Some of the testing has changed over the years from what I understand. A big one is the clothing material was changed to denim and/or fleece (Ive read both) instead of the down material.
Revisions to standard test:
Switch from Down to Polartec, January 1, 2004
The original test, created in 1988, used a down comforter (500-550 fill power) in a cambric shell (approx 232 threads per inch) as part of the heavy clothing mix. On January 1st, 2004, the protocol was changed to replace the down comforter with Polartec 200 fleece.
The switch to Polartec 200 was made in an effort to reduce uncontrollable variables in the test procedure and because fleece had become more prevalent than Down.
Down comforters typically consist of stitched baffles containing the down. As the comforter is laid in front of the gelatin block, it is not uncommon for down to migrate to the bottom of the panel. It was difficult, if not impossible, to ensure that each shot was subjected to the same amount of down. Prior to the switch, a comparison of bullet penetration, expansion and retained weight was conducted to see what, if any, changes would occur. Five shots were fired into a block of gelatin covered with the "down" heavy clothing and five shots were fired into a block of gelatin covered with the "fleece" heavy clothing. The validation numbers for the gelatin blocks were similar to ensure that the blocks were as identical as possible. Ten (10) cartridges, two (2) rifle and eight (8) handgun, were compared. The results showed that the penetration averages differed by .2" (a -0.8% change), the expansion differed by .01" (a 2.2% change) and the weight difference was negligible (a .5% change). Based on the testing conducted, it was determined that the consistency provided by a change to fleece would make the test protocol more scientifically repeatable and, therefore, provide better data for making ammunition selections.