300-375/408 Cheytac

Discussion in 'Long Range Hunting & Shooting' started by durak, Nov 8, 2011.

  1. durak

    durak Well-Known Member

    Messages:
    190
    Joined:
    May 29, 2011
    Has anyone here had experience with a 375/408 Cheytac necked down to .308? If so, what were the overall results?
     
  2. trueblue

    trueblue Well-Known Member

    Messages:
    2,277
    Joined:
    Feb 18, 2008
    No experience, but that would be a very bad idea.
    Maybe get 300 rds of barrel life.
    The smallest I would neck down a 408 case would be the 338.
     
  3. Rocky Mountain

    Rocky Mountain Well-Known Member

    Messages:
    393
    Joined:
    Sep 13, 2010
    Yip take the above posts advise say away from it
     
  4. durak

    durak Well-Known Member

    Messages:
    190
    Joined:
    May 29, 2011
    Explain yourself: dating Roseanne Barr bad or driving 10 miles over the speed limit bad?

    I got it - ultra short barrel life - I have friends that get that out of their benchrest rifles. What else would be a concern.
     
    Last edited: Nov 8, 2011
  5. Chase Curtis

    Chase Curtis Well-Known Member

    Messages:
    436
    Joined:
    Aug 15, 2011
    To much case capacity
     
  6. Sako7STW

    Sako7STW Well-Known Member

    Messages:
    434
    Joined:
    Feb 12, 2004
    Isnt some of the Allen Mags based off of the Cheytac case?? I bet Kirby would argue this some!
     
  7. Chase Curtis

    Chase Curtis Well-Known Member

    Messages:
    436
    Joined:
    Aug 15, 2011
    Yes some of kirbys are...all the way down to 338. Even his new raptors has a new hot rod 308 cal but its not based off the cheytac. You can't fill the case up even with the 338...maybe u could...but only once.
     
  8. Fiftydriver

    Fiftydriver Official LRH Sponsor

    Messages:
    6,848
    Joined:
    Jun 12, 2004
    Back when I developed my 338 Allen Magnum, some of you know this but many may not that I also developed a 300 Allen Magnum at the same time. THis is the reason why there is currently only a 300 Allen Xpress based on the 338 Lapua parent case.

    The 300 Allen Magnum wildcat was actually the first of my 408 CT based wildcats. I was working closely with the original Wildcat Bullet company and Richard had made me some amazing 290 gr ULD RBBTs. We both figured that with this huge case capacity that we would need alot of bullet weight for consistant powder ignition and efficent powder burn especially with the very slow burning powders we would need to use such as surplus WC872.

    Got the first rifle made up with a 1-8 twist barrel that we figured would be needed for this VERY long bullet. Started with some simple chrono velocity testing. Second shot out of the rifle took out the chrono, bullet came apart completely and happened to land dead center through the base of the chrono.

    I then decided to get out on paper and see what was happening, past 50 yards we never got bullets on paper. At 50 yards we would get occasional marks on target from metal frags. I was also able to find several bullet frags laying on the ground and they were perfect shape noses of the bullets. The jackets were ripping right where the ogive met the bullet body.

    In thinking this over, we both agreed that the length of the bullet combined with the twist was causing to much stress on the bullet as it was fired. The bullet would contact the lands and begin to rotate at the front of the bullet but because of the length and weight of the bullet, the rear section was resisting this rotational force and we believed the bullet was being rung out like a wet towel which was breaking the core/jacket bond and when this happens bullet integrity is gone.

    So, next up was a bullet that we knew would handle these stresses. I also replaced the barrel with a 1-10 twist. We started with the 200 gr Accubond and while accuracy at moderate range was pretty good, velocities were not what I was hoping to see. They did get into the 3600 fps range which would turn out to be only 100 fps or so over what the 300 AX could produce in a 3" shorter barrel.

    Even worse however was that the velocity spreads were far to wide, often ranging around 175 fps spreads and best I ever got was in the near 100 fps spread range. Obviously this bullet did not have enough resistance weight to get a consistant ignition and burn on this powder.

    Next up was the 240 gr SMK which did perform better but velocity spreads were still very high, well over 100 fps. Again, close range accuracy, sub 500 yards was pretty good but past that, the velocity spreads really showed up in vertical stringing.

    Many of you know about these tests but most likely do not know about my testing with this case design but with shorter case lengths. I tested two other wildcats off this same case design but with different brass lengths. One was at 2.850" case length and the other was 2.700. With the full length version we were using around 150 grains of WC872. The 2.850" version, which is basically the same length as the 300 RUM had roughly 15 grains more capacity then the 30-378 Wby class chamberings. The shorter 2.700" version was very similiar but slightly more capacity then the big Wby round but in a much shorter package.

    Certainly, as powder capacity decreased, the attitude of these wildcats in 30 caliber improved. In fact both of these wildcats showed pretty good promise in accuracy and even velocity consistancy. The hang up however was two fold.

    1. Case forming was a pain in the rear for lack of a better term, especially for the much shorter 2.700 case length version.

    2. These rifles would still require a CT class receiver so the rifles would be larger then conventional rifles and while they would outperform the best convenitonal chamberings in 30 cal, the work and size of the rifles did not make it worth while to offer this wildcat to the public.

    As such, attention was paid to the 338 Allen Magnum and then the 300 Allen Xpress, leaving the door open to future development in the furture with a 300 Allen Magnum wildcat.

    This eventually brought us to the 300 Raptor which I have been working on this year. The 338 Excalibur case is nearly as long as the CT case but similiar in diameter compared to the 338 Lapua (slightly smaller in dia). Capacity wise when converted to my highly modified case design is exactly 1/2 way between my Allen Xpress based on the Lapua and the Allen Magnum based on the CT parent case.

    Results have been extremely good so far and I beleive this is about the max capacity used with the 30 cal bore diameter. Expansion ratio is similiar to my 7mm Allen Magnum and while many have said that the 7mm AM is only a barrel eater, many that have used it find that while it does have somewhat limited barrel life, for big game hunting, it can offer many, many years of hunting service as I expect to see the exact same results with the 300 Raptor.

    The 300 Raptor wll use 122-130 grains of WC860 depending on what bullet you are using. These are actual powder charges, not case volume measurements.

    In my opinion, the full length CT case is just to large for the 30 cal bore. I do not get overly worried about barrel life, that has more to do with how the rifle is shot more then anything else, even with these ultra low expansion ratio wildcats but the problem comes in efficent powder burns and poor velocity consistancy.

    For those two reason, I do not see the 408 CT case as a viable option for anything smaller then 338 in caliber.

    Hope this helps some.
     
  9. TH

    TH Well-Known Member

    Messages:
    411
    Joined:
    Jan 22, 2003
  10. durak

    durak Well-Known Member

    Messages:
    190
    Joined:
    May 29, 2011
    Thank you for that info- that is what I was looking for. I knew there had to be a reason nobody offers one - - sounds like you had the same issues that I've seen in 6mm-7 mags and 22-284's, but on a larger scale. I'll have to look into one of your 300 Raptors when they are ready. Thanks again for the lightbulb