I have m60 Joe setting up a 223 host for my RLL and am really giving thought to doing a 9mm host gun down the road. What can I do/buy to prevent damage to the link for both this 223 host and 9mm down the road? I do have a protector and KNS anti rotating pins (not sure if the anti rotate pins do anything to help the link or just the receiver). Should I use a Wolf lower power ejector spring?

I dont own a RLL, but if you use the correct paddle, the kns protector, and m60joe doing your setup.You should be good.
I don't think there is anything else you can do besides inspect regularly for wear.

I totally understand your concern, when i got my RDIAS i was always worried about thing that dont matter.
These things last forever, if something bad happens a repair isn't a big deal. Youd have to have an incredible failure to have any serious issues.it would cost you many times the price of your RLL in ammo to have any appreciable wear.

Welcome to ther club, Enjoy

Thanks you. Do you feel the same for a link when it used with 9mm?

I had two RLL and still have one that I still use regularly.
With KNS protector, properly milled lower & correct paddle... you can't really hurt the RLL.

You might get some wear on the finish where it rides, but other than that the only thing that can happen is the ears break off. With the kns protector, that isn't an issue. Even if that happen m60joe can repair it. I've had mine now in m60 joe prepped lowers for years now. Don't get tempted to drop it into other people's  lowers where the kns protector doesn't fit, that is how you lose an ear, ask me how I know. You might also need to grind down the upper pin lug so the link rides smoothly.

I dont Think caliber matters with sears or LL..the damage/wear would be to the receiver.
For us with out RRs, it DOESN'T matter.

Its not really the caliber that makes the difference its whether there is a rotating bolt assembly in the mix.

The link takes a much harder hit when run on a upper that doesnt have a rotating bolt.  On a normal 5.56 upper the last 0.5 inch of closure on a rotating bolt assembly is much slower as the carrier hits the cam pin in an angular pathway in the carrier which slows down the speed of the carrier.

On a traditional pistol caliber arrangement there is no bolt to hit the barrel extension and the carrier to then ride home on an inclinded ramp via the carrier pin.  It just come to an abrupt full halt when it slams into the barrel at full speed.

The other killer of RLLs is folks who run them in improperly inletted/releaved receivers where the link can bind.  I also personally advocate running a reduced power disconnector spring as that will also take pressure/stress off the link when its trying to rapidly pull the disconnector backwards to release the hammer.  The less resistance it has to pull back the easier it is on the link ears and body.

If you have a properly inletted receiver, a reduced power disco spring, and good lightning link protector you can safely run a pistol caliber setup in my experience.

Guys thank you very much for all the great information. I just bought a reduced power disco spring today. Along with m60joe doing the work and having the protector, sounds like the link should work without damage. Up till now I've really been hesitant to build a 9mm host (even though I really want to do it). I think I'm going to jump on that as my next project... I love subguns.

I'll further stress this point.  Get the lower fully milled for your LL and protector.   I bought some lowers (556 and 9mm magwells) that were low shelf to run with a LL and KNS protector.  

Nope.  Still needed work.  So from my experience, buy what lower you fancy.   You need to get it fitted regardless.  I got the receiver, the bolt (9mm) or bolt carrier (556/x39), barrel extension and paddle fitted at the same time.  Works flawlessly.   I got all this done locally and it was quite economical.  If I remember, maybe $100 a rifle.

I did this and I no longer need to shave any off the rear lug.

If you don't remove any material from the upper receiver rear lug, the actual link will sit lower by the thickness of the protector (.040" usually) sitting on top of it.  This has the possibility of resulting in some mis-alignment of front of the link on the disconnector(s)...something to watch for especially with the notch cutout for the burst semi/auto modification, but an easy fix.  Probably best to keep all your uppers the same either way to avoid some mismatching with the disconnectors of various hosts. Similarly, too much vertical play back there under the lug area can also cause the link to rotate a bit.

The other downside is that the link will ride lower and likely contact/ride on the selector body more, potentially causing some wear on the link's lower surface.  This is why I just milled all my lugs a bit shorter.

v/r,
Esox