AR-15 problem-short stroking

[Bowdrie]

I need help sorting this problem out. I'm ready to pull my hair out(and I don't have that much left to pull out)I built this AR using an Aero upper with a nickel boron bolt, stainless 16 inch mid length barrel in 223 WYLDE. I have never had this problem with any other build I have done.
I have tried every ammo I could find and it all short strokes. I then lubed the hell out of the bolt. That didn't work so I tried switching bolts out.That didn't work. I then tore down the gas system to look for obstructions. The gas tube is clear. The gas block is clear and centered perfectly over the gas port on the barrel. The barrel gas port is also clear. I'm at witts end and don't know where to go from here.
Any help or suggestions would be much appreciated.

[Siggy-06]

Since you've covered lubrication, make sure you gas block isn't moving/leaking. Also, some brands of magazines sit a little higher than others so try another brand. Make sure your bolt key is tight, gas rings are good. Lastly, make sure your buffer isn't too heavy, heavy springs or the wrong weight buffer will cause short stroking too.

[Scorch]

Short stroking generally means not enough gas. So check the gas block for looseness and alignment, check the bolt gas key for tightness, and if all else fails check the size of the barrel gas port (we have had several barrels come into our shop with undersized gas ports).

[HiBC]

You have a 16 in bbl with a mid length gas system.
As I understand it,the 16 in short gas system carbines had problems with being over gassed. Over time,steps were taken to make them run,that mostly being with the buffer weight and design.

The dwell time of gas pressure after the bullet passes the port has been cut with the mid gas system.I'm not knocking the mid gas system that's what I would use.I might not go heavier than an "H" buffer.

I would not use any exotic recoil spring.

The 16 in H-bar mid I built ran fine,but it was a 1 in 9 twist and I only shot 69 gr bullets in it,propelled by Varget.

Point being along with the rise of the M-4 in the military,the old 55 gr load I believe is a thing of the past along with the M-16 20 in bbl..I'd shoot 75 to 77 grs if I had a 1 in 8 or 1 in 7. OK,you did say you tried variations in ammo.

But,there is one more thing.There are some minor variations in buffer tube lengths and buffers with all the aftermarket parts options.You might have a combination of parts that aren't compatable.

I once swapped an A-2 stock for an A-1.The 5/8 thick spacer went away.
The A-1 stock came without butt screws. Silly me,I used the A-2 screws. I got short stroking for the buffer smacking the butt screw.
How does the bolt stop work if you slingshot on an empty mag?
Hows your gas ring friction and end gap orientation? A tiny dab of grease on your cam pin won't hurt.
Gas tube come thrugh the barrel nut/upper straight and centered?

[JeepHammer]

I didn't see you comment on gas port size in the barrel.
Many 'Premium' or 'Semi-Finished' barrels are 'Pilot Drilled' and not drilled to full size.
The reason for this is gunsmiths will size gas port for specific ammunition the customer is using.
When laymen get hold of semi finished barrels they might finish chamber it, but miss the gas port sizing.

You say 'Short Stroke', where is the bolt hitting the next round in the mag?
A true 'Short Stroke' won't usually hit the side of the round in the mag, since the bolt doesn't actually move far enough to the rear for next round to pop up, the bolt simply slides over the round in the mag.

A true short stroke rarely bites into the side of the next round since it won't pick up the next round.
Biting into the next round, or not closing the bolt fully (into battery) is usually a spring, buffer, buffer tube or friction issue.
The bolt *Should* slide easily forward WITHOUT catching on anything.
Shouldn't catch on any internals without a mag in place, shouldn't catch on the mag at all when it's in place.
All this is a forward stroke problem, not a 'Short Stroke' problem.

Sometimes the mag lock is simply in the wrong place and the mag sticks up too far.
Sometimes the mag will have bent lips or be incorrect and cause friction/drag.

If the bolt *Seemingly* moves fully to the rear, but bites into the side of the round in the mag...
Check to make sure you have the right length buffer AND the correct buffer spring.
Buffer springs ARE NOT interchangable between carbine & standard length stocks.
Buffer springs ARE NOT interchangable between AR10 & AR15 formats.
Some suppliers play 'Mix-&-Match', and it never turns out well for the builder...

I get a TON of builders that have leaking gas blocks.
'Also Ran' barrel & gas block makers tell you to slather up that block with 'Goop', thread locker, etc.
If the gas block didn't need pressed on/off, it's leaking. Slip fits ALWAYS leak and it's sloppy building to use a slip fit gas block/front sight block.

A ton of builders show up in my shop with mismatched buffers/springs for the stocks they are using.
Not just 'Cheap' springs that don't have correct spring rate, but all together the wrong number of turns.
This is usually from buying 'Economy' stock & buffer kits from questionable sources.
Springs bind (too many turns for a carbine stock) will drive you nuts!

Leaking gas key on the bolt is common...
Incorrect screws, not staked into place, leaking between key and bolt carrier.
Not all bolt carrier & keys have gas ports that line up, something to watch.

If it doesn't take solid thumb pressure to get the bolt to seat into the bolt carrier then the gas rings are junk or the bolt carrier bore is oversized (junk).
This isn't real common, but it happens...

Charging handles will cause the BCG to tip DOWN in the back when hand charging.
Fire cycling will force the BCG, more or less, stright back.
Look for a wear mark on the recoil buffer tube TOP where the BCG isn't quite lining up with buffer tube/lower.
I've found that AREO often doesn't fit well with common non-Areo receiver offerings.
If you find that knock/gouge/rub mark, the upper & lower aren't aligned.
Sometimes the carrier will show rub, or even aluminum smear on the back/top of the carrier.

Keep in mind the bolt BARELY gets a bite on the back of the second round.
If the mag lips bite into the brass, it will slow the BCG down and often allow the bolt to jump the back of the round resulting in the bolt biting into the side of the round.

Feed ramps/guide grooves will often have sharp edges that will bite into bullet and cause the bolt to skip off the back of the round, biting into the side of the round.
Most 'Builder' barrels/kits DO NOT have the feed ramp edges deburred or rounded.

Just some ideas from things I've run into, hope it helps.

[JeepHammer]

One other thing that comes to mind...
Some barrels have gas port/handguard cuts on the barrel that keep common gas tubes from fully reaching the gas key/BCG.

Some non-standard uppers will space the barrel out so the gas tube doesn't quite reach to the gas key.
It's rare, but I've seen it, particularly with the aftermarket 'Target' uppers with raised picatinney rails for big objective optics and no dust cover.
I don't know who made them, but they were real popular before flat top uppers were common and sold by several retailers.
The receiver was simply too long where the barrel nut threads on the upper.
When faced off square (which I STRONGLY recommend with any brand upper, NONE come true & square because of the manufacturing/coating processes) that upper worked quite well since it was much heavier/stiffer than the factory uppers being offered at the time.

I suggest 'White Out' in the upper, on the bottom of the charging handle up around the gas key to see what's leaking... Just don't white out the bore of the upper where the BCG contacts it.