Weird load issue
- Thread starter 105gr
- Start date
Keith Glasscock
Gold $$ Contributor
Troubleshooting a poor shooting rifle (this qualifies) is an art. I don't think it's necessarily the load per se.
The reason I believe this is told in the story of adjacent groups not having even similar points of impact, and the average group size being excessive.
For the sake of argument, how does it shoot with the factory ammo? Is it consistently, for 5 shot groups, less than 1 MOA? If not, the problem isn't your reloads.
If I were a betting man, given the propensity for massive changes in velocity, I would look in the bolt first. Make certain there isn't a piece of primer cup (from a blanked primer) or any other debris in the bolt. While you are at it, take a spring changing tool and press the firing pin back so you can ensure the cross pin at the cocking piece is centered and not dragging in the shroud. Check the firing pin tip for damage and straightness. Reinstall in the bolt and let it down to the fired position. Does it have about .055 pin protrusion? Those are the things that are most likely to cause the excessive shifts in velocity.
If that doesn't bear fruit, check the barrel and brake for looseness. Remove the brake and shoot a couple of groups. If it isn't better, reinstall the brake and swap scopes. Those are the most common causes of the chaos when I encounter it.
You might have 2 separate problems, grouping and velocity consistency, despite Occam's razor.
I would encourage you to shoot a few groups with your stash of factory ammo. I've amazed myself more times than I can count at the ability of the nut behind the butt to increase group size. If nothing else, find another highly skilled shooter to shoot a group or two for you. If nothing else, it would eliminate the shooter as the issue.
Best of luck,
The reason I believe this is told in the story of adjacent groups not having even similar points of impact, and the average group size being excessive.
For the sake of argument, how does it shoot with the factory ammo? Is it consistently, for 5 shot groups, less than 1 MOA? If not, the problem isn't your reloads.
If I were a betting man, given the propensity for massive changes in velocity, I would look in the bolt first. Make certain there isn't a piece of primer cup (from a blanked primer) or any other debris in the bolt. While you are at it, take a spring changing tool and press the firing pin back so you can ensure the cross pin at the cocking piece is centered and not dragging in the shroud. Check the firing pin tip for damage and straightness. Reinstall in the bolt and let it down to the fired position. Does it have about .055 pin protrusion? Those are the things that are most likely to cause the excessive shifts in velocity.
If that doesn't bear fruit, check the barrel and brake for looseness. Remove the brake and shoot a couple of groups. If it isn't better, reinstall the brake and swap scopes. Those are the most common causes of the chaos when I encounter it.
You might have 2 separate problems, grouping and velocity consistency, despite Occam's razor.
I would encourage you to shoot a few groups with your stash of factory ammo. I've amazed myself more times than I can count at the ability of the nut behind the butt to increase group size. If nothing else, find another highly skilled shooter to shoot a group or two for you. If nothing else, it would eliminate the shooter as the issue.
Best of luck,
I tried doing that. After like 5 rounds the bolt closes hard. And I'm not exactly sure where the brass expands to because my fired brass doesn't measure the same. The longest one measured .004" over factory.
Thank you all for taking the time to read and reply. Keith: The 42.3 load that I chose to load (top row circled with a star) is the one I chose to load. It shot well. I sent that load 1,000yds on steel and it grouped 3 shots in a row in the bottom right corner of a 12x12 plate. If I cut that plate in even fours, it put 3 shots in a 6x6" plate at 1,000yds. That leads me to believe that I dont have a scope problem. Or a firing pin problem. I have had the firing pin/bolt apart. I*THINK* I get crappy 100yd groups because I have some wobble/yaw out of the muzzle and it straitens up after 100yds. I dont have the capability of setting out paper at 300yds. I have also found some issues with my brass prep. I am getting those worked out. I will update here when I get some new data.
This is true. I believe I saw an article in Precision Shooting magazine once that addressed this.
divingin
Gold $$ Contributor
Are you saying after 5 distinct and separate separate rounds (i.e. one group or string) the bolt closes hard? Or after 5 firings on a single piece of brass the bolt gets stiff?
If the latter, it points to a problem with your sizing process (i.e. the brass is not being reliably reduced to the point that it chambers easily.) [I would initially suspect the .200 line diameter, as that tends to be a slower-growing dimension that is often missed by standard sizing dies.]
If it changes while shooting a string of loaded ammo, it points to something in the rifle changing: heat expansion or maybe combustion products being left in the chamber or the like. That assumes your reloading process ends up with consistent dimensions.
This is all guesswork though. A Sharpie used to completely mark up a problem round and chambered a couple/few times (in the same orientation - work the bolt handle a few times without ejecting) should give you a good idea where the problem is occurring.
As an aside, in my 6BR, the base to datum measurement difference between unfired and fireformed Lapua brass is pretty close to .007" (my smith likes to cut long chambers.) I've gone to jamming all loads on new brass to keep body stretch to minimum. It also may take a couple or several firings to fully fireform new brass to your chamber.
I had some case sizing issues. They weren't being sized down far enough. I have discovered I have a tight chamber. I got that fixed. I just tested some loads today that were sized properly and I didn't have the issue. When the brass was really close the chamber would shrink as it heated up and they would get harder and harder to chamber.
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