Crazy Grouping change when increasing charge.

[Xeon64]

Using Shooters World Match(AA2520) in a 6.5 Grendel with 120gr Sierra Pro Hunter 22" Barrel.
28grs, 2350fps
Top Target. Bottom is a 350 Legend.


29grs, Chronograph Broke



The 29gr grouping was terrible. I stopped going up from there. No signs of over pressure just bad accuracy. I have never seen this level of change when reloading before with other calibers.

 

[Magdump]

Rifling, bullet weight and velocity. I have seen a few calibers lose all sense of accuracy when I stray too far.
The worst ever was trying to find a decent load for a bolt action 30-30. It was quite easy to improve on range by changing from the flat nose bullets but as soon as I started loading them toward the hot side accuracy suffered. I settled for a lighter pill and got the speed and accuracy for a flatter shooting load I was looking for.
Rifling twist rates generally favor a particular bullet weight, but speed/powder charge can definitely be a factor.

 

[shrxfn]

I don't reload but have followed quite a few reloading threads on other forums due to future interest in reloading. From what I have read there can be accuracy nodes in powder charges and if you are not at max load for your powder/cartridge combo you may want to try and move up a little and see if you hit another node at a higher powder weight most guys usually go up in small increments of .5gr or smaller. I am not sure how much you are moving up or how close you are to a suggested max load but it may get better going up a little bit or hitting different weights between 28 and 29 grains. Good luck and stay safe.

 

[theway109]

I've never seen a load change that dramatically between two charges. I would be checking for something else going wrong with with gun or reloads.

Sent from my Pixel 3 XL using Tapatalk

 

[Xeon64]

Nothing Wrong with gun. Shoots Factory Match Ammo very accurate. I was just looking for a hunting load. 28gr shoots consistently accurate. 29grs was all over. Did not try going over 29gr. Max load is 32.2 grs. I mean 28grs @ 2350fps will kill a deer. Better to be accurate than miss.

 

[drill sgt]

My experience in the 1980"s shooting a bolt action 30-06 (?? manufacture) Tasco 3X9 scope .. IMR 4350 58 gain load (??).... Nosler 150 grain ballistic tip.... 200yds 3 shot group all 3 rounds touching each other..... 300 yds with a 3 shot group 1/4 inch spread between the rounds. ..... With factory loads they were spread out over a paper plate at 200 yds. ... Nothing consistant.... My brother gave me some of this load and after testing started reloading this load myself. .................. drill sgt.

 

[shrxfn]

Nothing Wrong with gun. Shoots Factory Match Ammo very accurate. I was just looking for a hunting load. 28gr shoots consistently accurate. 29grs was all over. Did not try going over 29gr. Max load is 32.2 grs. I mean 28grs @ 2350fps will kill a deer. Better to be accurate than miss.

With 3 grains of room before max charge I would try going up a little and see if you hit a second accuracy node. You have a lot of wiggle room to play with there and may as well use it.

 

[Xeon64]

Gonna Try that.

 

[Request Dust Off]

Look at the OCW method of load development. In a nutshell it is a way to quickly identify where your accuracy nodes are. If you want the highest velocity with accuracy this will identify about where that is and then you can concentrate on further tuning the load in that charge weight ballpark. Main point is it's a good first pass load test to find where to look further, but should give you a fairly straightforward answer on what your charge weight range should be for a second test session.

Some bullets accuracy can go out the window if you go over a certain velocity.

http://www.ocwreloading.com/home.html

Even if you don't use the method it might give you some insight. It is a variation of Audette's ladder test.

I have found times when two charge weights were about even in accuracy and then tested in increments between the two.