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Designing My Last 7mm Cartridge

Using the fill to the top of the case method, these are the H2O capacities of the cases i shown earlier including the 7mm NSM. We will call it the New Short Mag (NSM) for now. I don't have a 7mm LRM case anymore to check it's volume. Anyone have one still?

1734742403708.png

I had a 7mm LRM and as I recall is pushed 180 VLD's at just over 3100 fps. Much faster than the 7mm PRC, but so is the 7mm WSM with the right powder. The 7mm LRM might be the best balanced. However cases have to be purchased from GunWerks Which is $230 per 100. My gut feel is the 7mm NSM would have a similar H2O capacity as the 7mm LRM as the NSM is based on the larger Jeffery's case while the LRM is base on the smaller diameter 375 Ruger case.
 
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Note that the case volume of the dummy 7mm NSM is approximate, as I formed it using 300 and 7mm WSM dies and a Nosler case.

If i proceed with this wildcat, reloading dies and set of 4 or 5 special forming dies will be purchased from Hornady to resize Nosler or RUM cases, through multiple steps, down to the required case size. To some this might be tedious but I enjoy the process as I watch one case turn into another.
 
BoatTail said:
In the Gordon Cartridge Design tool, when you click on the upper case S, the software highlights what looks like the 0.200" area from the end of the case. I used that in the design but it is showing red.
View attachment 626863
Click to expand...
The 200 line is where the PRC chambers had issues with the original chambering and reamer design. It was very sensitive to "clickers" and resulted in a design modification. @Alex Wheeler came up with the modification to fix the issue. Maybe he can chime in as to what's going on in your design?
 
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Varmint Hunter said:
After building rifles in 7 Rem Mag, 7 Wby, 7 STW and 7WSM; I concluded that the 7WSM was the perfectly balanced .284 cartridge. Apparently, the shooting public disagreed. Now I'm shooting a 7PRC like everyone else. :D
Click to expand...
Not sure they disagreed that the 7 WSM wasn't good. Think the 300 wsm just overshadowed it. Keep hoping it will find a resurgence in bench rest or f class and we can play with it more
 
Huntaddict said:
I love wildcats and this one looks great!
My fav recently is on I call 7-300 PRC. Easy name, easy wildcat
Took the 300 PRC case and simply necked it to 7mm and did a custom freebore to handle up to the 195 Berger while using full case capacity and mag length. Runs the 180 Berger VLD at 3120
For comparison, here it is on the L next to a recent 338 NMI build I did.
Click to expand...

Not to derail this thread but I'd like to see more on that 7-300 PRC 😏
 
7mm man said:
I second that.
Click to expand...
No huge secret - here is the reamer spec and the rifle - I think like Elon, patents and secrets are BS, the stifle innovation

Had the reamer made to standard freebore so that I could do the measurements and customize the seating depths and jump by hand. Hand reamed it to .225

BAT action
Bart - #13 in 8 twist - 25"
TT Diamond set to 1 1/4 lbs
AG Comp stock - pillars and fully bedded
NF rings
Kahles K624 scope
 

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Huntaddict said:
No huge secret - here is the reamer spec and the rifle - I think like Elon, patents and secrets are BS, the stifle innovation

Had the reamer made to standard freebore so that I could do the measurements and customize the seating depths and jump by hand. Hand reamed it to .225

BAT action
Bart - #13 in 8 twist - 25"
TT Diamond set to 1 1/4 lbs
AG Comp stock - pillars and fully bedded
NF rings
Kahles K624 scope
Click to expand...

That's what I'm talking about! Thanks for sharing.

Where did you end up for COAL with the bullets you've tried?
 
KH_Outdoors said:
That's what I'm talking about! Thanks for sharing.

Where did you end up for COAL with the bullets you've tried?
Click to expand...
I started with the 175 eldx which ran at 3220
I am now running the 180 Berger at 3190 due to the ELDX being a nightmare for quality control - had 4 different length and weights in the same box and lot UGH

Coal to lands with the 180 is 2.895
Coal to OGV is 2.885
 
BoatTail said:
Over the last 15 years I have fallen in love with the cartridges in the 7mm family. Working with, and modified multiple 7s including the 7mm RUM, 7mm Rem Mag, 7mm – 08, 7mm WSM, 7mm LRM, and the 28 Nosler, each has taught me something new as I struggled to find the optimum neck size, freebore and load for best accuracy and performance. I found that each had some value or purpose, except maybe the 7mm RUM that, without a muzzle brake, seemed to violate every part of me when I pulled the trigger.

With the end of my physical ability to hunt, I will be switching over to benchrest competition to feed my need for reloading, testing loads, bullets, powder, and shooting sports. Before do so, I wanted to build one more long-range hunting rifle. This one will be used occasionally, while taking advantage of handicap mobility privileges, for Antelope hunting. The rifle will be a 7mm wildcat that provides more than the 7mm Remington mag, 7mm PRC and 7mm WSM, but less than the 7mm RUM and 28 Nosler.

Care to guess what is? I have dubbed it temporarily as the 7mm Nosler Short Mag (NSM). Here is how it compares visually to some of the other 7mm 404 Jeffery based cases that I have worked with:

View attachment 626650
Basically, the 7mm NSM is the 28 Nosler case shortened to 2.35". It retains the neck length and shoulder angle of the 28 Nosler. The new case is close to the 7mm Blaser Mag developed in Sweden. Like the Nosler and Ultra Mag cartridges, the 7mm Blaser Mag cartridge is based on the 404 Jefferies case. The primary difference between the 7mm Blaser Magnum and 7mm Nosler Short Magnum's Body Taper and Shoulder angle. The angle on the Blaser is 30 degrees while the 7mm Nosler Short Magnum is 35 degrees. This 7mm NSM case also uses the neck diameter and Freebore of the 7mm PRC. This altered case has about 4-5 more grains of H2O compared to the 7mm Blaser Mag.

My challenge now is to validate third party load data for the 7mm Blaser Mag or to show the 7mm NSM can meet or exceed them. The Chamber drawing in QuickDesign seems to be right, but I need help with the Gordon Cartridge Designer. I have attached the Gordon drawing and data fore review.

Note on the Gordon Chamber drawing the "S" Dimension has a problem. I assumed incorrectly what is was. Can someone help me with it?
I thought it was the dimension from the base of the case to the base or start of the body. Thoughts?

View attachment 626651
View attachment 626652
Click to expand...
Kinda funny, I designed a line of cartridges almost identical to yours right after the RUM case came out. My first was in 8mm,l. Called it the 8mm IzmM for Intermediate Mauser Magnum. Then I did one in 7mm, 308 and 35. My diameter at the shoulder is a tad wider, and my case is about .006" shorter. I had a bunch of intermediate length Mausers laying around and designed it to function in them, but a standard length Mauser will allow bullets to be seated further out.
 

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