I have a .222Rem with an 18" barrel that I would like to load some subsonic ammo for.

Can anyone give me data or advice?

I would just shoot match ammo out of a 22 LR.

If you do it I would use cast bullets so as not to get a bullet stuck in the barrel.

I tried to go subsonic with my tripple duce. I was unable.

You might want to try looking at what can be done with red dot and very soft cast bullets.

I bought a 22lr conversion from Cabellas and haven't been happier.

EXPRESS,

WE do load sub-sonic ammo in a number of calibers, and have found that one has to develop loads for each particular rifle.

No one load works in two rifles!!

The easiest caliber to do this for is the 308 Winchester, if you can find some of the special cases that are factory loaded to be sub-sonic.

They have much less case capacity, and cannot be loaded with normal full power loads.

With the 222, we normally start with around 3 grains of powders such as Red Dot, Green Dot, Unique etc.

Increase the powder by 0.1 of a grain, as this translates to 30-50 fps, depending on the bullets weight.

I hope this helps.

I made an insert to shoot 22 LR's in my 222. It's a case made from brass rod but the inside is 22 LR size. The firing system is a steel piece attached to a brass piece. The rifles firing pin hits the brass and the eccentric steel piece hits the rim.

I made that about 40 years ago but it's still around here somewhere. If I find it I will make a picture of it.

Isn't SONIC [The speed of sound, just below 700 fps]?
I reload "Squib Loads" at about 1850 fps for .223 Remmington and .22 Hornet.
Buy the Lee PC program, for less than $20. They have facility for REDUCED LOADS. You can use your "regular" powder and drop the velocity for any load you choose.
My loads are for 55 grain bullets:
.22 Hornet...4.1 grains of UNIQUE
.223 Remmington...5.6 grains of UNIQUE
The above loads are tested and used at 25 yards.
.22 Hornet [45 grain bullet] 7.3 grains of IMR 4227 gives about the same point of impact and has been tested at 150 yards.

"Isn't SONIC [The speed of sound, just below 700 fps]?"
No! 1090ft./sec. at sea level roger