Looking for Help: POI Shifts

[johngood]

Hey folks!

Having some POI/Grouping issues with a rifle ive never had issues with...

6.5PRC
Defiance Anti Action
CF Bartlein Barrel - round count ~700
XLR Envy Pro Chassis
Kahles 525i

The above rifle consistantly shoots 1/2" 5 shot groups. After a PRS match i decided to clean it as i was getting some decreased velocity numbers (around 50 fps slower @ 2950fps) and was hoping there was just some build up in the chamber. I cleaned it and the barrel all the way down to white patches.

Additionally, I changed muzzle devices from the TBAC Ultra 7 to the 419 Hellfire.

When I took it to the range I noticed the gun was not grouping after 20 rounds. I thought this was excessive so I checked my action screws and bases. I shot 40 more rounds, and the gun still was not grouping. FPS was normal @ 2944

I took the gun home and double checked my ammo lot numbers, pulled the action and re-set the action in the chassis.

I took the gun back to the range and shot a 1" 5 shot group with a POI 1 inch high from my aiming point. As I took shots 6-10 I noticed the group expand to 2 inches with all of the shots low 1" of aiming point. My imediate thought was that the gun must be hot for shots 6-10 so i shouldent expect much more out of it.

To verify, I let the gun cool down and shot another 5 shot group. This time, the POI was 1" low of aiming point. Shots 6-10 were dispursed 1-2" low.

I let the gun cool down again and shot a 5 shot group. This time the POI was 5" low of aiming point.

I let the gun cool down again and shot a 3 shot group.... 3" low.

I packed up my stuff and went home.

Any advise from the pros out there would be greatly appreciated.

 

[OREGUN]

You checked the action screws but how about the rails and rings?

 

[OREGUN]

Or is that “and bases”?

 

[DocRDS]

I'd also suspect anything I had changed.
You didn't mention testing the brake.

Be OCD- if you touched it, it's a suspect.

 

[spife7980]

Put it back the way that it was before you started swapping parts like doc mentioned.

Factory ammo? Same lot?

 

[Supersubes]

When exactly did you change muzzle devices? The 419 would likely change POI from whatever other mount you were running on the Ultra 7(30CB?). Perhaps put the old mount on and test. There were some bad(not straight) 419 parts floating around a while back.

 

[johngood]

Thank you all for the quick replies

In resonse to each of the above:

-Bases and rings were checked

-Area 419 brake is new and was one of the things added after the cleaning (1 week ago). It has been on since the issue started. I measured the exit hole with a bullet and calipers to enure there is no contact. Additionally, after now 100+ rounds it shows no signs of damage so i know its not getting hit. Just to be sure I have now taken it off and re-installed the TBAC brake/supressor combo and will take it to the range in the same configuration it was in before.

-@DocRDS how do you test a brake?

-Same lots of factory ammo. I have tried Norma Match and Hornady ELDx and am seeing the same issues.

 

[OREGUN]

Did the groups tighten back up and shift around or is it big groups that are also all over the place?

 

[DocRDS]

Just like you did switch back to the Original. Once you idvthe faulty part, then u can try and figure out what the problem is

 

[Seymour Fish]

Hey folks!

Having some POI/Grouping issues with a rifle ive never had issues with...

6.5PRC
Defiance Anti Action
CF Bartlein Barrel - round count ~700
XLR Envy Pro Chassis
Kahles 525i

The above rifle consistantly shoots 1/2" 5 shot groups. After a PRS match i decided to clean it as i was getting some decreased velocity numbers (around 50 fps slower @ 2950fps) and was hoping there was just some build up in the chamber. I cleaned it and the barrel all the way down to white patches.

Additionally, I changed muzzle devices from the TBAC Ultra 7 to the 419 Hellfire.

When I took it to the range I noticed the gun was not grouping after 20 rounds. I thought this was excessive so I checked my action screws and bases. I shot 40 more rounds, and the gun still was not grouping. FPS was normal @ 2944

I took the gun home and double checked my ammo lot numbers, pulled the action and re-set the action in the chassis.

I took the gun back to the range and shot a 1" 5 shot group with a POI 1 inch high from my aiming point. As I took shots 6-10 I noticed the group expand to 2 inches with all of the shots low 1" of aiming point. My imediate thought was that the gun must be hot for shots 6-10 so i shouldent expect much more out of it.

To verify, I let the gun cool down and shot another 5 shot group. This time, the POI was 1" low of aiming point. Shots 6-10 were dispursed 1-2" low.

I let the gun cool down again and shot a 5 shot group. This time the POI was 5" low of aiming point.

I let the gun cool down again and shot a 3 shot group.... 3" low.

I packed up my stuff and went home.

Any advise from the pros out there would be greatly appreciated.

6.5 PRC, heated her up shooting PRS.

 

[CK1.0]

Unexplained patterns/groups could be a lot of things…

First off, white patches don’t mean anything unless you’ve checked your work with a bore scope, I’d start there.

But look out for weird stuff too…

This weekend I experienced the same sort of unexplained phenomena on the last stage of a match… gun was shooting great all day (me not so much) until suddenly it was all over the place, the gun went from hammering to me zeroing a stage and questioning my dope

Then I noticed when putting the gun in the truck for the ride home that my muzzle brake had loosened up and had flipped over from its correct orientation… No more “hand tight” for me, from now on I’ll be using a strap wrench.

 

[Aftermath]

Make sure you have lots of the same lot of ammo. Take it back to original configuration and verify with your ammo.
Change ONE thing and shoot. Change another SINGLE thing and shoot.

 

[johngood]

Good news guys.....

starting bringing the rifle back to its original set up and found a two things that I think were affecting the performance. First was a loose internal weight (added recently). the weight wasnt properly torqued and was slapping the barrel when it was fired. Additionally, my front action screw was slowly coming un-done causing the poi shifts. I secured the weight and action screw with vibratite and the gun held a 10 shot string around .6". I checked the action screws and let the gun cool down all the way then shot another tight 5 shot string with no POI shift.

Thanks everyone for the help!