With the Hogue rubber stock you can bend your mini and shoot around corners

Just kidding.
Like bushwack said they are made of fiberglass, with a bonded pistol grip type rubber coating. I used the Acraglas Gel Kit. It has about everything you need except model clay, and a brush to apply the included parting agent. There is enough to bed 4 or 5 rifles, and comes with dye to match your stock. I paid about $12 for the kit.
gutpile has a good attitude about the mini, he knows its limits, and usees it for his purposes, and has fun with it. For my purposes drop coyotes up to 300 yds, I had to change the limits a bit. Thats why I bedded the stock, trigger job, reduced recoil a bunch for quicker follow up shots if needed, firelaped my barrel, laped-gaped-torqued the gas block, installed a muzzle brake, installed bipods, a good scope, and reload; to get as close to 1moa as possible. Yea it would have been easier with a bolt gun, but not near as much fun. It works for me.
The bedding in any rifle will shoot out in time. With a semi auto, time wise, it will happen sooner, as you shoot a lot more than with a bolt gun. All you do is redo it. Just wipe old beding with alcohol to remove any oil, abrade with sand paper and reapply bedding material. Now we are talking several thousand rounds. Or when you start to notice the flyers creaping back in.