Originally Posted by
Parashooter
If using an issue-pattern full-length stock, shimming the front end of the forestock isn't a great way to apply pressure, as it's likely to cause undesirable barrel contact with handguard and/or upper band. Adjusting GI forestock tip pressure is accomplished properly by altering the angle at which the receiver sits in the stock, scraping or shimming wood to effect more or less pressure at the forward barrel bearing - while maintaining clearance between magazine box and receiver. Once appropriate pressure has been established, handguard and bands may be installed and checked for clearance. It should be possible to lift the barrel at least .010" without touching the upper band.
The 03-A3 stamped upper band can sometimes be "squooshed" in a vise enough to increase upward clearance significantly.