What is acceptable velocity variation

[ken snyder]

Guess I should of given a few basic rules to help.

Never mix brand or lot numbers - cases, primers, powders and sometimes even the same bullets from a different box.

Brass uniformity and Brass uniformity, they must all be identical twins and without differences such as wall thickness and flash hole - one thing I see people overlook is forgetting to clean the re-sizing lube out of the mouth of the case, some will end up with more or less and that's not good

Barrels in different states of fouling or cleanliness will not shoot the same velocities ( a forum topic with good but sometimes seemingly conflicting advise)

It's a willingness to be a robot and perform the same functions the same way every time. It sounds confusing but once you get into it then it is actually as simple as making cupcakes

The fastest jump start I know of is a book by Glen D. Zediker "Handloading for Competition" ( or similar reading) And all the forum space here on LRH

[Craig1972]

posted duplicate message.

[Craig1972]

I am not ready to start reloading, but I have been spending the money on quality factory loads and my Variation is much too high. It's at about 60 now. I use Federal Fusion 180 grain for my .300 Win Mag. My highest velocity out of ten shots was 3085 and my lowest was 2964. I believe that gives me a 61fps Velocity Variation. Is that the best I can expect from a Factory load? Even a quality one like Federal Fusion? Thank You.

[jasent]

Originally Posted by cornchuck

If a guy has a high variation in velocity, what can be changed to get it under 10 fps?

Jason

consistency! I sort bullets by bearing surface,uniform primer pockets,weigh every load! Here is a system I use and has helped me improve groups at long range and velocity spread. My 243 shoots es of 3 and sd of 9.
Hand Loading for Long Range 1: Brass Prep
Read all his steps.

[Bart B]

In my experience chronographing loads, the cause of large muzzle velocity spreads has nothing to do with the ammo or rilfe. It's how inconsistantly hard the shooter holds the rifle against his shoulder. I've seen a 55 fps difference in average velocity between me and a friend shooting the same rifle and 30 caliber magnum ammo. I could easily cause a 40 fps spread myself holding that 13 pound scoped magnum hard to soft to my shoulder. A friend reported he an another person had over 90 fps average fps difference shooting the same .308 Win. ammo and rifle. Therefore, I'm usually skeptical about quoted fps spreads for a given load.

If the huge human variable's removed and the ammo's shot in a fixed barrel or a repeatable rest, muzzle velocity spreads will be much smaller. Which is why arsenal and some factory ammo's tested with fixed barrels in universal receivers.

Ballistic software will show 180-gr. bullets from a .308 Win. will have about 3.7" change in drop for each 10 fps difference in muzzle velocity at 1000 yards. 30 caliber magnums' drop difference for the same velocity change and range is about 2.3 inches. At 600 yards, the drop numbers are 0.9 and 0.6 inch, respectively.

But often that difference is compensated for by bullets leaving on the muzzle axis upswing of its whip. Slower bullets leave later at a slightly higher angle and strike the same point as their increased drop down range is corrected for.

If you ammo's shows a 20 to 30 fps spread in velocity, that's good. If it's more, that may not be a problem. Your barrel may well whip such that compensation happens in your favor. Test your ammo at long range and you'll probably be surprised at its performance. I've shot more than a few rounds from prone through a chronograph and at 1000 yards, the vertical shot stringing was less than ballistic software calculated it to be. My barrel whip was compensating for the velocity differences.

[NMcCullough]

Originally Posted by jasent

consistency! I sort bullets by bearing surface,uniform primer pockets,weigh every load! Here is a system I use and has helped me improve groups at long range and velocity spread. My 243 shoots es of 3 and sd of 9.
Hand Loading for Long Range 1: Brass Prep
Read all his steps.

I could be wrong, but won't ST DEV always be less than ES?

[jasent]

Originally Posted by NMcCullough

I could be wrong, but won't ST DEV always be less than ES?

yes I got those backwards