I just acquired a new AR (Modern Materiel, built up in Keyport, NJ) and noticed the manual stated to use only brass cased ammo, built to SAAMI spec.  Is there any reason not to run non-brass (e.g. Steel)? Could it cause damage?  What would be their rationale to put that in the manual?

Thanks!

I can think of a few things offhand. 
 

Brass cases ammo is more ‘elastic’ than steel case...

Upon firing, the brass case tends to (for lack of a better term) ‘swell’, and make a tight seal with the chamber. This allows less blow by of combustion gasses into the chamber, making it cleaner to shoot. Less unburnt powder and mess in the chamber, and debris in the bolt. Steel is less elastic than brass, doesn’t swell as much, and allows for more blow by. 

The steel case rims are also harder on the extractor. 
 

Much of the steel cased ammo I have seen, the projectiles themselves are actually steel core coated with a copper wash. This would be harder on the barrels themselves. 
I once read an article on barrel wear comparing copper washed steel projectiles vs copper jacketed lead projectiles. I don’t remember all of the details of the article, but the conclusion was that copper washed steel increased barrel wear quite a bit. 
 

Some steel cased ammo isn’t loaded as hot...this could lead to function issues as well. 
 

 

Tex laid it out pretty well.  The bottom line is steel case ammo decreases the duty cycle of the firearm, and increases the general maintenance cycle. 

Whether you use brass or steel, you are going to have to replace things like the barrel and bolt parts.  With brass, you can confidently go 20k rounds or more.  With steel case the duty cycle could be well under 2k rounds before things start to break down. 

Due to increased blow-back and steel case coatings like lacquer, there will be more carbon and funk buildup in the chamber.  If that is not cleaned out regularly, it invites stuck cases and broken extractors.

Now, if you ask any AK owner about steel, they will say there is absolutely nothing wrong with it and  it's superior to brass. And you know what, they'd be right.  The AK platform was specifically designed to work with cheap steel case ammo.  The platform has a looser chamber and certain parts like the extractor are made of harder metals meant to handle steel.  The AR platform was designed for brass.

There are literally tens of thousands of post and scholarly write-ups on the topic.

Lastly, I will say this.  Brass = America, steel = communists.  I'd rather give my money to Federal Cartridge or Hornady than China or Russia.  You may as well be handing them money to build warships or reeducation centers.

This is an interesting read on brass case vs steel case....good testing data 

 

https://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/

8 hours ago, Displaced Texan said:

This is an interesting read on brass case vs steel case....good testing data 

 

https://www.luckygunner.com/labs/brass-vs-steel-cased-ammo/

Wow, really great study!

Thanks

5 hours ago, leahcim said:

Wow, really great study!

Thanks

It does miss one key thing about steel case ammo. It didn't dream as well and gets the chamber dirtier faster. Where to can definitely get extraction problems is with switching from steel to brass case without cleaning the chamber. This didn't Halen in a few rounds, but if you just shot hundreds of rounds of wolf then switch to brass, the brass can get stuck. Worst case i saw was going from cheap steel cased to cheap Indian brass cased stuff. It ripped right through the case rim because the chamber was scuzzed up and the brass cases were way too soft. 

I'm not one for lots of excessive cleaning, but steel cased ammo needs more frequent cleaning of the chamber and bore from my experience. 

Aside from the casings, bullet material matters too.

Rough estimate - Steel/Bi-metal jacketed bullets wear out your barrel at least 40% faster than copper jacketed bullets:
 

Quote

...The barrel of the Federal carbine had plenty of life left after 10,000 rounds at extremely high rates of fire. We subjected the Wolf and Brown Bear barrels to the same rates of fire and they were completely “shot out” by 6,000 rounds. ...

 

If you want your ar to last you a lifetime don't shoot it.  It's just a barrel.