Need some help troubleshooting horizontal grouping.

[BillNye]

I am working with a newly built rifle, all quality components with a Nightforce ATACR scope in Hawkins rings. The barrel has been fully broken in, 150 rounds through it fireforming brass. I put together a few loads for it with Hammer Hunters and Berger hybrids, ADG brass, and H1000. I have no reason to think the loads are an issue.

Consistently, with every load tested, I am getting minimal vertical dispersion and extreme horizontal dispersion. Approximately 2-2.5 MOA horizontal and 0.3-0.6 MOA vertical. It repeats this pattern at multiple distances, so far I have tested it at 100, 200, and 800. So far I have eliminated the shooter/environment by alternating shots with another rifle that patterned just fine. I used the same bipod and bags for both rifles. I also went through and checked torque on the rings, rail, and action screws. As best as I can tell it's not walking to the side as the barrel heats, just dispersing horizontally.

I'm looking for suggestions on what to look for next. It's currently in a Woox stock while I wait for a Manners to get finished and I suspect that's the problem. Judging from the marks on the chassis, it appears to be contacting the chassis on the sides of the recoil lug, on either side of the front of the action, and on either side of the pressure pad in the back. I don't at the moment have another stock I can put it in to test. Wondering if I should bed the chassis or look elsewhere?

Thanks

 

[lancetkenyon]

If the action is moving in the chassis, 99.8% that is your problem.

I would either bed it, or beg/borrow/steal another stock for testing.

 

[BillNye]

I'm not feeling significant play with hand pressure but that's not say it's not happening under recoil

 

[Reemty J]

Lance isn't a pilgrim, lots of experience and dam friendly helpful guy, LIke most on here…..i read most all of his posts, always good advice.

 

[VarmintBob]

Horizontal dispersion in both directions? What is the cartridge? What rest are you shooting from? Do you have a chronograph?

 

[ShtrRdy]

When you mounted the rail to the top of the action did you verify that the mounting screws weren't too long? Or possibly close to being too long.

 

[Sealesniper]

I had a trigger that caused me some similar issues years ago. I assume you have a quality trigger that breaks like glass. Sorry I cant be more help, but I only experienced this with a trigger that was not breaking clean repeatedly at same pressure.

 

[mudflap621]

Are you adjusting parallax? I'd probably also put another good scope on it just to eliminate a variable.

 

[BillNye]

Dispersion in both directions as far as I can tell. Cartridge is 300 PRC. Been using a magnetospeed chrono and the SD (hammer load) is around 13 after 20 chronoed rounds. I'm shooting off an Atlas bipod and a cheap Caldwell rear bag.

I have not verified that the front rail mount screw isn't touching the threading on the barrel but I will do that while I have the scope off for bedding. Thanks for the suggestion!

Trigger is a triggertech diamond set very light so I don't think that's contributing. I've been adjusting parallax but I will probably try a different scope on there if bedding and checking the rail mount doesn't fix it

 

[VarmintBob]

Does the horizontal continue without the magneto speed? If you are willing to make a couple of measurements, I can check the barrel time of your load. (what time the bullet exits from ignition). A magneto speed on my 300 WM makes it shoot about 8" high

 

[BillNye]

I have the magnetospeed on a mount separate from a barrel. It could definitely still be inducing the dispersion though. I havent really shot it much without except while i was fireforming. What measurements do you need?

 

[VarmintBob]

Cartridge, powder, bullet, cartridge OAL, bbl length, fired, unresized case capacity in gr of water (weigh empty case fill with water weigh again, get difference) I normally do at least 3. Some velocity with the above specs and the powder weight used for that velocity. With all that I can get a time in msec of when the bullet exits to determine how close it is to a quiet muzzle time. The target below is 5 shots from my skinny bbl 300 WM at 100 yds. It is an OBT load.

 

[mudflap621]

Cartridge, powder, bullet, cartridge OAL, bbl length, fired, unresized case capacity in gr of water (weigh empty case fill with water weigh again, get difference) I normally do at least 3. Some velocity with the above specs and the powder weight used for that velocity. With all that I can get a time in msec of when the bullet exits to determine how close it is to a quiet muzzle time. The target below is 5 shots from my skinny bbl 300 WM at 100 yds. It is an OBT load.

You lost me on quiet muzzle time and timing to the milisecond

 

[338 dude]

I am working with a newly built rifle, all quality components with a Nightforce ATACR scope in Hawkins rings. The barrel has been fully broken in, 150 rounds through it fireforming brass. I put together a few loads for it with Hammer Hunters and Berger hybrids, ADG brass, and H1000. I have no reason to think the loads are an issue.

Consistently, with every load tested, I am getting minimal vertical dispersion and extreme horizontal dispersion. Approximately 2-2.5 MOA horizontal and 0.3-0.6 MOA vertical. It repeats this pattern at multiple distances, so far I have tested it at 100, 200, and 800. So far I have eliminated the shooter/environment by alternating shots with another rifle that patterned just fine. I used the same bipod and bags for both rifles. I also went through and checked torque on the rings, rail, and action screws. As best as I can tell it's not walking to the side as the barrel heats, just dispersing horizontally.

I'm looking for suggestions on what to look for next. It's currently in a Woox stock while I wait for a Manners to get finished and I suspect that's the problem. Judging from the marks on the chassis, it appears to be contacting the chassis on the sides of the recoil lug, on either side of the front of the action, and on either side of the pressure pad in the back. I don't at the moment have another stock I can put it in to test. Wondering if I should bed the chassis or look elsewhere?

Thanks

I bed them all!