Whomever believes loading for bolt is same as gas is mistaken. Sizing cases without an expander is common practice for many bolt gun loaders. As xcount wrote, because semis ding the case mouth often, your expander button or mandrel will need to straighten out the inwardly poking ding.
Also, semis will not tolerate chamber pressure the same as a bolt gun. I refer primarily to the large chassis AR's like yours, rather than AR15's. Breaking cam pins, excessive / premature lug wear or even breaks, primer piercing, broken firing pins can occur in AR's when pressures rise to excessively high levels.
In other words, put too much propellant in a round and fire it in your AR10/Lr308, and do it enough times, parts will break. An AR clearly is not a bolt gun and is not intended to be used like one. For AR10/Lr308 rifles and carbines, use data proven to be safe in the M14 (H 4895, 155 - 168 grain bullets, 40.0 - 42.0 grains propellant). Otherwise, firing your semi-automatic rifle or carbine using bolt gun ammo and off-the-shelf hunting ammunition will be at your risk and peril, either bodily, or mechanically. At least wear eye protection.
By the way; run an expander mandrel instead of a button, but if you insist on the button, polish it, and expand the case mouth using a down stroke of the press handle. Expanding while moving into the case mouth, like coitus, works better than expanding while pulling the button out of the case mouth. The latter can stretch the mouth out of concentricity or affect bullet runout. Last, crimping might not hurt anything, depending on whether the crimped ammo shoots well, but if crimping is necessary to prevent coal changes, or runout, the ammo is not the cause. The cause for that is feed ramp issues directly, or indirectly by maladjusted magazine lips not presenting the round sufficient to facilitate proper feeding. Canelured bullets are designed for optional crimping if proven necessary.
Now do as you wish, but you have been warned.
