FPS variation

B&G Clinger

What is an acceptable variation in speed, of a bullet loaded to precise specifications?

Allow me to give you some background to my question because I am not a reloader. But my brother-in-law has recently taken up reloading. He is currently reloading rounds for his .308 rifle. I wish I could give you more specifics about the powder and the bullets he is useing but I simply dont have the answers. I can tell you he is very precise. He made up some cartridges from the low side of the specified charge to the high side of the specified charge and now makes all of his bullets at a specific powder charge that yield the best results for his particular rifle.

Now we were out shootin last week, and sending some rounds down range through a chronograph and we clocked rounds going around 2560 FPS. He had a difference in speed of about 25 FPS from the slowest to the fastest.
That seems very good to me, but is that normal? Or is factory ammo just as consistant as far as speed goes.

The factory ammo we were shooting out of our 40 caliber pistols were going less than 1\2 that speed and fluctuated over 100 FPS?

jonk

Best I've managed with handloading is to get within +/- 5 fps. With factory or surplus I've seen variations up to 100 fps, with about 20-40 being kind of average.

cpermd

8 fps +- is my best. But with a $180 chronograph.
Didn't group any better than my loads at 28+-
So crap! I just can't figure this stuff out logically.

CP

zimmden

20 fps variation is very good. Better than most factory loads. Variation of small amounts is not critical to accuracy. Many variables contribute to accuracy or lack thereof and to fps variation. Powder type and accuracy of charge, bullet variation even of same lot, primer variation, temperature and humidity, quality of prepped cases (neck tension, OAL of brass and load not to mention the variations occurring in the gun as it heats up or barrel fouls. By eliminating as many variables as possible, benchrest shooters can shoot sub 1/4 inch groups at 200 yards.

B&G Clinger

Not be a reloader, I thought it was pretty impressive. He shoots a "cold bore shot" then a three shot group to see how the accuracy is. At 100 yrds he can cover all three holes with a quarter every time.

Mobuck

I use a very low priced chronograph with many years use on it. I don't get really great consistancy and I don't think it's my loading proceedures. I hoped Santa would bring me one this year but got a shirt instead.

yonson

zimmden made some good points, there is another to add to the mix. According to Elmer Keith, if the powder does not fill the inner space after bullet is seated, the flame front can vary depending on which way the powder leans. He minimized this variable with a small ball of toilet tissue on top of the powder to fill the space & keep powder bunched up. Have heard of other things being used including dacron wool, corn meal etc. The list of variables goes on & on, but he felt this was important - the man did A LOT of shooting.

Rocky Raab

Elmer also blew up more than one or two guns.

Powders have MUCH improved since Elmer wrote his stuff on a manual typewriter by the light of a kerosene lamp. These days, fillers are strongly discouraged, especially in bottleneck cases where they can become obstructions under some circumstances.

To the original question, at all but long range, velocity variation doesn't predict accuracy very well - if at all. Why it doesn't goes against intuition, but that is so. That said, 100 fps spread is something I'd view as resulting from some basic incompatibility between primer, powder, and bullet. One of those things doesn't play well with the others, to put it simply. On the other hand 25 fps spread shows that the load is well balanced. If it also happens to be inaccurate, I'd look to other causes like the gun, the scope -- or the jerk on the trigger!