Thread: Lower than expected velocities

Originally Posted by grandpamac

Greetings No 3.
Trying to guess velocity based on range drops is a pretty rough method. Just chronograph the load and you will know the velocity assuming a half decent chronograph. The BC for a projectile is not carved in stone and varies with conditions and even from shot to shot. Most data these days is for 24 inch barrels and I think that your actual velocity is higher than you think.
Regards Grandpaneil.

I have a Magnetospeed V3, but problem was I had it set up with the can on the rifle and subsequent testing with the subs confirmed that the chrony does not like the extra clearance between the bullet flight path and the sensor bayonet when the can is fitted. I have seen people get a spare sensor bayo and trim the attachment belt area right down to fix this, or the other option is a Xero chrony I guess. The trajectory vs pill weight is coming out with a velocity figure within 25fps for everything I've run the numbers through - about 5 apps now.

It's indicating that the velocity is WAY below factory box figures (2880 muzzle vs calculated less than 2600) regardless of any other factors, and the impact point at 300m was stupid low. It's not confirmed for velocity but it's near enough that the other variables are only going to make a minor difference to the calculated fps - I need to find several hundred fps to get the impact point at 300m close to box trajectory. As is with a point blank hold the pill will drop right under a large bodied animal if aiming for the centre of organs/hilar area. Really need more than a 225m point blank range out of a .308 to be honest!

I agree it's not the most accurate but it's enough to know that the ammo is not useable as is, so the answer is more testing firstly and secondly abandon the Winchester ammo (not in stock now so can't be replaced anyway) and find a load that will perform. The Win ammo was a holdover from another .308 and I was just using it expecting similar performance out of the newer firearm but ended up with a WTF? moment.

If I could find three rounds of the Sako I'd bung that through and see what it does as a couple of 50-round boxes of that would see me sorted for the next few years of hunting out of this rifle.