What might be causing this strange grouping pattern?

Undrgrndprdcts

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What metric typically causes a load to shoot two distinct seperate but very tight groups? I'm sure it's a common issue in development. I'm thinking it's on the end of a charge weight node or the seating depth is right at minimum jump and bullet variation is putting it over ethe edge. Charge weight workup made this load appear like the good one but I'll admit I haven't had enough time to fine tune it. Might also try seating .010 deeper. Was in a rush to get ready for a match this weekend so it will have to do, but curious what direction to go afterwards. Thoughts?

Eta: It's not me, this rifle with other loads and my other rifles will shoot tiny 1 hole groups no problem.
 

hafejd30

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    Same lot brass? Fired same amount of times or all annealed? Same everything? Same neck tension?

    Did you check loose optic/mount as well?
     

    Undrgrndprdcts

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    Same lot brass? Fired same amount of times or all annealed? Same everything? Same neck tension?

    Did you check loose optic/mount as well?
    Same lot once fired, same everything. All optics and mounts freshly mounted and not loose. Hawkins heavy tactical rings.
     

    straightshooter1

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    What metric typically causes a load to shoot two distinct seperate but very tight groups? I'm sure it's a common issue in development. I'm thinking it's on the end of a charge weight node or the seating depth is right at minimum jump and bullet variation is putting it over ethe edge. Charge weight workup made this load appear like the good one but I'll admit I haven't had enough time to fine tune it. Might also try seating .010 deeper. Was in a rush to get ready for a match this weekend so it will have to do, but curious what direction to go afterwards. Thoughts?

    Eta: It's not me, this rifle with other loads and my other rifles will shoot tiny 1 hole groups no problem.
    It's not really clear what you mean "to shoot two distinct separate but very tight groups"??? o_O 🤷‍♂️ Of course, a picture should be a huge help.

    If it's what I think you mean, go to 3:50 minute position on this video:

     

    acudaowner

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    I always wondered just how much seating dept really affects the round after it leaves the barrel especially when I have shot factory rounds just as good or bad as hand loads the hand loads having a more consistent numbers lengths from 2.180 to 2.218 (CBTO) and most in between all firing pretty much all shot the same . I may pull or make a mistake on my timing or what ever it was I screwed up , but the bullets all fired and hit the target just fine . neck tension I sort of get tighter necks build more pressure before releasing the bullet than looser necks that makes sense sort of . Once the bullet is moving down the barrel what does seating length at the cartage do at that point . If your loosing too much pressure from escaping gasses then you end up with a squib or something like it , if not the bullet leaves the barrel on it's crazy fast trip to the target . Smart people can tell you more I do agree with the other post pics are needed .
     

    chevy_man

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    I always wondered just how much seating dept really affects the round after it leaves the barrel especially when I have shot factory rounds just as good or bad as hand loads the hand loads having a more consistent numbers lengths from 2.180 to 2.218 (CBTO) and most in between all firing pretty much all shot the same . I may pull or make a mistake on my timing or what ever it was I screwed up , but the bullets all fired and hit the target just fine . neck tension I sort of get tighter necks build more pressure before releasing the bullet than looser necks that makes sense sort of . Once the bullet is moving down the barrel what does seating length at the cartage do at that point . If your loosing too much pressure from escaping gasses then you end up with a squib or something like it , if not the bullet leaves the barrel on it's crazy fast trip to the target . Smart people can tell you more I do agree with the other post pics are needed .


    Seating depth affects group size.

    Using good brass, annealing, inside neck mandrel, fx balance scale, etc.

    I ran through seating depth over .015 and got a change in sd's and accuracy.


    Only reasoning I could think is barrel harmonics. Very minute changes in the dwell time as the bullet is traveling down the barrel causing it to exit the muzzle at slightly different angles as the barrel flexes.
     

    ShtrRdy

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    Have you tried re-seating the action and re-tourqiing the action screws.

    My first guess would have been scope but it sounds like you've checked over that part of the system.
     

    Feniks Technologies

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    If using modern good quality components and equipment, you should almost never have groups that are clustered and 1.5min apart.

    That’s nothing to do with “nodes” or anything else.

    It’s gonna be bad components/equipment, bad loading methods, or something up with rifle system.
     
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    Feniks Technologies

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    With modern components and equipment, you basically have to try to make bad ammo.
     

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    Also, any noticeable differences in SD when a relatively small amount of OAL difference like 0.015 is almost never actually the product of the OAL/seating depth change.

    It’s usually just the normal long term dispersion showing up as almost no one is using sample sizes large enough. And when they don’t use large enough (and even then you should) they don’t either understand or do the math on what the SD really means.

    For example:

    You shoot a 5 shot string and get an SD of 5.

    You changed seating depth, shoot another 5 and get an sd of 8.

    Most will take the 5 and 8sd as the actual sd of the load and reason the seating depth change affected the sd. Which at the surface and without a deeper understanding appears to be very logical.

    However, here’s what that first 5 shot 5sd string really means:

    Using a 95% confidence interval (allows for 5% error to cover several things) we are 95% sure that based on the 5 shots and 5sd that the true sd for that load is somewhere betweeen:

    3fps and 14fps

    We have no idea if the 5sd we recorded is correct, or if it’s on the high or low side. It can literally be anywhere in there.


    What that means is when you adjust seating depth and get an 8sd, that 8sd falls inside of the confidence interval for the charge weight.

    Which means you cannot confidently attribute the seating depth chance to the change in sd. And doing so is literally just guessing at this point.

    You would now have to shoot about a minimum of 25-30 shots of the charge weight with different seating depths to know if the sd is significantly different.
     

    hafejd30

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    My first thoughts (as I posted above as well) when I see guns group as op noted is usually a loose mount/pic rail or optic fail issue.

    OP,

    Is this just your reloads doing this? Have you shot other ammo that groups consistently in this setup?

    Don’t rule out the scope itself either. If you duplicate your issue with multiple ammo then optic or mount is my guess
     
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    SuperChop

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    I’m kinda thinking your parallax might be off just a bit. You build a position, shoot a pretty nice group, but then after you break position you possibly aren’t returning to an identical cheek weld, and if your parallax isn’t pretty spot on this would account for having another really nice group, but poi has shifted a bit.
    Just a thought.
     

    Undrgrndprdcts

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    Did this happen just after the freshly mounted optics/mounts ?
    It did, but I can't for the life of me figure out how anything would be loose or messed up. Steel base was torqued tight and loctited to action and hawkins heavy tactical rings have 6 screws per ring. Everything is torqued. I don't see how anything could be loose or jacked up. I'm meticulous about this stuff and have done it hundreds of times.
     

    Rocketvapor

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    I get two groups when shooting an 8X10 steel plate at my local 100yd range.
    Plate keeps swinging and I can't time it. I don't do moving targets :)
    (will reuse this excuse as needed)
    88ELD-10-shots.jpg
     

    hafejd30

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    It did, but I can't for the life of me figure out how anything would be loose or messed up. Steel base was torqued tight and loctited to action and hawkins heavy tactical rings have 6 screws per ring. Everything is torqued. I don't see how anything could be loose or jacked up. I'm meticulous about this stuff and have done it hundreds of times.
    This is likely your issue. It may be the optic itself. I would start here. A rifle that does what yours is doing tells you “I want to shoot” but “we have an issue”
     
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    Undrgrndprdcts

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    This is likely your issue. It may be the optic itself. I would start here. A rifle that does what yours is doing tells you “I want to shoot” but “we have an issue”
    I guess I could try remounting everything the same way I did 2 weeks ago? Optic is a mk5hd right now.
     

    hafejd30

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    I guess I could try remounting everything the same way I did 2 weeks ago? Optic is a mk5hd right now.
    I’m not saying redo the mount or the optic. Have you shot the loads that have done well and experienced the two separate groups?
     

    Undrgrndprdcts

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    Ok

    Did you fire anything besides these reloads since mounting the new optic/mounts?
    No. Probably doesn't help to narrow it down lol. I honestly thought this would be like a typical thing people see, X causes Y sort of scenario. I didn't expect a bunch of typical suggestions like loose mounts. I've just never experienced it before, that's why its strange to me.
     

    straightshooter1

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    No. Probably doesn't help to narrow it down lol. I honestly thought this would be like a typical thing people see, X causes Y sort of scenario. I didn't expect a bunch of typical suggestions like loose mounts. I've just never experienced it before, that's why its strange to me.
    Hmmm??? What do you expect when the issue isn't made clear? o_O 🤷‍♂️ Apparently, it's not the two tight groups describe in that YouTube video I posted???
     

    JimmyJr

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    I’m asking more than suggesting this, but rifle canted could be causing this?
     
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    Undrgrndprdcts

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    Hmmm??? What do you expect when the issue isn't made clear? o_O 🤷‍♂️ Apparently, it's not the two tight groups describe in that YouTube video I posted???
    What are you talking about? Everybody understands whats going on here but you. It's basically double grouping, like the video suggested.
     
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    Undrgrndprdcts

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    Just an update I reseated my action in the bedding/stock and checked my base (rock solid/tight) and retorqued my rings on base and optic. Will rezero tomorrow morning and see how the match goes.
     
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    hafejd30

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    Just an update I reseated my action in the bedding/stock and checked my base (rock solid/tight) and retorqued my rings on base and optic. Will rezero tomorrow morning and see how the match goes.
    What optic?
     

    Im2bent

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    What are you talking about? Everybody understands whats going on here but you. It's basically double grouping, like the video suggested.
    Well that video said that double grouping means your load is too hot. So I guess the question is how hot is that load?
     
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    Undrgrndprdcts

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    Well that video said that double grouping means your load is too hot. So I guess the question is how hot is that load?
    Its not hot at all. No marks on brass at all, no primer flattening or flow, 2718 fps out of 18" bartlein. Right in the ballpark for 130s. Below sierra book max.
     
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    ShtrRdy

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    I got caught up on the conversation. I'd say that if it still does the double grouping thing after you've re-seated the action and re-checked the mount and rings that it's the scope.

    If it still does it you'll need to try another scope.
     

    hafejd30

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    I've had this result from not using an expander mandrel in the sizing die. Once it was put back in, problem went away.
    You can run without. Just run expander mandrel through as extra step after sizing
     

    Undrgrndprdcts

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    The gun hammered out to 1200 today at the match. Shooting under half moa at distance. Extremely pleased with its performance. 92 degrees and no pressure issues with loads. Didn't shoot for groups at 100 but it doesn't seem to be a problem at distance. Not sure what to make of it all. I'm assuming a piece of something got stuck between base and ring maybe when mounting the first time who knows. At this point I'm running this load the rest of the season.
     

    oldfatjonwick

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    What metric typically causes a load to shoot two distinct seperate but very tight groups? I'm sure it's a common issue in development. I'm thinking it's on the end of a charge weight node or the seating depth is right at minimum jump and bullet variation is putting it over ethe edge. Charge weight workup made this load appear like the good one but I'll admit I haven't had enough time to fine tune it. Might also try seating .010 deeper. Was in a rush to get ready for a match this weekend so it will have to do, but curious what direction to go afterwards. Thoughts?

    Eta: It's not me, this rifle with other loads and my other rifles will shoot tiny 1 hole groups no problem.
    if you used the OCW process i'm guessing you selected the smallest group rather than the center charge weight of three groups with the same group center point of impact (size of group doesn't matter yet).
     

    Undrgrndprdcts

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    if you used the OCW process i'm guessing you selected the smallest group rather than the center charge weight of three groups with the same group center point of impact (size of group doesn't matter yet).
    No it was a load in the middle of the same poi and also the velocity was flattened out in this range as well. Group sizes themselves were similar at about .5 moa. Again I'm not sure what it was but the gun shot even better than I expected out at distance on Saturday.
     

    Feniks Technologies

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    No amount of load development is going to cause groups to be 1.5 moa difference in a 5 shot string unless there is something completely off with the ammo.

    You’d get a random 1.5moa spread. But not consistently 2 shots touching here and 3 shots touching there on several groups.

    One time would fall under random dispersion of a bad load/group. Consistently happening is indicative of something completely non ammo related.

    You seem to have got it worked out via reassembling things. Which is always good news.


    Most “load development” methods are the equivalent of randomly picking things anyway. But that’s another conversation.
     
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    Undrgrndprdcts

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    No amount of load development is going to cause groups to be 1.5 moa difference in a 5 shot string unless there is something completely off with the ammo.

    You’d get a random 1.5moa spread. But not consistently 2 shots touching here and 3 shots touching there on several groups.

    One time would fall under random dispersion of a bad load/group. Consistently happening is indicative of something completely non ammo related.

    You seem to have got it worked out via reassembling things. Which is always good news.


    Most “load development” methods are the equivalent of randomly picking things anyway. But that’s another conversation.
    Yes this does make sense to me. I'm guessing it was something that got stuck in a ring somewhere that wasn't visible. I'd like to say I'll shoot more groups to confirm everything's ok, but I'm not going to waste ammo and barrel at 100 yards.