cold bore shift / 300 Win Mag

[TackDriv3r]

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?

 

[troupe]

More info will be needed, as in bedding, factory barrel and contour, custom barrel, factory stock, etc. Bench techniques.

 

[hoz53]

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?

have you checked the velocity differance between the CB/CB and your other shots? for a cold bore clean bore shot on my 6br it can be 30 fps.

 

[TackDriv3r]

More info will be needed, as in bedding, factory barrel and contour, custom barrel, factory stock, etc. Bench techniques.

It's a custom rifle, Bartlein barrel 26 inch, Rem 700, free floated barrel, and pillar bedded. Used my Atlas bipod.
What is the torque specs and sequence if I were to readjust the action screws?

 

[TackDriv3r]

have you checked the velocity differance between the CB/CB and your other shots? for a cold bore clean bore shot on my 6br it can be 30 fps.

I believe about 10-12 fps, wasn't much between cold bore and the groups.

 

[Doom]

Is the cold bore shot after cleaning or is it occurring with a fouled barrel each time?

 

[K22]

I can tell you how I stopped it. I stopped removing the copper. I use a mild solvent that does not aggressively attack the copper. Once the bore is plated with copper, I have achieved bore stability i.e., equilibrium. I know no one believes this and that is fine with me. I just telling how I solved my issues with cold barrel flyers.

I cannot claim any super smarts figuring this out. A fellow shooter led me to gunblue490's web site. I watched his videos. I was skeptical but tried his simple cleaning method and it worked, at least for me for my purposes. This guy has hunted all over the US, is a factory trained armorer, and retired Police Captain with many years of shooting / reloading experience.

I currently have 11 centerfire rifles. All hunting rifles that I use a lot. None of them exhibit cold barrel or clean barrel flyers. I can't tolerate a cold or clean barrel flyer since the first shot is the money shot, and I am shooting critters (groundhogs and predators) with a vital area a lot smaller than presumably you are with a 300 Win Mag.

 

[TackDriv3r]

Is the cold bore shot after cleaning or is it occurring with a fouled barrel each time?

It's with a fouled barrel. Ran two tests prior with a few 3 round groups, this test was with 12 rounds. Had a cold bore shift twice already this week.

 

[46and2]

It's with a fouled barrel. Ran two tests prior with a few 3 round groups, this test was with 12 rounds. Had a cold bore shift twice already this week.

I work up loads on my hunting rifles COLD BORE ONLY. That's the one that counts 99% of the time.

I don't know your experience with 300wm or heavy recoil light rifles so don't take this personally , but make sure it isn't cold bore shooter instead of cold bore problem.

 

[hoz53]

I believe about 10-12 fps, wasn't much between cold bore and the groups.

i dont know what to do to eliminate Accuracy differances with a cb-cb shot. its usually vertical for me as the velocity is different. if i dont clean i dont have the issue so fouled bore sounds right.

 

[Doom]

It's with a fouled barrel. Ran two tests prior with a few 3 round groups, this test was with 12 rounds. Had a cold bore shift twice already this week.

If it is repeatable you may not be able to fix the issue (barrel related?). To me the one thing that struck me was that the action is only pillar bedded. You didn't mention the stock material. If it were me I would consider a new stock with an aluminum bedding block. Down side it weighs more. You could try bedding the recoil lug on your existing stock.

If this is a light weight barrel it is possible that free floating the barrel may be working against you. Many rifles actually have tabs on the end of the stock that are meant to ride on the barrel to change the harmonics. It probably would not change the behavior of the cold bore shot but might reduce the magnitude of the shift. You could try taping up the barrel to see it that would help.

You asked about the torque specs. Most synthetic stocks are about 65 in-lbs and most wood stocks are about 35 in-lbs. I would check the stock manufacturer's website. I have seen differing opinions on sequence. I personally torque the front action screw before the rear action screw (Rem Actions with bedding blocks). Savages are different.

 

[6MMsteve]

your barrel isn't loose is it, I had a loose barrel that done the same thing just throwing it out there.... u never know

 

[K22]

It's with a fouled barrel. Ran two tests prior with a few 3 round groups, this test was with 12 rounds. Had a cold bore shift twice already this week.

It may take a few cycles of shooting and cleaning (carbon removal only) to re-stabilize the bore condition or the problem could lay elsewhere such as bedding or flinching by the shooter on a heavy recoiling caliber like the 300 Win Mag.

Repeated aggressive removal of copper then firing a few fouling shots did not work for me. I had to eliminate aggressive copper removal since by not doing so, it became a repetitive cycle of stripping copper out, replating the bore, stripping it out, etc. and the bore never achieved any stability. Watch gunblue490's three older videos on (1) Gun Cleaning and Solvents, (2) How to Clean Your Rifle Professionally, and (3) Precision Barrel Break In and Cleaning Why, How and Do You really have to. Watch all three in that order, read the numerous testimonies, then make your own decision.

My barrels shoot relatively the same from either cold or clean barrels. All my range practice is with cold, cool, or clean barrels since this is the money shot in the field. Granted, I am not shooting magnums or these days, anything heavier than a 243 Win. but even in the days of 308 I didn't experience cold barrel flyers. Also, I am not a competitive shooter unless you consider competing against varmints and predators.

I am not an expert so this is going to give the bore scope crowd and experts hives but I can only report what I have experienced.

 

[TackDriv3r]

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.

 

[searcher]

A lot of times, folks have residue of bore solvent and/or a film of rust preventative they may have applied when cleaning their gun. Running a few patches with a degreasing agent which will remove all traces and at least eliminate the pressure variation caused by that. I run a few patches of Rem Oil though my bores after cleaning, followed by a few dry patches. If I fail to remove it before shooting that first shot, it is noticeable.