Accuracy on necksized rounds is getting worse

[Evan]

Might want to look at the crown of your barrel if you haven't yet. Damage to the crown can have huge effects on accuracy.

Has the stock warped, swelled of otherwise moved into contact with the barrel? Check that at least a piece of paper can slide freely between the barrel and stock all the way up to the action. I like even more clearance than that, but a piece of paper is a good starting place. Also check this in what ever rest or shooting position you use. Is the stock flexing and making contact with the barrel (from cheekweld or other pressure during shooting)?

 

[Zero333]

Sizing issues set aside... you will never go from half MOA to 3 MOA at 100 yards/meters with just the load going out of tune.

Since the rail and rings did not loosen, I suspect the optic might of taken a dump on you.

 

[bayjoe]

I did something right. After tightening all screws checking my scope and cleaned the barrel channel. Rifle is back to shooting good.
I did load some rounds that are full length resized and it did open up a little but I am happy

 

[chkunz]

One final point about neck sizing only, if your chamber is shaped like a banana then your fired brass will be shaped like a banana . I have nothing against neck sizing only but you need a good chamber job to make this work. But we are not talking about the major increase in group size that you experienced.

 

[Zero333]

You also could of hand a handful of shitty bullets that were not very balanced in flight.

 

[338 dude]

I cleaned my barrel really good after the last shooting lesson. Cleaned the copper fouling made it supper clean.
Barrel has 500 to 600 rounds.
I disassembled the few remaining rounds, soaked the primers and then full length resizing. And I had to cam over just a little bit to size the cases down .002. I used the 45acp round to measure the amount of shoulder push back to .002 and then double checked the cases that they cycle thru the action smoothly.
So I am going to put the rifle in a HS precision stock, load some more rounds and go see if the problem persists. I think if it still shoots large groups then i'll change scopes and see if that is the problem.
Many thanks gentlemen for your help

You are cleaning the barrel full length resizing and changing the stock you should only change one thing at a time if you really want to find the cause

 

[hogpatrol]

Have you borescoped to check for a carbon ring?

 

[INTJ]

@bayjoe . A cool thing about this site is you will get all kinds of suggestions. Most of the time each suggestion has fixed a similar issue for someone. You just have to sort them out.

And don't neck only size. You'll find the vast majority of competitors in disciplines that require extreme accuracy bump the shoulder when sizing. It is a myth that brass has to be snug in the chamber to get the most accuracy.

That said you may need to retune now that you have joined the top shooters in the world by ditching neck only sizing.