375 Snipe Tac...Barrel and Bullet tests

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Black Diamond 408, Aug 14, 2008.

  1. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    Hello to all fellow powder burners!

    Recently i built myself a 375 Snipe Tac (375-408 imp) mostly just for fun shooting. As most of you know its an improved 408cheytac case necked down to .375cal and shoulder blown out to 35deg and pushed forward about .050

    I ordered a McGowan barrel for this build, i talked with Jon there and he got the barrel out to me in about 3 weeks. It is a 32" light contour 12 twist, fluted, muzzle .925 I finished the barrel at 31.5" plus added a Lawton stainless muzzle brake.

    The Action is a 1.550" dia x 10" long Viersco single shot chrome moly with Stainless steel bolt body. The bolt is double diamond fluted, and accented with black Cerakote, as is the entire action. Jewel trigger, extended bolt handle, sako extractor are a few of the little things. On top of the action i cut a steel 40 MOA scope base for the 5.5-22 nightforce scope.

    The stock is a Lone Wolf 100% carbon/ hunting style. I completly gutted the inside of the receiver area and filled it in with fiberglass, carbon fiber and resin. I re-inletted the stock for my action and pillar bedded and layed several layers of carbon cloth to seal it all in.
    The stock is camo finished with dura coat and a special light weight recoil pad i make myself. The weight of the rifle alone was 13# with the nightforce and rings it came out to 15 3/4 # Here are a few pics of the finished rifle...

    [​IMG]
    375 Snipe Tac, Long range hunter

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    Viersco Mfg single shot magnum action with fluted bolt

    [​IMG]
    Barrel break in

    I finally got some time to get out and pull the trigger on this bad boy. I formed up some brass in my special forming rifle, saves on barrel life. I trimmed the cases and got them ready for the break in loads. I used 260 AB's for the first part of my tests. I ran the loads rather mild at 132gns of Retumbo, vel was averaging 3200fps. The groups from these loads
    were running in the .6 range. I also tested a few of the first run of the Sierra 350grn SMK bullets, same powder charge, 132 retumbo. These were flying at 3000fps, groups were about 1". The barrel was breaking in real nice, after the first 8-10 shots cleaning was a breeze. So i decided it was time to ramp it up to the full loads and 3 shot strings.

    Next day i loaded up some 260 AB's at 145gns of Retumbo. I moved the rest back to 275yds. I fired the three shots, speed was right at 3500fps, groups were terrible. Might be due to the longer throat and the bullet has too far to jump to the lands.

    I wanted to test some 333grain Lehigh solids he sent me. I loaded up two test lots, 140grns and 142grns of Retumbo. I set the bullets .065 from the lands. He told me the calculated BC was .941 From a clean bore i fired three shots on target at 275yds, all three landed aprox 5" left of center bulseye. Group was just at 2" Vel was 3250 average.
    The case extracted very easy so i pressed on to the 142gn load, same bullet. I only had three of each so i wanted to take a shot at my steel gong at 700yds and see what kind of results i could get. I fired up the exbal....shoot..batt dead. So i walked back to the house and input the numbers on the main computer, i figured 3250fps with 140grns , 142 should bring it up a bit more. I input the numbers for my area, 1400' elevation, 75deg, 60% hum, ect. BC .941, speed 3295 i put in, just a guess. It came up with 7.75moa at 700yards with a 275yd sight in. So i walk back to the range, a whole 200yds from my house, clicked up the nightforce, held dead center on the plate, BOOOOOOOM, WHAAAAAAAAAAAANG...i was amazed! I fired the remaining two loads and they both hit on target. That steel plate weighs close to 40# or more and it flipped it around like a toy. I got on my UTV and drove out too see what it all looked like, all three shots landed 1/2moa to the right of center with a spread of 4.5" I was happy with this for initial tests. The chrono ave for the three shots was 3297fps. I didn't think these Lehigh solids were going to stabilize to good in the 12 twist barrel, the bullets are right at 2" long, im very pleased. This weekend i will load up the new run of Sierra 350SMK bullets for testing, i might stretch the distance out to 1200yds.

    Here is the steel plate target.
    [​IMG]

    It looks like an upside down bell. If you look close you can see these were drops from cutting out man sized sillouettes for the tactical range. Its AR400 steel. Pretty pink!

    Dave
    Cowboy-Dave
     
  2. James Jones

    James Jones Well-Known Member

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    Very cool rifle , I can only imagine what kind of damage a 260gr accubond would do to an elk at 500yds running out at 3500fps !!

    PM inbound
     

  3. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    This wasnt even a full load, 3700+ has been reported from this chamber. I'm betting a faster burning powder would be needed with the light bullet. I'm going to stay with the 300grn as the lightest. 300-350 is a good range.

    Dave
     
  4. Gustavo

    Gustavo Writers Guild

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    Fantastic rifle!

    Please do not forget to post your 1200 yards results (data will be useful too!)
     
  5. Joel Russo

    Joel Russo Official LRH Sponsor

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    Very nice Dave.

    Let us know how the new SMK's work out of that 12 twist.

    Getting ready to barrel another up, but I went the other way on the twist. I wasn't 100% happy with the 11.5.
     
  6. 308 nate

    308 nate Well-Known Member

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    Dave,
    Another work of art! great report. Look forward to reading more on the
    big .375-408's.

    308nate
     
  7. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    Joel,
    What way did you go? 10? I wanted a 10 twist for this project but McGowan didnt offer it in this length, mainly it was to test their barrels as well for quality and such. I have 3, 8 twist barrels coming for some radical builds in this chamber.

    [​IMG]

    Top bullet is the Lehigh 333 grn
    second is the LM 119 408grn
    third is the Viking 403 grn
    The bullets are almost 3" long

    [​IMG]

    Look at the tiny Nosler 260 acubond with the giants!
     
  8. Tyler Kemp

    Tyler Kemp SPONSOR

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    PM inbound...nice gun!
     
  9. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    Nate, Thanks!
    I should have more info this weekend.
     
  10. Joel Russo

    Joel Russo Official LRH Sponsor

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    Dave,

    Give me a call when you get a chance and I'll fill you in on the twist in the new barrel.

    I have some of those solids from Dave but I'm a little reluctant to put them through the barrel due to their material.

    Cases of both my .338 and .375 are nearly identical to yours.

    Here's the picture of my .338-408 aka.. Big Baer that Paul from 6mm BR used when he wrote the article about the 3.806" group I shot at 1,680 in the early spring. It's next to a 6x47 Lapua and that's the 300 SMK in the neck.

    [​IMG]
     
  11. James Jones

    James Jones Well-Known Member

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    WOW , I realy want one of those big case rounds , but its realy hard to me to justify a 3000 yd gun when I have a hard time streching the legs on my 308's !!

    I guess I'll just have to move out west.

    Or maybe a slow twist rifle with lighter bullets ie the 260 Nosler at 3700fps , kinda like a 300 Varmiter on steriods !!

    Where's wildcat ?
     
  12. Augustus

    Augustus Well-Known Member

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    408, how close are you to testing the viking and adams tail. I have a build coming from Barney, the action is done and they were contouring the barrel last wk, it is an 8 twist and I have 300 of the vikings. Let me know how it goes if you get there first.
     
  13. Black Diamond 408

    Black Diamond 408 Well-Known Member

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    You will be the first, i have no intention of testing any of the Vikings or LM 119 bullets, i only have the 2 bullets a customer sent me to look at. I have 3 barreled actions going to Norway, they are going to shoot these bullets at 3000 yards or farther. I dont even know where to start for loading data, prolly Re25 or slower. I have a hard time finding a place to shoot past 700yds.

    Dave
     
  14. davewilson

    davewilson Well-Known Member

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    those big solids look like they're going at least 3k just sitting there on the carpet!

    Joel, i saw a couple guns just lying around at the shop we could test those things with...