standard deviation
- Thread starter Dskd
- Start date
- Location
- grunthal manitoba
what the? 10fps interesting, but imopsible. please explain in more words
A standard velocity deviation of 10fps is outstanding. Also extremely difficult to get. Climatic conditions can change it. However, meticulous loading techniques can get it consistent. A consistent group at a given distance is the important part.
Neither the .308 nor .338 LM are benchrest cartridges.
Neither the .308 nor .338 LM are benchrest cartridges.
Consistency at every step of loading is required to get such fine SD. Most people look for a maximum SD that does not exceed 1%. Sunray is correct that the cartridges you list are not necessarily going to yield the SD you suggest, though it is not impossible.
I just got back from this range this evening, shooting a 7mm WSM and a 7.21 Tomahawk and had SDs of 7 to 4 in velocities between 2900 and 3400 fps. It required attention to detail in each step of reloading. In fact, it is fair to say that it required a full evening of loading for each calibre with careful weighing and measuring at each step. Such consistency is not necessary for most situations.
I just got back from this range this evening, shooting a 7mm WSM and a 7.21 Tomahawk and had SDs of 7 to 4 in velocities between 2900 and 3400 fps. It required attention to detail in each step of reloading. In fact, it is fair to say that it required a full evening of loading for each calibre with careful weighing and measuring at each step. Such consistency is not necessary for most situations.
I agree with everything said above, but i find one of the main culprits is case neck tension, or the inconsistency, of Case Uniform Neck Tension, from here on in called C.%.%.T. It can be caused by case necks that are not uniform, in one way or another, usually requiring trimming and/or turning/reaming. I realize it is only one important consideration among many when looking for that kind of consistency. Oddly enough, the low SD figures are easier to arrive at when loading with Black Powder, this may be caused simply by the lower velocities however.
Are you meaning ES (Extreme spread) or SD (Standard Deviation)
I was getting SD's of 5-6 tonight for 10 shot strings in my 6BR with 3 different loads. Extreme Spread was in the 15-20FPS range.
Feet Per Second
String 1
1) 2859.0 -2.2
2) 2863.0 1.8
3) 2855.0 -6.2
4) 2860.0 -1.2
5) 2856.0 -5.2
6) 2856.0 -5.2
7) 2862.0 0.8
8) 2870.0 8.8
9) 2864.0 2.8
10) 2867.0 5.8
High: 2870.0
Low: 2855.0
E.S.: 15.0
Ave.: 2861.2
S.D.: 5.0
String 2
1) 2876.0 -7.7
2) 2885.0 1.3
3) 2882.0 -1.7
4) 2879.0 -4.7
5) 2887.0 3.3
6) 2879.0 -4.7
7) 2896.0 12.3
8) 2883.0 -0.7
9) 2893.0 9.3
10) 2877.0 -6.7
High: 2896.0
Low: 2876.0
E.S.: 20.0
Ave.: 2883.7
S.D.: 6.7
String 3
1) 2923.0 -9.9
2) 2926.0 -6.9
3) 2937.0 4.1
4) 2936.0 3.1
5) 2936.0 3.1
6) 2937.0 4.1
7) 2937.0 4.1
8) 2938.0 5.1
9) 2929.0 -3.9
10) 2930.0 -2.9
High: 2938.0
Low: 2923.0
E.S.: 15.0
Ave.: 2932.9
S.D.: 5.4
I was getting SD's of 5-6 tonight for 10 shot strings in my 6BR with 3 different loads. Extreme Spread was in the 15-20FPS range.
Feet Per Second
String 1
1) 2859.0 -2.2
2) 2863.0 1.8
3) 2855.0 -6.2
4) 2860.0 -1.2
5) 2856.0 -5.2
6) 2856.0 -5.2
7) 2862.0 0.8
8) 2870.0 8.8
9) 2864.0 2.8
10) 2867.0 5.8
High: 2870.0
Low: 2855.0
E.S.: 15.0
Ave.: 2861.2
S.D.: 5.0
String 2
1) 2876.0 -7.7
2) 2885.0 1.3
3) 2882.0 -1.7
4) 2879.0 -4.7
5) 2887.0 3.3
6) 2879.0 -4.7
7) 2896.0 12.3
8) 2883.0 -0.7
9) 2893.0 9.3
10) 2877.0 -6.7
High: 2896.0
Low: 2876.0
E.S.: 20.0
Ave.: 2883.7
S.D.: 6.7
String 3
1) 2923.0 -9.9
2) 2926.0 -6.9
3) 2937.0 4.1
4) 2936.0 3.1
5) 2936.0 3.1
6) 2937.0 4.1
7) 2937.0 4.1
8) 2938.0 5.1
9) 2929.0 -3.9
10) 2930.0 -2.9
High: 2938.0
Low: 2923.0
E.S.: 15.0
Ave.: 2932.9
S.D.: 5.4
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