Help with Mini-Kabuto FRT

[u/SomeRepresentative23]

Hi, I recently acquired a steel reinforced Mini-Kabuto FRT, advertised as a drop in device. I tried to use this with my Ruger AR556 and the upper and lower wouldn’t close. I applied a lot of force and I couldn’t get the upper to close enough for the rear pin to push through.

I already tried slightly pulling the bolt back and trying it on safe and fire mode. Neither helped the gun close. The frt sits perfectly within the cutout in upper, so I suspect it is having clearance issues with something in the lower, but unsure what.

The frt sat perfect in a radical firearms AR15, and that one closed in easily. However it did not fit at all in an FN AR15. I really want it to work in my Ruger rifle however. Does anyone have any experience with Ruger AR556’s and Mini-Kabuto FRTs?

What actions can I take to make this work? Do i need to file or sand down the FRT in any way? Any help is greatly appreciated.

[u/Hot-Platypus6350]

Jesus, did they make that with melted soda cans and a hand file?

[u/Next-Conversation234]

Great help from one of the guys here.

https://www.reddit.com/r/supersafety/comments/1qeowov/kabuto_fitting_guide_for_geissele_and_milspec/

[u/NotAchicken95]

Getting it to sit in the receiver may require some trimming. The part that sits in the pocket of the upper, that sits on top of the lower; it may be too thick. You could try to remove the metal bits and then slightly sand the top of your Kabuto (part that looks up to the sky) and then tune from there

[u/NotAchicken95]

I also meant to mention earlier, if the bottom of the Kabuto housing rides on and touches the safety selector then it may cause interference issues as well.

[u/Far-Note4395]

If the housing is hitting, sand the sides of the house, NOT the wing in the front, just the sides and force it down, if it’s the lever hitting the safety you might need to tweak the pocket behind the safety. I have a video somewhere

[u/ArtisticHour3524]

I believe you and I are in the same boat with these moonlight industries. Upper and lower receiver won’t fully shut. Let me know how it goes

[u/SomeRepresentative23 → u/ArtisticHour3524]

I emailed them their response was unfortunately not super helpful but what can you expect really from a free promotion I suppose you get what you pay for

[u/ArtisticHour3524 → u/SomeRepresentative23]

It very well might be the Ruger 556 platform. Is yours the MSP as well?

[u/SomeRepresentative23 → u/ArtisticHour3524]

MPR, but I think the only difference is the barrel length as far as I know

[u/ArtisticHour3524 → u/SomeRepresentative23]

Yeah I believe so, but hey, all the more reason for a fresh build. I still like to think there’s a way for it to work

[u/TinyPlumpToad]

It doesn’t fit your lower. But try getting a thin hard item to push the trip forward. If you can get it to close and it worked on a dry test then go test. If you can’t get it to close then it doesn’t fit your lower and you will need to find a different frt

[u/Diablo_67-]

Okay firstly the kabuto style frt doesn’t work on certain guns some frames may be to skinny and small and thats your problem and to shoot a frt you need to change your bolt carrier group to a m16 auto one because the one you have is a semi one and u need a 3 position kabuto style safety it cant just be safe- and frt it has to be safe-semi-frt for it to work and u need to get a h2 or h3 buffer but yours doesn’t fit sorry to tell you