[glockgod]

In the process of switching from Rainier 9mm 147gr plated to Precison Delta 147FMJ bullets. Precision Deltas are about .020 longer than Rainiers so I will need to seat them deeper to get a 1.155 OAL. Should I start low on the powder and work my way up or just seat em and go. Current powder charge is 4grs Unique.

[rcmodel]

4.0 Unique is at least 0.5 grain under max with a 147 grain jacketed bullet in the 9mm.

SO, you are already reduced about to the oft-recommended 90% starting load.

I'd load'm and go if it was me.

rcmodel

[ranger335v]

"Bullet OAL? "

Are you concerned about the OAL differences between those two bullets?

Or the OAL of the loaded cartridges?

In either case, you will need to load them to fit the magazine and feed properly. If that takes a powder adjustment, do it.

[glockgod]

There is a .020 difference in the bullets themselves. I think I might load a few to run thru the screens to compare to the Rainer loads. 950fps+/- is what I'm looking for.