I have Bushy M4 with a chrome-lined barrel, and I also have a kit from J&T built on an Oly lower, 20" model. I love the kit gun but there's always been that one thing that stood out about it and that is that it has no chrome-lined barrel. How much difference can it make? I don't bump-fire it at all. I know the chrome-lined barrel is supposed to last twice as long, but I also talked to a very competent gunsmith local to me and he insists that if I live to be 100 years old that the barrel will not wear out. How much truth is there to this? I love my J&T kit, but this is the one thing that I wish they offered. I sometimes think about getting the barrel swapped out just for this very reason. Thanks 4 info...

From a purely personal stand point, I'm willing to shoot about any dirty, cruddy out-of-spec mil-surp that comes down the pike in my AR's with chrome lined barrels but am more choosy with the two that have chrome moly.  Yes, the chrome lined will last longer but I haven't worn out a barrel of any type as yet !!

Womb;

They are two entirely different things. In the so-called "Chrome lined" barrel there is a layer of chromium inside the entire barrel cavity, both the chamber and bore are coated. Chromium is very hard and resists wear, abrasion and erosion.

Chrome-Moly refers to the composition of the barrel steel itself. The alloy includes (relatively) small amounts of both Chromium and Molybdenum disolved in the molten Iron when the steel is made in the mill.

Hope this helps. Cheers!

Funny I have the same two rifles and the same concerns.

Your buddy is right and the non-chrome barrel should last a couple lifetimes if you don't shoot it alot.

Hang around some of these gun heads on this site and it may not last a weekend. I went through a quite a number of rounds at Bulletfest.

Tj

I follow you so far. I believe in the Bushmaster catalog it states that their barrels are chrome-moly also with a chromium lining throughout the bore and chamber. The J&T kit barrels seem to be made of exactly the same thing with the exception of the chrome-lining. I don't really rapid-fire alot, I'm just one of those people who don't like to half-ass on anything.

Bottom line is the chrome moley barrels are just cheaper.  That's why you see that barrel used often in low end AR's.  Low end is a relative term of course as I believe Knight's uses the chrome moly in their SR-15 M4 at about $1400 while ArmaLite uses the chrome moly in their AR-180B at $650 and J&T uses chrome moly in their kit.  

Denny Hansen from SWAT magazine has an Oly AR that went 80,000 rounds on an unlined upper. Barrel was fine but the chamber had begun to erode.

[url]http://www.ar15.com/forums/announcement.html?b=3&f=118&id=172[/url]

The really damaging thing to any barrel, chrome-lined or not, is heat.  Dumping mag after mag and heating the barrel up will damage the barrel.  Rapidly dumping one mag will not hurt it.