Windham Weaponry recently started offering its forged-in-house WW-15 mulit-cal lower receivers as stripped-down, stand-alone components for at-home builders. This is good news for those who want to stick with Windham components while saving money with a bit of do-it-yourself sweat equity. As soon as I heard this news, I knew exactly what I wanted to build with this lower.

At a trade show earlier this year, I got to handle Windham’s .450 Thumper (RP9SFS-450M). This 9″ barrel, gas-impingement-operated pistol is chambered in the beefy .450 Bushmaster rifle cartridge. Here was a model that scratched my itch for big-bore handguns and rifle-action pistols at the same time. But I didn’t want to work with a gun similar to the Thumper—I wanted to work with the same gun I saw on the floor!

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