Have a milled receiver slr95 with both upper and lower buttstock tangs and a wood stock. The stock screws have been backing out and require re-tightening after each range trip.

Drilled out the screw holes and fitted them with wood dowels then re-drilled the screw holes slightly smaller. Thought that fixed the problem as the screws went in pretty tight, but they still eventually backed out.

Would prefer not to epoxy in the screws as that would be  trouble down the road if I ever wanted to remove the stock.

Some type plastic or metal screw anchor?

Did the commies have this problem as well?

Use red lock-tight or something like that.

Not sure that would work in a metal screw to wood application. I may wind up going the epoxy route. Perhaps a step down from epoxy would be just using wood glue, or general purpose Gorilla glue.

Where did you get the screws?  Are they factory screws?

It sounds like the fit of the stock to the receiver is too loose, which is allowing excessive movement during firing and subsequently causing the screws to back out. Is the stock loose when installed (wobbles) without any screws installed? If so, I would focus on tightening up the fit of the stock first, and then focus on the screws if that doesn't rectify the issue.

if the screws are not binding the wood, take some elmers glue, some match sticks with the tips removed, and put glue on the sticks and insert into screw hole. Let dry, reinstall screw.

Whenever I came across a wood stock screw that was stripped or wouldn't stay tight, I used an epoxy trick:

Apply a heavy coat of wax to the screw and anywhere you DON'T want the epoxy to stick.  As example both sides of the tang holes or both sides of a buttplate screw holes.

Mix up a small batch of 5 minute epoxy.
Pack the hole full of the epoxy and turn in the screw just to the point where it's snug.
Allow about 45 minutes for the epoxy to cure, then remove the screw and trim off the excess that oozed out of the hole.
Allow 24 hours for it to fully cure.
When the screws are put back in you can tighten them very tight and they will hold.

For wax, the best is to go to a hardware, grocery, or most Walmart stores and buy a big yellow can of Johnson's Paste Wax.  
This is also the preferred treatment and preservative for modern leather holsters and belts and is also perfect for use as a release agent when glass bedding a rifle or pistol grips.

This makes a stronger and much easier repair then the usual drilling out and installing a dowel, and it's a permanent repair that's stronger then the wood itself.
Since the epoxy forms a perfect fit to the screw, the increased contact prevents the screw from loosening.
It's also more professional then putting toothpicks or steel wool in the hole.