J
Jbordi
Guest
Can a bad bedding job on a rifle affect the shot to shot velocity?
Bill Wynne
Active member
P
pacecil
Guest
If the gun moves backward in recoil, or in the bedding, then bullet velocity will be reduced. Consider the extreme where a cartridge is fired in the open and the case is allowed to move away from the bullet, the pressure, and thus the bullet's velocity falls off considerably. The weight of the gun is much more than the bullet however, so gun movement's effect on velocity is very low.
L
Louis Boyd
Guest
A quick calculation shows that if an 8 lb 308 rifle shooting 168 grain bullets with 43 grains of IMR 4064 is fired, (about 2650 fps) then it is fired again with a two pound stock completely detached the difference in bullet velocity will will be close to 3 feet/second because of the reduced mass and higher recoil velocity of the barrel assembly alone . It seems to me that poor bedding is not a likely cause of significant bullet velocity variation.
So what does cause bullet velocity variation?
Some possibilities include:
Pressure variation:
a. charge weight variation
b. charge initial temperature variation
c. primer variation
d. firing pin strike variation
e. case capacity variation (brass weight or shape)
f. engraving force variation.
g. brass neck tension
h. anything which causes burn rate variation.
Blow by
a. brass neck thickness relative to chamber neck dimension.
b. seating depth (combined with neck space) can allow some propellant gas to blow around the bullet before it engraves and seals the bore.
c. bullet deformation can affect how well bullets seal on the lands before, during, and after engraving.
d. bullet diameter can affect how well the bore seals after engraving.
variable bore friction
a. propellant residue
b. metal fouling
c. barrel temperature, bullet temperature, differential expansion.
No doubt there are other factors. To get velocity variation either the mass of the bullet or some force(s) applied to the bullet must vary from shot to shot. That still leaves a lot of possibilities.
So what does cause bullet velocity variation?
Some possibilities include:
Pressure variation:
a. charge weight variation
b. charge initial temperature variation
c. primer variation
d. firing pin strike variation
e. case capacity variation (brass weight or shape)
f. engraving force variation.
g. brass neck tension
h. anything which causes burn rate variation.
Blow by
a. brass neck thickness relative to chamber neck dimension.
b. seating depth (combined with neck space) can allow some propellant gas to blow around the bullet before it engraves and seals the bore.
c. bullet deformation can affect how well bullets seal on the lands before, during, and after engraving.
d. bullet diameter can affect how well the bore seals after engraving.
variable bore friction
a. propellant residue
b. metal fouling
c. barrel temperature, bullet temperature, differential expansion.
No doubt there are other factors. To get velocity variation either the mass of the bullet or some force(s) applied to the bullet must vary from shot to shot. That still leaves a lot of possibilities.