Necking down 7mm STW to .257 STW

[aldeerhunter]

Thanks for all of the responses. The gun has a 26 inch 1:10 twist barrel.

I took one of the bullets I have left from Ferguson apart. 78.5 grains of powder. The bullet is a 100gr TSX. The velocity is 3905. These shoot quite well-.5 moa. They are phenomenal on deer.

I have sent fired brass to Lee for them to make me a die.

I was wondering why I could not use a 7mm stw bushing die to resize the necks and then trim the brass to appropriately OAL.

Does Quality Cartridge make good brass? I have not decided whether to use Nosler or Remington 7mm stw, or go with Quality.257.

 

[Pdvdh]

I was wondering why I could not use a 7mm stw bushing die to resize the necks and then trim the brass to appropriate OAL.

You could, using the appropriate neck bushings for the 257 STW.

 

[aldeerhunter]

You could, using the appropriate neck bushings for the 257 STW.

Ok. Because much of the necked down Nosler 7mm stw ammo loaded by Ferguson split the necks upon firing, and a few cases split before being firing, I want to try necking down in steps, and annealing.

I have .265 and .266 bushings for my 6br. My thought is to get a 7mm stw bushing die and use the .266 bushing as the first step, and to order the appropriate .257 bushing for the last step. I have not measured the neck diameter of a loaded round or fired round. I think I will measure off of the fired round, and go with a bushing .002 smaller.

 

[Pdvdh]

Annealing is the cure for split case necks / shoulders. Should always anneal case neck/shoulder area when swaging down a parent case neck. Otherwise you'll risk split case necks upon 1st firing, and excessive neck tension on seated bullets.
2-3 thousandths less than the outer case neck diameter with a bullet seated is the correct size neck bushing die.

 

[adam32]

I took one of the bullets I have left from Ferguson apart. 78.5 grains of powder. The bullet is a 100gr TSX. The velocity is 3905. These shoot quite well-.5 moa. They are phenomenal on deer.


Does Quality Cartridge make good brass? I have not decided whether to use Nosler or Remington 7mm stw, or go with Quality.257.

I wonder what type of powder? With Ramshot Big Game you're pushing 70,000 psi...

I like Quality Cartridge brass, I have a 6mm wildcat that I use their 6.5 Rem Mag brass for, seems to be good stuff. No complaints.

 

[aldeerhunter]

Not sure which powder. I will likely try Ramshot and 7828 starting out, or maybe H1000.

 

[MudRunner2005]

I always load a light load when fire-forming for my wildcats, and never run full-power. That's how you end up blowing-out your cases on the first firing. I avoid this by taking the time and doing the extra step to actually make fire-forming loads. Then once they've formed after that first initial firing, then I load to full power and run my ladder tests.

 

[aldeerhunter]

I measured the outside diameter of a couple of pieces of loaded brass. I was somewhat surprised to find that the diameter ranged between .288 and .289. Since the bullet diameter is .257, I was expecting a much lower outside neck diameter. I guess the neck thickness of the necked down 7mm Nosler brass has something to do with it.

It will be a couple of months before Lee runs the .257 dies so I figure that in the mean time I will get a set of 7mm stw x dies and start out with a .286 bushing and work from there, using 7stw Nosler brass since the reviews I have seen on Quality brass seem to be about 50/50.

 

[Edd]

If I wanted to do what you are doing, I would call Hornady and have them make me a custom form die.

 

[Cheyenne 1]

I have 2 of these. One is a regular 257stw the other is a 257 stw ackley proved.
I would use ramshot magnum. R-25 and a couple others I tried would be very erratic and would suddenly have pressure problems.
Also when using cci magnum primers I would have some hang fires. Changing to federal 216 fixed that problem.
As far as brass I necked down in one step. I either used a 257 wby neck die or the redding dies I have for it
Dies I have are a custom set of Redding.
Kind a neat thing to shoot. I kind of got out of the speed stuff and haven't shot them in a few years.
If you want i can look up the data I had.

 

[aldeerhunter]

Thanks. So I can use a .257 wby neck die to size the neck? I would appreciate the load data. Did you try 7828? I think I will get a pound of 7828 and a pound of ramshot magnum and give things a go.

 

[Cheyenne 1]

Thanks. So I can use a .257 wby neck die to size the neck? I would appreciate the load data. Did you try 7828? I think I will get a pound of 7828 and a pound of ramshot magnum and give things a go.

Yes you can if I remember right I just kind of went by feel.
Never used 7828
The load I have recorded was 81 Gr of R-25 with a 100 Gr e tip. Velocity was Just under 4000fps. That's where I gave up as it was very erratic on pressure.
Then I ended up with 83.5 gr of ramshot. That was way more pressure stable. Speed was the same.

My 257 stw ackley improved I was at 84 gr of r 25 and a 110 gr accubond at over 3900 fps. That is the only one I ever shot a deer with. It was 640 yards. Right behind the front shoulder clipped a rib on the way in and bullet was recovered against the hide on the off side. I wasn't excited about the performance.
Obvioulsy these loads work in my guns. Be careful and work up from a lower starting point.
And in mine they weren't on the ragged edge. Brass life was fine.
I will say that I shot way more deer with a 257 wby magnum. A 117 gr hornady btsp, that I would say is a deer killing machine. Put one through the boiler room and it would leave a blood trail a blind man could follow.
And it wouldn't be a very long trail.
Just my 2 cents worth.

 

[Pdvdh]

Never used 7828
The load I have recorded was 81 Gr of R-25 with a 100 Gr e tip. Velocity was Just under 4000fps. That's where I gave up as it was very erratic on pressure.
Then I ended up with 83.5 gr of ramshot. That was way more pressure stable. Speed was the same.
Just my 2 cents worth.

As Cheyenne has noted, large capacity .257 cartridges are prone to powder bridging when using extruded (stick) powders. It seems that the extruded powders jam up at the shoulder/case neck when the case neck diameter gets down to the .257 and smaller calibers. Kirby Allen identified this problem with his .257 Allen magnum. It causes very erratic case pressures when the powder dams up at the case neck. As a consequence, Kirby only uses and recommends ball powders in his .257 Allen Mag. Small diameter and short extruded powders might work? If you try 7828, I strongly advise the SSC version.

I own a .257 RUM, the 7mm RUM necked down to .257 which is very similar to Kirby's .257 Allen Magnum. I also experienced a few scary high pressure spikes with extruded powders. Live and learn... I now use Hodgdon US 869, a ball type powder. My case capacity is much greater than a 257 STW. I suggest you follow in Cheyenne's path. Use Ramshot.

 

[AZShooter]

No one has mentioned you can use a seating die for the intermediary necking down step. Going from 7mm to 257 should be easy with the use of that die.

I never did have good results trying to neck down with a series of bushings in a bushing die. Now if Redding would taper one side of those bushings that would make a big difference. I have considered grinding one side myself but haven't done it yet.

If you owned the reamer you could make an intermediary form die. I made one for my 6mm-284 using the 6mm-284 finish reamer and an old 264 win mag barrel. After reaming, the neck area was sanded and polished to make it a bit larger. Works great when necking down 284 win brass to 6mm. Die blanks can be purchased from Pacific tool and gauge if needed.