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Inconsistent groups.. How to troubleshoot?

Discussion in 'Ammunition & Reloading' started by Green Rabbit, Jun 15, 2014.

  1. Green Rabbit

    Green Rabbit Western WA Member

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    Hi,
    I know there could not be a definitive answer as too many variables are involved, but I'm rather looking for suggestions how to proceed on troubleshooting.

    Here is what I have: a newly built rifle, shooting reloads, getting very inconsistent groups from 100 yards. Some are under half an inch and others are well over an inch. Here are two pictures from today's shooting, out of five groups:
    Group 2
    photo 1.JPG
    Group 3
    photo 2.JPG
    Another group is around 0.5 (first one), fourth and fifth are also in 1.5 inch range

    The rifle is a German 98 mauser action, heavy varmint profile ershaw 26" barrel, chambered 260 Rem, 1 in 8 twist. Basic accuracy tunes are made: action squared, bolt lugs lapped, glass bedded, barrel is free floated until about 2" before the action, bold trigger is set under 3lb. Yes I know this is not a competition configuration by any mean, but I still would expect it to be better than 1MOA

    Out of three factors - rifle, ammo and shooter - I'm fairly certain that I am capable of doing better than 1MOA. I am shooting off sandbags, through 14x Leupold and clearly can see through the scope that rifle does not move more than 1/3 moa or less while I'm slowly pressing the trigger

    Now, the ammo. My own loads, I am using new Lapua brass (first run of virgin brass), Lapua scenar 139gr bullets, 42gr IMR 4350 powder (1gr under max, no signs of over-pressure). Not sure how good the load is, and I didn't do any case preps yet but the brass is brand new so I don't expect it needs any.

    So what would you recommend to do next? Decrease powder load? at what increments? Do case preparation (trim to length, turn necks)? I have not yet invested in the tools but eventually will do. Switch to a different powder? or bullets? Maybe replace factory mauser firing pin with Tubb speedlock? Barrel lapping with abrasive bullets?

    Or maybe the whole config does not worth the efforts and I should rather invest into a better rifle?
    I am still surprised by presence of those 0.3-0.4 inch groups, if the rifle itself can't do any better regardless of the loads...

    I'm very new to accurate shooting, but really want to get better.

    Thanks much for your time reading this :)
     
  2. Joe13

    Joe13 NW of Vancouver Opinionated & Blunt Bronze Supporter 2015 Volunteer 2016 Volunteer

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    I'd start by using a few different factory boxes and verify if you get better or the same results.

    Then you could maybe use that as a baseline for your hand loads.

    But I'm no pro... By a long shot:confused:
     
  3. Certaindeaf

    Certaindeaf SE Portland Well-Known Member

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    What seating depth? Many/most seat as long as possible (magazine allowing) while still not jamming into the rifling.
     
  4. Green Rabbit

    Green Rabbit Western WA Member

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    2.827 overall length. I was trying to make the bullet touching the lands (setting baseline with cross-cut case neck seating the bullet when closing the bolt). However I am under impression that it is a little longer than needed, as I can feel some resistance when closing the bolt. Is it a significant negative factor, if the bullet is pushing to the rifling?

    Would it be better to return to the factory length (2.800) and go from there?
     
  5. Certaindeaf

    Certaindeaf SE Portland Well-Known Member

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    Some guys do what you're doing.. at least we know that they're long! How many times has this brass been loaded? I woulda trimmed/tried to trim (I use a Lee trimmer) before even loading factory new brass. Especially with multi-fired brass, it could be very dangerous if they are too long.. and easily yeild sucky groups.
     
  6. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    What caliber/cartridge are you using? (you didn't state that)
    Since you got a couple of good groups from the first two, then it went south, I'd suspect either a scope problem or a bedding problem.
    Barring that, here's a few of my thoughts.
    I like the idea of trying a few boxes of factory ammo just to baseline the gun.
    Having new brass doesn't mean the brass matches the chamber and you may have better luck when the brass is used again, more so if you neck size.
    Jamming the bullet into the rifling isn't where I'd start either. You could load up a few rounds of factory length and then more batches where you increase the OAL by .010" for each batch. Usually you'll find a "sweet spot" for OAL, at least for that particular load.
    Good luck. I'll be interested in knowing what you find.
     
  7. Green Rabbit

    Green Rabbit Western WA Member

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    That's brand new Lapua brass, never been loaded. I bought a box of 100 and still going through that box. I checked the length on few cases - it's within the specs and very consistent.
    The primers seem not the best - that's WLR (the only LR they had at Cabelas), and out of 40 shots I already had 2 duds. But it's highly unlikely that primers can have such an effect.
     
  8. Certaindeaf

    Certaindeaf SE Portland Well-Known Member

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    Also, are you certain that the resistance you feel upon closing the bolt is due to the bullet or the case being too long? How long are they?
    Edit.. I saw you just said.
    And primers are very important.. that's probably your real problem.
     
  9. Green Rabbit

    Green Rabbit Western WA Member

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    That's 260 Remington. Not the best choice for factory ammo, although I could order some online (hate the price, though)
    I don't yet have a case trimmer (just starting) - you think it's a good idea to load once fired brass without trimming, if it is still under the max length?
     
  10. Green Rabbit

    Green Rabbit Western WA Member

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    Unlikely it's the neck that is pushed against the chamber. I shot slightly longer necks last week (2.05, while specs is 2.035 and lapua cases are about 2.025), sizing them just to the dimensions that bolt closes without resistance with sized case. Seems like there was enough clearance for the neck in the chamber with bullet seating to 2.8 overall length. Last week results were about the same (1.5 inch groups), but I found that trigger did not clear against the floorplate stressing on the receiver. I fixed that with a dremel, and expected better results with not stressed action - but it didn't seem to help much.

    Good idea on the primers.. Will probably be heading to Cabela's for CCI's next week, hope they'd get some.
     
  11. Certaindeaf

    Certaindeaf SE Portland Well-Known Member

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    Yes but check them all. Good luck and try some other primers. A lot of guys have them here in the classifieds.. if a couple out of a hundred or whatever don't even go off, that's a serious indicator that the primers are a main contributor to your inaccuracy.
     
  12. iusmc2002

    iusmc2002 Colville, WA Active Member

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    Really seems like something is loose to me. I can't imagine what would cause such large differences in the group sizes if YOU are doing your job (you say you are, and only you know if you're being honest)

    Action screws torqued the same? Scope base? Rings?

    I just put an ER Shaw 7mm barrel on and it was shooting shotgun groups.... until I realized that I didn't torque the scope rings down and the rear ring had worked itself loose. Got it tightened down and started making consistent little groups around .5 MOA
     
    Certaindeaf likes this.
  13. Green Rabbit

    Green Rabbit Western WA Member

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    Yeah, I am also concerned about the primers. 2 duds out of 50 or so. While I have left opened box in the garage for a week (my bad, forgot to put it to the safe with dehumidifier), it's fairly humid there but not damp by any mean. It shouldn't have killed them.
    It also could be firing pin maybe a little too short giving light strikes. The dent on the primer may seem shallow.
    Anyway, box of CCIs seem like a reasonable thing to try next
     
  14. Green Rabbit

    Green Rabbit Western WA Member

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    I am honest, but I might be honest in my delusion :). I don't have another proven bolt gun to compare my own scores. Anyway, through the scope it seems quite stable until firing.

    Yeah' I thought about that, just rechecked all the screws. The mount is POS, but it's tight on the action. Front ring is dovetail type, but also tight. Maybe I should try another scope, although don't want to blame $1000 leupold...
    Here is how the whole setup looks like:
    photo.JPG
    There are only 3 screws holding the mount (not 4), and screws are 6-48. I might replace it with something stronger in the future, but still don't expect it to produce such bad results..
    That's great... I wish I could get .5 MOA...
     
  15. Green Rabbit

    Green Rabbit Western WA Member

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    Here is what I'm going to do next based on the suggestions here:
    0) Disassemble and reassemble the scope mount to ensure it's tight
    1) Resize once fired lapua brass to "just clears in the chamber" length; measure case to ensure they are under 2.035
    2) Clean, prime and load with 42gr powder (I'll use fresh primers from dehumidified safe)
    3) Seat the bullets to about 2.85 inch length
    4) Go to the range with seating die and press, and start with pushing to 2.8 length before firing.
    5) Increase length by 0.01 every 2 groups to compare results

    Anything I should change in the plan?

    If it doesn't work out, different brand of primers will be next thing to try
     
  16. iusmc2002

    iusmc2002 Colville, WA Active Member

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    I feel I have to comment on your "its not a competition rig" in the first post.....

    I would feel confident shooting that mothertrucker past 1000 yards all day (once you figure the bug out)

    Sounds and looks like a beautiful rifle, in an outstanding caliber. 6.5 is the new .30 cal. Don't give up on it yet.

    How many rounds are down the barrel? How did you do your barrel break-in? Or did you? At what point in your shooting are the groups really opening up? (i.e. 1st group is tight, 2nd group is less so, etc. etc.) The reason I was asking is because you said the barrel is free floated until about 2 inches from the action, and I think that would be the hottest part of the barrel, therefore its going to "move" the most, maybe putting pressure on the bedding/stock and making things not go right?

    I've bought Lapua brass that had square necks, out of the box. I've had the same thing with Winchester brass out of the bag. I always do a full prep on my brass when I first get it because of that. A good FL resize, chamfer, deburr and I neck turn them after I've fired them once. I don't know how much that affects things, but I do know that the round bullet won't fit in the square case mouth :D

    One of the best things I've noticed about long-range shooting has been finding what works!! The trial and error, fixing bugs, all that has been great! Having a scope mount that isn't completely flat to your action can cause you to throw some crappy groups. Ask me how I know. I never had any little tiny groups though, when that happened. Good luck, man!

    Also, one last thought. Maybe take some of that once fired brass and neck size or partial resize it, load the same load as in your OP, and then fire some groups of those next to some groups of FL sized brass with the same exact load. Just to see what happens.
     
  17. 2506

    2506 Seattle Well-Known Member

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    Horizontal stringing is a tough one to diagnose. Wind, maybe?
    Also check

    Flinching
    Cant
    Barrel Float
    Trigger pull
     
  18. Jamie6.5

    Jamie6.5 Western OR Well-Known Member

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    Nice gun! I built something similar, but with a different brand of barrel, and chambering.

    Sorry, but I have to ask,...
    What are you cleaning this new barrel with? It's not at all unusual to have a new barrel load up on copper, with layers of carbon added in, during the break in, and actually for the fist 100+ rounds.

    If you aren't already, I would start with a good copper cleaner like Wipeout, to ensure that you aren't suffering from early copper fouling. Keep going with it until the patch comes out completely clean, with no blue-green residue.
    Then shoot a couple of fouling rounds before shooting for groups.

    My 6.5 project would start opening up groups after about 20 rounds when I first built it. It now goes to about 50 before groups start to deteriorate, and that's when I know it's time for cleaning. Yes it's a pain, but it restores my faith in both my rifle build and my choice of rounds for it.
    http://www.6mmbr.com/borebrushing.html

    Tubbs claims his treatment will eliminate this, but I have avoided it since there is really no way of knowing how much shorter the barrel life will be after using it. Others have had great success with it though.

    The next thing to start tracking with your shooting is heat. Specifically ambient temp vs barrel heat. This time of year it's not unusual to be shooting at 45-50* in the morning, and 75-80* in the afternoon, and worse if you're in the sun. Don't expect your pet load to behave the same under both sets of conditions. Especially as the barrel heats up.
    Unless of course you're keeping your ammo in a cooler.
     
  19. orygun

    orygun West Linn Bronze Supporter Bronze Supporter

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    It's highly likely you just found your biggest problem right here. I've never had trouble with Winchester primers, but I once had a batch of brass loaded with some old CCI primers that raised havoc with consistency. Pressures could be all over the map just because of inconsistent ignition.
    OR, if your primer strikes aren't very solid, same problem, just a different reason.
     
  20. Certaindeaf

    Certaindeaf SE Portland Well-Known Member

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    The second target indicates vertical stringing.. the target could well have been hung sideways but that's bad practice for archival purposes.