Accuracy Loss

[GrayCreed]

Make your seating depth .005" LONGER

 

[new2mud]

As mentioned by others, I have come to learn the action screws are the first thing to check, followed by scope rail screws.

I recently had a gun go down to 2.5 MOA, with one group at 1 MOA. When I got home I discovered the front action screw (which had been torqued to 65 in-lbs) was MISSING. I have no idea how that thing even shot an MOA group.

 

[Rick Richard]

Going from 1/2 to 2 is a significant change. Guess would be mechanical like mounting hardware, action screw or barrel over heating if rapid firing.

 

[Wedgy]

The .300WM is a real barrel eater but @ only 546 rounds it should have much life remaining.

When did the 300WM become a barrel burner ??

Scrub the throat and 1st two inches with some JB then foul the bore and check your groups. Look at your crown or a loose muzzle brake, even barrels have come loose. Obviously something is out but I doubt the barrel is shot out. I recently rebarrelled a friend's that started missing the target at 100 yards, bore scope found a bulge in the barrel near the end, you could feel it with the cleaning rod also. the bullet lost contact with the rifling(where the copper fouling stops) and would contact again about an inch further down. Must have got something stuck in it. have even seen a mud wasp clog a barrel up.

 

[Shane Lindsey]

I have had some Talley ring mounts come loose and not know it until I went to swap out the scope. It would not shoot very consistently. Strange things happen in this shooting voodoo we do.

As mentioned, check all the torque on screws (if pillar bedded would expect it to be around 65 inch pounds).

Clean the barrel back to bare steel. Focus on the throat as mentioned, short stroke it with JB, run a drill in it, whatever your process.
Load up five rounds at .010" longer than your current load (this is a bit extreme, but they grow on big magnums).
Then go out and with these five foul the bore.
Then shoot normal load and see.

I clean at regular intervals so I know the condition of the bore. I don't have a borescope, but I do clean the throat and have never had a problem with pressure spikes as some folks do. It also assists with ruling one of the many things out when things change...

Interested on your findings.

 

[aghunter]

Thanks everyone, keep them coming! Good suggestions so far. I. Below is my action list tonight then I plan to shoot Wed.

Check Muzzle & Brake
Check Action Screws and barrel free float
Deconstruct 1 round and double check powder charge. (maybe i screwed up somehow)
Scrub chamber and bore
Load 1 set of longer bullets

 

[oldno7]

I'm guessing you've lost your accuracy node of original BTO.
If you measured your lands on the new barrel, re measure now and adjust your BTO, accordingly.
If no initial measurement was taken, you'll need to re figure the node length through shooting 3 shot groups at
increasingly longer BTO lengths.
I'd go in 3 thousandths increments with 5 lengths.
I'm guessing your groups come back.

 

[LaHunter]

I am attempting to diagnose a sudden loss of accuracy in one of my custom rifles. I have an Aoudad hunt coming up this Sunday and am in dire need to get it back shooting properly. The rifle went from 1/2 MOA to 2MOA in the span of 1 shooting session. The rifle is a 300WM with Proof Carbon barrel. It has 546 rounds now and went bad right at 500. I have cleaned the rifling during this period with no improvement. I have eliminated the scope and rings by trying a proven optic from a different set up and still have issues. The ammo is hand loaded so nothing has changed on that front. I have been researching the elusive carbon ring and this is what I see through the bore scope. Do you think this could be causing my issues? I have not seen any noticeable pressure signs. Any other ideas that I can quickly try? Let me know what you see.

Looking at the photo, it looks like you have some carbon there. Sounds like you have some good info and a plan to address that. Carbon rings can be tough to remove. If a carbon ring gets bad enough, it can show pressure signs. How is your bolt lift after firing?
Take a close look at your fired brass looking for pressure signs. As mentioned above, a reliable chrono is a useful trouble shooting tool.

The 'cracking' is normal wear. You can begin to see signs of cracking in a 300 WM or 7 mm rem mag within 150 rounds if you look closely.
For your rifle to go from .5 moa to 2 moa in one session, that makes me think a mechanical issue or maybe you made a mistake while loading your ammo?? Is your current ammo all from the same loading session? Checking the torque on all screws is a good idea.


Good luck

 

[LaHunter]

I'm guessing you've lost your accuracy node of original BTO.
If you measured your lands on the new barrel, re measure now and adjust your BTO, accordingly.
If no initial measurement was taken, you'll need to re figure the node length through shooting 3 shot groups at
increasingly longer BTO lengths.
I'd go in 3 thousandths increments with 5 lengths.
I'm guessing your groups come back.

This would be an action item after I checked every other possible issue. The OP said his rifle went form .5 moa to 2 moa in just one range session. Usually accuracy degrading from throat wear is more gradual

 

[capona]

This kind of quick drop off, and dramatic, is usually mechanical.

 

[Jim’s Hunt]

I am attempting to diagnose a sudden loss of accuracy in one of my custom rifles. I have an Aoudad hunt coming up this Sunday and am in dire need to get it back shooting properly. The rifle went from 1/2 MOA to 2MOA in the span of 1 shooting session. The rifle is a 300WM with Proof Carbon barrel. It has 546 rounds now and went bad right at 500. I have cleaned the rifling during this period with no improvement. I have eliminated the scope and rings by trying a proven optic from a different set up and still have issues. The ammo is hand loaded so nothing has changed on that front. I have been researching the elusive carbon ring and this is what I see through the bore scope. Do you think this could be causing my issues? I have not seen any noticeable pressure signs. Any other ideas that I can quickly try? Let me know what you see.

You have received a large amount of good info I believe it's mechanical and cleaning the chamber an barrel till no copper shows. Good luck and keep us posted on the outcome

 

[Troutslayer2]

I had the same problem not long ago. My pic rail had come just a little bit loose. I had it pinned so it can't happen again.

 

[Tiny Tim]

If it happened during a range session, that "should" eliminate the ammo. That is a crazy increase and would likely point to a mechanical issue. Even a carbon ring shouldn't produce such a dramatic change. I had one barrel that required about 18-20 shots to foul before it would shoot consistently. Very dramatic change in POI and consistency. It had about 2500 rounds through it. It didn't start that way or get that way in one session.

 

[aghunter]

Crown and brake look good.
Action screws didn't budge at 55in/lb so they have not come loose. Barrel is not contacting stock.
Double checked picatinny rail and it was tight. Just had it bedded not long ago.
Powder charge correct from deconstructed bullet
WOW what a difference the bore scope makes in really knowing if your clean or not. Check out the before and after pictures. I used c4 and Iosso.
Will shoot tomorrow and let you guys know if there is any improvement.