climbing velocities

[mitchellchandler_au]

Hi all,

I was just wondering what could cause the velocities of my 6mmbr to slowly climb up from 2880 being the slowest to about 2909 at the highest over 10 shots. the increas was gradual with about 2-3fps increase from each shot I think the loads are pretty close so I was thinking the barrel was getting a little fouled or a bit hot. Any suggestions to the cause or how to fix this.

Thanks,

 

[steveyrock]

Mitchell
was wondering if this consistantly happens or was it that you noticed it in one shooting session.

 

[mitchellchandler_au]

This was the first time I got a chance to check the velocities of my reloads so Iam not sure if its a common occurance as yet but I will continue to do more testing.

thanks,
mitchell

 

[mitchellchandler_au]

the velocities are as follows.

2880
2892
2885
2883
2883
2889
2889
2900
2909
2894

this is with the projectile touching the rifling and with .20 into the lands the velocities dropped about 70fps and the ES and SD went through the roof.

 

[mysticplayer]

How did it shoot?

What chrony were you using? What type of light?

Check with your manf but most chronies have a 2% mechanical error so the machine is only accurate to at most +/-6fps at 3000fps readings. Some will give wider error levels depending on ambient light,shoot the same batch of ammo on a sunny vs cloudy day).

I used to really worry about my chronie data but don't anymore. I use it mostly to ensure I am not too far overpressure or for really bad velocity variations,over 20fps spreads).

Ultimately, I let the target decide which load to use and I test as far away as I compete. Min is 200yds. I have found 100yds to not tell me the full story as with my chronie data.

Hope this helps...

Jerry

 

[steveyrock]

if I knew the chrono used to establish those numbers was capable of reading to several fps accurately I would strive for a better ES but with my PACT chrono those numbers would not get me to concerned.

 

[JHardy]

Mitchell:

An increase in velocity is an indicator of possible carbon build up in the throat. Of course that will increase the vert. and therefore your groups at long range.

Carbon Killer and Bore Tech Eliminator and short strokes with a good brush will get you back where you need to be.

I hope Jason Baney responds to this thread as he has dealt with this very problem successfully with his winning 6BR.

Good luck,
Jim Hardy

 

[Forum Boss]

Mitchell,

In addition to carbon, simple heat in the chamber and ambient heat on the ammo box can make a noticeable difference. Were you shooting in the sun.

With Varget,ADI 2208) I observed a 50 fps vel increase just from heat. The ammo, which was sitting in the direct sun on a hot day, rose from 80 deg F to about 105-110 deg--warm to the touch. Now I always keep my ammo out of the sun and, between relays, in a cooler.

If you leave your ammo sitting in a hot chamber for a while it will also heat up.

 

[mitchellchandler_au]

Hi guys,

The chrono I was using is a chrony F1, the light was failing but I got all 10 shots down range before the sun had set.The load had grouped in the .100-.200 range with the 105 A-MAX but the best I can get now is around the .250-.350 mark, maybe Iam slipping a bit

thanks for all your help guys.

 

[jb1000br]

Mitchell:

An increase in velocity is an indicator of possible carbon build up in the throat. Of course that will increase the vert. and therefore your groups at long range.

Carbon Killer and Bore Tech Eliminator and short strokes with a good brush will get you back where you need to be.

I hope Jason Baney responds to this thread as he has dealt with this very problem successfully with his winning 6BR.

Good luck,
Jim Hardy

The velocity increase didn't happen that quick...

Honestly I don't see anything wrong with your data set...as you are still inside the error range of the chrony timer...and the last shot is the "same" as the first, so I wouldn't sweat it..

shoot it at 500yds or more, if you have 1.5" or less vertical at 500, you are GTG

JB

 

[mitchellchandler_au]

Thanks guys,

Iam very new to the long range BR game,only 4 months) but every time I shoot I learn something new. I greatly appreciate all the help. any info to make my learning curve a little less steep will be greatly appreciated.

thanks again,
mitchell