It's an early 90's LE6920 from research with a 20" 1:7 twist.
Initially it had all original parts plus a Good Iron brake, now it has a custom trigger (home brewed) and Tubb's flat wire spring, function didn't change, even tried without the brake just in case.
I've checked the gas system from barrel hole to bolt; all good without leaks, misalignments, loose/worn parts.
Ejection is around 4:30 with anything that does eject.
I bought it about a year ago  and it looked to have almost no use, I haven't counted but have easily put close to 1000 rounds through it.
As unlikely as it seems I think it has an overly tight chamber; here's my evidence, please let me know if I'm wrong and any other tests I should do.
Its spent brass will rechamber in it easily, but not the brass from other ARs.
Its brass will also chamber into my friend's Savage 223 bolt gun where other AR brass sticks a bit.
I've tried a few steel case ammos and have 100% failure to cycle even with an empty buffer, I pulled the weights one at a time to see.
I later realized that steel case won't chamber without a bolt drop, trying to ease one in and even pushing hard on the assist won't chamber it so I've never tried again.
Federal AR 5.56 XM 193 runs 100%, PPU .223 I think is also 100% if I keep it oiled.
Reloads from light to over book max are hit & miss as are some other .223 ammos.
All my reloads have been 62 and 64 gr. with Tac powder and have shot very little commercial ammo other than 55gr.
I'm going to get some 55gr. bullets to try and just got some H335 powder to try as well.
If I keep it wet it seems to work with most  ammos, I don't think I've tried wet and steel case.

Is this just one of those 'needs to be wet guns' and should I just accept that?
Does it sound like I have an abnormally tight chamber?
It's velocity also seems to run a little higher than expected with commercial ammos which I though could be in line with a tight chamber.

The chances of getting a Colt LE6920, which is built to USGI specs and standards is vanishingly small.
Lack of lubricant is only an issue after a fair number of rounds are fired and fouling starts to build up.

I think that what you have is a problem with your reloads and a not unusual problem with steel cased ammo..

The key here is that factory M193 Federal and the other factory ammo is all 100%.
When a firearm shoots new factory ammo but chokes on reloads, the problem is the reloads, whether you like to admit it or not.
Even thought the reloads SEEM to be all in spec, obviously they aren't.

Steel cased ammo is notorious for causing problems in American firearms.
Some firearms it works just great in, others of the same brand and model choke on it.
The problem is that steel cases don't expand and contract as well as brass.  Combine that lack of elasticity with a chamber that doesn't have the taper of Soviet ammo when fired in American chambers that have less taper, and you get problems.
With steel cased ammo, if it works, great.  If it doesn't...don't use it.

That a case fired in one firearm won't chamber in another without being resized is totally normal.  All chambers have slight differences that often cause a fired case not to chamber.
Trying to chamber a fired case in another firearm tells you nothing.

Advice:
Forget the steel cased ammo, it just doesn't "like" your rifle and there's nothing you can do about it other then to try another brand and hope it will work.  The steel cased ammo is made in former Soviet ammo plants and quality varies, often considerably.
If you can't find a brand that works, just figure on not using steel cases.

Obviously your rifle doesn't "like" your hand loads.
Check your loading system and process, and if possible have a more experienced loader look things over.
Often it's no more complicated then a case die not adjusted perfectly or a bullet going into the case off center slightly.

Bottom line: Your rifle works 100% with good quality factory ammo.
The problem HAS to be with the reloads and the steel cased ammo, not with a lack of enough lubricant.
An AR will work for a while bone dry.

It works with some, but not all factory ammo.

I can't imagine that a slightly off bullet seating would cause a short stroke.

Put some lubricant on the (cough)ing rifle. AR15 type rifles do not function well or for long without lubrication.

If your rifle continues to malfunction after properly lubricating it, then we can work on additional troubleshooting.

I'm not sure what you are using for a homebrew custom trigger, but possibly it's causing excess drag on the BCG which can cause this kind of malfunction.

Opinions of "proper" lubrication of an AR is all over the place, but lubed to mil-specs isn't enough for it to run reliably other than on a couple ammos.
Extra wet seems to fix it.
The trigger is a standard mil-spec that I modified; none of the mods changed how much it drags and the problem was the same before.
I also ran it with an RRA two stage with no change in function as well as attaching the upper to two other lowers; the problem is in the upper.
I thought maybe it was just undergassed, but the gas hole is around .091; .089 drill fits with a little room and a .093 drill doesn't fit and that's all I had to measure with.
I was initially thinking it needed to be drilled larger but that size hole  seems like it should be enough. (?)

Does anyone make a cartridge or measuring tool that would tell me if the chamber is tight or not?
I know the length is pretty loose, used a Sinclair chamber length tool, but if the diameter is tight I don't know of a way to know other than maybe casting it and measuring that.

I don't know that a snug chamber would cause the problem you are having. Plenty of target/match rifles out there with minimum spec chambers that do not have function issues.