Who makes chrome lined barrels besides Bushmaster? Thanks.

just buy a bushmaster.

I spoke to Rock River Arms yesterday by phone. They are now offering chrome lining in the M4 & Shorty BBL's. It's not on their website yet but they do have them. The 20" BBLS are still a ways off.

Do they chrome the barrels or are there chromed barrel blanks ?

Don't know...didn't ask that. Good point though I'll keep that one in mind.

armalite

What is the difference in chrome lining a barrel??? is it different than chromemoly barrel??
Can anyone elaborate on the process???

Quoted: What is the difference in chrome lining a barrel??? is it different than chromemoly barrel?? Can anyone elaborate on the process???

Chrome lining is applying chrome to the inside (bore) of the barrel. Much the same as the chrome on your car bumper is applied to the base metal. It makes the surface harder and smoother. This helps extraction of the spent case and makes cleaning easier.

Chrome Moly barrels are made from a steel which has Chromium & Molydemum as two of its ingredients. 4150 steel alloy is made up of Carbon
 0.48 - 0.53

Chromium
 0.8 - 1.1

Iron
 Balance

Manganese
 0.75 - 1

Molybdenum
 0.15 - 0.25

Phosphorus
 0.035 max

Silicon
 0.15 - 0.35

Sulphur
 0.04 max


4140 Alloy (another popular barrel steel) is made up of:
Carbon
 0.38 - 0.43

Chromium
 0.8 - 1.1

Iron
 Balance

Manganese
 0.75 - 1

Molybdenum
 0.15 - 0.25

Phosphorus
 0.035 max

Silicon
 0.15 - 0.35

Sulphur
 0.04 max

I don't know which is better as as rifle BBL but the Mil-Spec calls for 4150.

Pretty much all steel rifle barrels, except stainless, are some form of chrome-moly alloy.  Most common are 4150 (ordnance steel) and 4140.

A chrome lined barrel is chrome-moly which has been lined with hard chrome in the chamber and (often, always in military barrels) bore.

hard chome, tho is a much different process than bumper chrome. Bumper stuff is plated onto copper plate which is plated onto the steel. so there is more like a surface buildup (acretion) of .005" with the bumper chrome, and it tends to flake and peel. Hardchrome's surface accretion is .001", and it bonds directly to the steel. However, inside a bore, that accretion is DOUBLED, so a bore that is to be chromed must be made with an .002 oversize inside diameter, to allow for the "buildup of the chrome, without increasing chamber pressures.