In rereading this thread, I wonder if part of the difference we are hearing in regards to accuracy is that some guys are talking about the copper bullets (MTH, MTAC, FBH) and some are talking about the raptor bullets which are brass solids with the screw in tips.
I know that their copper bullets are a very soft copper so soft that one has to be careful with the bullets during reloading and carrying in the field. I have also heard they are much softer the Barnes copper bullets. Brass on the other hand, depending on its formulation, could be quite a bit harder and from the info in some of the posts here that seems to be the case.
Hardness obviously would affect expansion too which may be why we see some bullets that appear to be performing as a true hunting solid with very little expansion.
BnG, This info copied from their site seems to back up what you were saying about tight chambers possibly being an issue. They are talking about more of a safety concern but as we all know sometimes high pressures blow groups and erratic pressure for sure will.
Driving Band - Portion of the bullet that is between the SealTite Band and bore rider or ogive. This portion of the bullet engages the lands, or rifling, ahead of the SealTite Band and gets the bullet tracking true to the rifling before the SealTite band enter the lands. It is absolutely critical the bullet is tracking properly before SealTite Band engages or "stripping" occurs and seal is lost. Our bullets are tested to ensure the driving band is long enough to ensure this does not happen. Since seal is not achieved with the driving band on our bullets its diameter is under nominal caliber diameter to prevent excess pressure. Caution! It is extremely important that if any individuals had a custom barrel made undersize, the driving band diameter must first be measured to ensure it is smaller than your groove diameter or you will get excess pressure. Solid copper does not give like lead core bullets and custom size barrel users must be very cautious. Any SAAMI spec. or factory rifle barrel will not have this problem. The Driving Band length can be customized to allow for more or less jump into the throat to bore angle.
Scot E.
