Thread: Subsonic load for 308

Greetings All,
Articles appeared in Handloader Magazine in 1987 and 1990 written by Roger Stowers about loading for the 240 Gibbs. The 240 Gibbs was a wildcat from the 1950's developed by Rocky Gibbs. It was basically a 6 mm-06 Max with the shoulder moved forward and increased to 35 degrees. Roger's first article dealt with his struggles with start loads. Roger used 49 grains of IMR 4831 in fire formed cases with Speer 105 grain spitzer projectiles. This should have been a mild load but blew primers, case heads and extractors. Roger found that he could minimize the problems by elevating the muzzle prior to firing, seating the bullet backwards or increasing the jump to the lands. Velocity was 2,800 feet per second, a pedestrian load for the .243. In his second article Roger works up to a max of 57 grains of IMR 4831 with the 105 grain projectile for 3,224 fps with no problems. Roger felt that the excess air space in the case was the problem and eliminated all loads with more than 1/4 inch or more air space between the powder and the base of the bullet. Incidentally Roger had the same problem with IMR 7828 and a little less with H 4831.
So there you have it, pressure excursions with non case filling loads of a slow powder related by someone who was actually there and cleaned up the mess afterward. The factors seem to be: case large for calibre, steep shoulder? and load over 10% less than max.
Should this be a problem in the .308? No. Could we stick a projectile in the bore with a light load of powder? Definitely. .308 Mauser could be right that current powder has been improved to eliminate the problem but we should not take any chances.
Regards Grandpamac.