6mmBR

[No i deer]

11 hours ago, Big Al said:

Speed of wind isn't an issue, if it was a constant 10mph with no variances then the most accurate round would still be the most accurate round. When the big boys come into their own is when the wind switches during the bullets flight, they will be blown off course less than the smaller bullet so have an advantage.

Even a 1mph change in the wind over 1000yds will blow your bullet away from the last one, the less it blows it away in the smaller the group will be. Big bullets with high BCs cope with switching conditions better wether is a 1-3mph change or a 15-16mph one. 

That said Ive won a few 1000yd matches with a 6 Dasher against much bigger calibers including .338 Lap Mag on windy days so a cartridges inherent accuracy should not be overlooked.

You wouldn't expect the br to out perform a 338 in any stretch of the imagination.

[No i deer]

I didn' realise the 6mm bullet was even close in ballistic terms.figures for 1mph wind is say 2 inches then add another 9mph then the difference is really showing but this little cartridge laughs in the face of adversity it seem and is what appears to be the holy grail calibre.

Looking forward to trying one when my 6.5x47 is worn out.

BC isn' b all and end all either then.

[Big Al]

1 hour ago, No i deer said:

You wouldn't expect the br to out perform a 338 in any stretch of the imagination.

There will be a point where conditions favour a less accurate 338 simply because the bullets are less prone to being blown off course but for most of the time I will take accuracy with good BC over superior BC with less refined accuracy.

 

[gbal]

The advantages/disadvantages are relative.Though no one seems able to do it really well consistently,IF the shooter reads the wind  and allows accordingly,then there is no advantage for higher BC (assuming loads are appropriate to the distance). 

   There is a trade off,otherwise - precision (the bullet/rigs intrinsic grouping  ability) against BC,but it is not unlimited,and the balance depends in individual cases on just how much better accuracy and just what BC  advantages. A little more precision will not always compensate  for a very substantial decrement in  BC,nor vice versa.

  One other issue is probably at least as important -the accuracy potential (what the shooter adds to precision in terms of the shooting solutions added) This is quite a factor favouring some very precise relatively lightly recoiling cartridges over the "harder to shoot fast" boomers.

This  is because the string of shots can be fired off far faster  with the lighter recoil (15 -20 seconds for 5  for a good shooter),as even the weight limits in competition are often not enough to damp  the boomer's heavy recoil-and that means they cannot get back on aim so fast,so the string takes longer to shoot,and the probability of a wind switch occuring within the string is correspondingly increased,increasing bullet dispersal.

   The  "6BR" class  does well where conditions are especially benign (assuming of course a top rig,ammo and shooter). When wind gets up,the "heavier" cartridges have a bit more 'tolerance' of wind reading error-don't blow out so much for the same wind error. But note the balances/trade offs and the number of factors involved.

At some variable point (for rigs,ammo  and shooters),the absolute balances of these factors becomes precarious-and relatively unpredictable-especially given the variable human factors. The popularity and success of the mid cartridges ( the better 7mm especially) perhaps  indicate  where  the best choices/compromises are likely to be,given the modal wind condituons in UK,but no one cartridge can be optimal in every condition (unless the  judged shooting solutions  applied to it are always superior enough.)

VInce mentions the US ace who reckoned that the 6BR advantage might be  best in the mid ranges-never really convinging,but the basic point is that the advantage is not linear-at the leas it will vary with range,and might reverse under more extreme parameters. Indeed-such interactions complicate,and our mind does not like them-  we like what Nobel prize winner Kahnemann describes as  process 1-the fast easy,no if/buts/maybes conclusion,rather  than the more rational and logical process 2-which takes effort,much more likely to be better and  isn't compatible with a simple (but dodgy) process 1 decision.......

The central issue is not wind speed,nor even change in wind speed,but the rate of change of wind speed.(in the context of a shooter making shooting solutions-a perfect read at trigger pull,might be way off by target reach-that's rate of change,and is mathematicall more complex,and not readily detectable-in advance....an unpredictable switch happened!

Lauries detailed post gives examples of all this with numbers,and  adds the very relevant point that choice may be further complicated buy the logistics of the competiion-here,the delay iposed between (your) shots. There may effectively be no 'fast string' strategy available.

In general,no one is perfect,so you can see choice of  cartridge as a risk management decision-the 6BR class may enable a really good performance,but is vulnerable to a 'train crash',while the "7light mags" won't be so optimum sometimes,but  often reduce your vulnerability to (your) error.....now,risk assessment isn't something humans excel at....It's also not very predictable here.....so differnt choices persist.

 The relative merits  also change with the scoring method-ie whether  score or group,as  in the common UK  long range options-(F)TR or BR respectively, though some BR is now including a score option. A small deviation of a shot from the 'group' may or may not drop a point in score shooting-it will of course,always increase the 'group' size.

   Put more entertainingly, the great pioneer Bench Rest shooter Warren Page, said in this context (back in the fifties-it's not new):"It's differences of opinion that make  horse races."   But the horse,track and jockey are in it too.    :-)

gbal

 

[No i deer]

Well said G.

I went on the Berger site and played with the ballistic calculator rather than use mine.my 6.5x47 has done 900 shots now so plenty of life innit until it will need replacing.ive got around 1500 bullets so that should see it out.6mm br is cheaper to run than the 7mm's too.

What' there not to like ?