338 LM Improved w/ gain twist barrel

[JeffVN]

I shot 8 more of the 276s again today, to verify velocities so I can add more info to the mix from yesterday's range session. Today it was nearly identical as yesterday for weather. I shot my last 295 6.5 Caliber as teh 100 yard zero calibrator and get the ball rolling. I then shot 8 of teh 276s, watiing 2-3 minutes between shots.

The load was not a developed one, but simply one that I know was going to be safe (it was 2.0 grains less then what had popped/leaked on my yesterday). Anyway, the load produced an average velocity of 3,106 fps an ES of 30, and was a 1.0 minute load. Given that teh minute was mostly verticle, I suspect a real accurate load is nearby, but not the 103 grains of Retumbo that I was using. I also think that today's velocities confirms my estimate yesterday of 3,150 to 3,200 fps for the top tested velocity.

FYI until I can do more at distance elevation and drop testing with known loads and color coded bullets, I'm calling the ball on BC on the ZA 6.5 at 3,200 fps as roughly .940. That does not suck too bad at all... But since that speed is not one thatI can or want to replicate it is likely of interst only to the 338/408 shooters where I believe 3,300 - 3,400 fps is easily within reach.

Noel wanted me to also mention that given my recent success with the 6.5 caliber ZAs, he wants me/us the start testing the 7.0 caliber projectiles as soon as he can get some produced.

When I get them and shoot them, I'll let you know what they do.

JeffVN

 

[davewilson]

Jeff, thanks for all the info, i'm sure most of us fund this stuff very interesting. my question would be how you determined to use a 5.4" exit twist? this just seems flat out way outside the box and was just wondering if it was determined you needed something this fast. did Noel or someone with experience recommend this fast a twist?

 

[Augustus]

My goodness Dave, where have you been for the last two yrs. There have been lots of tests run on this class of bullet for at least that amount of time. None of it has been kept secret and it is still available for you to review on various threads both here and on Snipershide. Granted, I did most of the early testing and I may not have the " Experience " needed to perk your interest; however, if you care to spend the money and time to acummulate the barrels, cases, copper etc to do your own tests Im sure the bullets will act the same whether fired by a vastly experienced person such as yourself or some inexperienced hillbilly like me. Better yet why dont you amble on down to the house and I will let you use my stuff to verify how these things act. I still have a few of each of the various prototypes and several twist rates. I bet you will leave more experienced, even if the experience was handed to you from a dumb-*** like me you may find it usefull. Oh, by the way have you noticed even with the jacketed bullets, longer bullets require tighter twist.

 

[JeffVN]

Dave

Yes I had input from both Noel, Agustus, and Frank at Bartlein, in figuring out the 5.4" exit twist on that barrel. I suspect a 5.0" would be better, as with the very long solids (as in 6.5 calibers or LONGER in length) I'm not sure you can ever twist them too muhc. Its not like they will come apart; nowI have had some go unstable like the ones I test ed the other day, but they dop not go poof after leaving the muzzle, just kind of wobble then carwheel off into the netherworlds never to be seen or heard from again.

The good news is it looks like there are several folks moving aggresively into the solids realm, and I'll be testing and shooting lots of the bullets this coming spring and summer. I'll be noting which ones work and which ones don't from my rifle. All in all its a learning curve for both myself and the manufacturers.

JeffVN