At least half of you coming to this thread are wondering if the author misspelled glass as brass. This is not the case.

A couple of weeks ago I bought a new standard 9202 M1A. I brought the gun home and made sure it was functional and lubricated, then took it to the range for a look see. With crummy cheapo 762*51 ammo it lobbed in 2.5 inch groups (5 shot 100 yards iron sights).

So I took it back home and started to give it a closer inspection and found multiple minor issues.
The gas system was not timed correctly which is fixed with a couple of washers which stabilizes the flange holding the bottom of the stock ferrule and the hand guard.
The receiver sits in the stock with no upward tension on the ferrule.

Most people faced with this situation would end up glass bedding the receiver. And, indeed, later I might.

But today I went to the hobby store and bought two thin strips of brass. Then I proceeded to make several shims and figure out how to lock the receiver in the stock without altering the stock in any way. I opened up the front ferrule for adequate clearances that night also.

Based on the way the receiver was sitting in the stock it was clear that one of the times on the receiver should be moved towards the other so the receiver was centered in the stock. I made a shim that fits in the slot of metal in the stock and limits the horizontal slop on the receiver tines to about 0.002. That is you can tell its not tight, but if you did anything more it would be.  Job 1 done.

Then I made two thinner shims to fit the horizontal recesses between the stock and the receiver (where the magazine goes) These are 0.032. I cut to size, and then used a peaning hammer to fit the shims to the receiver. The peaning was done on the vise in case anyone was wondering and took quite a bit of time to get the angles right and the edges straight. A bit of work with the dremmel tool and they fit both the stock and the receiver.

However, the trigger group would not go in. So I took the shims and used a flat fine file to tin down one end of each shim until it was just about 1/2 as thick as when I started. A bit of fiddling and I got them working and the trigger group installed at not-abnormal-closing-pressure.

So, now the stock has proper downward pressure on the barrel through the <tight> gas cylinder group, the receiver has no movement laterally or longitudinally, and everything else works properly.
For a little less time that it would take to prepare an M14 stock for glass bedding, I brass bedded mine.

In a couple of day I will return to the range and see if the groups have tightened up. Wish me luck.

Interesting. My Poly wasn't much of a shooter, perhaps something like this would have helped.

Good luck and report back soon.

Interesting approach!

In for results.

My polytech will shoot a two inch group at 100 with irons, with handloads,on the right day.