I wasn't clear: I meant an 18" barrel with an "intermediate," not a "medium-length" gas system. From what I've read, people debate over whether a rifle-length gas system (like the Ruger has) is better or a standard mid-length (which seems to be ideal for 16"). But a couple manufacturers have made a distinct "intermediate" length tailored to the 18" barrel of the SPR configuration.

Here's Noveske's gas tube for their 18" barrel:
https://www.noveske.com/products/intermediate-gas-tube.
And their barrel:
https://www.rainierarms.com/noveske-...6mm-barrel-18/

The only thing that gives me pause is I'm less-than-certain a 1:7 twist rate is ideal for non-hunting applications (where the incentive seems to be to load with heavy grained bullets, for the sake of versatility), especially if accuracy would suffer past 150 yards using standard 55-grain or even 62-grain target ammo due to over-stabilizing.

But again, I won't be worrying about that for a few years, anyway. For now, I'll have a 1:8 twist rate. By the time I'm looking to replace the barrel, there could be a lot more options in the "intermediate" gas length category.