Will this work on a 601 with the grenade retainer spring?   thanks

https://www.keepshooting.com/m1a2-rifle-grenade-adapter.html

Yes.
It will also work without the retainer spring, but will slide off the barrel if tilted down.

Ooooh looks fun

I have one of these for my Garand, fits the spigot well:

Yes, will work. May have  to play/adjust to get the hand grenade properly situated on the adapter and being thin metal, they get banged up/ broke falling on hard ground.

I have never used w/ a "real deal" rifle grenade cartridge, but have used w/ standard 5.56 blanks- both USGI and DAG?.

Will launch the adapter and dummy grenade 40-60 yd or so.

The M-16 flashiders are 22mm NATO standard.

I've also found that the "Services of Supply" dummy rifle grenades work well. They are aluminum coated w/ rubber. Eventually the ring will break or the grenade front end separate, but, they last a good long time.

Recommend that you fire plus or minus 45 degree angle to reduce adapter/ fake grenade skimming along the ground breaking fins/ ring etc.

And, firing from shoulder will not break your bones, nor hurt.

Thanks for the comments. I got a couple coming. one for the 601 project and one for the Garand.
Mostly for display purposes. Nice to also get them for under 10 bucks.