Lost Speed

Printable View

03-12-2015, 06:44 PM
Rwt

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
03-12-2015, 07:22 PM
MSL

Weather conditions affecting the accuracy of your chrony, ie bright and sunny versus overcast and darker?
03-12-2015, 07:58 PM
veitnamcam

Quote:

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.
03-12-2015, 08:11 PM
Cartman

On a side note got any spare 215 bergers for sale haha

Sent from my SAMSUNG-SM-G870A using Tapatalk
03-12-2015, 10:24 PM
Rwt

Quote:

Originally Posted by Cartman

On a side note got any spare 215 bergers for sale haha

Sent from my SAMSUNG-SM-G870A using Tapatalk

Haha nah the things are hard enough to come by at the best of times. Are they sold out in NZ again?
03-12-2015, 10:28 PM
Rwt

Quote:

Originally Posted by veitnamcam

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.

Cheers, It was an overcast day last time so Ill try a bit of light.
03-12-2015, 10:32 PM
257weatherby

As VC says, different light conditions change the readings, shoot lots across varied light conditions, then average the readings, then check on steel at the actual distances needed. I get my averaged my number then test at 300yds to cross reference it. I keep known loads to confirm the chrony reading on any given day, prior to testing a new load.

Past 300yds, no guestimation allowed!
04-12-2015, 03:09 AM
ARdave

The real problem is the cartridge - designed by elton john , it will eventually decrease in velocity daily until it goes backwards. shoulda brought a rem mag...
04-12-2015, 07:50 AM
zimmer

Quote:

Originally Posted by Rwt

Cheers, It was an overcast day last time so Ill try a bit of light.

If the day was a constant overcast (obviously not dark dark though) with conditions constant that is what my old F1 used to like. The bright sunny days gave it hell, even with diffuser screens attached. One outing CED was telling me every second 22RF shot was doing 3300 fps and a mate shooting at the same time with an Oehler 35P was missing shots. Just the issues with an optical chronograph.
If you have genuinely lost 170 fps you should see that at the target with a change in group centre but you said your elevation was only a bit low. A drop in velocity of 170 fps when shooting to 1000 meters is roughly 1.8 meter shift in elevation but I guess you have already worked that out.
04-12-2015, 08:06 AM
zimmer

If you have access to another chronograph stick that in series with yours and that may show up an issue with your F1. However, if conditions are causing the problem the second chronograph may be affected as well so not an ultimate check I guess. Next, buy a MagnetoSpeed :P
04-12-2015, 06:53 PM
Rwt

Quote:

Originally Posted by ARdave

shoulda brought a rem mag...

already got a bunny rifle thanks...
04-12-2015, 06:58 PM
Rwt

Quote:

Originally Posted by zimmer

If the day was a constant overcast (obviously not dark dark though) with conditions constant that is what my old F1 used to like. The bright sunny days gave it hell, even with diffuser screens attached. One outing CED was telling me every second 22RF shot was doing 3300 fps and a mate shooting at the same time with an Oehler 35P was missing shots. Just the issues with an optical chronograph.
If you have genuinely lost 170 fps you should see that at the target with a change in group centre but you said your elevation was only a bit low. A drop in velocity of 170 fps when shooting to 1000 meters is roughly 1.8 meter shift in elevation but I guess you have already worked that out.

Yea I might just have to bite the bullet and get a magspeed. I was only got a chance to test out to around 500m at which point it was around 0.1-0.2 Mils low. If it was 170 fps slower it would have been around 0.5mils low. Im not sure of any other chrony's round so I might just have to take it to a km or so and see what happens. Further the better I guess?