bellavite1
06-10-2012, 15:33
Hello guys.
I finally purchased a cronograph.
I now have access to a 500 yds range so I want to get some decent trajectory computation.
My 308 is a DPMS SASS, 18.5" barrel, flash hider.
Load is 42.5 Varget pushing a Speer match 168 gr HPBT.
Very accurate at 100 yds (about 1/2 MOA 4 rnds group, + a flyier...[Bang]).
I have set my cronograph (CHRONY F1) at about 14 feet, and I am getting readings all over the place, from a 2490 to an unrealistic 3059 (!).
I know my charges are NOT that off from one another, even with a powder measure, tipycally I get a + - 0.2 gr variable, not enought to give a velocity sread pf almost 600 fps.
Averaging 19 shots it comes up to 2853.5.
However, the drop seems to match a 2315 fps trajectory (or somewher around there...).
All of this is obtained through the Shooter Android app.
So I came to the conclusion that my 308 readings are not at all accurate, since the Lyman manual shows, with a 3 gr HIGHER charge and a 5.5" LONGER barrel, a velocity 100 fps LOWER than the one I averaged from my rifle
The readings I get from my 338 LM, however, are spot on: 2725 fps, which translate in the correct adjustment when shooting the rifle at various distances, so my ballistic app is doing a decent job and so is the crony.
So, the 308 readings do not match the real world trajectory, the 338 LM readings do.
Readings for both were taken at 14 ft, on the same morning. so what gives?
Could it be that, with the 308 lacking a muzzle brake which redirects the gasses away from the cronograph, like the one on my 338LM, what I am measuring on the 308 are actually the gases rather than the bullet?
Even 14 ft away from the muzzle???
How far shoul I set this cronograph from the muzzle in order to get an accurate reading?
I hope this was not too confusing...
HELP![Help]
I finally purchased a cronograph.
I now have access to a 500 yds range so I want to get some decent trajectory computation.
My 308 is a DPMS SASS, 18.5" barrel, flash hider.
Load is 42.5 Varget pushing a Speer match 168 gr HPBT.
Very accurate at 100 yds (about 1/2 MOA 4 rnds group, + a flyier...[Bang]).
I have set my cronograph (CHRONY F1) at about 14 feet, and I am getting readings all over the place, from a 2490 to an unrealistic 3059 (!).
I know my charges are NOT that off from one another, even with a powder measure, tipycally I get a + - 0.2 gr variable, not enought to give a velocity sread pf almost 600 fps.
Averaging 19 shots it comes up to 2853.5.
However, the drop seems to match a 2315 fps trajectory (or somewher around there...).
All of this is obtained through the Shooter Android app.
So I came to the conclusion that my 308 readings are not at all accurate, since the Lyman manual shows, with a 3 gr HIGHER charge and a 5.5" LONGER barrel, a velocity 100 fps LOWER than the one I averaged from my rifle
The readings I get from my 338 LM, however, are spot on: 2725 fps, which translate in the correct adjustment when shooting the rifle at various distances, so my ballistic app is doing a decent job and so is the crony.
So, the 308 readings do not match the real world trajectory, the 338 LM readings do.
Readings for both were taken at 14 ft, on the same morning. so what gives?
Could it be that, with the 308 lacking a muzzle brake which redirects the gasses away from the cronograph, like the one on my 338LM, what I am measuring on the 308 are actually the gases rather than the bullet?
Even 14 ft away from the muzzle???
How far shoul I set this cronograph from the muzzle in order to get an accurate reading?
I hope this was not too confusing...
HELP![Help]