Thread: Lost Speed

Originally Posted by Rwt

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

I have had one for a few years now, it is telling porkys would be my guess.
The only way I trust mine is to shoot a validated load over it then immediately shoot the test round and add or subract the variance on the known load on the test load.

They can change as much as 150fps from a cloud going over.