Since bulldog's original query has been answered, evidently "to his satisfaction", it would be best to let this thread go, however mhb is apparently in need of further discourse:

Can anyone help him out with the length measurement for the 285gr Grand Slam bullet? I've shot my 50 away of course, ages ago, and won't be buying any more for the obvious reasons given.

Although most of us lead full and busy lives, we are usually more than willing to race off and source information or measure something if it will genuinely help a fellow poster, but the enthusiasm wanes when it is likely to simply prolong an argument.

As I said, mhb, I will have to re-measure the twist-rate on my .444/.375, but in my own time please!

...and BTW, there is no "puzzle" here. The heavier slower GS bullet wouldn't remain stable at longer ranges, however the lighter faster bullet does. No mystery there.