With a mixed bag of brass my previous chrono results made me think about it - some Starline and Lord knows what else - 692, 641, 692, 690, and 665.
I'll start with
I am not saying you are wrong, but I will suggest that you consider: the chrono results are not accuracy results.
I say this because technique sometimes has a lot to do with chrono accuracy.
I believe that a chrono can sometimes return results that don't necessarily reflect the
accuracy performance of the load, and I also believe that different holds for each shot can throw off chrono results that may not have any affect on accuracy. And there are other anomalies that can affect bullet speed as we measure them. There is also that BIG mathematical and scientific thing that seems to often get lost when folks chrono loads and then come to fast conclusions, and that is called sample size. The affect of sample size doesn't get nearly enough thought when it comes to making fast conclusions from chrono results.
A chrono can be an exceptionally valuable tool, especially for rifle shooters who need to calculate drop over distance. For handgun shooters, it's also valuable for competitors who must make a velocity or "power factor" floor for ammo that they will compete with to stay legal within the rules of that event.
But my (often
unpopular opinion) is that chrono results are misinterpreted and over valued in a lot of situations,
especially for handgun shooters.
We can make phenomenally accurate handgun ammo even when we may see some less than thrilling chrono results. And in the context of this conversation, your post seems to suggest that different headstamps are the cause of your different chrono results and I'm simply saying that we definitely don't know that for certain. It could be variances in the weight or diameter of your bullets, it could be a slight variation in one or two of the chambers of your revolver, or an inconsistent powder drop on your handloads or if the bullet crossed the chrono in a different place or in changing light/cloud conditions.
When we chrono one HUNDRED rounds, we can better see a pattern of results that might be more trustworthy.
I'm not trying to pick on your post, I'm just adding some food for thought -- the answers we seek are not so easy to find and the time-sucker-fun-sucker-speed-checker box doesn't give easy answers to complex things.
And if we have the choice between ten rounds from a solid rest in to a paper target at 25 yards --OR-- ten rounds through a chrono to decide if a load is decent or a load is questionable, I would answer that choice by driving over my fun-sucker chrono with a dump truck.