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180s are the default... but there's no reason not to use the 165s... you'll use slighly more powder to make the same velocities (if you care about power factor for IPSC or something)... if you're just target shooting it doesn't really make any difference... the two will feel different so you might like one better then the other... your gun might also... one round (or particular load) is gonna be more accurate or consistent then some other might, so a little experimentation will provide the answer to a somewhat subjective question... depends on your supplier but the 180s might be slightly more common / easier to get, but that's not likely to be an issue...