The expansion of the M-14 wooden stock, due to moisture, caused problems during the disassembly process for the weapon. With both the M1 and the M14, the stocks were to be oiled with Linseed or Tung oil, only the exterior of the gun was to be oiled, however. If the inside of the stock was oiled, according to the manual, the oil would heat up and smoke if it was near the barrel. This lead to the potential of moisture being drawn into the un-oiled areas. In 1967 the US Army Human Engineering Lab conducted a study called: SMALL ARMS USE IN VIET NAM: M14 RIFLE AND .45-CALIBER PISTOL, in which feedback from Marines about the M14, among other things, was gathered. It was noted that: "Wood on rifle stocks for M14 is swelling too much in rain. After taking rifle apart it is impossible to put it back together without drying the stock first." No feedback regarding accuracy being affected by the swelling stock was recorded in this report. In the book 'Fighting Garand Owners Manual' by Nolan Wilson (1984) it states that: "When fitting a new Garand stock...stocks, although made of walnut and treated with linseed oil, sometimes swell due to moisture, thus causing binding of the working parts. In such cases relieve the binding by using a flat file.". It would appear that the Garand had similar problems with swelling of the stock, but this could remedied by filing the stock down. The WW2 era M1 technical manual does not state this however, and the sources for Nolans book are unclear, and a 'drying the stock' remedy for the Garand is not mentioned. The Garand and the M-14, could be cleaned without being fully disassembled, and according to Nolan, repeated complete disassembly was to be avoided as it caused "excessive wear of parts". Also of note is the fact the Vietnam era Sniper M-14's were provided with stocks that were pressure treated with epoxy, to reduce issued with swelling, suggesting that the issue caused accuracy concerns as well. The Garand has similar swelling issues as the M14, but it did not affect its functionality to any great extent, but this problem was exacerbated in the M-14's design causing more issues than its predecessor.

Sources:

The Fighting Garand Owners Manual. Nolan Wilson. SMALL ARMS USE IN VIET NAM: M14 RIFLE AND .45-CALIBER PISTOL M-14 technical Manual. The M-14 Battle Rifle by Leroy Thompson The M1 Garand by Leroy Thompson.