CAN I USE STEEL AMMO(CHEAPER) THAN BRASS IN MY NEW AR15?

Yes

WHY DO OTHER SAY NO ? They want to tell me that steel will tear it up . This seems like a pitch to sell more brass. the guy who build the gun and has been doing so for 25 years and even outfits Navy Seals said Wolf steel is what he uses.

Well if it is good enough for the Navy Seals armorer then it shoudl be good enough for the rest of us.

But seriously, Wolf is fine you just have to make sure you keep up the cleaning.

Maybe because OTHER is ill informed.
Steel cased ammo (Wolf, Bear, et al) is fine.  Happy shooting.

Thanks. You guy's advise are priceless! I did read that the steel won't expand like brass and thus can cause carbon buildup but if I clean it and oil well that I can stay ahead of any problems. I also rea that the extractor can wear a bit more with steel over brass. but they are cheap. What do I know. I havent even shot it once. It's alearning process. thanks again.

Okay, THEORETICALLY;
Steel is harder than brass,steel on steel is harder than brass on steel.
Steel cases don't expand and grip the chamber as well as brass, which allows gas to blow back. conversely steel doesn't "relax" as fast as brass, and causes extractor ,extracting problems.
Steel cases need some kind of lube/ coating , to function and this wears off and builds up in the chamber.
It's not the way my Daddy did it.
My cousin's brother-in-law's ,mailman said don't
Enough?
If it works in your gun and you want to shoot it, shoot it world won't stop rotating.
If you have problems under warranty, don't admit it.
These are just reasons armchair experts have espoused.
Your mileage may vary.

I would find your guys claim of being a SEAL armorer and using steel very suspect.

#1 SEALS use issue military (brass) ammo..
#2  alot of SEALS are very avid shooters and the recruiters i used to train with never used steel..
#3 Armorers who outfit SEALS are Navy men again see #1..

That said 9 out of 10 times the shooter is the problem not the ammo..

This is the only thing I can agree on with you.

Steel can be incredibly hard, but steel cartridge cases are made from fairly soft steel-no harder than the brass used in cases.

Steel cases indeed don't expand like brass to seal the chamber.  Steel isn't as "springy" as brass.  This allows gasses and soot to flow backward into the front part of the chamber.  But only a little gunk at a time.  And if the case hasn't expanded enough to seal the chamber, how can it cause extraction problems?  It can't, but the soot can if you let it build up by not cleaning it out.

Steel cases need a coating to prevent rust.  NOBODY uses "lacquer" today, even the stuff that looks like lacquer is a plastic of some kind.  It does NOT come off or build up in chambers.  This is something people blame their extraction problems on when it's actually that they don't bother to clean their chambers.  The US government experimented with steel cases with a zinc coating during WWII-it worked very well.

Daddy didn't have access to Russian ammo plants where all the tooling to make steel cases is all set up and running.  Daddy missed out.

Those people who said "don't" probably just passed on what they heard at the gun shop.  And unless they could demonstrate exactly how using steel ammo had kicked their daughters and got their dogs pregnant, I would give them exactly as much credence as any other uninformed person giving advice.  They may mean well, but if they don't know what they're talking about, that advice is worthless.

Remember, the Soviets kept half of Europe under their boot heels for 50 years using steel cased ammunition; that's not something you can do if your ammunition causes failures and wears out guns.

Never had a problem with steel.  I like to run the BCG a little wetter when I shoot it.

I dont think the OP said that the seller/dealer has the SEALs using steel...i think the point was that the seller/dealer outfits SEALs, inferring that he is qualified and experienced, and that this same seller/dealer uses steel ammo in his own guns.

ETA: and the OP didn't say the guy is a SEAL armorer...just that he 'outfits' SEALs.  Without clarification, for all we know, the guy is 'outfitting' the SEALs with socks and canteens.

I have never shot anything but silver bear hp in my bushmaster. Not a ftf or fte so far - about 700 rounds. I know that is not much but so far so good.

All Ill say is for me my rifle better be capable of eating anything its fed or its worthless to me.Theres a lot oy myths about steel cased..plain and simple it wont do harm..shoot it its fine and its reliable.