.300 CT based wildcat

Topshot

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I have been playing about with a .30 cal wildcat of my own design and thought I would share some of the details with you guys.

I have a .375 Cheytac and thought that a short .30 cal cartridge based on this brass would be interesting. A full size .375 Cheytac case necked down to .30 cal would be ridiculously overbore so a short version was required.

My Stiller 408, single shot action has a bolt face designed to suit the .640" rim diameter of the Cheytac case. After plenty of searching I was unable to come up with any .30 calibre rimless cartridges that had a .640" rim diameter. So the only way to go was to get a custom chamber and resizer reamer made and build the thing to my own specifications.

To do this I had a look at some of the design features of the super accurate cartridges. 6mmBR, Dasher, 6.5x47 etc and scaled up from there to fit the .640" rim diameter. A short fat cartridge,35 degree shoulder angle and long neck seemed to be desirable features. So I sent off my design with an order for finish and resizer reamers. At the same time a ordered a 32” heavy fluted barrel to match the existing .375 Cheytac profile.

After receiving the reamers, the first step was to make some brass. This proved very difficult as the parent brass is so thick in its side walls. But after making five different forming dies with the resizer reamer, some brass thinning, annealing and finally neck turning, I had a process sorted that produced cases ready for fire forming.

Following fire forming the cases came out looking very nice and ready for load development.

Some details....
Case length 2.400"
Shoulder angle 35 degrees.
Neck length .350"
Case capacity prior to fire forming, 110gn H2O
Case capacity after fire forming 117gn H2O, So a bit more case capacity than a .300RUM but not so much as to be too overbore.
Barrel twist 1 : 10 to use 230gn Berger Hybrid projectiles.

Load development is about to start so I will update the thread once I have further data.

The final product., Left a .300WSM 180gn factory load. Right the wildcat I call a .300NSM loaded with a 230gn Berger Hybrid.

300nsmcomp2.jpg




The cases ready for fire forming using 97gn Retumbo and 155gn bullets at 3200fps.

300nsmfform1.jpg
 

LoneTraveler

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Neat looking cartridge, May be very efficient with the short wide powder charge. A 300 WSM on steroids. Will be interesting to see what velocity you get once you get enough cases fire formed to work up full power loads. Hope it meets your expectations. Good Luck.
 

TH

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Jan 22, 2003
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Location
Ohio
Two years ago Tom at Thunder Valley precision built me a 300 Thunder Hawk. This is a 408 Chey Tac case shortened to the same length as the 300 Norma mag case with a 35 degree shoulder. Im using a 34 inch barrel pushing the 215 Bergers 3586 fps. My load is 98 grains of H-1000. I have shot the 230s but prefer the 215s my accuracy load with the 230s was 94.5 grains of H-1000 velocity was just over3400 fps.

You should be extremely happy with accuracy I'm shooting one hole groups with the 215s at 100yards. One calm evening at Thunder Valley I hit the mile target which is 10 inches by 10 inches 6 times in a row. I have noticed this cartridge likes a lot of neck tension. I wanted an extreme powder so I have tried retumbo H50bmg and H1000. I have had the best results with H1000.

Last year I used this rifle to kill 2 elk one at 802 yards the other at 1037 both animals dropped dead in there tracks. The insides were completely destroyed.

Good luck with your new cartridge I know you will be extremely pleased.
 

Topshot

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TH,

That sounds very similar to my cartridge. What H2O capacity do you have.
What dies are you running to form brass etc.
Very interested in how you overcame some of the issues associated with making .300 Thunder Hawk brass from 408 Cheytac cases.
The velocity you are getting is very encouraging.

Anyone that has an action that can shoot a .375 or 408 Chey tac can shoot these .30 cal wildcats. It would be even worth getting a large action just to make one.
 

TH

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Jan 22, 2003
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424
Location
Ohio
Topshot

I am traveling it's going to be a few days before I can check the water weight.

John Whidden made the resizing dies. Forming the brass was a nightmare. It's definitely the hardest case I have ever formed. After making the first 50 cases I told my self I completed the masters reloading program. There were so many blood blisters on my hands from turning brass I didn't want to form another round until I saw the performance of this cartridge.

I also have a 5 die process to shorten and neck down my brass. Stage 1 2 and 3 were not bad 4 and 5 was impossible with my rock chucker press. I went out and bought the RCBS 50 caliber press to complete stages 4 and 5. Honestly I went through at least 75 pieces of brass to form my first 50 this was with the Cheytac Jamison brass.

Once the brass was shortened the first time I used a small pipe cutters tool to trim the excess brass off each case then I put the case in a Wilson trimmer and trimmed them to length. The second time I made the cases I trimmed them to length by using my gunsmiths mill. Once the cases were trimmed to length I tried to expand the case in order to neck turn. This step was a mess because the brass kept snapping back into place. I figured out that I could only expand one case at a time and I would inside neck ream each case then outside neck turn. The necks were so thick that I had to outside neck turn three times and a 4 time once they were fire formed.

BTW I did not have any luck at all with Bertram brass. When I got to the 5th stage of the case shortening process every piece of brass crushed inside the case. I ended up throwing away all 60 cases.
 

Topshot

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TH,

Your experience sounds exactly like what I went through, although I used a lathe to turn down the brass so that part was easy.

I used Bertram brass and at step 3, turned down the long neck at that point to 20 thou thickness. Then after step 4, I dropped the thickness to 15 thou.

Doing it this way the last two steps were easy but alignment with the die had to be right or the neck would catch and crush easy.

Once fire formed I have had no problem. It will be interesting to see how your case capacity compares to mine. My cartridge length is 2.400".

I plan to use this round for hunting but also 1200 yard competition work on windy days. The accuracy you are getting is great.
 

TH

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Jan 22, 2003
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Location
Ohio
Topshot

The Thunder Hawks over all length is 2.5 inches. The water weight filling the case completely full of water is 131 grains. I believe your cartridge will be more efficient because I have noticed shooting H1000 that there is room to shorten the case even more. I'm curious to see what velocities you achieve and which powders you have the best success with.

Best of luck with your project I look forward to seeing your results.
 

Topshot

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TH.

I did some velocity testing today.
85gn Retumbo and 230gn Berger Hybrid gave 2885fps average of 5 shots.
Seems I have a donut problem with the longer bullets being seated deeper. So just like you I will need to inside neck ream and have ordered a Wilson neck reamer for the job.
This has put the brakes on this project until I receive the reamer and sort out the donut issue.
 

Topshot

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Nov 3, 2008
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I took another photo today to show how this cartridge looks in comparison to the other two rounds that are used with this action when I switch barrels.

Left .300NSM, center .375 Cheytac, right .510 Skidmark Express.

ctcomp.jpg
 

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