7mmRUM & Retumbo

[speedbump]

Thanks for the replies.

S1,
I haven't tried AA8700, but it's a thought. Anyone have any results from it in a RUM sized case?

Tim,
These will hold @ 103gr of water if memory serves. This is the full sized RUM necked down to .284, not a short action magnum.

4mesh,
This is nowhere near full. It looks like there is @ 3/16" left unfilled below the shoulder. That's been a consistent problem too, most powders I've tried leave a disturbingly large amount of case unfilled. The BMG powders are better in that regard, but with this overbore, a 7RUM acts like it likes something between say, H50BMG & IMR7828. It doesn't know what it really is yet....that's why I was curious about the Retumbo's burn rate properties.

BH,
Good point. 200 is all I have access to on a day-in-day-out basis. There's a severe shortage of LR ranges available here. I have to drive @ 6+ hours north to near Iowa, or 4.5 hours southeast to Fatboy country [img]images/icons/grin.gif[/img] in Tennessee to get a 1,000 yard range. Some pals in Indiana have access to 1K, but only if the crops are out & the weather's dry. It's a tough combination to achieve around here! I can go out to 600 in the next couple of weeks I think.

Feel free to fire any more thoughts & opinions out - I'm wide open....

[Warren Barrett]

S1 and Speedbump, I can`t say this will help you but, these three powders are nearly maxed out in my rifle in the following:
1) RL25 - 78grs.
2) MRP2 - 83grs.
3) Retumbo - 88grs.

[4mesh063]

Sorry, I thought this was the 7mm RSAUM insteaad of the RUM. Yea, the Retumbo will fill to about 115 grains if I remember right. Several of the guys at the range shot it last year. Boyd shot it in his heavy gun, He could give you info about where it stands compared to H1K R25/22 and so on.

[Boyd Heaton]

I found with the lot # I had was.Retumbo was 3gr slower....I also found it to be more consistant in e.s and s.d's.I got e.s. below 10fps with retumbo.And only 15fps or so with the Rl25

[Boyd Heaton]

Phil,Killer is shooting SWEET [img]images/icons/shocked.gif[/img] [img]images/icons/shocked.gif[/img] [img]images/icons/grin.gif[/img]

Speedbump

I read somewhere the other day that MRP II was slower than RL-25. The person wrote that it was looking about 5 grains slower, but there was also a comment about it being
"close in burn rate". This confused me because I do not consider a 6 percent difference close at all, and it made me wonder if there was a typo and the guy meant 5 tenths of a grain slower.

My point being that there is a big GAP in powder burn rates, right where the Ultra MAGs and Wolfs and other wildcats want to operate. 50 BMG is a tad too slow, and H1000 is a tad too fast. Retumbo is only 3 grains slower than RL-25 and does not quite equal the velocity to pressure ratio of RL-25. I think if MRP II is actually 5 whole grains slower than RL-25 it would be closer to IDEAL than anything I have tested, it would just about split the gap in burn rate, and would be very interesting to me if I was testing for a 7mm UM.

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The MRP-2 came highly recommended from a good source, but this thing doesn't like it at all.

S1, your results copy what I inferred from testing all those powders - it falls right smack dab on the cutoff between moderately slow & really slow burn rates. There was just about ZERO data out there last year when I began the project, so all the maxs I came up with were developed in-house, by necessity.

Warren B., the ones with lower charge weight at max were faster powders (for the most part), at least in mine. They left as much as 5/16" of the case unfilled below the shoulder at max pressure. About the only thing that really filled it up was H50BMG. The 5010 isn't bad, but the super fine-grained WC860 BMG powder is shallow too.

My bad on the water weight - it's 111-113gr in an unimproved 7RUM case. I checked. Duh!?!
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