I had posted some of this in the long Aero M5E1 thread below but wanted to make a separate one.

I assembled this a few weeks back and the first time out with stock buffer and spring that came in aero kit, I couldn't cut the gas down enough to get it to run. Way too overpassed as the cases were bouncing around inside the ejection port. I swapped to a springco orange and that made a big difference. Although even with SLR gas block 12 clicks open, it wouldn't lock back unsuppressed. Did lock back suppressed.

Second trip with it I moved focus to accuracy testing at 100Y from a bench with bipod and rear bag. Unfortunately with FGMM 169 and PPU Match 168 it was around 2" at 100Y.

So I took the upper completely apart, rechecked head space, cleaned up each piece again and retorqued it all down. Gas block was lined up correctly even though I have had issues with it cycling unsuppressed. Before taking it apart I rechecked the torque values of all pieces and they were correct.

Third trip focused on accuracy with FGMM 168 & 175, Hornady Black 168, PPU Match 168 and AE 155gr and did 3 round mag fed groups as that is what BA's MOA guarantee is based on.  

Results at 100Y unsuppressed:
AE 155gr would not do much better than 1.5"
PPU Match 168: .75"
Hornady Black: 1.05"
FGMM 175: 1.55" (the first two were .59" then it got a stove pipe trying to load round 3 so I had to stop and clear that before shooting a third round)

Results at 100Y suppressed:
PPU Match: .429" & .959"
Hornady Black: 1.13" & 1.47"

Results at 200Y unsuppressed:
PPU 0.148" (this was only two rounds. I stopped and went to check as I thought surely they weren't in same hole, but somehow they were at 200Y)

Results at 200Y suppressed:
Hornady Black: 1.80" & 1.79" (the 2 closest rounds were 0.68" and 0.62" respectively)

These results were satisfactory as I am still new to 308 semi autos.

Next on list to troubleshoot (assistance requested):
- First six rounds of day were AE 155gr. First 6 were single loaded in mag and locked back each time. However rounds 7-10 (single loaded in mag) all failed to lock back. What would cause this change? The gas block was not adjusted.

- With the FGMM 175gr, I twice loaded three rounds into magazine, first two loaded and ejected but third round on each mag mailed to feed. The bolt was jammed on top of it about half way down case both times. Cause for this malfunction? It appears this is indicitave of overgassed or weak mag spring. Was using new 10rnd PMAG.

- Suppressed towards the end of the trip (round count about 50 at that point) I could not get Hornady Black to cycle. Would load three rounds and when it ejected the first it would stove pipe, each time with another round partially in chamber in front of the stove pipe. Perhaps overgassed?

I think I am going to stick to PPU and determine the unsupressed and suppressed setting on the gas block. 12 clicks from closed on the SLR block I was able to get PPU to cycle and lock back multiple times.

Build specs: Current round count of about 160
M5E1 set
BA SS Premium 18"
SLR Sentry 7/melonite gas tube
Aero nitride BCG (headspace has been checked twice with ejector/extractor removed and chamber/bolt cleaned and dried)
Springco Orange and stock Aero M5 buffer in carbine extension
Aero M5 LPK and Laure MBT
SWFA 12X in Aero mount
Used a G reaction rod for barrel nut (tightened/loosened three times to 65 Foot Lbs per AP; then removed and retightened once to 65 Ft Lbs when I stripped it and reassembled a few days ago)

Only odd damage I have noticed is to front edges of barrel extension (on 12 oclock lug and 3 oclock lug) where the bolt seems to be hitting it right on edge and left small dings. When I lock back the bolt and then slowly lower it onto empty chamber, sometimes the bolt face hits those edges of barrel lugs and sometimes it slides right in) Also sliver of backside edge of one of the bolt lugs is showing bare metal instead of the nitride finish.

Trip Four Results:

Only one malfunction (bolt locked back but spent round was just sitting on top of follower) when I did not cut gas down enough going unsuppressed to suppressed. It cycled and locked back every other time whether it was one round or five. Seemed that 12 clicks from closed unsuppressed and 4 clicks from closed suppressed did best. Some rounds (especially last round in mag), suppressed, still ejected about 2 o'clock but all others were 3-4 o'clock and landed a good bit away. This was all with 168 FGMM.

Accuracy results @100Y suppressed:
2 rounds: .468, .545
3 rounds: .825", 1.22"
4 rounds: .775"
5 rounds: 1.09", 1.05"

I’m thinking the same as ^^^bfoosh

Try heavier buffer (H3 or H4) first, then maybe the spring, Tubbs Flatwire or Springco Red spring.

I’m worried about having the same issues once I get my M5 together, both suppressed and unsuppressed hence I went with a Spikes ST-T3 and Springco Red with an SLR Sentry7.

Hmm, interesting numbers.

So the Tubbs .308 offers somewhat similar rates as the Springco Orange but is much “softer” on the BCG???

Might be something to consider with my present setup:

Springco Red, Spikes ST-T3 and SLR7 on a Criterion 20” ‘Hybrid’ Rifle length barrel.

If I’m having similar issues as you did Bfoosh, I may pick a Tubbs up.

When I get a good position behind it, suppressed, it is reasonably smooth cycling. With that said I have never shot any other large frame AR so I have nothing to compare it to. When the gas was opened more on the block, I could really tell it beating the gun up. With gas turned down, I can notice it being smoother.

The buffer is the exact one that comes in the AP M5 carbine buffer kit they sell. I am unsure the weight as I do not have a scale.

I went to the orange spring at suggestion of folks here. It does seem to close with authority and the nitride on the bolt face is starting to wear off in two spots (round count about 200). First nitride BCG so perhaps the finish wear is normal.

Could you explain your numbers below? Does the .9 difference between orange and flatwire "closed" make that big of a difference? or is it the difference between 16.7 and 24.8 that accounts for how much force the BCG comes back forward?

Thanks

By guesstimation, I’m assuming it’s the 16.7 that makes for the smoother/softer ride of the BCG. An extra 8 plus pounds of force on the BCG might be the reason it’s getting “slammed home.”

Standing by for further intel . . .

And, Roger.