Speed decreases with more powder

[cbrick]

Utilimately it seems that I've made a booboo. The 308 info was for a cast boolit and now I see read that I should keep them under 2k fps.

36.1 2233
37.0 2264
38.0 2381
39.0 2382

Nothing wrong with cast over 2,000 fps "IF" it's working. By working I mean is it accurate? Is it consistent? Is it leading? You never said what bullet your using, if it's a light bullet velocity will of course be higher. In my 308 I shoot 160 to 180 grains right around 1900 fps. Not because it's under 2000 but because as I worked up the load that's where these bullets grouped well and with repeated 10 shot chrono tests the chrono told me it is a very consistent load. Also for the shooting I mostly do with this rifle it is at a power level that is adequate, mostly 200 meter handgun silhouette targets.

Consistency of the load is the prime reason and prime value of using a chrono. If all you want is a vague idea of velocity fine, shoot 5 shots but that's all you will have . . . A vague idea.

The more shots fired the more confidence you can have that additional shots fired with that load made with the same components in that firearm will fall within the parameters of the tested rounds. When 5 shots are fired and the one shot that is screaming at you that this load IS NOT consistent is omitted you can have full confidence that many of the additional rounds fired will be well outside the parameters of the test rounds.

Hope this helps.

Rick

[popper]

Echo - average and mean are NOT the same thing. Sum/# vs 1/2 above, 1/2 below.

[geargnasher]

Echo - average and mean are NOT the same thing. Sum/# vs 1/2 above, 1/2 below.

You gots it.

Gear

[C.F.Plinker]

I thought 1/2 above and 1/2 below was the median.

[HangFireW8]

I thought 1/2 above and 1/2 below was the median.

You thought right.

Mean = Average.

Median = midpoint.

C'mon folks, just type "definition:average" into Google.

HF

[felix]

This one might be mo'betta'............

http://www.purplemath.com/modules/meanmode.htm

... felix

[303Guy]

Perhaps the root mean square would be more meaningful? Oh shucks. I don't even remember what the root mean square is! Just kidding.

[bobthenailer]

I ran into this same thing when working up loads for 454 Casull revolvers , i peaked velocity at 38 grs of 296 with the Hornday 240 gr mag XTP , I tried 39 & 40 grs and got less velocity than with 38 gr charge.