257 STW or 6.5 STW

[blacktailslayer]

What would I be getting into building one of these rifles? I am thinking of a fast twist barrel and the wildcat heavy for caliber bullets. What is needed for handloading,as far as necking down etc? Detailed help would be much appreciated, especially guys that have built one.What kind of velocity would you be looking at with say the 142 wildcat in the 257 STW? Thanks guys!

 

[Fiftydriver]

Blacktailslayer,

I have built dozens of 257 STWs and there are about as easy to load for as any factory round.

With the size of this case capacity, with either caliber, you will be far better off using heavy for caliber bullets as this will greatly tame down these rounds and velocity spreads and consistancy in most cases improves dramatically with the heavier bullets.

in the 257 version I recommend starting with a 130 gr bullet weight for a minimum to get the most consistant performance. From there up to the 142 gr ULD RBBT and 156 gr ULD RBBT, this round works extremely well. THe 142 should work plenty well in a 1-8 twist and the 156 gr will also in most cases but I prefer a 1-7 because that is what I have always used.

The 6.5mm has a wider selection of bullets but to be honest, most of them are designed for much lower velocity rounds. I like bullets starting at the 140 gr range for this chambering and with the new WIldcat 168 gr ULD RBBT, it will offer a dramatic ballistic jump in performance.

If I had to choose between the two, I would probably go with the 257 STW simply because I am very familiar with that chambering and know exactly what it will do with the 130 and 156 gr ULD RBBT.

As far as necking either round down. With the 257 version, I recommend a step down die. These are cheap, get in a 264 Win Mag FL die and it works perfect for a set down die with the expander removed. Then run it though the 257 STW FL sizing die and your ready to roll.

The 6.5mm version would not need a step down, just go right from 7mm to 6.5mm in one pass through the 6.5mm STW FL sizing die.

Best powders I have found are H-1000 and Rl-25 for the lighter bullets and Retumbo and Ramshot Magnum for the middle weights. Also US869, AA8700 work very well for the heavy bullets.

The 257 STW will get right around 3300 to 3325 fps with a 142 gr ULD RBBT. Around 3450 with a 130 gr and 3100-3150 with the big 156 gr ULD RBBT. These are out of 28-30" Lilja barrels.

The 6.5mm version will get roughly the same velocity with 10 grains more bullet weight or 50-75 fps more velocity with same bullet weights as the 25 cal.

Good Shooting!!

Kirby Allen(50)

 

[blacktailslayer]

Thanks very much for the information Kirby, very much appreciated. What kind of barrel life have you gotten out of this caliber? Do you have to reduce the necks after necking them down, with the excess brass in the neck?
I was also wondering what BC's you have got for the big 25 cal Wildcats?

 

[Fiftydriver]

I like to think I build big game rifles that shoot like BR rifles. That said, when I design a reamer, I design it for accuracy big game hunting. I do not like to turn case necks but many do. Because of this, I design my reamers so that they work with the 7mm STW brass necked down to 257 with no turning needed. If you want to take a light truing cut on the case necks they still offer a very quality neck to chamber fit but not needed.

The BC numbers I have come up with are from measuring actual bullet drop out to ranges in excess of 1000 yards with the 142 and 156 gr ULD RBBT and out to 800 yard with the 130 gr ULD Flat base.

As such, realize, these are just the numbers I had to use in my ballistic program to get the generated model to match up with actual bullet flight using my muzzle velocity and three drop values at three different ranges. I am not saying these are scientific BCs, just what allow me to hit what I shoot at in real world shooting.

130 gr ULD FB...............0.520
142 gr ULD RBBT.............0.710
156 gr ULD RBBT.............0.820

Also remember these were at velocities out of my 257 Allen Magnum. THe velocities were 3650, 3510 and 3330 fps respectively so they may be slightly different at the lower velocities of the 257 STW but not much.

Kirby Allen(50)

 

[blacktailslayer]

This sounds like the ultimate deer and sheep round!!! I live in British Columbia, Canada, where the Wildcat bullets are made too! What kind of barrel lfe can be expected with the 257. It will only be used for hunting, as I shoot my .223 for practice all the time. I was wondering Kirby if you know any smiths in Canada who are building these types of rifles? Thanks!

 

[Fiftydriver]

Depends on how the barrel is cared for. Could be as short as 500 rounds or as long as 1000-1200 rounds if you really baby the barrel.

I do not have any smiths in Canada that I can recommend but I am sure someone on this board will refer you to a top quality smith in Canada as there are many up there.

Kirby Allen(50)