Here are a couple of pictures of the USR's with their respective hardware options. We are currently working on updating the website based off your suggestion. So, thank you.12" is the sweet spot for about a third of my rifles. Works well on several Manners stocks that have a shorter fore ends or long actions. 12" also works well on AR platforms with 12.5" - 15" hand-guards. You lose about 2-1/4" -2-1/2" of hand-guard for the barrel nut section.
As for weight kits.....I'd be tickled if you just offered the same rails in an all steel nitrited version. KRG does this for their chassis, but there not universal. Most people I've talked to at matches with the 419 weight tuning rails, have all the weights installed. myself included.
Actually it looks like you've already done exactly what I was hoping for. I just wouldn't have picked up on it from the pictures on the web sight.
Maybe I'm a little slow, but the first time I looked at the USR rails I thought the Key-mod/M-locks options just applied to the attachment fateners. Having lugs that engage is a really attractive feature that deserves to be highlighted a little better on the web-sight.
I thought the drop in adapters where flat on top. I was wanting lugs that engage either M-Lock or Key-mod & that's exactly what you did I think?
Best pic I could find below appears to be M-lock lugs.
I will get the 340mm & the SC-ARC.
Thanks
View attachment 7754268
In the first image from left to right the hardware options are M-Lok, Keyslot, Stock, and Chassis. You're correct that the M-Lok eyelets have an extra lip that helps them positively engage with the M-lok slots. The rest of the eyelets are the same without that. In the second picture, you have from top to bottom M-lok, Keyslot, Stock, and Chassis hardware options.
I hope this helps give a better look and more detail into the USRs and their hardware options. Please let me know if you have any additional questions.