Standard Deviation Relevance... ?

[hoppes-no9]

In my experience, a high SD load is less likely to be accurate. But there are no hard and fast rules -- a low SD load can be inaccurate, and a high SD load can be really accurate.

It's fun to measure the SD and interesting to see how it changes as you get towards the hotter end (usually) but ultimately once a load is "fast enough" I go by the target not the SD.

[Park ranger]

General rule of thumb is you want a SD of 15 for 600 yards, and 10 for 1000, over 22 shots.

[Uncle Duke]

Here's an interesting article about the effects of differing standard deviations at extended range. Good vs. better vs. great, if you will.

While SD matters, the data suggests a point of diminishing return.

https://precisionrifleblog.com/2015/...oes-sd-matter/

[Pinecone]

Originally Posted by Moorvogi

0.7 inches of drop difference at 350 yards between slowest to fastest bullet.

YES, it makes a difference if i'm trimming the nut hair off a gnat at 100 yards but it's not going to make a difference for my application.

The good news is, this goes for STD DEV too.. pick middle of the row and now were're about 0.4 +/- at 350 yards. I can deal with that groundhogs cant though HAHAH.

In THEORY.

But if the load is not showing a 3/4" vertical spread, then who cares?

Case the numbers if you want, but it the load shoots a small group, it is accurate.

[Pinecone]

Originally Posted by Moorvogi

Yes it was. That’s why I write them down. I TYPICALLY take out the first and last shot but, in a hunting application ... the first shot is the one that matters most so I still document it.

For hunting, I would match my POA and POI for the cold bore shot. Or maybe split the difference between the 1st and 2nd shot.

For long range match or similar, I would set POA and POI for when the {POI settles down. But document the POA to POI difference for the first couple shots to compensate.

Hunting, I want the least things to think about for the first shot. So sight in for maximum point blank zero, POA = POI for first shot.

At the range, I use 100 yard zero, distance charts, and can dial or hold off for first cold bore shot.

[Seabee]

Neck tension was the biggest problem for me and getting numbers and groups to line up. Retired my old brass and began anew. The bullet seating effort was very noticeable between cases. Annealing helped but wasn't a cure.

[dist1646]

Originally Posted by Moorvogi

0.7 inches of drop difference at 350 yards between slowest to fastest bullet.

YES, it makes a difference if i'm trimming the nut hair off a gnat at 100 yards but it's not going to make a difference for my application.

The good news is, this goes for STD DEV too.. pick middle of the row and now were're about 0.4 +/- at 350 yards. I can deal with that groundhogs cant though HAHAH.

That is .7 just for the load difference. Now factor in the level of accuracy the rifle is capable of, then add in shooters error and that .7 rapidly becomes a miss. Something to think about.

[Pinecone]

Originally Posted by dist1646

That is .7 just for the load difference. Now factor in the level of accuracy the rifle is capable of, then add in shooters error and that .7 rapidly becomes a miss. Something to think about.

That was 0.7 inches drop difference at 350 yards.

A 1/2 MOA rifle will be shooting a 1.75 inch group.

You have to be a pretty bad shooter to make that a miss.

[Speed3]

Originally Posted by Seabee

Neck tension was the biggest problem for me and getting numbers and groups to line up. Retired my old brass and began anew. The bullet seating effort was very noticeable between cases. Annealing helped but wasn't a cure.

So I thought neck tension was always my vertical also....but baffled after a shot yestersay.

So shooting buddy was getting a sticky bolt, dropped powder charge by .7gr to get rid of that. Still grouped well.

He is loading using k&m press with force pack (measures force to seat a bullet).

First 20 pounds were 28-36lbs, the rest were double that pressure. One would assume varying neck tension would drive the seating force, yes?

His vertical at 600 was the x ring....how does that happen? Doesnt make sense in my brain.

Dropped a 599-41x! For those that dont know fclass, x ring is 3 inches.

[dist1646]

Originally Posted by Pinecone

That was 0.7 inches drop difference at 350 yards.

A 1/2 MOA rifle will be shooting a 1.75 inch group.

You have to be a pretty bad shooter to make that a miss.

I didn't take the time to run the numbers but, take that 1/2 MOA rifle shooting a 1.75" group and add the .7" difference in drop and you already have 2.45". Now, factor in a really good shooter with about a 1 MOA hold and you have 4.2". Pretty easy to miss a groundhog when optimal conditions give you only a 4.2" group, and that is without factoring in outside conditions like wind.