Sudden loss in Groups

[moe africa]

Good Day All
I recently got a new bbl on my tikka 308 and it shot amazing
I had 3 shots groups over 1gr which were all on average 0.3"

My hornady ELD Match load shot about 0.4" for 5 shots
This last week I took the rifle out to zero and loaded from a new box of bullets and new tin of powder
And my groups opened up to 1 moa
I've checked all torque settings
Rifle is not bedded, yet it shot well before bedding as well
Any suggestions?

 

[Dolomite]

What powder are you using? Is the powder from the same lot?

 

[Doom]

What powder are you using? Is the powder from the same lot?

Also bullets?

Seating info and load info may help.

 

[jackieschmidt]

If you are sure everything else is as it should be, except changing to a different lot of bullets, then the bullets might be the culprit.

Mass produced bullets are notorious for lot to lot differences that can affect performance as defined by overall accuracy potential.

 

[Sandstorm]

the bullets might be the culprit.

This right here Sir.

 

[ShtrRdy]

If you were able to measure velocity on the good load and on the bad load that might have given a clue. Different lot of powder can make a big difference too.

 

[L.Sherm]

100% what Jackie said, ive seen as much as .015 change in ogive from lot to lot

 

[FeMan]

In addition to the above, I would also check action screws, barrel-to-receiver, and scope mounts to make sure nothing is loose. Tikkas have plastic plugs in the holes on the top of the receiver. They usually stand proud. If you put a pic rail on the rifle without removing these, it could be creating issues.

 

[L.Sherm]

If you have a CBTO measurement from your previous lot of bullets you can check new lot and adjust if necessary, I would also get the rifle bedded I dont know how many times unbedded rifles turn into problems

 

[K22]

As stated in Post # 4 this is the first culprit I would suspect. Changes in bullet is the most significant factor I have observed in changes in results on target assuming all the equipment / mechanical issues have been ruled out.

The second would be if you used an aggressive copper solvent and stripped the barrel now to bare metal. In my experience, this produces erratic shot dispersion until the barrel is re-conditioned which may, depending on the barrel, take several shots.

 

[Relic]

Sounds like copper build up if everything else checks out. Cleaning copper can be a chore on some barrels, but necessary evil. You will need to shoot a bit before accuracy returns after Cleaning.

 

[BoydAllen]

Good Day All
I recently got a new bbl on my tikka 308 and it shot amazing
I had 3 shots groups over 1gr which were all on average 0.3"

My hornady ELD Match load shot about 0.4" for 5 shots
This last week I took the rifle out to zero and loaded from a new box of bullets and new tin of powder
And my groups opened up to 1 moa
I've checked all torque settings
Rifle is not bedded, yet it shot well before bedding as well
Any suggestions?

Do you have a bore scope?

 

[LCazador]

If you are sure everything else is as it should be, except changing to a different lot of bullets, then the bullets might be the culprit.

Mass produced bullets are notorious for lot to lot differences that can affect performance as defined by overall accuracy potential.

Bullet is probably the culprit. What Jackie says.

 

[64Rambler]

This is 2 different lots of 7mm Berger 168 VLD-Hunting (@200 yds). Same Lot and charge of powder, Same seating depth (Cartridge Base to Ogive), but the bullets were 0.016" different in the Bullet Base To Ogive.

 

[markm87]

Garmin Chrono.

 

[Straightshooter1]

Good Day All
I recently got a new bbl on my tikka 308 and it shot amazing
I had 3 shots groups over 1gr which were all on average 0.3"

My hornady ELD Match load shot about 0.4" for 5 shots
This last week I took the rifle out to zero and loaded from a new box of bullets and new tin of powder
And my groups opened up to 1 moa
I've checked all torque settings
Rifle is not bedded, yet it shot well before bedding as well
Any suggestions?

Am confident that it's both the new powder and the new bullet that's the main thing at play with the difference you're seeing.

Bullets and be significantly different from one lot to another. For example, I found .067" difference in bearing surface lengths between two different lots of 168 SMK's. Also, there was a .008" average difference in their OAL's. Weighing them, there was no significant difference. This was 4 years ago and I decided to see what that difference in bearing surface lengths might make out of my .308. As it turned out, there was a significant velocity difference between two 20 shot averages of 36 fps. There was a very noticeable shift in POI at only 100 yds.

I find it very common that a new lot of powder of mine will perform different than an older used lot where I tend to see the difference being the moisture content of my older powder reduces over time (I measure moisture every time I reload, these days). That reduction in moisture content has had a definite effect down the road when comparing it to the newer lot or even the same lot that's not been opened over a significant amount of time, like 6 months or so.

 

[6.5 forever]

This is 2 different lots of 7mm Berger 168 VLD-Hunting (@200 yds). Same Lot and charge of powder, Same seating depth (Cartridge Base to Ogive), but the bullets were 0.016" different in the Bullet Base To Ogive.View attachment 1623479View attachment 1623480

Wow that sucks! And it's Bergers.

 

[JMayo]

I've been playing with seating depth. Went from hard jam to .003 off touch and saw a .25" difference it tightened up.

 

[searcher]

I can't recall ever switching to a new lot of powder and not having to make some tweaks on the powder - as velocity can vary 50 fps+. On a good load, that 50 fps won't usually open a group up that much - so I'm with many of the others in looking at the bullets primarily. A chrono will tell you a lot.

 

[Bill Norris]

Recently changed powder lots moving to a new container. (Varget) Had to change charge and seat depth to get back to my established 5-shot groups @ .250 at 100 yds. and speed as well.