JDJones75, 257 STW information...

[Donham]

I would think the .257 140 ULD would require close to what a 140-150 gr would in a .264, they are only 0.007 dif., or to round it off, only really just over 1/2 a caliber apart, (more than 1/2 and less than 3/4)..
I know this sounds like a bunch of mumbo jumbo, but round them off to the nearest even dbl digit number under "." and they are both 0.26 bores...
I would start looking for 6.4 loads on the net with the same low drag 140's in the same case or smaller to get a "GENERAL" idea to be on the safe side...

I think your 1-10 might be okey, my 06 fires the 115 vld's...
and a 06 might require a 1-8 to stablize the 140's, but I would bet your getting close to the same bullet RPM as I am with a 30 grn less bullet... it's all about rpm's
The faster you push it, the more RPM's. amd the less twist you need... a 257 roberts would probably need a 1-9 to stablize the 115 Berger VLD..
a 140 ULD in a 25/416 Rigbly case (with a 36 inch tube) might only need a 1-12 or even 1-14 at 4000 fps...

I think that 257 STW will handle the 140's or be darn close

I would like to build a 25 WSSM or a 25-06 with a 1-14 to shoot the 85 BT's..
I have launched them at 3700 fps, no big pressure signs.. but the 1-10 doesn't seem to like them.. they are 1.5 moa at 300 at 3700, and .75 moa at 300 at 3400 fps..

scott

 

[Fiftydriver]

Donham,

Your last post got me thinking.

I have been shooting the 140 gr A-Max in my 6.5-06 AI with 1/2 moa accuracy out to 500 yards.

This rifle has a 26.5" barrel with the industry standard 1-9" twist. I was told by some that this twist would not stabilize the 140 gr A-Max but decided to try it anyway.

At 3000 fps this bullet very accurate figuring the action I built the rifle on is a Mauser 98 and the first custom accuracy rig I even built.

With your comment comparing the 6.5mm with the .257" I realized I had a 500ct box of the grand 155 gr Sierra Mk's on the shelf waiting for my 1-8" 6.5 WSM that I am building for my next XP-100 big game handgun with a 15" barrel.

I figured that if the big 155's would stabilize in the 1-9" twist 6.5-06 AI at 2800-2900 fps then I would have a good chance to get the 140 gr RBT ULD bullet to shoot well out of the 257 STW loaded to 3300-3400 fps with a 1-10" twist.

I loaded up three loads using H-1000 and the CCI-200 primer. All loads were seated to 3.222" which is 0.005" off the lands and very short for this bullet.

The first group averaged 2855 fps and the group at 100 yards measured .945" for three shots CTC. I was not interested in doing a major load developement session, just wanted to see if the bullets would land on point.

Obviously they would.

The next load up, 56.0 gr cut a .698" ctc three shot group at 2897 fps average.

The last group at 57.0 gr suprised me a bit with a ctc group of .326" ctc for three shots and 2935 fps average.

Now I am under no impression that this bullet will average this group size but obviously it is stabilized plenty well out of the 1-9" twist.

This give me good reason to believe the 140 gr ULD will stabilize in the slightly slower twist but driven to substanially faster velocities.

We will have to see.

Just thought I would fill you in on the results of this little experiment. I may explore this bullet further in my 6.5-06 AI but think I should lengthen the throat about .250" to get that extremely long bullet out of the case farther. IT take up alot of powder capacity.

My 6.5-06 AI reamer was designed for use with the 120 gr Ballsitic Tip and 140 gr Partition, with those bullets to be seated to an oal to allow feeding through a magazine.

This is not real good for this very long bullet. I will need to do some serious thinking before I lengthen the throat this much as it may limit what other lighter bullets I can shoot well out of this rifle.

GOod Shooting!!!

Kirby Allen(50)

 

[brianwinzor]

Donham, I agree that the number of revolutions per minute achieved by a bullet is the key to it being stabilised and also being accurate.

Unfortunately the Bullet manufacturers don't publish the number of revolutions on the side of the box, only sometimes they publish that it needs a 1 in 7 to 1 in 9 twist, etc.

I agree that increasing the velocity sufficiently can stabilise the bullet, but often the velocity increase needed is beyond the capacity of the case being used.

I have found out that in many cases you have to shoot to find out, and will use several personal experiences.

About 5 years ago, I decided to try the Hornady 75 grain Amax in my .224 Clark, and thought that the extra velocity I would be achieving should stabilise it in my 1 in 10 twist barrel. However, despite recording 3,830 fps and 275,760 revolutions per minute the bullet keyholed into the target. I subsequently found out that some benchresters had done extensive research into the 75 grain Amax and they found that you needed 280,000 rpm to stabilise it, best accuracy was around 290,000, and that the bullet started to come apart when 320,000 rpm was reached.

In 1986, I had a 220 Swift AI built up and used a 1 in 12 twist which my gunsmith thought would stabilise the newly released 69 grain Sierra HPBT. Despite achieving 3680 fps and 220,800 rpm, the bullet keyholed into the target.

Yet my 1 in 10 twist barrel (that was formerly used for a .224 Clark, and currently is a 22/250AI), will stabilise the 69 grain Sierra HPBT at velocities ranging from 3100 fps (223,200 rpm)to 3400 (244,800)

My 25/06 AI with 1 in 10 twist barrel is achieving sub 0.5 moa from the Nosler 115 grain BT at 3250 fps (234,000 rpm), and I estimate would push a 130 grain bullet to about 3150 fps and 189,000 rpm, which seems a low number for what is probably a long bullet.

The 257STW should achieve 3400 fps with the 130 grain bullet and with 244,800 rpm, may stabilise it. However, long bullets require high rpm to stabilise, as in the case of the 75 grain Amax.

However, I agree with you suggestion that twist rates used for 140 - 150 grain bullets in the .264 calibre should work for the 130 -140 grain bullets in the 257.It will be interesting to see if this eventuates.
Regards, Brian.