Thread: Lost Speed

Hi guys, I'm at a loss for whats happen,
I'm shooting a 300win mag with Norma brass, Fed 250M primers, Berger 215 Hybrids, and 74gns of 2217 Powder. Its in a Rem 5R with a 26inch barrel.

Anyway I had originally measured the velocity at an average of 2870FPS for this particular load and the other loads I tested on the day came in around the same. After shooting out to around 1000m I found the elevation to be pretty much on so I was happy that the speed was where it should be.

A week or so ago I got a chance to shoot a few rocks at a bit of range, the rounds were landing a bit low and I figured I got the atmospherics a bit off,(The extra drop would have only accounted for around 30-50FPS).

I decide to re-check my speeds since I brought some new brass anyway.
After 25 shots I ended up with an average speed of around 2700 FPS! I somehow seem have lost 170 or so FPS although I haven't changed anything between now and then.

Things I can think of possibly - The chronograph is lying (Although it seemed fairly consistent at the time, its a chrony F1)
- The throat has eroded and the ammo is a lower pressure (Seems unlikely as the barrel is only 200rnds old)
- I got the speed wrong the first time (I tested a number of loads that day and the drop seemed to confirm it)
- Dirty or copper fouled barrel
- Setting up the chrony wrong, although I moved it a few times to check.

I will head to the range again to check things out, but is there anything you guys can think of that I may have missed?

Cheers