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which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

 
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  #1  
Old 01-29-2004, 05:09 PM
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which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

i'm building a 700 bdl in 7mm ultra mag. i'm going with a 32" douglas. rate of twist has yet to be determined. i would like to shoot 139gr sst interbond. what rate of twist should i get? and what powder should i use? any comments or suggestions would be great. thanks [img]images/icons/smile.gif[/img]
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Old 01-29-2004, 05:42 PM
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Re: which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

Forknhorn-

As far as twist, I'd suggest 1-9 or 1-10 as you may eventually want to shoot heavier bullets (factory is 1-9.5).

My Sendero with factory barrel (26", 1-9.5, and so much freebore a 139 falls out of the case neck before it touches the lands) likes RE25 with the 139 Interbond. 3553 fps with 96 gr, 3.600 oal, no mark, easy bolt lift (slight mark, easy bolt lift at 97gr, 3623). That's only in MY rifle! I'd start no higher than 90gr and work up (I'm sure all that factory freebore is letting me load a couple extra grains of powder).

With the Interbond's .486 BC, you can't ask for anything much flatter to 400.

[ 01-29-2004: Message edited by: JGH ]
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Old 01-29-2004, 06:08 PM
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Re: which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

I originally built my 7STW with the intention of only shooting 140gr or similar weight bullets. I had my Hart barrel made with a 1-11 twist. It is very accurate with the light-midweight bullets.

However, the case capacity is so large that the cartridge is more compatable with heavier bullets, especially when shooting looong range. Most of the 168gr-180gr bullets require a faster twist and will not stabilize in my barrel.

IMO a 9.5 or 10 twist would be a better choice in the 7RUM. You could still shoot the 139's and will also have enough twist for the heavys, should you ever decide to go that route.

As to the powder, I got very good results with RE25 and H1000 with the 140gr bullet in my 7STW. I believe that the 7RUM has a bit more case capacity than the 7STW.

VH

[ 01-29-2004: Message edited by: Varmint Hunter ]
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Old 01-29-2004, 08:49 PM
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Re: which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

jgh, what do you mean when you say "mark". i'm new to this so i don't know what to look for as far as too much pressure. right now out of my 26" barrel i'm using 93.5grs of h1000, thats with a 140gr silver ballistic tip. i don't notice anything unusual. thanks.
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Old 01-29-2004, 09:19 PM
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Re: which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

forknhorn-

When the pressure starts to become excessive, it can cause brass extrusion into the ejector and/or extractor cuts on the bolt face. These show up as bright or shiny marks on the case head. That's what I was referring to as "mark".
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Old 02-02-2004, 09:51 AM
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Re: which powder ? 7mm ultra mag w/ 32" barrel & 139gr sst interbonds.

Try some IMR7828 or WMR in that case, should be real good, shoots great in my 300RUM.
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