Seating the Bullet for ULR

[Ralpharama]

I am about to get around to experimenting with the seating depth of the ELD-Ms fro my 6.5 Creedmoor and later on the their big brothers for the .338 Lap

I always do such development in an indoor 100yard range to eliminate wind issues and tend to use a bench rest to remove as move of my own incompetence from the recipe as possible.

In the past I have found that group size and minimum SD haven't seemed to go hand in hand. I have had amazing groups at 100 yards but the SD hasn't been the best and the best SD hasn't equated with the tightest group. 

WHat I don't know is which is the most critical. Does a tiny group at 100 necessarily equate to a similarly tiny group at 1000? Or does the minimal SD have more meaning at a long distance than a miniscule group at 100?

 

[DaveT]

To me a Low SD indicates that you should minimise  vertical dispersion at range because most of your shots are around the same MV.

Logically you would think that this tends to support tight groupings but anecdotal evidence varies.

Once beyond close range grouping all sort of issues can start dispersion which queers long range grouping.

Quirky winds,  bullet no longer supersonic, mirage, not getting atmospherics rignt, ... a long list!

Either way a low SD (<10) is obviously desirable.

[Popsbengo]

1 hour ago, Ralpharama said:

I am about to get around to experimenting with the seating depth of the ELD-Ms fro my 6.5 Creedmoor and later on the their big brothers for the .338 Lap

I always do such development in an indoor 100yard range to eliminate wind issues and tend to use a bench rest to remove as move of my own incompetence from the recipe as possible.

In the past I have found that group size and minimum SD haven't seemed to go hand in hand. I have had amazing groups at 100 yards but the SD hasn't been the best and the best SD hasn't equated with the tightest group. 

WHat I don't know is which is the most critical. Does a tiny group at 100 necessarily equate to a similarly tiny group at 1000? Or does the minimal SD have more meaning at a long distance than a miniscule group at 100?

 

Firstly an SD from say five rounds is statistically highly suspect.  I'm not suggesting that's what your doing but it's not uncommon on shooting forums to get people claiming SD of groups of three to five shots !

Of course the less variation in muzzle velocity the better but to realise the benefit the barrel harmonics need to also be optimised.  If your bullets exit the barrel while it's 'off node' then variations down range are amplified.

Just to complicate matters, there's the effect of positive compensation where Mv variation and barrel harmonics work to reduce elevation errors at certain distances - Lee-Enfield .303 is the usual cited example.

Bullet stability isn't necessarily optimised at 100yds so groups may give false readings that are shown at greater ranges.

I zero .338 at 200yds as this seems to give me a better reading of my groups at long ranges.  Obviously this means outdoors however I've not experienced any problems at that range with wind on typical weather days.