Powder compression and H870 or WC872

[Poodleshooter]

Has anyone played around with compression in these rather bulky powders?
In 7mmRem Mag, the max load for this powder just tops out at 79grs. This load applies for bullets from 100grs-160 or so. So apparently this would indicate that the bulk of the powder is the limiting factor,rather than pressure. In playing around with the drop tube last night,as well as vibrating the case to settle the charge, I was able to get 83grs in the case and still keep the powder level below the base of the neck of the case.
So has anyone pushed this powder a little further in a large magnum loading with lighter bullets? As a slow powder, it seems that it might be fairly safe to experiment with.

 

[griz]

There was a thread here where somebody (Clark?) mentioned double compression. I believe he used some kind of home made die to squeze the powder as far as it would go, then added some more and compressed that with the bullet.

My own experince was accidental as it makes me a little nervous to feel the granuales crunch as I push on the press handle. I was setting up my progressive press and had an old die that only flared the case, a 38 special. For some reason I had it set way to deep, and crunched it down on a case that I had already charged. The part of the case that wasn't up into the die bulged out and the powder was compressed into a lump that had to be dislodged. I still have the case as a reminder that Murphy is always watching me.

 

[griz]

Here is the thread.

He's talking about straight walled handgun cases though and I have no idea how that would work for a rifle round.

 

[Poodleshooter]

I'm actually not double compressing,just trying two different methods to do the same thing-compress 870. I'm a bit syntax impaired in my last post apparently I've compressed with several extruded powders,but that was with factory data and the pressures were near max. I'm curious about the factory data on 870,because the pressures listed for the maximum load are something like 20% less than the max pressures for faster powders with the same bullet. They just stop at that load for some reason, and never show hotter loads. So it seems like it could be loaded a bit hotter,but Hodgdon didn't bother with compressed loads. You can fit a bit more than 79grs in a 7mmRM case. Hodgdon has ignored my email about it so far.... They probably don't care since they don't sell 870 anymore.
Anyone have experience compressing really slow powders in bottleneck rifle cartridges?