Pretty much daily I get the question “Is it okay to shoot steel cased ammo in my Windham Weaponry AR15?”
With ammunition in short supply and good ammo priced very high, many people are buying cheaper steel cased, bi-metal jacket ammunition from Wolf, TulAmmo, Herter’s, etc.
While I don’t generally recommend steel cased ammo, it’s not going to hurt your rifle in limited amounts. If used exclusively however it will reduce the barrel life by about 4,000-5,000 rounds. Most if not all of this ammo uses a copper coated steel jacketed “bi-metal” bullet which increases wear on the barrel. In testing done by LuckyGunner Labs, rifles using Federal brass cased ammo were still shooting decent groups up to 10,000 rounds. With steel cased ammo the groups were all over the place at 6,000 rounds with many bullets tumbling and key holing.
The other problem with steel cased ammo is that the cases don’t expand the same way that brass cases do. This causes carbon build up between the case and the chamber wall. This build up can cause stuck cases. Sometimes these cases will stick so severely that it is difficult to remove them even with a cleaning rod. It is even worse if you fire a bunch of steel cased ammo then fire brass cased right behind it in a dirty chamber. Then the brass case expanding normally really sticks to the carbon left behind in the chamber.
So if you are going to use steel cased ammo I recommend breaking the rifle in with decent brass cased ammo first. Up to 100 rounds, the more the better. Another problem with steel cased ammo is a lot of it seems to be somewhat underpowered which can cause short stroking issues. If the gun is broken in first with brass cased ammo this helps seal the gas system somewhat which will make the lower powered steel cased ammo work a bit better. Also, make sure to keep your chamber clean. Keep in mind that it is going to foul pretty quickly with steel cased ammo.
Here are two excellent articles regarding the issues with steel cased ammunition that I always recommend. One of them is the excellent LuckyGunner test.