Standard deviation.

[headhunter1111]

I went out to my range today to test a few loads I've been working on for a 243 Varmint rifle. My question is, what should I look for as far as SD goes in my loads? My best group was right around 3/4 MOA which I am not worried about as I was only experimenting with powder charges so far and more tuning will shrink this. The extreme spread was 31fps and SD was 10.25. This seems pretty promising to me but I won't know for sure until I test it further. I am wondering what you guys would suggest I aim for in a long range P-dog round. Is it worth making any major changes to this loads primers or powder charge or should I stick with this and just tune it in (ie minor changes in powder charge and seating depth)?

 

[jonbearman]

What kind of rifle and what twist is it.From what you are saying I think you need to do more load development to get the numbers down to single digits. I think you should try different powders like varget and h4831sc and maybe others. What bullet weights do you like?

 

[cmillard]

i found with my loads that the es/sd shrank considerably if i jammed the bullets vs jumped. went from high double digit es to near single digit es when i jammed them. give that a try if you want and report your test

 

[K22]

If you have a heavy barrel 243 varmint rifle you should be able to squeeze the groups down to 1/2 moa or under. This shouldn't be hard to achieve with IMR 4350 and bullet weights in the 80 to 87 grain range. Try the Sierra 80 grain Blitz or 85 Boat Tail Hollow Point. If you can shoot consist five shot groups around 1/2 moa I wouldn't be concern with the standard deviation of the velocity.

By the way, in my opinion, the 243 is the best long range varmint rifle going and I've tried just about everything.

 

[Steve Blair]

I went out to my range today to test a few loads I've been working on for a 243 Varmint rifle. My question is, what should I look for as far as SD goes in my loads? My best group was right around 3/4 MOA which I am not worried about as I was only experimenting with powder charges so far and more tuning will shrink this. The extreme spread was 31fps and SD was 10.25. This seems pretty promising to me but I won't know for sure until I test it further. I am wondering what you guys would suggest I aim for in a long range P-dog round. Is it worth making any major changes to this loads primers or powder charge or should I stick with this and just tune it in (ie minor changes in powder charge and seating depth)?

The 31 fps will probably mean about 2" elevation at 500 yards. It might mean a miss but might not. Most rounds would likely have velocity toward the mean. It is always desirable to reduce ES/SD as much as possible but may not show a practical benefit. Primers often have a large influence on velocity variance. Milder primers in case capacities like the .243 are proven performers. Wolf or CCI are good candidates.

 

[headhunter1111]

Jon, I would like to get it down a bit, I'm just wondering what the practical benefits are going to be of switching around major components. I'm thinking I'll keep tweaking this load a bit to get the numbers down. It.s a 10twist douglas 5A contour air gauged xx barrel set on a Ruger action. I've shot some 1/2 moa 5rd groups with several loads using match bullets but I'm trying a load for 95gr Nos Ballistic tip now (higher bc with the explosive effect I like). I've heard these are a bit tricky to tune. I'm using 4831sc right now as I've found my rifle likes this with any bullet over 75 gr so far.
Cole-I'll give that a try and see what happens.
k22- I have been wanting to try the blitz kings for a while. I might get a box to play with. Usually if I get a load to shoot 3/4moa or better on the first time out I can shrink the group size down to 1/2 moa pretty easily. 1/2moa is my ulitimate goal as I have not found any practical value (in a varminter) that warrants buying extra components too shave 10ths of an inch off group sizes.
Steve, I'm currently using CCI br primers I might try some 200's and I've been wanting to get a box of Wolf for some time, Never have them at the local reloading shop so I may order some.
Thanks for the input gentlemen.

 

[K22]

Believe me, IMR 4350 works really well in the 243 especially with the 80 grain and above bullet weights. I agree, chasing that extra 1/10 moa is not a worthwhile endeavor for a varmint hunter unless you are rich or like doing that sort of thing.

At the range I see shooters chasing ultra tiny groups off sand bags and that's fine if that's your game. My game is knocking out groundhogs and coyotes in the field so I rarely shoot off the bench, only when testing loads and or sighting in a scope. When I go to the range I practice shooting under field conditions which for me is using a shooting stick. I get a lot of weird stares but I'm a hunter, not a target shooter.

My point is that once you get a reasonably accurate load, spend your time and money practicing in your choose field position. It will pay big dividends as opposed to a few tenths tighter group.

 

[artbosco]

I went out to my range today to test a few loads I've been working on for a 243 Varmint rifle. My question is, what should I look for as far as SD goes in my loads? My best group was right around 3/4 MOA which I am not worried about as I was only experimenting with powder charges so far and more tuning will shrink this. The extreme spread was 31fps and SD was 10.25. This seems pretty promising to me but I won't know for sure until I test it further. I am wondering what you guys would suggest I aim for in a long range P-dog round. Is it worth making any major changes to this loads primers or powder charge or should I stick with this and just tune it in (ie minor changes in powder charge and seating depth)?

Work on tuning with ... powder, seating depth, and neck tension [if you have that capability].

When you have your barrel tuned to the point that bullets are going through the same hole or very close to it, using two or three of the components above, then take note [for historical purposes only] of the ancillary or noncontributory measurements of velocity, ES, and SD.