MRP 18" SS vs. custom SPR upper

[decodeddiesel]

I just wanted to say, I have really enjoyed this thread. I was not that familiar with the actual way in which rifling is formed (or cut) into a precision barrel. This is especially fascinating being a mechanical engineer who is into manufacturing engineering.

[eesmith4]

some info on 5.56 ss LMT/rock creek barrels...

I ordered a 16" SS 5.56 barrel for my LMT MRP, and I received it last friday. Upon examination I noticed it was a 6 groove barrel, and called LMT to find out if 5R barrels were available. I was told that all current SS barrels are 6 groove 1/7 button rifled, and as far as the tech knew they had always been that way for as long as he had been there.

I then called rock creek, they told me that all current production 5.56mm blanks sent to LMT are 6 groove button rifled. (They only ship them blanks, LMT does the chambering, contouring, gas port drilling, etc)

I asked about past 5R cut rifled 5.56mm production, the guy told me he was aware of a few that had been made, but all current 5.56mm production for them was 6 groove button rifled.(SS MWS 7.62mm is still 5R cut rifled)

So in short, you order a SS 5.56 MRP barrel today, you'll get a standard 6 groove button rifled like me.

ETA: my barrel is marked "MP SPR 1/7 SS" like the others in this thread, only difference is it's marked behind the gas block so it's under the rail when installed. I'd take a pic but I'm offshore ATM.