02-02-2017, 05:44 AM
I keep the fired and unfired cases separate when I shoot. I always crimp with a Lee bullet crimping die, I randomly measure with the Hornady comparator and have recently switched to using a single stage press to reload my Grendel. I usually reload in batches that I keep together. The only thing that is different is that I'm running a compensator on the barrel now. I don't know if that would change anything. What's kind of weird is that most of the time I can keep my groups pretty close (pretty close is a relative term for me) within 1" at 100yds.. Today is the first time that I've strung them out (vertical) like this. I'll have a couple of months to think about this as I'm having a shoulder replaced Friday and will be off of the range for a bit.
Klem Wrote:OK it sounds like most things are in order as much as I can tell from what you have written. Things like lose mounts and rings would certainly blow the groups out but vertical stringing is more specific. Thin barrels heat up quickly, especially when shooting more than 1rd/min (which usually happens in auto loaders). This leads to vertical stringing.
I note you are using some new cases and some fired. Different neck tensions here mean different velocities. The result on the target will be vertical spread.
The AR is a difficult platform to shoot as well as a bolt-gun. It's purpose light weight doesn't lend itself to being stable so you have to lock it in. Other things like returning the gun to exactly the same position on the rest after it has recoiled will reduce stringing. Some shooters use a mechanical stop on the underside of their handguard like a barrier stop. Push the gun forward after recoil until the stop comes up against the rest before the next shot.
If the length of the loads are touching the lands or close to it then the difference between jump and no-jump will definitely result in vertical stringing. Or maybe a high impact and low impact. Loosely held bullets in the neck can shift forward on being loaded into the chamber and come up against the lands. If some do and some don't then you will get stringing.
These are some mechanical possibilities but potentially the easiest fix is to lock that gun in and fire it at exactly the same position and hold on the rest.