Subsonic load development

[Rogue111]

Hey Guys, I am putting together a 300blk SBR & would like to start load development planning for subsonics. I do not have a chronograph but here is my plan:

Without Suppressor:
- Start with load a few 1/10gr above of similar postings of subsonic loads & work down
- I’m hoping I will be able to tell when the load becomes subsonic with hearing protection on an unsuppressed shot?
- Once first subsonic unsuppressed load is found, drop down a few more 1/10gr to account for the fps boost from suppressor
- Confirm rounds are stabilized & not keyholing

With Suppressor:
Test final suppressed subsonic load

Does this seem like a valid plan? Any other recommendations?

 

[Hogshooter]

I would start more than a couple of 1/10s above what others are using. I would go 2 -3 grains above and work your way down from there. You do not want a stuck projectile in your barrel.