POI Shift Head Scratcher

[Cfshooter]

Here is a good one. I have a Shilen 6 dasher 26” .800 muzzle barrel that I screwed onto a savage action. It shoots tight but POI seems to shift down as session goes. Ended up about 1.5 moa lower last range session of 25 rounds. Even after barrel cools for 20 minutes the POI is still low. The next range trip POI starts back normal and after a few 5 shot groups it starts working down again. I shoot groups slow and let barrel cool between but seems to “flex” into a new “place” as session goes on. Groups stay tight as well. So far I have had 3 range trips with it (about 80 rounds total) and happens each trip.

I swapped stocks and glass again, same issue persist. Target pic of last trip below. I also attached the chrono results, it is not from velocity change, and you can see the 20 minutes between groups to let barrel cool some.

Thoughts? Just a lemon barrel? I have had barrels change POI some and groups have open up when some barrels get hot, but this POi continues to get lower as a session goes but groups stay tight.

 

[JFrank]

Weird for sure, if it were a lemon barrel I would think the grouping would be poor but that’s not what we are seeing.

 

[Cfshooter]

Weird for sure, if it were a lemon barrel I would think the grouping would be poor but that’s not what we are seeing.

Maybe this is what is expected from the Shilen button barrel, I sent them an email about a week ago but no reply yet. I can say the Savage barrel I took off did not behave that way.

 

[JFrank]

POI shift

My F Class 223 shoots very well at 600yds. But as the match goes on, it shoots lower & lower. After 10rds of a 30 shot in 30 minutes relay, it drops 1.5". The longer we go the worse it gets. When cooled off, it's back to normal. It's a #12 Savage in an aluminum bedded Choate stock. Schillen...

forum.accurateshooter.com

 

[K22]

Frustrating for sure - of course you don't need that point made.

Sounds like you eliminated the stock and scope which would be the first places I would look for a problem of this nature.

I find it hard to understand that it is the barrel since the groups are so tight. To me, this means that for whatever reason, the barrel / action is moving between strings. Is there any possibility that the barrel is loosening and resetting?

I am not a gunsmith but mine claims that in rare instances, some barrels may shift POI after being shot due to do metallurgical stresses and that those barrels need to be stressed relieved to shoot consistently. This way out of league so maybe some of the knowledgeable gunsmith members can chime in on this.

 

[nmkid]

Could be totally unrelated but, one of my nephews had a rifle doing the exact thing yours is doing. The Picatinny rail was loose! Why it would hold a group and then go awry...We never figured that out.

 

[Cfshooter]

POI shift

My F Class 223 shoots very well at 600yds. But as the match goes on, it shoots lower & lower. After 10rds of a 30 shot in 30 minutes relay, it drops 1.5". The longer we go the worse it gets. When cooled off, it's back to normal. It's a #12 Savage in an aluminum bedded Choate stock. Schillen...

forum.accurateshooter.com

I am not alone lol, but I would be fine with a 1/4 moa drop, I’m at 1.5 drop after only 20 shots at 100 yards.

 

[Cfshooter]

Frustrating for sure - of course you don't need that point made.

Sounds like you eliminated the stock and scope which would be the first places I would look for a problem of this nature.

I find it hard to understand that it is the barrel since the groups are so tight. To me, this means that for whatever reason, the barrel / action is moving between strings. Is there any possibility that the barrel is loosening and resetting?

I am not a gunsmith but mine claims that in rare instances, some barrels may shift POI after being shot due to do metallurgical stresses and that those barrels need to be stressed relieved to shoot consistently. This way out of league so maybe some of the knowledgeable gunsmith members can chime in on this.

It is very perplexing for sure lol. I am going to unscrew and re install barrel next and see what happens I guess.

 

[Cfshooter]

Weird for sure, if it were a lemon barrel I would think the grouping would be poor but that’s not what we are seeing.

Yeah, I am stumped lol. Hoping Shilen will shed some light.

 

[marazzi59]

I no the jury is still out on this but for the $$$$ I would try it. Ship the barrel out for cryo treatment for stress relief.

 

[Bill K]

Could you be having a slight pressure point/touching in stock, as that barrel even starts to heat up ? Causing this shift down. Or just something in the makeup of this barrel and harmonics causing the shift ?
Will be interesting to see what Shilen says, if and when they answer.

 

[6Creed73]

Have you tried a mirage shield to rule out barrel mirage? I have seen barrel mirage cause exactly what you are describing.

 

[Cfshooter]

Could you be having a slight pressure point/touching in stock, as that barrel even starts to heat up ? Causing this shift down. Or just something in the makeup of this barrel and harmonics causing the shift ?
Will be interesting to see what Shilen says, if and when they answer.

I tried two different stocks to try and remove that variable. I’m thinking just the metal of barrel. Shilen responded and said they will have someone with more knowledge reach out.

Have you tried a mirage shield to rule out barrel mirage? I have seen barrel mirage cause exactly what you are describing.

I have not, but I am pretty certain is isn’t from mirage, there has not been any and no issues with other rifles shot during same sessions.

 

[Forum Boss]

Could be the scope -- an internal issue.
Also a different position of the rifle on rear bag, if it moves and settles after initial groups.

Certainly you can see that change from a different shooter's head position or weight on the stock cheekpiece.

I would: 1) Let another shooter try it; and 2) Change the scope.

 

[ShtrRdy]

Could the bolt face be touching the breach end of the barrel?

 

[Fast14riot]

When I rebarrel a nutted barrel, I take a quick swipe of the mating surface of the nut on some 400# sandpaper on a known flat surface to make sure that it is at least flat. If you can, I would try loosening the barrel nut and reseating it against the recoil lug. Also, make sure the lug guide isn't bottomed out in the notch of the action.

 

[Cfshooter]

Could the bolt face be touching the breach end of the barrel?

Hmm, how would I check that? Wouldn’t it not headspace then? I would love to check though.

 

[Cfshooter]

When I rebarrel a nutted barrel, I take a quick swipe of the mating surface of the nut on some 400# sandpaper on a known flat surface to make sure that it is at least flat. If you can, I would try loosening the barrel nut and reseating it against the recoil lug. Also, make sure the lug guide isn't bottomed out in the notch of the action.

Next step was to remove barrel and install again, I will clean it up a little like you mentioned, thank you!

 

[M-61]

Hmm, how would I check that? Wouldn’t it not headspace then? I would love to check though.

I would think headspace would be impossible.
Have I ever seen this? Not on such a regular basis.
The picatinny rail being loose got me one time group.of 3 and then 2 flyers.
Savages are touchy with proper action torque and sequence. You’ve swapped the scope… good eliminating that but not the rail.
And yes. Let someone you know soot it that is a shooter and see what they get.

 

[Cfshooter]

I would think headspace would be impossible.
Have I ever seen this? Not on such a regular basis.
The picatinny rail being loose got me one time group.of 3 and then 2 flyers.
Savages are touchy with proper action torque and sequence. You’ve swapped the scope… good eliminating that but not the rail.
And yes. Let someone you know soot it that is a shooter and see what they get.

I have swapped scopes including mounts, stock, and bipod 3 times. I have not had anyone else shoot it, but the fact that it happened all 3 range sessions and the exact same way each time, I do not think it is shooter. I also had a secondary rifle with me each trip, and it shot as normal, so I could rule out environment.