chronograph question ?

[stpeterhunter53]

how is it possible to shoot 50 ft. slower with .5 grains of more power first three 68 gr. h4831sc ave.3404 waited 5 to 7 minuts shot three rounds this time 68.5 h4832sc ave. 3350 everything the same except .5 grains more power and its slower ???? out of a 257 wby used 110 accubonds

 

[440sixpack]

If you're sure everything is the same, cases, including how many times they've been fired, primer, same lot of powder ect are the same it must be your chronograph.

At least I've never had that happen anyway.















Stay thirsty my friends

 

[RELH]

Several things could have caused that beside your chrony being off. If the group with the powder increase had the bullet seated out further, that would drop internal pressure which drops velocity. 20-30 thousand difference in seating depth can change pressure up to 6000 psi and beyound if you are near a max load.

Another cause could be your brass. A different brand of brass can increase or decease the pressure again and drop velocity. Good example is Remington brass Vs. Winchester brass. The Remington brass has slighty thicker walls and less internal space compared to Winchester. What may be a max safe load in the Winchester brass, could become a hot load that opens primer pockets in the Remington brass if powder and bullet and seating depth is same for both brands.

Using new brass can up velocity over once fired brass that you only neck sized and the brass is larger after fireforming in your rifle chamber and has more internal space over the new brass.

Switching cans of powder with different lot numbers can do it even if the powder is the same on the can label.

RELH

 

[chessidawg]

what the others have said and are you running a bore snake or cleaning the bore between your 3 round string or 5 round strings that will slow your bullet speed to

 

[stpeterhunter53]

everything the same.power out of same can,primer same,coal same,cases some shot 5 times some shot 2 or 3 times ,fl all cases,just 1/2 gr.more of power and it 50 ft.slower?? thank guys its a hard one for me

 

[mtmuley]

Do it again. mtmuley

 

[BIGJOHNT]

Temperatures the same ?

 

[greyghost]

I had the exact same thing happen to me with the same cartridge and same bullet you are using. The only thing different from your load to mine was I am using IMR 4831. I was under the impression that at some point with a charge you can go over the max velocity and start losing fps with a larger charge. My brass powder and length were all contestant. The only difference I had with my load was the bigger charge giving me a loss of FPS.

 

[Pre64]

>I had the exact same thing
>happen to me with the
>same cartridge and same bullet
>you are using. The only
>thing different from your load
>to mine was I am
>using IMR 4831. I was
>under the impression that at
>some point with a charge
>you can go over the
>max velocity and start losing
>fps with a larger charge.
>My brass powder and length
>were all contestant. The only
>difference I had with my
>load was the bigger charge
>giving me a loss of
>FPS.


That was my thought also. At some point you may have more powder than will burn before the bullet leaves the barrel. Especially with slower burning powder. Plus, you have a dirtier barrel and a hotter barrel. I don't three to seven minutes is enough to cool a barrel.