What is your opinion for a chrome vs moly lined barrel for a AR .556 shooter that may shoot a couple of 100 rounds per month. A lined barrel is $40 cheaper but I don't have experience to make the call.

Moly lined????? I expect you mean just plain chrome-moly alloy barrel.

OK, the chrome lining greatly increases resistance to gas erosion. It's not so much how many rounds you fire per session, but how fast you fire those rounds. If your use is slow fire target shooting with no mag dumps, a plain barrel will work fine. I've got a plain barreled 5.56 mm that's 40+ years old, yes it was used in some practical competition and practice so there was some rapid fire. No mag dumps, maybe 3K+ rounds total. New it was a ~1 1/4 MOA gun, now we're a 2 MOA combination. Unknown how much is wear and if so on the barrel, me or both. However, the $40 extra for chrome lining is much, much cheaper than replacing a barrel.

I know a gent who ran the Army Match Training Unit. His comments were that the plain and/or melonite bore finish barrels were much inferior to chrome lined when used in rapid fire matches. Obviously, he didn't see any significant alleged affect on accuracy of the chrome lining of a quality barrel.

There is a difference between a Chromium-lined barrel and a barrel made from a an alloy steel containing Chromium, Molybdenum and Vanadium (sometimes referred to as CMV).

ALL AR barrels will be made out of either an alloy steel known by the desigation 4140 or 4150. BOTH alloys are CMV steels, but with 4150 having concentrations of C, M & V that are slightly higher than in 4140.

A Chromium-lined barrel is a barrel with Chromium plated inside of the steel barrel (generally 4150 alloy). As WR Moore already explained, the Chromium plating improves durability in extreme conditions. But, because the Chromium plating is not as uniform as the surface of a machined, but un-plated, barrel the accuracy of Chromium-plated barrels may not equal that of high-quality un-plated barrels.

Bottom line is there is no "best barrel" for all conditions and it is futile to look for one. Do your homework and pick a barrel that balances 1) durability, 2) corrosion resistance, 3) accuracy, and 4) price, to best meet your needs.

If your only planning on shooting a hundred or so rounds a month any quality barrel would do you well in my opinion. I 've been googling shot out nitride/m&p / budget barrel etc. No luck. I currently have two ar's both with nitride lightweight profile I shoot weekly anywhere between 100 and 150 rounds alternating rifles. plus a 150 or so pistol rounds. my budget doesn't allow for much more. I doubt I'll ever shoot either barrel out. That said Guns / mags /ammo barrels etc. are cheap right now. buy em cheap stack em deep.

Everyone else before me gave the technical answers. Chrome lined v.s. CMV unlined (4140 v 4150). What I have to offer is dumb practical observation. To give context to my opinion, I currently own an IWI Tavor that has an 18" chrome lined barrel and a home-brew AR-15 with a 16" Colt Competition 4150 CMV nitrided barrel. I don't get out to shoot as often as I'd like. When I do bring either out to the range, I shoot between 100 - 200 rounds. I don't claim to be an expert anything. I'm just a dude who goes to the range. If I'm shooting close and fast, my goal is combat accuracy. If I'm shooting 100+ yards, my goal is nice little groups.

1. When I'm not over-caffeinated at the range, the unlined 16" Colt barrel is slightly more accurate than the lined 18" Tavor barrel. Keep in mind that the Tavor isn't built to be an accuracy rig. I didn't build my AR to be an accuracy rig either, the Colt barrel happened to be on sale.

2. Given my more relaxed cleaning style, I find the chrome lined barrel easier/faster to clean than the unlined barrel. Typically I give a quick twist with a chamber brush, then pull a brush/patches through with a flexible rod.

Given that your question is specifically for an AR, your round count per month, and $40 cheaper for CMV barrel:

IMO, go with the unlined CMV barrel. If both the 4140 and 4150 can be had for the the same price, go with 4150. If not, go 4140. To shoot the least expensive commonly found off the shelf ammo, 1:7 or 1:8 twist rate on the barrel will do you well.

One other piece of advice I've learned from being a newbie blow-hard (here on this forum) to having "been-there-done-that", checking account depleting, idiot over the years...

The AR-15 is modular. It can be fully disassembled with some hand tools and a vise. If you happen to shoot out a barrel, then replace the wear items on the upper assembly:

• Barrel
• Gas Block
• Gas Tube
• Bolt

I say this knowing how to perform the procedure. I say this never having to have performed the procedure because I've shot out a barrel.

Cheers.

-John

__________________
-John