Groups "shifting"?

[philcox]

UPDATE: Had this big long post (see below), then said to myself "did you really check ALL the screws?" ... pulled out the rifle and lo and behold, scope bases were loose. I would have expected more erratic POI, but now with them solidly torqued, time to "go do it again", this time properly!

Moral of the story: The simple answer most always is the right one ...

Thanks @Formidilosus for the recent podcast (

) this is what got me to thinking about that is might be something loose!

I really hope this tightens up those groups and maybe N565 will be an RL26 replacement ... more to come.


========= Previous, now irrelevant post ===============
So this has happened twice in back to back days. I am shooting an "OK" group, then POI shifts and stays.

Gun: 7PRC, XLR Chassi, new Maven RS1.2, TIkka action, UM Rings
Load: ADG, CCI 250, 168 LRX, 67.5 RL26, 3.20 COAL

This was yesterday. X is the sighter/first shot. I slipped the turret, and shot the next 10. They are listed here in order of hit (based on video review). While it may not be "great", shot 1-8 were in a "group", then shot 9 which was in the same "flow" as 8, was WAY out. I thought "weird" must have did something, then shot 10 ... nope, not a fluke. I only had 2 more rounds, and 11 & 12 were "in the new group" POI.



The velocity of each of those 12 were:
2978
2973
2980
2984
2994
2987
3000
2994
2987
2977
2988
3004

So no clear, Velocity must have caused it.

Next day (today). I tried a N565 load (because RL26 is a ghost). While not quite as dramatic, a shift, but this time lower ...



Similar with velocity, no clear "cause"
2976
2995
2987
2992
2995
2988
3002
2995
2999
2991
2984

I came home and checked scope screws, action screws and muzzel break, all tight. There is no problem with Barrel clearance in the XLR chassi.

 

[Formidilosus]

UPDATE: Had this big long post (see below), then said to myself "did you really check ALL the screws?" ... pulled out the rifle and lo and behold, scope bases were loose. I would have expected more erratic POI, but now with them solidly torqued, time to "go do it again", this time properly!

Moral of the story: The simple answer most always is the right one ...

Thanks @Formidilosus for the recent podcast (

) this is what got me to thinking about that is might be something loose!

I really hope this tightens up those groups and maybe N565 will be an RL26 replacement ... more to come.


========= Previous, now irrelevant post ===============
So this has happened twice in back to back days. I am shooting an "OK" group, then POI shifts and stays.

Gun: 7PRC, XLR Chassi, new Maven RS1.2, TIkka action, UM Rings
Load: ADG, CCI 250, 168 LRX, 67.5 RL26, 3.20 COAL

This was yesterday. X is the sighter/first shot. I slipped the turret, and shot the next 10. They are listed here in order of hit (based on video review). While it may not be "great", shot 1-8 were in a "group", then shot 9 which was in the same "flow" as 8, was WAY out. I thought "weird" must have did something, then shot 10 ... nope, not a fluke. I only had 2 more rounds, and 11 & 12 were "in the new group" POI.

View attachment 726692

The velocity of each of those 12 were:
2978
2973
2980
2984
2994
2987
3000
2994
2987
2977
2988
3004

So no clear, Velocity must have caused it.

Next day (today). I tried a N565 load (because RL26 is a ghost). While not quite as dramatic, a shift, but this time lower ...

View attachment 726694

Similar with velocity, no clear "cause"
2976
2995
2987
2992
2995
2988
3002
2995
2999
2991
2984

I came home and checked scope screws, action screws and muzzel break, all tight. There is no problem with Barrel clearance in the XLR chassi.

Bed the chassis.

 

[philcox]

Bed the chassis.

Dumb question. I currently swap actions (all Tikka's) in the chassi. I swap my 7PRC & 65CM in and out so I get practice with the same "platform". Since I have never "bedded" any of my stocks, it seems that if I bed to a specific action, then I would lose the ability to swap, correct?

 

[Macintosh]

Curious to hear others take, but I have swapped tikka actions between bedded stocks with no issues. Unless one action got twisted or something when pulling a barrel off, my thought is they should all drop into the same bedding without any odd pressure, the differences between actions being irrelevant for anything anyone would likely use a tikka for. In this case I believe its movement between action and stock that the bedding prevents, as well as compensate for any pressure or torque caused by the chassis itself.

 

[Formidilosus]

Dumb question. I currently swap actions (all Tikka's) in the chassi. I swap my 7PRC & 65CM in and out so I get practice with the same "platform". Since I have never "bedded" any of my stocks, it seems that if I bed to a specific action, then I would lose the ability to swap, correct?

Maybe, probably not. However, chassis can and will have point of impact shifts, though yours are larger than I would expect.

 

[Castle Rock]

Dumb question. I currently swap actions (all Tikka's) in the chassi. I swap my 7PRC & 65CM in and out so I get practice with the same "platform". Since I have never "bedded" any of my stocks, it seems that if I bed to a specific action, then I would lose the ability to swap, correct?

Tikka actions are that consistent that it doesn’t matter, bed one and it will be fine with all others , with ONE exception
Stainless actions have an S engraved under the front
If you bed a stainless Tikka there will be a raised S in the compound so a carbon steel action will rock on that
The fix is simple, just scrape the raised S off with a chisel it comes off easily without any issues if you are not too hamfisted

 

[Castle Rock]