How to stop cold bore shift?

[asd9055]

Dropped the 200 Accubonds, and went back to my old load with 180 Accubonds, did not get the cold bore shift today, cold bore in the same group with the remaining shots. I'll check again another day to confirm.
I did retighten the action screws yesterday as well.

I have never experienced this issue. Mine has always been the 5th round that was a flier. I used the 180 and 200 grn, BT, AB and PT in 3 different 300Wby MKV. Let us know what yiu find out

 

[Horse1]

I'm getting cold bore shifts in the 300 Win Mag, it has some fire cracking in the throat, but not much. Using H4831 and 200 Accubonds for big game hunting, Cold bore is an inch high at 12 o clock, and remaining rounds are in a group an inch right and low at 2 o clock. Happened on three sessions when testing. How to I stop this cold bore shift?

Rifle, stock, scope, mounts, and bedded or not bedded would be good things for the OP to answer as folks try to help narrow down the cause of the shift.

The scope itself could have an issue w/flexing in the mounting system, backlash in the internal adjustments, or an element with just enough movement in it's journal to allow the shift.

In general, I'd be looking for a mechanical issue regarding something that's predictably and reliably wonky:

A screw head spacing on the distal end rather than the screw-head.

A scope-ring shifting in a base, like the slot in a Weaver/Picatinny.

Foreign material impeding proper mating of the bolt lugs to the receiver face.

A stock making contact
The fore-end bouncing off the bbl during recoil
dragging sling studs over the front or rear rest during recoil
a wood stock heating up and creating pressure, including factory tip-pressure
an internal mag-box binding the action creating a teeter-totter

Basically, recoil sets right whatever is wrong until things cool back off and the tension is relieved or re-set and you start all over again.

There's certainly a case to be made for stress in the barrel as well at which point you can heat-treat and temper, cryo-treat, or start over w/a new bbl.

 

[nksmfamjp]

I'm getting cold bore shifts in the 300 Win Mag, it has some fire cracking in the throat, but not much. Using H4831 and 200 Accubonds for big game hunting, Cold bore is an inch high at 12 o clock, and remaining rounds are in a group an inch right and low at 2 o clock. Happened on three sessions when testing. How to I stop this cold bore shift?

Shoot 7 groups of 3. Clean & cool between groups. What do your composite groups and composite cold bore shots look like?

 

[8x68s]

Dropped the 200 Accubonds, and went back to my old load with 180 Accubonds, did not get the cold bore shift today, cold bore in the same group with the remaining shots. I'll check again another day to confirm.
I did retighten the action screws yesterday as well.

I have read (many times over the years here and elsewhere) when searching for cause, change only one thing at a time so that if you find a solution, you're not guessing about which solution actually worked.

 

[Taj]

Cold bore shift can't always be eliminated but can sometimes be mitigated. You probably already know this but running a clean patch with some carb ( or alcohol) cleaner on it before your first round down range from a clean barrel may help. An oily barrel will definitely affect the first few rounds down range. Properly stress relieved barrels are less prone to shifts (or at least big shifts) The carb cleaner was pretty much SOP on out LE sniper rifles before we deployed them. Make sure your bedding is stress free, and guard screws are tight. Sometimes, some barrels just do that and there aren't any real ways to make it go away. We used to see some really big shifts on Styer SSG sniper rifles with their cold hammer forged barrels. We had a couple of the worst offenders cryo stress relieved and it did help some. Finally just got rid of them. Lots of stress on barrel steel with that process and good stress relieving is crucial.

 

[Frank in the Laurels]

..I've seen it dozens of times in various cartridges and calibers...simplest solution was don't clean after you sight it in....I wouldn't say 100% but the vast majority of times the clean, oiled and not fouled bore was a bigger easier problem to solve than casings, bedding etc..

 

[TackDriv3r]

I have read (many times over the years here and elsewhere) when searching for cause, change only one thing at a time so that if you find a solution, you're not guessing about which solution actually worked.

After my hunt with the 180 Accubonds in a couple of weeks, I'll check again with the 200 Accubonds and see if the action screws was the issue with cold bore

 

[Shane Lindsey]

BLUF=Voodoo man, Voodoo

Clean to bare steel.
Shoot ten shots, taking note of first two (cold clean/follow up). Put it away until next outing without cleaning.
Shoot one and a follow up. Put it away until next outing without cleaning.
Shoot one and a follow up. Put it away until next outing (probably not needed)..

Shoot all of these on the same target with a date next to it. Next time out use the same target and date stamp it. If this does not show a repeatable combo, may need a new barrel. Some bullet combos come together really fast after cleaning, others, not so much. I have a 6.5 PRC that needs about five down it with copper monos, before it is consistent. Same rifle with 140 Bergers, cold/clean is in the same group.

I have had good luck with 65 inch lbs on all my Rem style pillar/bedded actions.

 

[Taj]

..I've seen it doesn't of times in various cartridges and calibers...simplest solution was don't clean after you sight it in....I wouldn't say 100% but the vast majority of times the clean, oiled and not fouled bore was a bigger easier problem to solve than casings, bedding etc..

Absolutely agree and some of the philosophy about cleaning and bore shift has changed, however a dirty bore vs a clean bore is not always all of the issue. Cold bore shift can be a bigger issue than a clean bore and can be harder to isolate. We saw this during rifle testing during my tenure at one of the major manufacturers. Some manufacturing processes of rifle barrels put more stress on the barrel steel than others and things like action barrel face and barrel shoulder squareness can dramatically affect cold bore shift. Even minor temp changes will start to affect shift if all isn't right with the machining gods. we had test barrels and actions mounted to massive blocks of steel and were often amazed at how much even small influences could make on shot dispersion if tolerances weren't maintained at a very high level. Just my 2 cents.

 

[asd9055]

BLUF=Voodoo man, Voodoo

Clean to bare steel.
Shoot ten shots, taking note of first two (cold clean/follow up). Put it away until next outing without cleaning.
Shoot one and a follow up. Put it away until next outing without cleaning.
Shoot one and a follow up. Put it away until next outing (probably not needed)..

Shoot all of these on the same target with a date next to it. Next time out use the same target and date stamp it. If this does not show a repeatable combo, may need a new barrel. Some bullet combos come together really fast after cleaning, others, not so much. I have a 6.5 PRC that needs about five down it with copper monos, before it is consistent. Same rifle with 140 Bergers, cold/clean is in the same grou

I have had good luck with 65 inch lbs on all my Rem style pillar/bedded actions.

Absolutely agree and some of the philosophy about cleaning and bore shift has changed, however a dirty bore vs a clean bore is not always all of the issue. Cold bore shift can be a bigger issue than a clean bore and can be harder to isolate. We saw this during rifle testing during my tenure at one of the major manufacturers. Some manufacturing processes of rifle barrels put more stress on the barrel steel than others and things like action barrel face and barrel shoulder squareness can dramatically affect cold bore shift. Even minor temp changes will start to affect shift if all isn't right with the machining gods. we had test barrels and actions mounted to massive blocks of steel and were often amazed at how much even small influences could make on shot dispersion if tolerances weren't maintained at a very high level. Just my 2 cents.

My big question is why with 200 grains and not with 180? Are the stresses that different?

 

[skipglo]

I'm getting cold bore shifts in the 300 Win Mag, it has some fire cracking in the throat, but not much. Using H4831 and 200 Accubonds for big game hunting, Cold bore is an inch high at 12 o clock, and remaining rounds are in a group an inch right and low at 2 o clock. Happened on three sessions when testing. How to I stop this cold bore shift?

Hunting gun? Then your cold bore shot is perfect. Don't change a thing! Unless....you give all your game a warning shot...first

 

[Taj]

My big question is why with 200 grains and not with 180? Are the stresses that different?

Every bullet weight sets a new dynamic with most any rifle. Sometimes they are small differences but sometimes they can drive you crazy.

 

[Northkill]

Can you please define precisely how many jumps and at what point in the jumping phase the posterior emissions are to occur?

Gotta get the harmonics right for accuracy. I see where yer comin from.