Flat shooting Elk gun?

[Fiftydriver]

Brent,

The .820 b.c. number I give for the 156 gr ULD in 257 caliber is what is needed to get my drop chart to match up with real world impacts out to 800 yards. I know several have scorned at this method but it works. Is it accurate, probably not enough so for many but it will allow me to hit a 12" target from 0 to 1000 yards or come within 1/2 moa of that target with a first shot so I am satisfied with the number.

I have to seen this with the Sierra Mk bullets using the same testing proceedures out of my 338 Kahn. The 300 gr Smk produced a B.C. in the .790 range over 1000 yards. The 300 rg Wildcat ULD produced .810 over the same range and even out to 1760 yards.

My 338 Kahn cases hold 136 to 138 gr of water and has a neck length of .365". For all practical purposes it is identical to the 338-416 imp in case capacity.

Actually if it had a 40 degree shoulder instead of a 35 degree it would hold very slightly more then the 338-416 but at this level a few grains is meaningless in performance.

My barrel is a 34.5" Lilja so I will have to test the WC872 and see what I can get. Did you have any load data from Darryl. I would be curious and with these case capacities being so similiar I would suspect starting loads would be nearly identical, as would top end loads.

The 156 gr ULDs measure 1.545" in length and at full blown velocities from the Allen Mag will stabilize in a 1-8 twist.

At starting load velocities, 2700 to 2900 fps, they are not fully stabilized and you will see slight nose tears on target at 100 yards. At 3000 fps this goes away and at 3200 fps thy shoot very well out to 1000 yards.

I discussed this with Dan Lilja and on his recommendation as well as advise from Richard Graves, we all decided that a 1-7 twist would be best for this bullet as it will be used as a big game hunting bullet and cartridge.

Dan also stated that there would be no velocity drop with the slightly faster twist either as that is a wifes tale.

So as a result I am having Dan get tooled up as we speak for the 1-7, 3 groove 257 barrels for the 257 Allen Mag.

This twist will also allow rounds like the 257 WSM to be used with this bullet for extreme range match use which would make a better higher volume shooter then the huge 257 Allen Mag which is designed for big game hunting.

Good Shooting!!

Kirby Allen(50)

 

[Fiftydriver]

Brent,

While I will admit that in general, a beltless case is a better design the a belted, I have not found any consistancy problems at all using the Norma made 338-378 Wby cases. I cut my chambers very tight and I have never seen a variation problem with the belt in any way.

This is certainly not the case with American made belted magnum brass and is one of the main reasons I looked to build a better mouse trap in the big 257 class as the STW left me a bit sour. Performance was good but I could not chamber the rifles as tight as I wanted with the belt variation and either had to add 0.005" to the headspace so all cases would work or sort cases.

The Allen Mag solved this problem and gave me an extra 200 fps to boot, not a bad deal!

Still I have been very impressed with the Wby hulls and see no disadvantage compared to a beltless case. I am getting ready to build a 338 Kahn repeater here very soon so we will see how it does out of the mag. The receiver is a Wby MkV in 338-378 so I know it will feed perfectly.

Good Shooting!!

Kirby Allen(50)

 

[Brent]

Day before yesterday we fit a new Wyatt centerfeed mag box (4.0 internal length for Rem.700) in a friends Win M70. which someone had previously chambered in 378 Wby. The bullets were seated way deep to fit in the previous box but now have plenty of room to move forward, plenty far enough so that the belt on the bottom cartridge gets ahead of the top cartridge and makes for less than smooth feeding. It definitely works, and once he seats the bullets out where they can be seated now it can help but, they canelure will be away from the case mouth a bit too far to crimp. Still, the beltless Rigby case would offer much less hastle loading through the top and also feed smoother ta boot.

The other fact that the belt lies "above" the case web, unsupported by the casehead's strength, it expands and can not be sized down with a standard die, also the very front edge ahead of the belt is not able to be sized down enough and creates problems too. The Rigby, or any beltless case does not suffer short life from this because it can be kept sized properly. In general, these problems only surface if loads are hotter than 63,000 PSI or so, but the problem will get worse and worse if loads are just a little hotter than that. So, after the initial firing, monitoring further belt expansion is a REALLY wise thing to do if you're concerned with case life. If it expands in the slightest after the initial forming, it will keep expanding by about the same amount each time until it will no longer chamber, then the case is toast unless you make a die to size the belts back down. It's up to the individual if the hastle is worth it, kind of like neck turning, forming brass for a wildcat is etc.

If you get more than 5 firings on the 338/378 Wby case I'd say you're running less than 65 Kpsi.

I believe the other problem with belted cases can be almost as bad as setting the shoulder back too far on a beltless case, although works the brass a little different and may not suffer from sudden casehead seperation, they will weaken and crack very rapidly.
This problem with belted cases is, if you only bump the shoulder back far enough to just chamber them, you do not end up sizing down the area immediately ahead of the belt because the die isn't screwed down far enough, so it gets tight there now. You turn the die down and size right up tight to the belt and you end up pushing the shoulder back way further than you would have needed on a beltless case, then cases begin to stretch QUICKLY and seperate at the pressure ring. First time this results in you ripping a casehead off on extraction and you can't chamber another round you'll realize that only hunting with new brass is the sure way to go if it's belted.

I don't really care what it is, I just dislike ****-poor designs, and I really like a good one. /ubbthreads/images/graemlins/smile.gif

 

[Brent]

What brand chrono do you use? Generally I've seen higher indicated speeds than actual from Chrony brand chrono's but usually not lower readings, but this would make one believe he had a lower than actual BC not a higher one.

The Kahn seems to hold just about what I figured it would, 136-138gr water.

I agree that the 40 deg shoulder would be meaningless in terms of case capacity increase, also the 2-4gr case capacity increase the Rigby based 338 has is virtually the same. That increase with an addition 1.5" of barrel length Darryl has might make a bit of difference but you probably have a real good idea just how much already.

Someone here may remember what charges he used in his 338/416 Rigby Imp, I don't remember what it was but he stated it on many occation. I'm sure he'd tell you if you email him. I know he used one load for hunting and another lower load when concious of brass life.

What OAL is your Kahn throated for?

Thanks for all the info. /ubbthreads/images/graemlins/smile.gif