Seating depth affecting sd and Es

[BBR]

Morning looking for some opinions before I go playing with seating depth too much I shot some groups last night and found that the Berger vld shot great 10thou off the lands they were 5.4 Sd and 12 es but when I moved to 20thou off the group wasn’t quite as good but the Sd dropped to 1.4 and Es was 4 both 6 shot groups could that be seating depth or more to do with my reloading eg neck tension

 

[Muir]

You need to shoot a much larger sample.~Muir

 

[Mungo]

Out of boredom in a Zoom meeting, I ran a quick statistical simulation.

As Muir says, this tells you nothing - it could easily be a fluke. To be certain, you need to do another 5 groups (minimum) of each. You effectively have a sample size of one (a single group).

People don’t like hearing this because getting statistically robust sample sizes is slow and expensive...

 

[BBR]

Out of boredom in a Zoom meeting, I ran a quick statistical simulation.

As Muir says, this tells you nothing - it could easily be a fluke. To be certain, you need to do another 5 groups (minimum) of each. You effectively have a sample size of one (a single group).

People don’t like hearing this because getting statistically robust sample sizes is slow and expensive.

 

[BBR]

don’t mind doing more tests was mainly just wondering if seating depth has that bigger impact on Sd and Es I’m pretty new to reloading really and still learning everyday cheers for reply’s tho

 

[Leics_stalker]

I found an interesting piece on the Berger website when looking for something else this morning, hope this helps. Link below :

VLD - Making it Shoot

VLD bullets are designed with a secant ogive. Berger VLD bullets are consistently and exceptionally capable of putting game down quickly

bergerbullets.com

 

[Loler UK]

An sd5.4 Sd and es12 is exceptional if it is that good consistently. Like muir & others said, I'd guess that your sample just saw the stars align on both groups.

Different depths may bring a more consistent bullet release and your es & sd improve. Charge, seating depth depth and neck tension optimisation will all contribute.

What range are you shooting at? You may find a harmonically sound combo that prints tiny groups even with a larger es & sd

 

[Tim1]

You need to shoot a much larger sample.~Muir

Punctuation might help too.

 

[BBR]

An sd5.4 Sd and es12 is exceptional if it is that good consistently. Like muir & others said, I'd guess that your sample just saw the stars align on both groups.

Different depths may bring a more consistent bullet release and your es & sd improve. Charge, seating depth depth and neck tension optimisation will all contribute.

What range are you shooting at? You may find a harmonically sound combo that prints tiny groups even with a larger es & sd

I’m shooting at 100 yards at moment but plan on shooting upto 800yards ive been trying loads of different combinations between n555 and rs60 with 130vld Berger 140eldm and 143eldx to be honest I’ve messed about far too much I’ve had some amazing groups and sd/Es but never been happy with the speed so now I’ve just said **** it and gone with rs60 43gr and Berger 130vld 2700fps .3” 6shot group probably not ideal but think a lot of my problem now is my shooting technique just don’t want to mess with seating depth if it’s not going to dramatically change things at the moment

 

[Brave Echo Niner]

Rifle Caliber – What The Pros Use

Welcome to “What The Pros Use” 2018 Edition! I recently surveyed the top ranked shooters in both the...

precisionrifleblog.com

This may be worth a look, these guys are shooting 100-1000m as a regular course, the section about average SD at the bottom may be of interest.

If the SD of 1.4 is a true representation (as pointed out sample size may bias this) then you're doing pretty well!

Ben

 

[xavierdoc]

I’m shooting at 100 yards at moment but plan on shooting upto 800yards ive been trying loads of different combinations between n555 and rs60 with 130vld Berger 140eldm and 143eldx to be honest I’ve messed about far too much I’ve had some amazing groups and sd/Es but never been happy with the speed so now I’ve just said **** it and gone with rs60 43gr and Berger 130vld 2700fps .3” 6shot group probably not ideal but think a lot of my problem now is my shooting technique just don’t want to mess with seating depth if it’s not going to dramatically change things at the moment

I think you're identified the trap that many fall into: excessive development and change. This produces a lot of data, but usually of poor quality (see statistical significance, above in this thread and in the Precision rifle blog that Ben linked.)

Don't forget that the throat erodes during all this development. See here for a summary from which this quote is taken:

<<<we saw it is common for that lands of a barrel to erode by 0.004-0.007” every 100 rounds.
That means if we’re in a major PRS/NRL match where you fire 200 rounds over two days, by the last stage our bullet jump will be 0.008-0.014” more than it was on the first stage! So, if the experts are saying that changing bullet jump by just 0.002-0.005” can have a “dramatic” impact on precision, what will 2-7 times that much do?>>>

The above is the justification for developing a "jump-tolerant" load. Instead of seating for 10thou jump, you work up a load at 100thou jump: the subsequent erosion is a smaller percentage change when you start at 100thou jump compared to 10thou.

Alternatively, chase the lands by periodically reducing seating depth (but this can influence internal ballistics and neck tension so...!)

 

[xavierdoc]

Out of boredom in a Zoom meeting, I ran a quick statistical simulation.

As Muir says, this tells you nothing - it could easily be a fluke. To be certain, you need to do another 5 groups (minimum) of each. You effectively have a sample size of one (a single group).

People don’t like hearing this because getting statistically robust sample sizes is slow and expensive...

So true.

I guess he could do a (statistical) power calculation and use it to determine how many groups he needs to shoot to detect a statistically significant difference between load recipes but personally I don't have the time to do this or the multiple shoots to try it!

 

[jcampbellsmith]

You're off to a good start with better SD and ES than I ever get. https://www.youtube.com/channel/UCianqsXOUlcWAnyTsQ4FlIw is worthwhile having a look at. I like Erik's style.
Best regards
JCS

 

[BBR]

Thanks everyone but now I’m head scratching again just been out and shot multiple rounds at 10and 20 off lands and my Sd is all over first 6shot string was Sd of 8 then next was 10 then jumped upto 22 really tight groups but I just seem to be all over now gutted as I really thought ide cracked it for this load

 

[Mungo]

Rifle Caliber – What The Pros Use

Welcome to “What The Pros Use” 2018 Edition! I recently surveyed the top ranked shooters in both the...

precisionrifleblog.com

This may be worth a look, these guys are shooting 100-1000m as a regular course, the section about average SD at the bottom may be of interest.

If the SD of 1.4 is a true representation (as pointed out sample size may bias this) then you're doing pretty well!

Ben

There is no way that an s.d of 1.4 is a true representation with a sample of 6.

None whatsoever. There is absolutely no point at all of making any decisions at all based on that sample.

 

[Mungo]

Thanks everyone but now I’m head scratching again just been out and shot multiple rounds at 10and 20 off lands and my Sd is all over first 6shot string was Sd of 8 then next was 10 then jumped upto 22 really tight groups but I just seem to be all over now gutted as I really thought ide cracked it for this load

What you’re discovering is that groups of 6 don’t give you any real idea of what your actual distribution is.

And if the groups are tight, it’s also beginning to tell you that the variation doesn’t matter.

 

[BBR]

What you’re discovering is that groups of 6 don’t give you any real idea of what your actual distribution is.

And if the groups are tight, it’s also beginning to tell you that the variation doesn’t matter.

I know 1.4 isn’t achievable all the time and probably an anomaly but over the last 100 rounds my Es and Sd have been low and when I shoot 6 I do shoot multiple sets off the same round iam going to load up 20 or 30 tonight and go shoot them tomorrow