Semi-Auto's
Winter time I've started using Mobil One 5w-30,
Summer time I use Mobil one Wheel Bearing grease on the slide rails.
Revolvers
Mobil One 5w-30 year round
Both available at Wally World. Since I do my own oil changes on my cars I end up with 1/2 to 1 Qt left over out of a 5 qt container. I usually save the extra until I have enough for a complete oil change; every so often I siphen off some for the important things in life, my guns.