What barrel profiles do the military use (beneath the handguards) on both the 18" SPR and 20" DMR?  I have some HBARS that I'd like to turn down for SPR / DMR builds.  I'm looking for specific diameters, if anyone knows.

I've seen DMR barrels that are fluted, which I don't really need.  But I'd like to achieve roughly the same weight reduction by reducing the profile of a 20" HBAR.  Any idea how thin to go to achieve this?

SPR is .850 under the handguards.

The SAM-R (Krieger match) and SDM-R (Douglas Match) are a full inch under the handguard I believe, with the SDM-R fluted w/12 flutes.

SPR barrel profiles, specifically look at the 18"

Thank you for the info.  The diagrams are interesting––-I was under the impression that all SPRs were 18".