Is there any correlation between low standard deviation and good groups? I've started recording the average velocity and standard deviation for each 5 shot or 10 shot string and was told the smaller the standard deviation the more accurate the load. Yet, the lower standard deviations so far does not mean the smallest group size. I may be answering my own question but can I deduce that if I get low standard deviation but not good groups the fault is mine and I need to question my own ability and tecnique?

quote:

Originally posted by steyrl:
Is there any correlation between low standard deviation and good groups? I've started recording the average velocity and standard deviation for each 5 shot or 10 shot string and was told the smaller the standard deviation the more accurate the load. Yet, the lower standard deviations so far does not mean the smallest group size. I may be answering my own question but can I deduce that if I get low standard deviation but not good groups the fault is mine and I need to question my own ability and tecnique?

Maybe, but not necessarily. There are other possibilities.

The other variable is the suitability of the load for the particular rifle. One can have low extreme spread, low standard deviation, shoot well, and still have bigger groups if the load isn't tuned to the gun. The dynamics of a rifle and bullet are complex.

Low extreme spread and low SD are really best used as indicators of the quality of some parts of the reloading job. Getting extreme spreads down into the teens on a regular basis only means the reloading process is producing consistant ammunition.

I've had one powder charge with ES in the teens produce a group twice the size of the next powder charge that had an ES over 50 fps simply because the high ES load was a better match for the rifle. To see a dramatic demonstration of barrel dynamics and cartridge interaction, load up 4 rounds of 5 powder charges in 0.5g increments to cover 2 grains. Shoot off a good rest (that allows recoil) with a scoped rifle at 100 yards. The groups will move around on the target from group to group and vary in size in rather amazing fashion. Both variations are well in excess of the expected deviation caused by shift of aim point.

I've seen groups go from 1-1/2" to all shots in a barely ragged single hole in a half grain step. What I look for is a powder/bullet/rifle combination that consistantly gives tiny groups and which exhibits less sensitivity to small powder variations of the sort normal to the reloading equipment I use.

Fitch

IMO low SD is one of the points; more important are a small runout and a good choice of bullet and bullet weight, well adapted to the barrel twist; last but not the least, the rifle ability to print tight groups, as well as shooter's skill, of course

SD realates only to the consistancy of the velocity, it has nothing to do with small groups, per se. It is really nice to have at load that shoots a small group AND at a low SD but it's coincidental when it happens. Part of the chase for a good load is attemping to get them together.

Low SD is really not very important when shooting out to as much as 300 yards but past that a low SD really shows up in the vertical stringing of a group.

I have had several loads with very low SD one was federal premiums 165 they had a 5 fps sd for 10 shots Shot them out of a 1.5 inch gun got 1.5 inch groups.

The other was a 315 gr hard cast load not sized no gas check 44 mag load had a sd of about 2 fps. about a 2 inch group out of a red hawk. Gased checked and sized the bullets same load sd about 30 one ragged hole at 20 yards lost 50fps over all vel.

Does in matter yes and no is it nice to have yes. More so when one gets out past 300 yards.

SD is about the consistency of the load, and will really make a difference for the long range applications. However if the barrel doesn't like the harmonics generated the load may shoot for SH_T!

I always work my loads up without the chronograph until I get a consistantly accurate load. THEN I use the chronograph to find out what the speed and standard deviation is. I can play with it a bit to see if improving the SD helps or hurts the accuracy but I would rather have a load that shoots .5 MOA with a 2% SD than one that shoots 1.5" groups with a single digit SD. My experience has shown that at normal hunting ranges there is no correlation between the standard deviation and accuracy.

Thanks everyone for the replies and "food for thought".

Glen Zediker (Handloading for Competition) states that lowering the SD below 12 doesn't correlate to any improvement in grouping. Sounds like an empirically derived statistic, but Zediker has plenty of experience.
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quote:

Originally posted by PaulS:
I always work my loads up without the chronograph until I get a consistantly accurate load. ...

Hey Steyrl, That is the way to go about Reloading. Locating a Barrel harmonic that provides excellent accuracy is way more important than anything a chronograph can give you.

Even knowing the actual Velocity is of no use once a person realizes they can "guesstimate" the velocity close enough to get onto the Target at distance. Then the actual Drop Rate should be determined by what the Points-of-Impact indicate rather than some computer generated Drop Chart that has no correlation with the firearm.

Best of luck to you.

quote:

Originally posted by Hot Core:
[QUOTE]
Best of luck to you.

Thanks Hot Core for the reply.