Lapua OTM

[mag41uk]

I got a few thousand 123gn and 139gn Lapua bullets which are now called open tip match.
The hollow is massive on these compared to the previous style.
I haven't measured them but by eye seem to be twice the diameter.
That said, I was using them at a 1000 and there didn't seem to be much difference.
Why would Lapua purposely make the hole so much bigger?
I wouldn't have thought it would help with long range shooting?

Tony

[saddler]

Send me a few 100 of the 139's & I'll test them & let you know

Chances are it's due to changes in tooling or a different bullet forming die/process being used

[kennyc]

I got a few thousand 123gn and 139gn Lapua bullets which are now called open tip match.
The hollow is massive on these compared to the previous style.
I haven't measured them but by eye seem to be twice the diameter.
That said, I was using them at a 1000 and there didn't seem to be much difference.
Why would Lapua purposely make the hole so much bigger?
I wouldn't have thought it would help with long range shooting?

Tony

I wouldn't have thought the larger hole would cause any problems, as the air would surely flow over the compressed air already in the hollow, maybe the larger hollow allows the weight distribution to be brought back, and outwards from the centreline increasing the stability? (just guessing but seem to dimly remember some work done on rotational stability of bullets, may all be the ramblings of a tired mind)

[Laurie]

The meplat is left fairly large for the bullet-ejector pin on nose-forming die to have something to bear on. A stuck bullet and/or broken pin is very bad news for a bulletmaker, not to mention bullet consistency. Both Berger and Lapua have recently increased meplat diameters presumably to address production issues linked to this factor.

It does make a difference at anything other than the shortest distances as a friend who recently mixed up 6.5X47L rounds loaded with old and new Scenars having moved onto to a newly bought lot mid session. His elevations at 500 or 600 were poor compared to his usual. Bryan Litz says that the BC will be improved by 3-7% by pointing depending on the amount of meplat area reduction, bullet nose shape and calibre, small calibres getting a bigger benefit for the same meplat area reduction than large. Even a 3 or 4% BC change is potentially significant - the 123gn 6.5 Scenar has an out of the box average G7 BC of 0.265. Improve that by 3% and it rises to ~0.273. At 2,950 fps MV, retained velocity at 1,000 rises from a predicted 1,417 to 1,454 and windage decreases a little by around a third of an inch per 1mph crosswind. So a 2 or 3mph wind change between shots will see an inch less movement for the pointed bullet, half an inch for a quartering wind shift of the same magnitude. Of course, Litz's results are based on the 'old' bullet form before the change, so the actual out of the box BC may have dropped by 3 or 4% in the recent batches.