@ 07:45 am (GMT)
Nathan FosterHi Clarence, I do not normally answer mail or threads which show a lack of respect (hello / please / thank you). But you have asked a good question so I will answer it for the benefit of all.
The faster you drive these (and most other) projectiles, the closer they like to be seated to the lands. Also, if we can seat close to the lands, it gives a great deal of room for harmonic experimentation. The ELD-M is particularly sensitive to jacket upset during ignition, the ELD-X is very sensitive to lead angle and can require experimentaion both in close and out long if the magazine and cartridge design allow for this (the RUM does not).
The slower we go, the more we can get away with a measure of jump.
In the RUM's, you cannot seat close to the lands unless the throat is cut short which can open up new problems.
I have often thought that rather than cutting a magnum throat long or playing with bore riding throats (still suffer a sudden upset due to final sharp step down lead angle) a more harmonious approach would be to utilize a Brenneke style throat which is in essence an extremely long taper. I believe (but have no evidence) that this could help a RUM's a good deal.
Again, this subject is covered in my book series.
This is the last time I will answer this thread.