375 CT Rifle trouble

Frost84

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Nov 28, 2022
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Greetings! New member here but not new to shooting, reloading, custom rifles, etc. Looking for some advice and wisdom here on the hide. Just recently purchased a low round count (>100) custom rifle in .375 CT and am struggling to get it to shoot better than MOA groups at 300 yds zeroing rifle. Rifle is built on a Stiller 408 TAC action with Krieger 1.45" shank barrel tapering to 1.15" at muzzle with radial brake. I believe it has a 1-10 twist. McMillan A5 Supermagnum stock that appears to have been bedded to the action. Jewel trigger. Stiller 1913 Picatinny base with unknown amount of cant. Warne Mountain Tech 34mm rings. Nightforce ATACR 5-25x56mm Mil scope. I have right at 25 mils of elevation travel with this setup with 300 yard zero.

100 rounds of ammo was included with the rifle. New Peterson brass, 350 gr. SMK bullets, Reloader 33 powder, CCI 200 primers. COAL is 4.095" I pulled a few bullets and weighed powder charge out of curiosity. 144.9-145.0 grains is where they seem to checking out at. This seems like its on the upper end of load data shared I have seen here.

I'm not impressed at all with the accuracy of the rifle with the included ammunition. At best I have had 2 groups that were just hovering outside of 3" at 300 yds. Most all of the other groups it throws a wild flyer. 2 shots near the point of aim and then a flyer 6-8" outside group is common. I have purchased Whidden bushing dies to reload my own ammo. I have checked the distance to lands and the COAL of the ammo is just off the lands .020 or so it appears. I loaded up a few sets of ladder test loads starting at 135.0 gr. of Reloader 33 but seem to be getting the same results with the flyers. Not real sure what's going on here. I am starting to suspect the scope or mounts but nothing appears to be moving. Scope seems to track correctly but could possibly not be holding zero? Just thought I would pick some brains here before I send scope back into Nightforce for them to check.
 

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perttime

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How does it group at 100? What happens if you shoot 5 or more rounds into one group?
 

bohem

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Perhaps you're seeing why someone sold off a new, custom built rifle for a good deal.

Start with cleaning the rifle really well. If it was shot with solids there might be nasty fouling in there depending on the alloy used. Most solid bullet companies have learned not to use C101/110 by now but some still do it and the fouling from those is nasty in big guns.
 

FisherT&C

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  • Jan 1, 2020
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    A lot of things could be going on here. Less than 100 rounds through the barrel could mean the barrel hasn't sped up yet and that load is not going to work. Throwing fliers could mean the bullet is right at the edge of a jump node or it could be an ignition problem and you need to try a different primer. Also neck tension can contribute to fliers; so many factors.
    I would start over by running a ladder test to find pressure and a flat spot in velocity comfortably below pressure signs. Then try different seating depths to find the ideal jump; .020" off the lands is not always the answer. I want to be north of 150 rounds on a barrel before I finalize a load.
    Furthermore, I'm not a fan of radial brakes; they're not very efficient. I would use a big ported brake for 375 CT.
     

    Frost84

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    Nov 28, 2022
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    How does it group at 100? What happens if you shoot 5 or more rounds into one group?
    I didn’t see the point in firing more than 3 rounds when it wouldn’t hold them MOA or better.
    I have not tried to shoot groups at 100 yds.
     

    Frost84

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    Nov 28, 2022
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    Iowa
    Are you used to shooting bigger guns?
    I shoot a .45 smokeless muzzleloader shooting 70 gr. of powder and 225 gr. bullets.
    Also a .358 Norma Magnum that shoots bug hole groups.
    So the answer your looking for is no I’m not flinching. That is the best the rifle can do. Had my dad shoot it also and he gets similar results and he’s shot a lot of bigger bore guns as well.
    Truthfully I don’t think the gun kicks that bad for what it is. It weighs in at 26 pounds as it sits.
    51F52ED5-D77C-4D35-BFCE-54BD7FDF340A.jpeg
     
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    perttime

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    Oh. Looks as if the fliers are in pretty random directions. When you are shooting 3, is there some specific one that is usually of?
     

    Frost84

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    Nov 28, 2022
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    I have checked the mounts and tried other handloads. Even tried some Retumbo powder and get similar or worse results at 130 gr. with same COAL.
    I am suspecting the scope holding zero at this point. Seems like the scope might not be holding zero to me. My groups seem to migrate on the target.
    I have a Sightron SIII 8-32x56 I could steal off another rifle just to eliminate that variable. Think that’s where I’m headed.
    I have cleaned the rifle throughly when I first got it. Since then I’ve put 25 rounds through it. Trying to get it figured out.
     

    Geno C.

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    What’s your case growth after firing compared to before. If it is setup with a go gauge, that chamber could be pretty long for Peterson brass. My current lot of brass was .015” short of the go gauge. Check that. Also, check that a bullet can freely slide into a fired case to rule out neck interference. Peterson has a lot thicker necks than bertram. If your reamer was for bertram, you’ll have a problem.
     

    232593

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    What is your chronograph reading for velocity and ES for the loaded rounds and the hand loads you are testing?
     

    Frost84

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    Nov 28, 2022
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    What’s your case growth after firing compared to before. If it is setup with a go gauge, that chamber could be pretty long for Peterson brass. My current lot of brass was .015” short of the go gauge. Check that. Also, check that a bullet can freely slide into a fired case to rule out neck interference. Peterson has a lot thicker necks than bertram. If your reamer was for bertram, you’ll have a problem.
    I trimmed the once fired Petersen brass to 3.020 after their first firing. They weren’t crazy long after first firing. Like 3.050 to 3.070 I believe.
    I chambered the new Petersen brass after I pulled bullets and it chambers easily and so do my resized brass and loaded rounds.
     

    Frost84

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    Nov 28, 2022
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    What is your chronograph reading for velocity and ES for the loaded rounds and the hand loads you are testing?
    I will chronograph loads next time I shoot. I hadn’t set it up yet hoping for something to try to develop that looked promising first.
     
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    Geno C.

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  • Oct 24, 2007
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    I trimmed the once fired Petersen brass to 3.020 after their first firing. They weren’t crazy long after first firing. Like 3.050 to 3.070 I believe.
    I chambered the new Petersen brass after I pulled bullets and it chambers easily and so do my resized brass and loaded rounds.
    Not total length. Base the shoulder datum.
     
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    Wannashootit

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  • Sep 3, 2010
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    No experience with the CT...
    But with every rifle I've owned (including magnums up to the Lapua) I never stopped at one powder.
    Maybe N570, Retumbo, even BMG?
    Could be the rifle, could be the shooter (not uncommon with boomers), could be you need a different powder...
     

    232593

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    I will chronograph loads next time I shoot. I hadn’t set it up yet hoping for something to try to develop that looked promising first.
    Who made the ammo? Does the CBTOL vary by more than .001”? If so by how much?
     

    232593

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    I have not had the opportunity to try RL33 with 350 grain bullets. For those that do does the OPs charge weight seem within the norm?
     

    232593

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    OP did you get to chronograph the ammo you have or conduct any further testing?
     

    amymorgan20

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    Check the headspace with a new round and one from a fired round in your chamber. Peterson makes their Cheytac brass a lil shorter and if your chamber was cut with a standard reamer, that improper fireforming of the new brass may be causing the inaccuracy issues.
     
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    Frost84

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    Nov 28, 2022
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    Update. Shot the rifle yesterday with a different scope mounted on it with the same ammo. It shot 3/4 MOA groups with no flyers. Nightforce is sending RMA for their scope to be sent in for repair. I’m sure with some testing I can squeeze out a little more accuracy with different loads but at least I found the problem I was fighting. Thanks for all the help and trouble shooting.
     
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