Looking for a 180gr cast load for 308Win that will funtion in an M1-A1. Have gotten good accuracy with 20gr of IMR4227 but only about half will funton the action.

I think I would try a bit more powder, or go to a slightly faster one, for quicker impulse.

Just an opinion so right off you know what it is worth, but I would bump the 4227 load up a tad til you start reaching the upper load limit to try.
If that woun't get you an accurate load that will work the action I would suggest you go to slower powder and more of it. You need to move the pressure curve down the barrel to actuate the action. WC 846 was powder of chice in the 7.62X51 as I remember it so somethg just a tad faster that will perform with cast bullet load levels and with accuracy!
Thats not too hard, only juggliung 3 variables in one load to consider.
You may want to ask one of the folks over at the Cast Bollits group about this one!

I'm useing about a casefull of AA3100 with the RCBS 308-165-SIL. It functions the M1A well and is reasonably accurate.