I finally got to shoot my M5 build.  This was not a pre built upper.  Anyways, it is an AP upper, barrel and rail, with an SKR Sentry 7 adjustable GB.  It will eject the spent Cason, but not pick up the next round.  I can manually rack the CH and get another round in the chamber.  The GB was opened all the way up.  This gun has always been tough to charge, much harder than any of my AR-15’s. Is it possible the spring is too much?  It seems to be a standard carbine length spring, but much stiffer than any of my AR-15 springs. This was a complete lower that I bought brand new.

Thanks for any info or ideas.

It will lock back sometimes, but more times not.  The only marks inside the upper are in the CH valley, where the CH is running on the upper.  
Yes, it is a complete lower from AP.  Just messing around I installed and AR-15 buffer spring, and it is much easier to rack, more like I think it should.  But I know I can’t run that spring.  I have read about a lot of people having this same problem with this setup, and getting it fixed with the correct buffer/spring setup.  I just need to know what that setup is

Pics of the spring, buffer tube, and gas block? Something does sound off. Also replied in the M5 thread.

sounds like the assembly is moving too quickly to strip the round reliably (or lock back).

Have you tried closing off the gas port a bit?

Heavier buffer?

Close the gas block completely and open it back up.  Each click is 0.007”.

I agree, sounds like over gassed. Did you start out with the GB fully open? I would go down to 4-6 clicks from closed and try that.

I started with the GB open about 5-6 clicks.

I was under the impression that it was under gassed, but now that you bring it up, it did have quite a bit of recoil.  More than I would expect from an AR-10

What length gas system? What was the cycle like when you had it 5-6 from closed? I have the Faxon 20" fluted match bbl on mine. It has rifle length gas system and I run my gas block at 4 from closed with JP silent capture spring and standard weights.. If I go past 6 it will skip over the next round in magazine and fail to chamber.

Mid length gas.  The ejection seemed normal.

I had this same type of function your having with my first AR10 build. I use a low powder charge with 175gr TMK and I still am running at 4 from closed with SLR block. Now its ejecting at 4 o'clock and not damaging brass at all with 100% function with or without omega attached.

You have a mid length so I am willing to bet 3-4 from closed.

What other symptoms should I look for if it is over gassed?

The extractor will leave a pretty good mark in the rim if it's really overcycling.

That I did not notice.  The brass looked pretty good.

On the gas block, should it but up to the shoulder, or should there be a small gap there, like in an AR-15?  I think I am going to take the GB off and measure everything, and make sure it is aligned.  I will try and get a few pics posted this evening.

Methinks you have gas block placement misunderstood.  There's no set location for a gas block "in an ar-15".  Nearly all barrels made these days are made with the understanding a low-pro gas block will be used, and no handguard cap will exist.  The *PROPER* way is to actually measure gas port location from the shoulder, and then measure the port inside the gas block, and place it appropriately.

That being said, 99% of the time the gas block is intended to butt against the shoulder.  An easy way to tell is, most gas block manufacturers (assuming set screw) will drill the rearward set screw hole in line with the gas port in the block.  Remove the gas tube, unscrew the set screw, and rotate the block upside-down.  If the gas port is centered in the hole when butted against the shoulder, good to go.  If it's offset, then you probably will want to have it set forward just a smidge.

However, if the rifle is cycling and the block adjustable, it either doesn't matter if it's a teensy bit "off", or it just isn't off at all to begin with.  Either way I wouldn't go fucking with it juuuuuuuuuuuuust yet.  Crank the gas down and then slowly open it up until it locks back reliably.

Well that could be part of my problem.  I will check into it.

Here are some pics of the inside of the upper:
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With the rifle unloaded and empty magazine in place pull the charging handle all the way to the rear.

How much clearance is there between the bolt face and the bolt stop? If it's not going back far enough to catch the bolt stop with 1/8" to spare +/- it doesn't have enough clearance to allow for reliable function.

I had the opposite problem, too much clearance and was hammering my bolt stop.

What ammo are you using?

What size is the gas port?

Did you measure the distance from the barrel's shoulder to the center of the barrel's gas port and double check the gas port location inside the gas block to insure alignment? Some barrels/gas blocks need to be shimmed like they are incorporating a front handguard mount.

With the rifle unloaded and empty magazine in place pull the charging handle all the way to the rear.

How much clearance is there between the bolt face and the bolt stop? If it's not going back far enough to catch the bolt stop with 1/8" to spare +/- it doesn't have enough clearance to allow for reliable function.

I will check this when I get home

I had the opposite problem, too much clearance and was hammering my bolt stop.

What ammo are you using?
ZQI 7.62x51

What size is the gas port?
.0730

Did you measure the distance from the barrel's shoulder to the center of the barrel's gas port and double check the gas port location inside the gas block to insure alignment? Some barrels/gas blocks need to be shimmed like they are incorporating a front handguard mount.
I did measure from the shoulder to the gas port.  I haven't been able to measure the GB yet, because I would have to take of my muzzle break and all that, and I was hoping to not have to do that.  I emailed SLR to see if they could tell me the measurement.

The bolt is about 1/2” back from the bolt catch.  Is that too much?

Waaay too much. You don't want more than 1/10 to 1/8" behind the bolt catch. It's plenty to allow for reliable function, but any more than that and the BCG has too much room to accelerate on return and you will break bolt catches left and right. That's far enough back I have to wonder if you weren't given the correct buffer.

How would I go about checking/correcting this problem?

Now that I think about it, an incorrect buffer would be too long, if anything. The M5 carbine buffer is 2.5", AR15 would be 3.25" and would keep the BCG from coming back far enough.
A short spring, maybe? or is the buffer tube not installed deep enough? If those are correct, quarters work well as spacers to put in the bottom of the buffer tube to achieve the proper depth.

THIS! I’ve had to “time” the BCG in all of my 308 AR’s. The specs are all over the place. I use the “quarter behind the recoil spring” method. Usually 1 or 2 quarters does it. I go no more that 3/16” bolt face to bolt catch (max travel). Between 1/8 - 3/16 is optimal (could do 1/4”, but it’s not necessary and it’s entering the zone of too much bcg speed). This is one key area where AR 308 is very different (5.56 will usually have well over 1/4”).
Unfortunately, most people don’t time their 308 carriers, and that’s why so many broken catches and other issues.

I had the same issues with an aero 308 spring before.Its insanely hard to pull back compared to my sr25's(literally had to use 2 hands) and gives a ton of extra overt travel for the bcg.I ended up swapping out to the regular polished jp 308 specific spring and its the perfect length.I don't think aero did much research on what really works with the 308 systems because they send the spring from a car shock absorber and a super light carbine buffer out with their kits. I had the gas almost turned off on my gas block and thebuffer spring was still overpowering the mag spring on the ride home.

I ended up installing a Brownell's flat wire AR-10 spring.  It was pain to get in, but is much easier to charge now.  I have also moved the GB to the shoulder.  I will hopefully be able to go shooting soon to check it all.

Sentry 7 is not spaced to go against the shoulder. On all of my Sentry 7's, I used a their dimpling jig, which placed all of them with about the thickness of a business card between the block and shoulder. They are designed with the space to be able to run a handguard end cap if desired.
I HIGHLY suggest getting their dimpling jig. It's low cost (around $35-ish IIRC) and absolutely will perfectly center your dimples (or dimple, you really only need to one to center it. I do both though, and then also cross pin them just because I like them built like a tank). They use a pointed screw on one side that goes into the port hole, and the other side has a collared hollow bolt to act as a drill guide. They're the best I've ever used. Even if it's a nitride barrel, your everyday carbide bit in a hand drill will do just fine.

For springs, I've switched all mine out to GunTec 308 carbine springs and they're shorty buffer (for use with mil spec carbine tubes). They are also low cost (Aim Surplus has them), and are Chrome Silicone (unlike most others) so they'll probably out live you. They are also the smoothest/lightest I've used (vs PSA, Aero or DPMS), yet stout enough for positive lockup (you don't want ultra strength when you're using an adjustable gas block).

Think you guys could give me some advice? I have never shot any other AR-10 or owned one other then these two described below so I have no way to know if this is all normal. They are pretty new. Is there anything I should look to change?

I have two Aero precision ar-10. I have shot about 80 ish rounds through each gun. After lubing them up BIGLY and putting 80 rounds through each they are working pretty good. Brass ends up about 3 to 4 o-clock in front of the gun. Is that where it should end up???

The brass is mostly not deformed. Some times there was a little deformed wobble looking thing on some of them but not most. Up on the top part of the case. But I only remember seeing this when I first started shooting them.
The brass is scratched up around the neck or top area. There are brass shaving inside the chamber & on the bolt face. Scratches. There is a bit of wear already inside the upper where the bolt slides.

When I pull the BCG back there is about 1/2 inch ish between the BCG face and the bolt catch. Does this need to be changed?

Pulling back the charging handle is pretty stiff. I can do it with one hand if I hold the gun with the other. Maybe ruffly twice as stiff as my ar-15's. Is this normal?

Once in a while I'll pull the trigger and the firing pin slams forward but it does not fire. This happened quite a bit when I first start firing them. probably 1 in 4/5 rounds. After 80 ish rounds and lots of lube it almost gone but still happens. I figured it was form a stiff bolt & needing lube and breaking in?

I have shot 3-4 different brands of expensive hunting ammo through it & PMC, federal, and prvi 7.62. All seamed to work and function just fine. Could tell no difference between any of it.

Should I just leave the buffer, spring, and gas block alone since it seem to work fine? Any reason to change any of them?

- They both are using DPMS patterned lowers. Aero BCG, Aero buffer kit, and Areo Upper (below info).
- They are using the stock gas block. Not adjustable
- They are using the stock buffer, spring, and tube

- Aero 308 / 7.62 Bolt Carrier Group, Complete - Black Nitride - APRH308186
- Aero M5 .308 Carbine Buffer Kit, No Stock - APRH100158
- Aero M5 .308 Standard Lower Parts Kit - APRH100160 (nothing changed or swapped out with the trigger. all stock parts.)

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Aero AR-10 - M5E1 Complete Upper, 16" .308 CMV Barrel, EK-15 Handguard - Anodized Black - APAR308554P22 - $560.00
16 Chrome Moly Steel CMV-Mid Length Blk Hard Coat Anodized Brl Finish
Unit of Measure: EA
DPMS LR308 Pattern Upper Receiver
Manufacturer #: APAR308554P2
Type: Complete Gas Impingement
Caliber: 308 Winchester/7.62 NATO
Barrel Material: Chrome Moly Steel
Sights: None, Optic Ready
Barrel Length: 16"
Twist: 1:10"
Threading:5/8 x 24
Barrel: CMV-Mid Length
Gas Block Journal: .750
Gas System Length:Mid
DPMS Barrel Extension
Receiver: 7075-T6 Aluminum M4
Handguards: EK-15
Barrel Length: 16.00"
Weight: 4.7000
Barrel Finish: Black
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Sorry, but I didn't see what trigger you were using.  whichever brand, style, did you change the hammer spring to a lighter spring?

Oh, sorry missed that. Aero 308 lower parts kit. nothing changed with it.

M5 .308 Standard Lower Parts Kit - APRH100160

Mine will occasionally have a non fire too (std mil spec trigger/hammer springs) with NATO ammo (hard primers). This seems to be common. You could move up to a heavier hammer spring, but that will also increase pull.
Your ejection pattern is great, no issue there.
The 1/2” overtravel (bolt face to catch) would bother me. I’d at least put a quarter behind the recoil spring to lessen that gap.

Thanks for the info. I'll stick a quarter or two in there and shorten it up and give it a try.

Is PMC, federal, and prvi 7.62 all considered NATA ammo with hard primers?

Instead of quarters I use these Hillman stainless steel fender washers. You just need to take off a tiny bit around the circumference with a bench grinder so they fit in the buffer tube.