6.5CM Tuning

[J.Firebaugh]

I’m having a hell of a time trying to get my Aero build 6.5CM to work properly.
-Matching Aero M5 receivers.
-20” BA barrel.
-Rise Armament 6.5CM BCG
-Superlative Arms Adjustable Bleedoff Gas block.
-Rifle length Extension.
-308 spring and weight. I believe the weight was 5oz.

I basically have a bolt action gas gun. Wide open gas block, it will fire and sometimes ejects the spent casing. Will not pick up the next round. Will not hold open either.
The gas block is aligned.
Is the problem my buffer weight? Or is is my spring?
Looking at the Aero rifle buffer kit, the weight is 5.3oz. That’s more than my current weight.
can someone point me in the right direction please.

 

[E. Bryant]

When you say "wide open gas block", what you mean? Do you have a full understanding of the Superlative Arms gas block adjustment? Not trying to be condescending; it's not necessarily the most intuitive process?

If indeed you have the screw backed out 4-1/8 turns from full closed per the instructions, then it's time to look elsewhere. Less buffer weight would generally not be my first preference.

EDIT: posting this in the Semi-Auto subforum might yield more responses.

 

[Clayman]

I’m having a hell of a time trying to get my Aero build 6.5CM to work properly.
-Matching Aero M5 receivers.
-20” BA barrel.
-Rise Armament 6.5CM BCG
-Superlative Arms Adjustable Bleedoff Gas block.
-Rifle length Extension.
-308 spring and weight. I believe the weight was 5oz.

I basically have a bolt action gas gun. Wide open gas block, it will fire and sometimes ejects the spent casing. Will not pick up the next round. Will not hold open either.
The gas block is aligned.
Is the problem my buffer weight? Or is is my spring?
Looking at the Aero rifle buffer kit, the weight is 5.3oz. That’s more than my current weight.
can someone point me in the right direction please.

What gas length is the barrel?

If I had to guess it's an issue with gas or adjusting the gas block correctly. The superlative can be confusing. Are you using the bleed off setting? I'm personally not a fan of it. I prefer restricting gas until I get it to reliably last round bolt hold.

That buffer, spring and barrel length should operate fine.

 

[kentuckyMarksman]

I'd check your gas block / gas port alignment, and make sure that the gas block is properly adjusted.

If that doesn't do it, I'd check your gas port size as well.

 

[BLEE]

It's been my experience to stick with Aero's components, as they "usually" work well with each other. You may have a heck of a time figuring out the solution to your problem. My M5 6.5CM, 22" barrel uses Aero's fixed gas block, a Dark Storm 4.7oz carbine buffer and Sprinco Orange spring. I got lucky when I didn't use an Aero buffer. The rifle runs like a top and ejects at 4 o'clock consistently, with Hornady American Gunner 140gr.

 

[LV Precision]

I have 2x 6.5cm builds with Aero sets (M5 Enhanced receivers, Proof barrels, Superlative Arms gas blocks, JP lightweight BCG, JP SCS buffer), and they both work fantastic. I also only have my gas blocks opened up 4 full revolutions that produces reliable lockback. A lot of variables to go through:

• Alignment of the gas block
• Gas block tuning
• Bolt carrier
• Buffer weight
• Buffer spring
• Ammo

Hornady American Gunner 140 is also overpowered, and will produce relatively high velocities (and which will push enough gas backwards to drive heavy buffers). You could use lighter weight buffers, buffer springs, and BCGs to ease up on the gas requirements.

 

[J.Firebaugh]

When you say "wide open gas block", what you mean? Do you have a full understanding of the Superlative Arms gas block adjustment? Not trying to be condescending; it's not necessarily the most intuitive process?

If indeed you have the screw backed out 4-1/8 turns from full closed per the instructions, then it's time to look elsewhere. Less buffer weight would generally not be my first preference.

EDIT: posting this in the Semi-Auto subforum might yield more responses.

Yes i have the GB open to full gas, no bleed off and no reduction.
well crap, I didn’t know I posted this in the wrong place.

 

[J.Firebaugh]

What gas length is the barrel?

If I had to guess it's an issue with gas or adjusting the gas block correctly. The superlative can be confusing. Are you using the bleed off setting? I'm personally not a fan of it. I prefer restricting gas until I get it to reliably last round bolt hold.

That buffer, spring and barrel length should operate fine.

Rifle length gas.
that’s what I thought but the GB is perfect. No bleed off and no restrictions, it’s on correct as well.

 

[J.Firebaugh]

It's been my experience to stick with Aero's components, as they "usually" work well with each other. You may have a heck of a time figuring out the solution to your problem. My M5 6.5CM, 22" barrel uses Aero's fixed gas block, a Dark Storm 4.7oz carbine buffer and Sprinco Orange spring. I got lucky when I didn't use an Aero buffer. The rifle runs like a top and ejects at 4 o'clock consistently, with Hornady American Gunner 140gr.

I think I will try the Aero GB, I have an extra one.

 

[Cynical]

Make sure gas tube wasn’t installed upside down in the gas block.

 

[Yondering]

What do you mean by “rifle length extension”? Are you referring to a 308-length buffer tube, or actually a rifle buffer tube?

It sounds like you might have the wrong combination of buffer and tube, and that will definitely cause issues. If this is the case, your gas key may be running into the charge handle or lower, because the buffer combo is allowing too much travel.

For a carbine style buffer, you can use a 308 buffer in a standard carbine extension, or a carbine buffer in a 308 extension. Do not use a 308 buffer in a 308 tube, it results in too much travel. The 308 buffers are shorter than carbine, and the 308 tubes are longer than carbine.

There is also the potential mixup of gas tube lengths, which can be verified by looking at the location of the end of the tube inside the receiver. There are different tube length requirements depending what spec your barrel was made for.

The 308 stuff is not like building an AR15; it’s not all standard parts that work together.

 

[J.Firebaugh]

Make sure gas tube wasn’t installed upside down in the gas block.

It sounds dumb that someone would put it on upside down but to be honest, I’ve done it. This one is on correctly though.

 

[J.Firebaugh]

What do you mean by “rifle length extension”? Are you referring to a 308-length buffer tube, or actually a rifle buffer tube?

It sounds like you might have the wrong combination of buffer and tube, and that will definitely cause issues. If this is the case, your gas key may be running into the charge handle or lower, because the buffer combo is allowing too much travel.

For a carbine style buffer, you can use a 308 buffer in a standard carbine extension, or a carbine buffer in a 308 extension. Do not use a 308 buffer in a 308 tube, it results in too much travel. The 308 buffers are shorter than carbine, and the 308 tubes are longer than carbine.

There is also the potential mixup of gas tube lengths, which can be verified by looking at the location of the end of the tube inside the receiver. There are different tube length requirements depending what spec your barrel was made for.

The 308 stuff is not like building an AR15; it’s not all standard parts that work together.

-I bought a 308 buffer tube, or it said it was a -308, it’s 10” long with 1” diameter.
-My buffer is 5 1/4” long and is just over 5oz.
-I have two 308 springs, JP 308 rifle spring 30 coils 12 1/2” long, Luther AR 308 rifle spring 38 coils 12 3/4” long
-gas tube is rifle length and its correct.

I know very well that AR308/AR10 stuff isn’t like AR15, I’ve built 4 other 308’s and never had an issue like this. This is my first 6.5CM AR though. Trying to find the right combo to make this run hasn’t been anywhere near as easy as ever other caliber I’ve built.

 

[Midpack]

Rifle length has system on a 20" 6.5 creed you aren't undergassed if you're gas block is indeed lined up correctly. So first when your day your gas is wide open are you wide open in the bleed off settings or in the standard settings. Now I know of several guys that found in the bleed off mode it doesn't get rid of enough. So a couple things to make sure of. 1 make sure your are plenty lubed. The ar10 bcgs tend to prefer to be lubed more then the 15s especially since new. 2 if you can, record your ejection port when firing. Most likely you are actually over gassed and it can lead to all the other problems you described. Are you running handloads or factory ammo? These are all things to start with and go from there.

 

[Yondering]

-I bought a 308 buffer tube, or it said it was a -308, it’s 10” long with 1” diameter.
-My buffer is 5 1/4” long and is just over 5oz.
-I have two 308 springs, JP 308 rifle spring 30 coils 12 1/2” long, Luther AR 308 rifle spring 38 coils 12 3/4” long
-gas tube is rifle length and its correct.

I know very well that AR308/AR10 stuff isn’t like AR15, I’ve built 4 other 308’s and never had an issue like this. This is my first 6.5CM AR though. Trying to find the right combo to make this run hasn’t been anywhere near as easy as ever other caliber I’ve built.

Better inspect your rifle for signs of overtravel of the BCG to be sure.

The gas tube thing isn’t as simple as “it’s rifle length so it’s correct”, there are some minor length differences (IIRC about 1/8-1/4”) between the different 308 systems and AR15, and your barrel could be made to use either one.
Do you know how to verify the correct length by looking inside the upper? The difference is minor, but can cause function issues like you’re having. It’s an easy thing to miss.

 

[Im2bent]

Is your gas tube ar10 or dpms? Ar10 is 1/4 inch shorter and will not engage the gas key completely. Your gas tube should end in the middle of the cutout in the upper. You want the upper pic.

 

[Yondering]

Is your gas tube ar10 or dpms? Ar10 is 1/4 inch shorter and will not engage the gas key completely. Your gas tube should end in the middle of the cutout in the upper. You want the upper pic.

Thanks for the pic, that's what I was referring to but didn't have a good pic handy.

 

[J.Firebaugh]

Rifle length has system on a 20" 6.5 creed you aren't undergassed if you're gas block is indeed lined up correctly. So first when your day your gas is wide open are you wide open in the bleed off settings or in the standard settings. Now I know of several guys that found in the bleed off mode it doesn't get rid of enough. So a couple things to make sure of. 1 make sure your are plenty lubed. The ar10 bcgs tend to prefer to be lubed more then the 15s especially since new. 2 if you can, record your ejection port when firing. Most likely you are actually over gassed and it can lead to all the other problems you described. Are you running handloads or factory ammo? These are all things to start with and go from there.

I am wide open in standard with no bleed off.
my BCG is plenty lubed and is smooth as silk, Rise Armament 6.5CM BCG.
I don’t think I’m overgased, sometimes i get malfunctions like double feed or stovepipe. Sometimes it doesn’t eject.
I have used factory Hornady ELDM 120g and 140g. Nosler 140g BT. Browning 130g long range pro. Hornady 129g SST.

 

[J.Firebaugh]

Better inspect your rifle for signs of overtravel of the BCG to be sure.

The gas tube thing isn’t as simple as “it’s rifle length so it’s correct”, there are some minor length differences (IIRC about 1/8-1/4”) between the different 308 systems and AR15, and your barrel could be made to use either one.
Do you know how to verify the correct length by looking inside the upper? The difference is minor, but can cause function issues like you’re having. It’s an easy thing to miss.

Yes my gas tube is centered in the cutout. It really feels like the spring is too stiff. I was using the JP 308 rifle spring. I haven’t tried the Luther 308 rifle spring, but it’s longer with more coils so I don’t know.
I think I’m just going to order the Aero 308 buffer kit with tube, spring and buffer

 

[Yondering]

Yes my gas tube is centered in the cutout. It really feels like the spring is too stiff. I was using the JP 308 rifle spring. I haven’t tried the Luther 308 rifle spring, but it’s longer with more coils so I don’t know.
I think I’m just going to order the Aero 308 buffer kit with tube, spring and buffer

That sounds like a good idea.

The DI gas system is actually pretty simple, with only a few things that can go wrong; most of the problems like this happen when parts are mis-matched, so it makes sense to try again with a complete buffer system that all works together.

Along the same lines, I think it’d be a good idea to go back to a standard gas block as well (you mentioned maybe having an Aero block). I’m not at all a fan of the Superlative blocks and it’s possible that may be causing issues.
Might as well run a stiff wire through the gas tube while you’re at it and make sure it’s clear. Unlikely but I’ve heard of one that was partially blocked by a machining chip.

 

[J.Firebaugh]

That sounds like a good idea.

The DI gas system is actually pretty simple, with only a few things that can go wrong; most of the problems like this happen when parts are mis-matched, so it makes sense to try again with a complete buffer system that all works together.

Along the same lines, I think it’d be a good idea to go back to a standard gas block as well (you mentioned maybe having an Aero block). I’m not at all a fan of the Superlative blocks and it’s possible that may be causing issues.
Might as well run a stiff wire through the gas tube while you’re at it and make sure it’s clear. Unlikely but I’ve heard of one that was partially blocked by a machining chip.

Agreed, tomorrow I will put the Aero GB on, I already checked the gas tube and it’s clear and good. I order the Aero 308 buffer kit today.
my 308 build was so easy and everything worked perfectly, I wish this 6.5 was as easy.

 

[Yondering]

Agreed, tomorrow I will put the Aero GB on, I already checked the gas tube and it’s clear and good. I order the Aero 308 buffer kit today.
my 308 build was so easy and everything worked perfectly, I wish this 6.5 was as easy.

The 6.5 should be easy too - that's why I have to wonder if some of the buffer system parts aren't intended to work together, given your description of the issues. I suspect it's gotta be something like that or some other small "doh!" kind of detail like missing gas rings on the bolt or a loose gas key, etc.

If it were just a gas tuning issue and difficult to find the sweet spot with proper function but without early unlocking and case head swipes - well that's sorta common for the 6.5, but it should at least be able to function, same as a 308.

Just a thought, since you mentioned it feels like the spring is too stiff - if it feels stiff pulling the charge handle back, does it push back forward equally as stiff? I ask because I helped a friend diagnose his mix-match 308 setup, that turned out to be a misalignment between the upper and the lower, so the bolt carrier was dragging on the inside of the buffer tube. In that situation, the upper and lower simply weren't compatible, the bore of the upper was slightly higher than the bore of the extension tube in the lower. I think the lower was DPMS but forget the upper brand, but it was something "DPMS pattern". With some further investigating, I'm pretty confident it was the DPMS lower out of spec, which isn't much of a surprise.