's a wonder my rifles run at all then. Look at the weight of the carrier, that "test" grew up around the little brother and is much more an indicator than a diagnostic test. Hell there are BCG makers that have purposely left that part of the system loose as part of their gas timing "fix" and charged more for doing it.

Again you say "luck", what do you mean, failures due to the gas ring or just not "passing the test"? Real world now, not what you think might happen.

[Rockin308]

No just not passing the gas ring test, the rifle functions but yes still needs the correct buffer and spring.

 

Edited July 13, 2022 by Rockin308

[Rockin308]

On 7/8/2022 at 10:09 PM, 98Z5V said:

18" rifle gas .308 barrels with 0.750" gas block journal diameters need a gas port that's 0.095".

Now, I discovered a #41 drill bit is 0.096" can I drill it out to that diameter and still be gtg? 

Currently drilled out to 0.0945 would like that extra bit. 

Edited July 13, 2022 by Rockin308

[98Z5V]

2 hours ago, Rockin308 said:

Now, I discovered a #41 drill bit is 0.096" can I drill it out to that diameter and still be gtg? 

Currently drilled out to 0.0945 would like that extra bit. 

Probably won't need it.  Get the recoil system fixed first and test it out. 

[Rockin308]

Just now, 98Z5V said:

Probably won't need it.  Get the recoil system fixed first and test it out. 

Okay, 

Again, thanks for the info. 

[98Z5V]

We'll get it running, don't worry. 

[Rockin308]

I knew that this Lr308 build was going to be a learning experience, glad I discovered this forum and your experience with this platform. 

Thank you 

[Rockin308]

I really wish I went with my gut on this build, was goin to just get the enhanced Aero buffer tube, the Springco Orange spring and the 5.3 oz buffer. 

Also, was going to order both size gas tubes, Armalite and stand rifle. 

Guess from now on I'm following my gut, and listen to your fellow brother's in arms. 

Buddy told me a few month before I started this build what to get, now he's giving me a big,.I told you so. 

Edited July 13, 2022 by Rockin308

[LR308Shootin@45]

Well, 
Back to the range again. I got the gas port drilled out to .096" and this was still not enough, was still getting feeding issues with 7.62x51 NATO ammunition but would run okay with 308 ammunition. So, I found a 40-drill bit that is .098" and I just drilled it out to that diameter, getting an adjustable gas block after going from .089"-.090" up to the .098" gas port diameter figured an adjustable gas block will help just in case I went too far and am over gassed. The adjustable gas block I went with is the Aero Precision model, since this rifle is an Aero Precision build. 
Also, changing out the muzzle brake from the Strike Industries J2 comp to the Precision Armament M4-72 comp. I will use 7.62x51 with the gas block fully open and one round in the magazine and close the gas off until it doesn't hold back on the lower power 7.62x51 ammo then open it up just that bit more to cycle the lower power ammo then shoot the higher power 308. 

Also, what a good round to use on white tail deer and hogs? I was going to use soft point ammunition but that at time has issue feeding and the tips can get damaged while feeding causing accuracy issues, from what I've read about soft point in semi-auto rifles. 
Thank all. 
 

[FOGeologist]

On 10/10/2022 at 12:27 PM, LR308Shootin@45 said:

Well, 
Back to the range again. I got the gas port drilled out to .096" and this was still not enough, was still getting feeding issues with 7.62x51 NATO ammunition but would run okay with 308 ammunition. So, I found a 40-drill bit that is .098" and I just drilled it out to that diameter, getting an adjustable gas block after going from .089"-.090" up to the .098" gas port diameter figured an adjustable gas block will help just in case I went too far and am over gassed. The adjustable gas block I went with is the Aero Precision model, since this rifle is an Aero Precision build. 
Also, changing out the muzzle brake from the Strike Industries J2 comp to the Precision Armament M4-72 comp. I will use 7.62x51 with the gas block fully open and one round in the magazine and close the gas off until it doesn't hold back on the lower power 7.62x51 ammo then open it up just that bit more to cycle the lower power ammo then shoot the higher power 308. 

Also, what a good round to use on white tail deer and hogs? I was going to use soft point ammunition but that at time has issue feeding and the tips can get damaged while feeding causing accuracy issues, from what I've read about soft point in semi-auto rifles. 
Thank all. 
 

You can use the Federal Fusion rounds; the 150 grainers would be good for the smaller whitetails and hogs, but you could go with the 180 grain bullets if you're hunting some of the larger Western counterparts. The open nose on these rounds is tiny - probably 1/16th or 3/32nds of an inch. They don't seem to interact on the feed ramps of my rifle, and they are certainly "hunting accurate" (3.5 MOA to 1.6 MOA in my minimal testing), so you should get good performance at a price.