Hey everyone, I finally got out to test my new 6.5CM build yesterday and had all kinds of issues. First off, it's practically an AERO Precision rifle, the Lower, Upper, and BCG are all AERO parts and the barrel is a 22" Ballistic Advantage barrel ... so all parts as if you just bought a complete rifle from AERO.

Here are the problems I experienced yesterday, using factory Hornady American Gunner 140gr BTHP ammo, and a 10 round magpul mag:
1. Failure to strip a round from the mag - had several instances where the BCG slammed home but did not pick up the next round.
2. Failure to feed - this was the most common issue, when the BCG did grab the next round it would jam about halfway into the chamber and dent the crap out of the case shoulder.
3. I think the OAL of the Hornady ammo was too long as it looked like the bullets were getting jammed into the lands. It also seemed like the chamber was way too tight, which may have been part of the problem with the failure to feed issue. If I tried hand loading a single round it would not fall into the chamber, but get stuck about halfway in and I would have to press it down further with some force, and only slamming the bolt home would get it fully into battery. Then if I tried to pull the bolt back it would be stuck (I'm guessing because the bullet was stuck in the lands) and I'd have to slam the butt stock on the bench while pulling on the charging handle to get the cartridge out. Once out, you could see the land marks on the bullet.

When single loading by hand verything fired and ejected fine, but looking back it probably wasn't the smartest decision if I had the bullet smashed into the lands. I ended up single loading / firing about 30 rounds, 1 had a light primer strike but a second hit lit it off.

Any thoughts on where I should start to try and troubleshoot this thing? My gut says the chamber is not cut correctly considering I have bullets / cartridges getting stuck up in there.

These are common problems with 6.5CM and .260 Rem if the rifle isn't built and designed from the ground up by a competent shop, set up correctly with the right gas port, ammunition spec worked out in advance, buffer, action spring, chamber, etc.

Your malfunctions are symptoms of excessive cyclic rate, where the magazine doesn't have a chance to lift the cartridge stack up in time for the violently-moving BCG to strip the next cartridge off correctly.

This is pretty common with 140gr loads in 6.5CM or .260 Rem when using RLGS that hasn't been tamed somehow.

A short throat, if that's the case, will make the problem even worse by spiking chamber pressure.

Do you have any cratered, pierced, or blown primers?  Those are also common if the gun isn't set up right.

Yeah I was hoping that using the major components from the same manufacturer would help alleviate any "build problems," I didn't have the budget to buy the rifle so I just slowly bought the parts as I could.

The spent primers look ok, maybe just very slightly flattened but honestly it's too hard to tell, nothing alarming there at least. I am using a JP silent capture spring with the default spring installed, as well as an SLR adjustable gas block set to the default settings. I forgot to take the extra spring pack or tools to adjust the gas block with me, but between the spring and gas block I do have plenty of room of adjustment to play with the cycle rate of the BCG. I just finished stripping and cleaning the literal crap out of it, re-oiled and it does seem to be functioning a little better now so we'll see how she does on the next range day. Thanks for weighing in with your thoughts, I think you're right that the cycle rate is on the aggressive side.

I think you've got cyclic issues.  Adjusting the gas down can help with that.

More importantly, it sounds as though the chamber and throat need attention.

Factory Hornady ELD-M are 2.80" COAL and should work in every rifle.  I would verify that the marks on the bullet aren't from it moving up the feed ramps OR being ejected and catching the 2-3oclock barrel extension lugs.  If they are in fact jammed into the rifling, I'd send the barrel back yesterday.

JMHO.

I had this very same thought after I got done cleaning it this afternoon as I remembered one of my first 5.56 builds dinged the bullets up pretty good as they went up the feed ramp. After a thorough cleaning the cases seemed to have a better fit in the chamber and didn't get stuck, but were still getting marked up like I saw yesterday when shooting. I used a permanent marker to "paint" a bullet and then fed it through the rifle, after inspecting it afterwards it does look more like feed ramp marks rather than marks from the lands. I think the "sticking" that I had yesterday was more a result of either a dirty chamber, or possibly the BCG. The tolerances on the BCG are super tight and doesn't move all that smoothly at this point, I'm guessing it'll be fine once it gets broken in a little bit.

At this point I think I'm good to try shooting again, would you guys recommend first swapping the JP buffer springs to a lighter spring or just skip straight to adjusting the gas block down?

I'm no expert, but I believe taming aggressive cycling is done either with a heavier buffer, stiffer spring, less gas, or some combination of the three.

I don't think you'd want a lighter spring...

When you single fired a round would the bolt lock back?

I bought a 20" 6.5 Creedmoor upper from Aero Precision last year which I believe would be a BA barrel.  It was almost a single shot.  Long story short, the gas port was too tight and it was under-gassed.  I had to open it up a touch to get it to run.

ETA:  I believe the gas port was .068".  It would not run there.  I opened it to .081".  Should add this was with a standard rifle buffer, recoil spring, etc.  All from Aero Precision.

Turn your gas down.  Leave the springs alone.

Oil your bcg well. I put a dab of grease on the cam pin slot, but it's not required.

Eta: try the gas setting on 5.  6 will probably work better, but try 5 first.  Close it completely (screw all the way in), back screw out 5 clicks.

Yes, and no. So it's weird but the bolt locks back in 2 places. I discovered this today after I was cycling it back and forth after I finished cleaning and lubing it. I noticed the bolt still wasn't picking up a round and then as I looked into the ejection port it looked like the bolt wasn't far enough back so I threw a mag in it and sure enough, the bolt was locked back, but forward of the rear of the case head so there's no way it could pick up that round. I dropped the mag, pulled the bolt back to the full rearward position and it locked back, put the mag back in, hit the bolt release and it picked up the round and slammed it home. Cycled the BCG again and it ejected the round and locked behind the mag. Since I was single loading though I wasn't paying attention to where the bolt was locking back so I'll have to look closer at that next time I go out.

I suspect your gun may be under gassed.  Next time you shoot it, fire single shots and see it the bolt will lock fully back.  Check gas block alignment and adjustment.  If those are okay I would not be surprised if the gas port is undersized.

FYI a #46 drill is .081" and a #44 is .086".  Mine runs good at .081" so I stopped there.

My technical specs call for a .082" (+/- .001") gas port diameter in the rifle length gas length for .308 Winchester based calibers
like the: .243 Win., 6.5mm CM, .260 Rem., 7mm-08, .308 Win.(7.62X51mm NATO), .338 Federal .

Since many factory barrels in this caliber class tend to be over-gassed (over sized gas port usually ) a stiff buffer spring and/or a
heavy buffer are in order...a adjustable gas block can also work  if your running a standard buffer and buffer spring.

If your barrel has a undersized gas port, then getting to run is just a matter of increasing the gas port diameter till it cycles
correctly with factory ammo...

A factory barrel with a correctly cut chamber and throat should function correctly with a appropriately sized gas port.

With that said, I would recommend polishing your chambers on a factory new barrel after a good cleaning/scrubbing since
I have seen chambers that were poorly cut or showed ruff cut chambers causing failures in the above calibers...

Good luck.

I do plan to single load the first shot next time out and see what happens with the bolt. If it doesn't lock back I'll know to increase the gas flow (I have the SLR adjustable gas block installed with the factory setting), if it does lock back then I know I can start to dial the gas down little by little. Hopefully with the adjustable gas block I won't need to worry about opening up the gas port.

That is small.

.086" is pretty common for 6.5CM and .260 Rem RLGS 22-24" barrels.

Tag.

Ive got a savage with similar problems, may start a thread on it but in for info in this one

If a new gun is under gassed, I would do Hellbenders fluff and buff on bolt, carrier, and extension before opening a port.  There might be plenty of gas when everything is slicked up.

https://www.ar15.com/forums/Precision-Rifles/Hellbenders-guides-to-Ultimate-AR15-and-or-AR10/4-42/

Knocking down the sharp high points on the extension will save your bullets from getting scratched up...

This is great info, thank you for the link! One of my first AR-15 builds tore bullets up pretty good during the chambering process and I did some of this stuff to that rifle, but not not to this kind of detail. I'll definitely look into doing some of these mods next chance I get ... hoping to get back out to shoot the rifle again this weekend.

I absolutely think packing oils in the chamber contributed to some of my issues to some degree at least. Next time I have the barrel off I'll look at polishing up the feed ramps as well, had to do that to one of my .223 barrels a couple years back so I'm familiar with that at least.

Anecdotal info, my early Armalite 10T in 243 with 24" barrel had a gas port of .065" ish. Or as close as I could measure using drills and a mike...
It was a very soft shooter.

I cut and reprofiled the barrel to 18", and opened the port till it ran reliably at .077"

For me at least, I would prefer to have a port undersized so I can set the rifle up my way.  Not a big fan of adjustable gas blocks

My 6.5 Creedmoor I had some similar functions. Combination of gas adjustment and buffer tuning pulled it right in line.  I also have the SLR adjustable gas block as well as the silent capture spring. For the SCS, I have the yellow spring with two tungsten rings. Cycles well with everything I've tried which is 120's on up both suppressed and not even though I usually load heavy projectiles.

I have the same setup on my 6mm Creedmoor with the same results. That I've stuck with shooting 103's on up.  Only thing with it was a pierced primer every now and then on the 6mm. No consistency when it would happen, but happened with Hornady factory ammo and any loads using CCI 200, BR-2 & No. 34 primers. Again,  pierced primers would be haphazard here and there.

Switching to WLR primers and I've never had another one.

Both are 22" barrels with rifle length gas systems.

It didn't.  Even replaced it with a brand new one and same results.  Gone through a couple hundred rounds now using same brass, powder,  charge weight and projectiles.  Only thing changed,  the primers. Not one pierced since.

I had the rifle out earlier to adjust the scope positioning and played around with the bolt catch a little more to see where it was catching forward of the rear (and normal) bolt catch position. You can see in the picture that the bolt lugs are catching and stopping on the magazine (magpul) follower ... is this normal? With enough spring force forward it doesn't get caught on the follower, but if you're manipulating the BCG slower it catches pretty easily. Hitting the bolt catch releases it forward, or a firm smack on the ground with the butt stock and it'll slam home. This makes me think even more that it was under gassed. There was just enough gas to push it back to the follower with it caught, and that's why it wasn't picking up the next round correctly.

Still trying to get out and shoot it again. My membership at the local range is expired so I've just been shooting at a friends place but he's been busy with work and we haven't been able to get together to shoot again. I also checked the JP silent capture spring I had installed and it's the medium, so I do have the option to swap those springs in addition to the gas adjustment. I'll take all the above when I get to shoot again so I have plenty to play with.

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Concur with first couple posts. First thing I thought was that your gun is cycling too quickly (or too slowly, sometimes the two can have similar looking problems). There’s a lot of ways to fix this, but fixing it closer to the gas port is usually preferable to further.