Took the new Bushmaster out plinking yesterday and shot the last 100 rds I had. Had some Monarch .223 55gr Steel case FMJ ammo. I noticed the bolt didn't lock back after the last round was shot except one time with this ammo. Shot 20 of the Wolf 5.56 62 gr HP and the bolt did lock back after the last shot. Was wondering if this is due to the "cheap" .223 ammo and if the 5.56 pressure was enough to get the bolt to lock up. Only had 1 jam with the Monarch ammo and was thinking it was due to the bolt not picking up the round good enough. The jam was also in a 20 rd mag a guy gave me and he said it would jam his gun and was going to throw it away anways. Shot 60 rds thru it and only had that one jam. I have 500 winchester cases due tomorrow and was going to start reloading using 55gr soft point bullets I have on hand. Was also wondering if the bolt not locking back would be a sign I need a little more pressure? Have never loaded for a semi before. Any help would be appreciated...I will have more questions in the future I am sure.

I'd venture to say it was the magazine.

Did you try a different mag?

Yes, I shot out of two different mags. One was a pmag I purchased when I bought the rifle. The other was the mag the guy gave me at the range when I was sighting in and was the one I got the jam with. The gun returned to battery after the last shot was fired with both and also stayed open after the last shot was fired with both.

As a technical question...what is it that is supposed to hold the bolt open after firing the last round from a magazine? Does the magazine follower actuate the bolt locker thing? (not sure of the proper nomenclature) Hope this makes sense. I will try to be more "educated" in the future.

Yep, the follower in the mag pushes up on the bolt stop. Unless you are using this for combat or life saving at home..... you can actually take the spring out of the bolt stop totally. Or at least clip off coils till it really does nothing.

The only issue you'll have there is the gun may not lock open if you have to shoot it upside down.......

Before you try anything with cutting springs or removing parts, best to have a spare spring or two around just in case the first one goes flying and removing it doesn't make you happy after you shoot it a bit.

I"ve got a gun by the bed sometimes that has no forward assist, no bolt stop spring and a few other only sometimes needed parts gone.... its lubed well and its never had a hiccup, doesn't bother me any.

Combat role would be another story though.