These are used in RF barrels in the schutzen rifles where they also have a BR class. These particular barrels are well regarded in these circles. Interestingly, the same maker also swears the left hand twist barrels shoot a bit better than right hand twist (he makes both).
Speaking of the MI rifling, Pope claimed a barrel could be rifled with coarse emery and it would perform well but not for long. GD
With ELR shooting the different spin direction makes them shoot to the right vs. the left... freaky deekie until you’ve seen it 2-3 times, even then.
But if we’re talking freaky... shooting east then west at past a grand changes your POI elevation... I know the earth is spinning but WTH !!!
Again until you see it under controlled conditions it’s folk lore.
For “twist gain” - remember the crowd you are talking about is trying EVERYTHING to get an edge on the other guy..
If it’s right, the entire crowd ends up there.
For me it’s is it repeatable, and proven under controlled conditions - which costs me a frigg’n huge amount of money because I experiment.. but the bug holes are worth it.
