You should post what powders you have on hand. I have a number of accurate 155 OTM loads using Varget, H-4895, IMR 4064, Reloader 15, AR-Comp and IMR 8208 XBR in my GAP 10. As in all hand loading procedures, you will need to start low and work up a safe load in your rifle. Gas guns usually cannot take the same powder charges a bolt gun will.
My .308 Win. gas gun powder charges are usually 1-2 grains lower than my bolt gun loads.