First Time Reloading Question

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codypage76

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texas
Howdy
I'm new to reloading, and my last trip to the range left me befuddled.
bullet: .308 168gr. AMAX
case: federal match
primer: CCI Larger Rifle No. 200
powder: IMR 4895
I loaded up a latter to see how man grains of powder my rifle liked the best and I got some unusual results.

41grains 41.5grains 42grains 42.5grains 43grains
2699 2666 2634 2622 2559
error 2640 2620 2603 2554
2692 2638 2620 2607 no shot
2685 2684 2635 2597 2495
2699 2664 2672 error error

2693.75 2658.4 2636.2 2607.25 2536 <- MEAN
14 46 52 25 64 <- Hi-Lo Range

Why do my velocities drop? shouldn't they increase in FPS with increase in powder! I never exceeded the recommended max load for the powder? Someone please give me some insight.
 
I've seen numbers like this before when a friend insisted on placing his chrono about 6 feet from his muzzle. If you were less than 10 feet away try shooting about 15 feet from the chrono. The blast may be messing up the reading. You should see a significant increase in velocity with a 2 grain bump in charge.
 
Point of no return.

Google your issue.
I've seen a mathematical explaination for diminishing velocity.
But I don't remember where I saw that or I'd provide a link.

But at some point when you increase the powder, you go beyond that sweet spot.
 
I also believe the chrono is too close. Looking at the whole of the data, the numbers are not changing either up or down over the entire test. There are some outliers, but they could be caused by many factors.

;)
 
Many thanks for they help every one. I was shooting at the only range in north houston that will let me chrono. The down side was that the range ran down hill so quick that the chrono tripod was Maxed out in height so it may have been a little close.
Also to anybody who uses load manual Hornady 9th Edition.
There are two sections in .308 and .308 service rifle.
If you look at the powder IMR 4895 for 168gr AMAX
one says max load is 43.3 and the other says 41.4
is this because the service rifle has a faster 1:10 twist over the 1:12?
 
No.

It is because a gas operated semi-auto will not handle as much pressure as a bolt-action.

The service rifle loads are tuned to prevent OP rod damage on gas operated M1 or M14 rifle.

rc
 
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