ok so I built this
18" sanders stainless barrel with midlength gas
cheapo set screw style gas block
anderson lower and parts kit
standard carbine buffer

I go to the range last weekend, I've got 4 brands of ammo
tula steel case
perfecta/brass max (brass tula)
PMC bronze
Scott's reloads
all 55grain bullets

so the wierd part, steel tula runs like a swiss watch, no problems what so ever, feeds perfect, bolt holds open on last shot, no fail to fire.
all the rest are short stroking, ejecting the empty case but NEVER picks up the next round, doesn't lock open when empty

so this is wierd right? tula steel is supposed to be WEAK, JUNK ammo and it's working the best, switched back and forth several times with the same results.

OK so saturday I look into things, looks like I'm getting quite a bit of blow-by around the cheapo gas block, SO I have another gas block (clamp on style) I switch it out with.

then fathers day at the range, exact opposite, all the brass ammo runs great, feeds perfect, bolt holds open on last round
tula steel, still runs ok, had a couple fail to pick up next round but bolt does not hold open on last round

same 4 brands of ammo, most likely from the same batches
any thoughts?

The first instance sounds odd, as an undergassed rifle would run WORSE with lower pressure ammo, but based on the new gas block symptoms, it sounds like it is now slightly undergassed.

I'd check to make sure the gas block is lined up correctly with the gas port in the barrel, and that the gas tube isn't binding on the gas key on the bolt inside the upper. If all of this works and lines up right, i'd suspect the steel cased ammo to be the problem. However, it might need some break in time for things to wear in together to cycle the weaker loads. Where is the brass ejecting with the good loads?

Possibly you didn't have the port and gas block right both times?

ports are lined up both times

first block was leaking pretty good, second block doesn't seem to leak at all.

Check the width of the gas port.

The first set up might have been so high of a cyclic rate ("overfunction") that the BCG was skipping over the cartridges in the magazine.  What was the ejection like?

originally I was getting all brass tossed about 5-6 feet at 2oclock, steel was going 5-6 feet at 3-4 oclock
second time brass was going 4 feet at 1oclock, steel 5-6 feet at 2 oclock 

I think the gas port is .078

interesting
I have a heavier buffer, I'll try that

thanks