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7mm SAUM Wildcat!

 
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  #22  
Old 03-28-2012, 01:47 PM
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Join Date: Feb 2011
Posts: 31
Re: 7mm SAUM Wildcat!

Quote:
Originally Posted by britz View Post
fyi, one of my biggest issues with my 300wsm is the short action. If I was to build a custom I would fit it with a long action to allow for long bullets to be seated out.. utilizing case capacity for the heavy High bc bullets... oh and to allow for feeding out of a repeater.

food for thought.
That's the conclusion I came to--especially with the 195 Bergers coming out. I went for the Winchester long action.
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  #23  
Old 03-28-2012, 10:50 PM
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Join Date: Jan 2012
Posts: 166
Re: 7mm SAUM Wildcat!

Calinb-

So here is where I'm at after reading some of the ideas of Mr. P.O. Ackley,
1. Shoulder Angle- 40'
2. Pushback- .2685" from the SAAMI WSM (1.5700 to shoulder / neck)
3. Body Taper- .0085"/in. of body
4. Trim length- 1.854"
5. COAL- 2.840"

There is what I am thinking right now, I really would like to know where this comes out on H2O capacity, if anyone has any insight.
From my figures this should be one of the most efficient 7mm cases ever made! and should be able to do maybe 3000 fps with the 180's (I'm just comparing and wishfull thinking!) The nice thing also is that the brass ahould be easier to make.
Anyways, run this throught and see shat you get that would be awesome, then lets get some guns built and get to shootin'!!
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  #24  
Old 03-29-2012, 03:47 AM
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Join Date: Feb 2011
Posts: 31
Re: 7mm SAUM Wildcat!

Quote:
Originally Posted by redneckclimbing View Post
Calinb-

So here is where I'm at after reading some of the ideas of Mr. P.O. Ackley,
1. Shoulder Angle- 40'
2. Pushback- .2685" from the SAAMI WSM (1.5700 to shoulder / neck)
3. Body Taper- .0085"/in. of body
4. Trim length- 1.854"
5. COAL- 2.840"

There is what I am thinking right now, I really would like to know where this comes out on H2O capacity, if anyone has any insight.
From my figures this should be one of the most efficient 7mm cases ever made! and should be able to do maybe 3000 fps with the 180's (I'm just comparing and wishfull thinking!) The nice thing also is that the brass ahould be easier to make.
Anyways, run this throught and see shat you get that would be awesome, then lets get some guns built and get to shootin'!!
Great! I'm a bit too tired tonight to do the trig to figure out where the 40' shoulder angle comes back and meets the taper angle where the body ends. Maybe you've already calculated it and can give me the base to shoulder dimension (body/shoulder).
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  #25  
Old 03-29-2012, 06:37 PM
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Join Date: Feb 2011
Posts: 31
Re: 7mm SAUM Wildcat!

Here's my progress, so far. I could've easily messed-up the math, because it's tedious and I don't have the RCBS program (which is still over $100 at Natchez). I used the web page calculator at the website http://kwk.us/cases.html to reduce the math required of me, once I figured out the remaining case dimensions.

I haven't done any Quickload runs yet, but I think this 7mm GT wildcat will be powder-constrained; I came up with 64.8 water grains capacity. For comparison, QL data has 66.0 grains for a 284 Win case.

Here are the highlights from my calculations. I used the numbers from the SAMMI 7mm WSM print as the starting point. http://www.saami.org/PubResources/CC...t%20Magnum.pdf

Looking at the shoulder position, 1.8565" - 1.57" = .2865. Did you swizzle a couple of digits, Travis?

One thing that prints don't show, but is needed for the case capacity calculator, is what I'll call the head to body taper length. The angle is 45'-6'' on the print. I come up with a length of .03737" using the published angle. Add this number to the head (.054") and extraction groove (.040") lengths and the case body is found to start at .131 inches--at least for the purposes of using the capacity calculator web page.

Doing the trig (I'm too lazy to reproduce my napkin scratches here), I get:
....................................7mmGT.......................7WSM

shoulder length =...........0.12614".......................0.1547"
shoulder position =.........1.44386".......................1.7018"
shoulder dia. at body =....0.53269".......................0.5377"
neck position =...................1.57".......................1. 8565"

The remaining numbers should be the same for the two cartridges.

The case capacity calculator says, If you have a rimless cartridge, enter for the rim the inner diameter and the average width of the extractor groove. A correction is made for the primer pocket.

I'm not exactly sure what is meant there, but I got the best correlation with the Quickload value for 7WSM when I subtracted the .131" for the total case head length from the position values. The case head doesn't hold much powder and my website calculator result agrees well with the 7WSM capacity value from QL (81.1 grains). I don't have any actual cases to measure with water and a scale.

7mm SAUM Wildcat!-7wsm_ccap.jpg

Using the same method for the 7mmGT:

7mm SAUM Wildcat!-7mmgt_ccap.jpg

The greatly reduced case capacity is due, of course, to the much shorter case length. Also notice that the body taper of the 7mmGT is actually more than the 7mmWSM. The 40' shoulder angle doesn't help much to increase case capacity by maximizing body length volume.

I'll try some QL runs when I get a chance.

-Cal
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  #26  
Old 03-29-2012, 07:21 PM
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Join Date: Feb 2011
Posts: 31
Re: 7mm SAUM Wildcat!

I was worried that my calculator "calibration" technique, above, resulted in extra powder capacity from an artificially long neck region for the 7mmGT. Here's another approach to "calibrate" the case capacity calculator with the 7 WSM QL case capacity value (80.1 grains) and then changing all but the case head region numbers to reflect the wildcat modifications to the case.

As before, I used .131" as the rim length (to reflect the length of the head and extractor groove region). For comparison, a primer is .13" deep. Because the head and extractor groove area doesn't hold much, if any, powder, I subtracted .131" from all the other lengths (including the neck length this time), Finally, instead of using an average groove diameter, as instructed in the directions (whatever "average is for a cylinder and a taper), I adjusted the "rim" diameter to obtain the 80.1 grains result for the 7 WSM case.

7WSM:

7mm SAUM Wildcat!-7wsm_ccap-2.png

It makes the capacity look even a bit worse than before for the 7mmGT:

7mm SAUM Wildcat!-7mmgt_ccap-2.png

If someone could run my 7mmGT numbers (from my post immediately preceding this post) through another tool, like the RCBS tool, it would be most helpful.

Last edited by calinb; 03-29-2012 at 10:19 PM.
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  #27  
Old 03-29-2012, 08:24 PM
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Join Date: Feb 2011
Posts: 31
Re: 7mm SAUM Wildcat!

Here are my first QL runs. First I ran 2.840" COAL and then increased it to match a shank seated depth of 66% of the Berger 180 gr. diameter, though I have no idea if that works well with the Berger. Seating it shallower results in a COAL of 2.971", which should still easily fit in an AICS short action mag (2.985"). The extra powder space does provide a little improvement in velocity using a couple of the bulkier powders, but the powder capacity constraint isn't as much of a problem as I thought it would be. I used the lower 63.9 grain total case capacity for these runs, which I suspect is fairly accurate. I wonder how things will look with the new 195 gr. Berger!

These 7 WSM GT runs use absolute max. pressure of 64,542 PSI (7mm WSM SAAMI max.) and 105% max. filling (compression) ratio. The 7mm SAUM runs use the SAAMI 65,000 PSI maximum. QL always reports pressures close to max. as "DANGEROUS."

2.840" COAL:

7mm SAUM Wildcat!-gt_berger_2.840_coal.jpg

66% shank seated depth/2.971" COAL:

7mm SAUM Wildcat!-gt_berger_2.971_coal.jpg

7mm SAUM 2.985" COAL (max. SA mag length):

7mm SAUM Wildcat!-7saum_berger_2.985_coal.jpg

7mm SAUM 66% shank seated depth/3.142" COAL (LA mags only):

7mm SAUM Wildcat!-7saum_berger_coal_3.142.jpg

Last edited by calinb; 03-29-2012 at 08:57 PM. Reason: Added 7mm SAUM results and notes
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  #28  
Old 03-29-2012, 09:45 PM
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Join Date: Feb 2011
Posts: 31
Re: 7mm SAUM Wildcat!

And for my final post for the day...a 2850 fps efficiency study. Yup--full cases are more efficient (but don't know if I'm willing to give up the velocity of the SAUM--especially now that I've got a LA Winchester). I have to take some time to digest all this data myself!

GT:

7mm SAUM Wildcat!-7gt_2850fps.jpg

SAUM:

7mm SAUM Wildcat!-7rsaum_2850fps.jpg

-Cal
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