ES/SD vs group sizes...

[Judd]

I had something happen that I haven't had happen before last weekend and I wanted to get y'alls take on it.

Normally the groups that have low ES/SD #'s group well or at least I can find a seating depth that will shoot tiny. I have a load that is shooting better with CCI450's than the Fed205's but the ES/SD numbers are 44/18 first 5 shots and 41/17 the second 5 shots. Interestingly enough they group.

I normally find the low ES/SD and then fine tune that to tighten up. Would you even mess with this load? Just shoot it and don't worry about the numbers? Just a little confused as to where to go with this deal.

Equip - 6 dasher, Varget and over an Ohler 35 chrono

 

[Terry]

They may group at 100 yards, but they won't at 600 or 1,000.

 

[22BRGUY]

They may group at 100 yards, but they won't at 600 or 1,000.

Ditto that

 

[Judd]

This was 200...I should've specified that, thanks. Are the Fed's normally lower in ES/SD or just depends on the barrel?

 

[searcher]

The S.D's can vary from load to load. Changing anything can affect them, including primer selection. When getting bad S.D.'s - a primer change (or a powder change and keeping the same primer) - can often cure the problem. I often have had bad (high) S.D.'s using magnum primers when the powder was not a 100% fill. I too believe you won't see good groupings further out.

 

[ShootDots]

I will give you a REAL LIFE scenario that happened to my 'smith. He built a straight .284 and was shooting 180 Hybrids. He had almost no time to develop a load as our 1000 yard match was less than a week away. He put a "known load" (I don't know what the load was exactly BUT it was with H4831) in it he developed for a few of his customers that usually worked pretty well. He went to our club and he shot several 5 shot groups @ 300 yards that were in the vicinity of 1 inch. When he was at the match he could not buy a 10 ring hit. 12 o'clock / 6 O'clock back and forth... He was frustrated because it shot so well at 300 yards. I told him it looked like his e.s. were high. He went back later and ran the load over the chrono>> His e.s.'s were 35-40f.p.s.! He was at a loss. I told him that in many instances H4831 is well served by Fed 210GM's. He switched and immediately his e.s.'s went down to 12-15f.p.s. He continued work on the load and got his e.s.'s inside 10f.p.s. My telling you this is to show how sometimes PRIMERS can and do make a very significant difference. That is only one aspect.. Powder, powder charge(s), seating depth(s) and neck tension can all contribute to high OR low e.s.'s... It is the "cumulative effect" of all those "areas" symbiotically working towards accuracy and low e.s.'s.. Any one of them can make a significant difference.. Trial and error is the only way to find out and NEVER change more than one item at a time..

 

[amlevin]

They may group at 100 yards, but they won't at 600 or 1,000.

Ditto that

A recently developed ballistics app shows how SD increases drastically decrease the probability of a hit at 1,000 yards. An SD of 10 or less can yield 1st round hit probabilitys of over 90%. Let that SD grow to 20 or so and the probability of a first round hit drops to less than 5%. Of course it's not all SD but accuracy of wind calls as well. Point being, if you have high SD's they probably won't show up as big errors in short ranges but as the bullet starts to naturally loose velocity, the built in error at the beginning becomes huge.

 

[Judd]

Thanks guys, that is what I thought. I will figure it out.