Not no, but hell No.

Get a large spray can of BreakfreeCLP, and use it to not only clean the rifles, including a chamber brush to scrub the bores by hand with CLP, then remove all the fouled CLP and lube just the upper Receiver  bearing areas with Clean CLP.

For starters, CLP has a cleaning agent it it that will get all the old oil and grease out that may be collecting fouling to cause problems, but used as a lube, cleaner continues to work to keep the rig from fouling choking out as well.   As for solvent to clean the rig like Hoppes, do not belong in the same room as the rigs, since Hoppes leaves behind a protective coating that will foul choke out an auto loader quickly as well.  If you need a solvent to clean the copper out of the barrel alone, then sweets cleans copper fast, and does not leave behind a protective coating that will attract fouling.


Next, on your testing of the CLP cleaned and lubed rigs,
Single round in mag, insert mag, charge round and leave empty mag in well, and fire the round.
The bolt should lock back on the bolt catch (in front of the face of the bolt), and spend case should be ejected 10'~15'.
If bolt does not lock back with the catch in front of it, or spent case is not ejected this correct distance, go police the spent case to take a look at its spent primer, the outside of the case, and even the rim of the extractor.

Primer pressure flowed all the way to the edges of the primer pocket, round when over pressure.
Sides of the case all marred to hell with scratches, chamber is less them mirror smooth/flat as a mirror.
Spent case rim bent backwards, bolt is unlocking too soon, and will cause a form of short stroking, since spent case is still too residual bore pressure bound to the chamber walls, for the bolt/extractor to pull is cleanly.  

Now if spent case is not showing signs of any of the above, then either problem not enough gas pressure to the bolt to unlock it at the correct time, and it a mater of finding the leaks, buffer mass/weight to great for the load, or there is binding going on in the action that is slowing down the bolt unlock speed isntead.  Hence don't screw with the gas port yet, but instead make sure that is not gas system action leakage (including key to top of carrier), and no binding of the B/C coming all the way back.  
To check the gas system, CLP around the front and back of gas block to barrel, and around gas tube to block, then use an air compressor gun with rubber hose to send 100lbs of air down the gas tube from the inside of the receiver.  You will get air flow through the barrel gas port, but will be enough resitance to show you if you have leaks at the gas block to barrel and tube.
On the B/C, CLP around the Base of the key to top of carrier, and them hold the bolt in while you send 100lbs of air down the key entrance.
To add here, after you check the carrier key for leakage to the top of carrier, pull the bolt and dry fit the carrier with key in the upper receiver, to make sure you have the gas tube tweaked correctly to align with the key.  Hence gas tube will enter key when face of carrier is about 1" off the barrel extension face, and should only take a light pull with your finger inside the carrier to pull it back off the gas tube, if the tube is correctly index aligned tweaked from the center of the barrel.


Also, from the start, do a full charging handle pull on each rig, and make sure that the face of the bolt stops 1/8"~1/4" in front of the back edge of the ejection port window, and the last inch of CH pull is the same tension as the middle of the pull.

Get us this far, and trouble shooting the problem should be simple, on what problems you found above.
Also, short of the 69gr plus ammo, all the rigs should be running standard weight buffers.  So make sure that you do have standard weight buffer for testing.  If you are finding that the only problem alone is spent case rims bent backwards from the bolt unlocking too fast, then you can drop in a heaver buffer to slow the bolt unlock down isntead.

If you are experiencing the same issue on all 3, then I would have to think that the cause is the same on all 3.  I would suggest trying a few different things for process of elimination.

Have you tried any factory 5.56 ammunition like Federal M193 or M855, as the extra pressure may give you different results.  

Try inserting just the bolt carrier (No bolt, cam pin, or firing pin assembly) into the upper receiver, and see if it freely moves forward and backwards inside the upper receiver with no resistance.  The bolt carrier should basically free float inside the upper receiver, as the bolt carrier should only be making contact on its raised rails (2, 4, 8 & 10 O-Clock if you are looking at it as if the bolt carrier is at 12:00), the only resistance you should feel is when the gas tube mates with the gas key but it should be very little.

You mention that you verified that the gas blocks were mounted correctly, but again check to confirm that the gas port inside the gas block is perfectly centered over the gas port on the barrel.  I've had several people bring me uppers and rifles that had the same issues you are experiencing, and when I removed the gas blocks I could see from the carbon residue left behind that the gas blocks were just barely off center, and when I used a gas block alignment fixture and got things properly aligned, the guns ran 100%.

Along the same lines as checking gas block alignment, check your barrel nut alignment, to make sure the gas tube has side to side free float movement.  A good way to look at this is to look at the back end of the gas tube where it sits inside the upper receiver charging handle track.  What you want to see is that the gas tube is centered inside the charging handle track area, and not off to one side, you should be able to push the gas tube slightly side to side with the same amount of play of which will show that the gas tube is centered correctly so it can mate correctly with the bolt carrier key (gas key).      

You state that you are lubricating everything, make sure that you soak the 7 bolt lugs, as if these are dry you may experience short stroke issues.

Another thing you can do for process of elimination, is try swapping bolt carriers and then just the bolts from know working rifles, make sure you are checking headspace to make sure things are within proper spec, and see if you can find any possible combination of bolt and or carrier that may work differently.  I have had a few rifles cross my path that wouldn't run on one bolt, but would on another, and it came down to a stacking of machining tolerances and the angle of the back of the bolt lugs that were causing issues on the unlocking cycle.

You do mention that you are using a Vltor A5 set up, and also mentioned that you tried different buffers and springs.  I would suggest trying to get things to run off a standard carbine buffer and spring, and not something heavier until you get it running reliably.  Keep in mind that if you add a heavier buffer or stiffer buffer spring, that these add more weight and resistance, which will result in the rifle running slower.  So I would suggest starting with less resistance, and get it running reliably, then add more resistance if you need to slow things down.



CY6
Greg Sullivan "Sully"
SLR15 Rifles
TheDefensiveEdge.com
(763) 712-0123

Sully nailed it.

I also suggest break in with full power 5.56 ammo.

And double check the gas block location. If you installed them against the barrels shoulder.... you might "need" to take into account the space a "Handguard Cap" ( the front bracket used to hold a handguards in place ) would have used... so your gas block location might be to far towards you.

.

To lube the upper receiver bearing areas, lube the inside and outside of the B/C parts on the wetter side, insert the B/C into the empty rifle, then just cycle the B/C a few times to migrate the lube from the B/C, to the upper bearing areas.   Also, when you where cleaning the buffer/recoil spring/inside of the extension tube, just lube the cleaned buffer and spring with CLP, and install.  The CLP from the buffer and spring, will migrate enough to the inside of the tube.




Huge red flag here, since minor leak with the parts cold, means even work leak as the parts heat up from firing.
Options are to either send the carrier back for replacement, or if you want to solve the problem yourself, will need need key bolts.
Down and dirty, remove the key and throw away the bolts. Use a counter sink to remove the ridge ring burs from the top of carrier and bottom of the key channels (gas passage and the two bolt channels). Now with the surfaces dry, use some lapping compound to lap the two together so they are flush against each other, clean up the surfaces with some acetone to get them dry, add a drop of 272 loctite on the top and bottom of the key and work it into the surface (being used as a gasket, not thread locker) install the key to top of carrier and work it a up and down so the Locktite works is way across the surfaces all the way, then install the new key bolts and torque to 32inch lbs.  Now before the loctite set up, Acetone on Q tip to clean off the excess that leaked out the side, and give the front of the key a light air blow to blow out any loctite that may have tried to bridge the gas passage channels (can use the acetone Q tip inside the carrier gas chamber to clean up an loctite blow there.  Now just re-peen the key metal into the side spines of the bolt heads, and let the carrier with key sit over night for the loctite to cure.

Light leak at the gas tube to gas block is normal.



Slight resistance of the gas tube entering the carrier key is not the end of the world so long as the tube is correctly indexed to fully mate up with the key all the way to carrier to barrel extension touch, but would check the bottom of the entry chamfer of the key entrance, to make sure it does not have an inner ring edge bur from machining that is causing the ID as that point to be slightly smaller.  

So, until the do get the key leakage problems solved, may want to mark a carrier with key that is not leaking, to use for the testing if you do end up with a problem from one of the carriers that the key is leaking now.


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One last thing, and that is when you do have the B/C's apart for cleanings, take a good look at the tail straight sections to bugle section, to make sure you don't have a nasty larger step there that may be biding on the back of the carrier gas channel passage for the tail of the bolt during bolt lock up.  Hence tail's of the bolt's should be all the same OD, until is start to fair out at the bugle section.


Here is a bolt with step up at the tail rear of the flat section before bugle, and could possible cause some problems with the tail of the bolt binding in the carrier bolt channel at lock up.

Not oil, but CLP that has an active cleaning agent in it, to keep the fouling from building up to the point that is chokes the rifle out.

Short of the barrel bore that may need a copper solvent like Sweets to clean out the copper fouling quickly, think of the cleaning of the rig, just a CLP change from fouled to clean CLP.  Hence what you do miss during cleaning, the pre lubing of the upper bearing areas will add enough new CLP to clean what you missed during the last cleaning.

Hence on barrel cleaning, start with Sweet and clean the bore (always push from chamber to muzzle from the chamber and will take less then a few mins to get the fouling out of the bore, since Sweets dissolves copper that fast).  

Once the bore is cleaned and dry (patches not longer coming out blue), then go to the chamber to scrub it out with CLP and chamber brush by hand, and push the fouled CLP from chamber out the muzzle.  When you think that you have patched the chamber and  bore dry, there is still a trace of CLP on the barrel chamber and bore surfaces that will prevent rusting for short term storage of the rig.

Yes, use the old carrier keys, and once you have chamfered the mating entrances to clean up any ridge burs before lapping them in together, make sure that the gas ports to bolt channels are matching as well.  Hence been a while, but was a batch of keys that there gas port location on  the bottom was wrong, and would not mate up to the carrier gas channel correctly when bolted down.

Since you have a few B/C's that needed to be corrected, here is a 10 pack of new carrier key bolts for $6 .
https://doublestarusa.com/bolt-carrier-key-screw-10-pack-ar105

And again, use the old bolt spec of 37in lbs to tighten the bolts, and make sure to peen key metal into the side of the bolt head with a pointed punch; not trying to peen the hardened bolt head material into the sides of the key channels.

Verify that the gas blocks are not start to leak as they heat up (their set screws should be 272 loctite in place), and always police the brass to make sure that is not a over gas problem with bent rearward spent case rims.or rough reamed chamber marking the hell out of the sides of the cases to start with.


If we can weed out the above of any leakage or binding problems, and still an slight under gassed problems, then may be time to either go with a lighter buffer if possible for the ammo at hand, decreasing the tension strength of the recoil spring, or increase the gas port by 1 number size bit.

https://www.custompartnet.com/images/size-charts/drill-size-chart-english.png

Also, I bring up ammo at hand, since some of the import 223 ammo is weaker in strength than most  of the USA made 223 55KPSI working pressure ammo, while USA 5.56 nato ammo is loaded to 62K PSI working pressure instead.