I have never put any belief in the mysterious voodoo of "trans sonic" problems. Shooters have a pattern of making up "unscientific theories" to explain things that they don't understand, and this is one of them...[catshooter]
You may or may not believe some things, but others who know rather a lot about the subject do actually believe in transonic speed problems.
For instance, the US Army who over several decades have researched the subject in some depth and built up a wealth of emprical knowledge as to what works and equally important doesn't work in L-R match and sniper ammo.
I refer you to a pair of articles by FS titled 'Cartridges: 7.62 NATO Long Range Match Cartridges' republished in the 'The Rifleman's Journal' blogspot. Here's how Mr Salberta summarises the US Army's position on this:
Although not well understood by many, at around 100 fps above the speed of sound, there is sufficient turbulence that some bullet designs have their subsonic accuracy seriously compromised when they fall to below this speed. Many well designed bullets fired from an appropriate twist barrel will have minimal transonic perturbations, though there is generally some degradation associated with making the transition from the sonic to subsonic region. Through many years of testing, the US Army has decided that the threshold above which this effect can be ignored is 1226 fps in standard atmosphere conditions. Ideally any load will be above this speed at the terminal target distance.
And .... a considerable part of the descriptions of the development of US match and sniper ammunition in the two-part feature is about efforts made to stay above transonic flight at the 1,000 yard mark, or at any rate staying 100 fps faster than the prevailing speed of sound. Still, what does the US Army know?
Another group of people who know a little bit about this subject are British and GB Commonwealth
Match Rifle competitors, a strange discipline that has no US equivalent and which like FTR is limited to the 308 cartridge but with other bells and whistles including a pretty restrictive ceiling on barrel weight. MR is shot normally at 1,000, 1,100, and 1,200 yards stages in a single fixture, although where the range facilities exist, it can be shot at still longer distances. Unlike FTR / F-Class, MR stays with standard NRA sized targets, ie double the F-Class diameter for each scoring ring.
These guys (and a few ladies) have been shooting at ultra long-ranges with first the 303 (with specially loaded heavy BT bulleted 'streamlined' ammo) and in more recent times they've been shooting the 308 at 1,200 yards sometimes further, long before Bryan designed his first bullet for Berger or anybody else. They were experts at coaxing serious MVs out of the 308 with heavy bullets long before F-Class was dreamt up by George Farquarson in Canada and used Sierra 180s (the old shallow angle boat-tail model), the 190 SMK (a favourite used by almost all competitors pre VLD days) and the 200/220 SMKs. I should also add that they discovered what worked long before anybody mentioned G7 BCs or for that matter half reliable BCs were available at all for this type of shooting and distance.) It was believed that if you could drive the 190 fast enough it remained supersonic at 1,200 but rigging huge metal foil screen chronographs behind a target at Bisley showed that this wasn't so. Another (minority) school of thought in MR at one time was to load cartridges low to the point where the last quarter of the bullet flight would definitely be subsonic. This approach sometimes worked it's said, but not infallibly by any means, and most competitors preferred to go as fast as possible. Either approach was to avoid transonic flight at or near the target.
There was a very enlightening discussion of this subject on the US Rifle Teams Long-Range Forums back in early 2010 after the GB Match Rifle team's tour of Australia over the 2009/10 winter (the Antipodean summer, of course) which included a series of matches up to and including 1,500 yards at Coonabarabran Range which is 1,700 ft ASL and saw very high temperatures during the fixtures.
http://www.usrifleteams.com/lrforum/index.php?showtopic=12577&hl=coonabarabran#entry92568
I refer you to post number 7 and a couple of sentences in the middle of it:
I would suggest ANY bullet going into the transonic and/or subsonic zone will go awol at 1200yds if the wind gets up. On still days you may get away with it.
These are the words from somebody who is a member of a select group which has been experimenting with the 308 and similar cartridges at extreme ranges for a long, long time and whose members really do know what works and what doesn't. Note the reference to 'Barry, Pendine, and Dunlossit' over 60 years [of MR] in post 8.
You make a reference to over 2,000 yards with 308 and 303 in England in one of your posts and these three venues are what you're referring to, none of which have been in use at these distances (or in two cases for shooting at all) for a long, long time now. (I'd also be careful about just which Brit you talk about 'in England' to, as none of these ranges is in England, two being in Scotland and one in Wales.)
Dunlossit was the the most interesting of these being a private facility built in a deerstalking estate on the Isle of Islay at at time when there would be precsious few tourists, hillwalkers and other liable to blunder onto such an informal range. Islay is one of the southern group of the Inner Hebrides islands off the west coast of Scotland, a remote and wild place even today in the wrong weather and season, and shall we say well off the beaten track in the 1960s when the range was in use. Matches were shot at up to 2,640 yards, but the targets were as large as houses and in some weather conditions, a top score saw fewer than half the shots hit - but some groups were remarkable.
Today, and for many years past, there is no 2,000 yard competition in the UK nor anything like that distance. The only ranges that offer this sort of distance are military 'field firing' ranges which do not have formal targets set up as on normal distance 'gallery ranges'. They are designed for military training using crew served support weapons, anti-tank missiles, and large calibre sniper rifles. AFAIK, the sole civilian recreational target shooting use is their hire on the basis of a handful of days each year by the UK 50-Cal Shooting Association as .338 LM and heavier rifles are banned on ordinary MoD gallery rifle ranges. UKFCSA shoot 'targets' at long ranges, 1,500 yards and up but that is the odd Fig 11 military advancing soldier type and other larger objects such as old armoured vehicles and suchlike.
