Sushae: I have reloaded for friends who shoot 30-06 and 308 semi-autos and have found that the faster burning powders are recommended and preferable. With bolt guns you can use any of the powders listed in the reloading manuals for the caliber(s) you intend to load but for the semi-autos the recommendation is to use the faster burning powders to assure semi-auto cycling.
Some one will please correct me if I am wrong but one of the recent posts on a similar topic indicated that some of the 'Light Magnum' loads were labeled not for use in semi-auto rifles. This was not a high pressure or unsafe caution, it was more a statement that the powders used were slower burning that would not allow semi auto actions to cycle. I encountered this while loading for the 30-06 semi-auto - the loads were accurate but they would not cycle the action. I then went to the faster burning powders and the problem was not encountered.
I am not aware of any damage to the action or rifle, only the effect of not cycling the action. However, there is the possibility that you could clog the gas port with slower burning powder residue but I am not certain what, if any, damage that would cause. Hope this helps. Mikey.
