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Big Seven Case Capacities

 
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  #8  
Old 12-11-2003, 03:42 PM
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Re: Big Seven Case Capacities

Len,

Chiming in as you requested. I've tried 10+ powders in the 7mmRUM + 5 bullets, the most recent being some of 'Shaky's' Groove Bullets. The barrel was starting to slip a little at @850 rounds, but a great many of those 850 were near-max loads doing initial testing. It's been re-set once & I have a Pac-nor 3 groove tube enroute for Spring.

Here are some links previously posted. I'll look for more, but this'll get you started:
www.reloadbench.com/ubb/Forum5/HTML/000103.html
www.reloadbench.com/ubb/Forum29/HTML/000265.html
www.longrangehunting.com/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=4&t=000227&p=2
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  #9  
Old 12-13-2003, 11:17 AM
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Re: Big Seven Case Capacities

Speedbump

You made some very helpful comments on "Big Sevens" over on the LRH Rifle Series thread. Here are my thoughts. I have next to zero experience turning necks and forming cases for wildcats. I have been approaching my goal of a super accurate rifle sort of from the bottom up. Never quite satisfied with each iteration in the process.

Now I'd like to make a big jump up and work at it from the top down in terms of effort necessary to own and manage the cartridge combo selected. In a couple months I wll have gained experience with turning necks for a tighter necked version of my favored 7mm Dakota. I am now having it rebarelled as previously discussed. Then, by using a bushing die I hope to better control neck/bullet tension and reduce velocity spreads...and reduce vertical dispersion at 1k ranges.

If I am comfortable with the marginal payback/effort result I will then proceed with a faster version of a 7mm cartridge. In choosing which cartridge to use, case prep and therefor case life (effort not cost) then gets to be a bigger factor. If my tight-necked 7mm Dakota justifies turning necks then I think the Lapua brass will be my choice for the "Big Seven". Sounds like you are getting only a few firings from the Rem brass?

Plus, as you said, there is the "fun" factor to consider.
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  #10  
Old 12-13-2003, 11:53 AM
 
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Re: Big Seven Case Capacities

Len, with the lapua case I think you could get better than 3600 fps with the C176. You may need to go to a 9.5 or 10 twist.
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  #11  
Old 12-13-2003, 02:23 PM
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Re: Big Seven Case Capacities

This is quite interesting.

I wonder how, for equivalent barrel lengths, with powders currently available, a 176 grain 7mm bullet could be pushed 150 fps faster than a 178 grain 30 cal from the same Lapua case?

I mean, conventional ballistic wisdom says powders have to get slower, or charge weights have to get smaller for equal pressure performance. Or barrels have to get longer (maybe significantly so) for the same weight bullet in a thinner tube to go as fast, let alone significantly faster. Interesting...
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  #12  
Old 12-13-2003, 05:17 PM
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Re: Big Seven Case Capacities

STL

I agree. I would expect the 7mm version of a Lapua improved cartridge to be slower than the 30 version by 100 to 200 fps all else being the same in the barrel and load. Pressure goes up as the size of the pipe goes down.

I forgot what you said you could get with the 178 AMax?
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  #13  
Old 12-13-2003, 05:24 PM
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Re: Big Seven Case Capacities

Len,

Yes, I've very few firings per case in 7mmRUM with anything near max pressures. The primer pockets are horribly stretchy. Never had a pierced primer or split neck - just those [img]images/icons/mad.gif[/img] primer pockets!

With the Lapua case volume vs. 284 bore diameter, powder burn speed will be an experiment in itself for you. I ate up a SIGNIFICANT percentage of my barrel life just gathering max data when there was virtually none available. I hope you stumble onto one earlier in the process.

I fully understand the 'interesting' aspect of your quest - it's one reason why I jumped on the 7RUM before it was available (besides the incredible ballistic potential). You'll see a trajectory of a 22-250 out to 400-500, then it'll smoke almost anything, INCLUDING a 50BMG to 1,000.

I asked Santa to bring some Lapua, Norma, or even Winchester brass in RUM. I don't think even the jolly one can pull that off! [img]images/icons/frown.gif[/img]
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  #14  
Old 12-14-2003, 12:03 AM
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Re: Big Seven Case Capacities

Len,

Max pressure was reached at 3450 over the Ohler with 95.5g of RL-25 with the 178 A-Max...

Another interesting thing we should probably start noting is the chronograph brand - my ProChrono regularly reads 75-125 fps faster than the Ohler... That kind of thing makes a big difference when decision time comes, of course!
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