We've looked into it, and even built a prototype. It's not worth it. Here's why: 1. To support threads on the endcap, the end of the tube would have to be larger, or we'd have to use thicker tube, IE, bulk it up. 2. It would also add considerable weight vs. the current Ultra design 3. The suppression difference would be extremely slight. Consider that a dedicated 6.5 Ultra 9 is only about 3 dB quieter than a .30 cal Ultra 9 when shot on a .260, and to get that difference, the 6.5 Ultra 9 has a complete baffle stack cut to 6.5 mm. Changing only the endcap is going to only give you a fraction of that difference, so we're looking at "maybe" 1 dB difference-- maybe. That's less than the standard deviation you get when metering as string of shots. We don't really do gimmicks. Compromising one of the core benefits of the Ultra series (extreme light weight and suppression in a given size) just so an endcap with a smaller hole can be used, when the difference in suppression in the non-typical application is basically nil, would be a gimmick. If what you want is the best suppression with the least weight added, even if we only made a .30 cal Ultra 9, you would literally have better performance over those two factors using the .30 Ultra 9 on a .260 (or .223, etc) than if we made a switch-endcap version of the same.