That Forster FL die will arrive with ~ 0.302" neck.
I would send that die body back to Forster and have them hone it out on one of their Hardinge collet lathes to 0.307".
Custom Machining Services | Custom Case Trimmer Pilots | Custom Case Trimmer Collets
CUSTOM neck honing of Forster FULL LENGTH SIZING or NECK SIZING DIE to your specification. We custom hone the inside neck diameter by using a diamond stoning process. We enlarge the inside diameter to prevent over-sizing of the case neck due to thick neck walls. You may require this service for two reasons: 1) If you use some brands of brass cases, such as Norma or Lapua, which have thicker neck walls. 2) If you do not intend to outside neck turn case necks that have thickened after repeated firings. Please specify desired inside neck diameter. Note: 1) No more than .008" stock removal from your existing die neck diameter is possible. 2) Honing is done in increments of one half thousandth of an inch (.0005"), meaning that your specified inside diameter must be either.XXX0" or .XXX5".
$12.00 plus actual return shipping cost & insurance Please allow 1-3 weeks.
I have sent (8) FL die bodies back to them.
I did not send my Forster 7mmRM FL die, becuase I have a Bonanaza FL die that someone, it seems, already sent it back to get honed out to .307".
I am measuring the pin gauge that is a GO.
Forster measures what is a GO.
Neck bushing are measured with the highest NO GO.
Since I complained about that, Forster has gone to the half thousands system.