Cold Bore Shot, Barrel Length/Profile Effects questions

[Qbeam]

Just some questions regarding cold bore shots:

How does barrel length affect the difference between follow-up shots and the first shot?

Does stress relieving the barrel reduce the cold bore shot and follow-up shot deviation?

Does the barrel profile (fluting/heavy barrel/taper) have a noticeable affect on the cold bore shot and follow-up shot deviation?


Any knowledge on this would be appreciated as a learning experience.

Q

 

[outrider58]

My uneducated guess is not much. At least not until you go beyond 5 shots.
My concern, as a hunter, has always been clean bore shots and follow up shots. That's where there can be a problem.

Never do 'business' starting out with a clean bore. Always foul the bore first.

 

[Qbeam]

Thanks, Outrider. I forgot about the clean versus fouled barrel. I remember E. Shell talking about cleaning the barrel only when accuracy starts to degrade.

Q

 

[Doco Overboard]

Heres what I think,

How does barrel length affect the difference between follow-up shots and the first shot?

None that I'm aware of. Barrel Vibrations begin to set up as soon as the trigger is pulled.
The system begins to move before ignition completely occurs and there is inherent error in every shooter regardless of the skill level due to harmonics created by the movement of the parts. Just as there is mechanical error in every sighting/ optic system. This is a known trait.

Does stress relieving the barrel reduce the cold bore shot and follow-up shot deviation?

Barrel stress is part of the manufacruring and material selection process. I do not know of any means to measure its effect other than a barrel that performs well. No two barrel perform exactly alike. This has been proven with a Mann accuracy cradle in government laboratories and through Arsenal testing. Consistent bedding and bearing points have a pronounced effect on barrel harmonics as does internal ballistics which is variable through lots of powders amd metallic cartridge components as does atmospheric conditions such as elevation and temperature.

Does the barrel profile (fluting/heavy barrel/taper) have a noticeable affect on the cold bore shot and follow-up shot deviation?
Yes, I believe it does. As any barrel begins to warm its internal stresses become more or less evident based on the methods employed during its construction, ability of the shooter to make corrections based on atmospheric conditions with repetitive shots and the amount of heat generated by ammunition selection. A heavy barrel is not only used to absorb heat, its addtional weight counteracts the efffect of rotational movement before forcement occurs just ahead of the chamber. Recoil starts before the bullet quits the bore and the cartridge case actually. Many methods of barrel construction have been employed to determine the most efficient means of production and overall performance characteristics.

 

[4g64loser]

"cold bore" is, in my experience, BS. It's cold shooter, bad support construction, etc. "Clean bore" is going to induce an offset and lower speed.

Firing rifles from zero interference rigs (think a sled and hydraulic or mechanical trigger actuation), the first shot goes right where the following shots go until heat related stringing gets to be an issue. How.much powder you burn, how precise you are shooting, and how thin the barrel is will.determine when that becomes noticeable.

In a more "hick" test, I swapped rifles (identical classroom rigs) on a guy who wouldn't shut up about cold bore shots. When what he thought was "his" already warmed up rifle fired it's first shot of the day into his target with no offset, I asked him to explain it. He said the gun was warmed up. My coworkers watched me switch the guns and about lost their shit laughing. The shooter being warmed up is what mattered.

CLEAN bore is a totally different thing. Especially if you strip the barrel down to bare steel. The main difference is velocity. Assuming that you didn't do something absolutely retarded and.shoot the gun with liquid still in the bore, the main change observed is in muzzle velocity/barrel time......you are effectively shooting a different load when you fire the first shot(s).

Example: my 6br typically shoots a berger 88 at 3031 avg in 70deg weather. Extreme spreads are usually under 10fps, often around 7 to 8 for five shots. In cooler weather, the average is usually 5fps lower per ten degrees of temp drop down to around freezing. Then it really falls.

Last October, in 52deg weather, I took it to the range completely clean. Scrubbed out, JB bore paste, bore scope checked, I mean clean. That barrel had maybe five or six hundred rounds on it at that point. Still pretty new. The first (clean) shot went 2971. The next shots were 3005 and 3010. Incidentally, these three shots printed a vertical line starting half an inch above POA and descending, by the third shot, to the dot in the center of a 1" circle. These three shots were what the rifle needed to lay in fouling and come back up to speed. I shot a five round group in the high twos (a bit over quarter inch ce ter to center) and the shots were 3022, 3018, 3018, 3013, and 3016.

All shots were captured by Labradar chronograph. Measurements were with dial calipers at the range on cardboard backed paper targets, so they should be considered plus minus one hundredth of an inch.

 

[TI-tick]

I'd agree with Outrider on this.
Tikka T3 Lite 30-06; cold bore is dead nuts on the mark.
Keep things cool.

 

[Russ D]

I’ve never seen in anything that I would attribute to “cold bore” poi shift. From pencil barrel hunting rigs to heavy barrel bench guns. I would think being fresh on a trigger you haven’t pulled in a while would be a bigger factor than minuscule vibrations of steel that a few degrees colder. Not to mention cheek weld and eye alignment variations.

 

[Speed3]

Cold bore doesn't exist, it's poor positioning more than anything. It happens to me more than I'd like to admit.

As stated above clean bore is a real thing. You can experience POI variances.

 

[Doco Overboard]

Just some questions regarding cold bore shots:

How does barrel length affect the difference between follow-up shots and the first shot?

Does stress relieving the barrel reduce the cold bore shot and follow-up shot deviation?

Does the barrel profile (fluting/heavy barrel/taper) have a noticeable affect on the cold bore shot and follow-up shot deviation?


Any knowledge on this would be appreciated as a learning experience.

Q

So one other thing is if your shooting a 22 rifle, which consequently are equipped with heavy barrels in some cases your question certainly does apply.
Usually before shooting for record the barrel is customarily warmed by about 10 shots thats has an effect on how the bullets lubrication qualities impacts the score tally.
Probably a good way to tell I think for the question being posed here though is to clean your CF rifle after shooting and then dont to see how it reacts.
I think what you may find is that you can tell a degradation regarding accuracy when it gets dirty even when your shooting very well unless its a lubricated bullet.
A clean bore simply has less friction which means a diffrence in impact due to a variety of circumstances like length vs barrel dwell cartridge velocity and all that sort of thing. Sheaf of fire in machine gunning comes to mind in that reagrd and probability of hits at maximum range in a predicted manner They knew all about that sort of thing to understand how troops moved forward under volley fire.
I forgot to mention earlier, a heavy barrel rifle dependent on how its fitted/stocked up is more resistant to changes in impact due to sling tension whether its cold or warmed. Cook off is another reason in some forms of gunnery for a HB'd gun that I remember more.

 

[Trigger Time]

My uneducated guess is not much. At least not until you go beyond 5 shots.
My concern, as a hunter, has always been clean bore shots and follow up shots. That's where there can be a problem.

Never do 'business' starting out with a clean bore. Always foul the bore first.

I would agree with this, but it also depends on the rifle you are shooting.
Lever guns tend to exhibit vertical stringing as the barrel warms up, three or more shots. Free floating barrels are anyone's guess.
It should be easy enough to test with your gun shooting off of a rest.

 

[outrider58]

Cold bore doesn't exist, it's poor positioning more than anything.

I would agree with this. Not so much a cold bore problem as a 'cold shooter' problem. Carried on into archery as well, if you don't hit a bullseye with you first arrow of a practice session, you need more practice.

 

[KRC]

"Does stress relieving the barrel reduce the cold bore shot and follow-up shot deviation?

Barrel stress is part of the manufacruring and material selection process. I do not know of any means to measure its effect other than a barrel that performs well. No two barrel perform exactly alike. This has been proven with a Mann accuracy cradle in government laboratories and through Arsenal testing. Consistent bedding and bearing points have a pronounced effect on barrel harmonics as does internal ballistics which is variable through lots of powders amd metallic cartridge components as does atmospheric conditions such as elevation and temperature."

This explanation doesn't seem to answer the question. The correct answers is yes and no.

No, or not much - If the barrel has already been properly stress relieved as part of the manufacturing process. All(?) top aftermarket barrelmakers do at least one heat induced stress relief after rifling. Some do another after contouring. Some do cryogenic stress relief at some point (or twice) during the manufacturing process. And the steel makers also stress relieve before shipping 416R SS.

Yes, possibly - A mass produced, hammer forged factory CM barrel? These barrels often have quite a bit of internal stress that may shift follow-up shots to a varying degree, depending upon the amount and location of stress within that particular barrel (which is often "luck of the draw"), and the amount of heat generated by the cold bore shot. Stress relief of a significantly stressed barrel might possibly reduce follow-up shot POI shift. But not likely worth the cost.

 

[E.Shell]

"cold bore" is, in my experience, BS. It's cold shooter, bad support construction, etc.

Unless there is something WRONG with the barrel: ^^ This ^^

We have proved this time and again, where a 'cold shooter' blows the first shot, but if you put a shooter that has warmed up on a cold rifle, somehow that first shot goes into the group. About every 3rd or 4th class we'd have a 'believer' in cold bore deviation that would leave class understanding what was really going on. Time after time.

"Clean bore" is going to induce an offset and lower speed.

A "clean bore" deviation is most often a "wet bore" deviation and if one wipes the bore with 90%+ alcohol, that "clean bore" deviation (velocity AND POI) no longer exists.

I’ve never seen in anything that I would attribute to “cold bore” poi shift. From pencil barrel hunting rigs to heavy barrel bench guns. I would think being fresh on a trigger you haven’t pulled in a while would be a bigger factor than minuscule vibrations of steel that a few degrees colder. Not to mention cheek weld and eye alignment variations.

^^ This ^^

Cold bore doesn't exist, it's poor positioning more than anything. It happens to me more than I'd like to admit.

^^ This ^^

As stated above clean wet bore is a real thing. You can experience POI variances.

F.I.F.Y.

Remove all traces of solvent and oil and the first shot stays in the group.

I would agree with this. Not so much a cold bore problem as a 'cold shooter' problem. Carried on into archery as well, if you don't hit a bullseye with you first arrow of a practice session, you need more practice.

^^ This ^^

 

[Doco Overboard]

I would think a top barrel maker would straitened a barrel before even reaming it prior to rifling it.
Which put bends or at the very least kinks into a deep drilled hole.
Which creates stress. How this is measured between two barrels is beyond me.
Maybe someone can explain.

 

[4g64loser]

Unless there is something WRONG with the barrel: ^^ This ^^

We have proved this time and again, where a 'cold shooter' blows the first shot, but if you put a shooter that has warmed up on a cold rifle, somehow that first shot goes into the group. About every 3rd or 4th class we'd have a 'believer' in cold bore deviation that would leave class understanding what was really going on. Time after time.

A "clean bore" deviation is most often a "wet bore" deviation and if one wipes the bore with 90%+ alcohol, that "clean bore" deviation (velocity AND POI) no longer exists.


^^ This ^^

^^ This ^^

F.I.F.Y.

Remove all traces of solvent and oil and the first shot stays in the group.

^^ This ^^

Yeah, the ol singapore swap trick switching out guns on the "true believer" made the guys at work laugh.

I'll try the alcohol wipe thing. I usually pushed acetone soaked patched through after cleaning and then follow up with dry patches til they don't have any odor or sign of coloration. Always figured that was enough. Guess I need to up my game. I did try the LockEez (graphite and alcohol) on a patch prior to first clean shot to eliminate the offset but it didn't work as some described. I still got a slow round or two. In worn bores, several slow rounds til the copper laid down.

Side note, this effect seems more pronounced in hyper speed rounds like my 22-250ai barrels that sling 40s at 4200+.

 

[KRC]

"I would think a top barrel maker would straitened a barrel before even reaming it prior to rifling it."

Top barrelmakers don't "straighten" barrels.

 

[E.Shell]

Due to the twist-drill boring used even today, the bore is a long spiral, even in a top-quality "straight" barrel.

This is why aligning the reamer to the throat produces reliably precise barrels, while aligning the reamer to the muzzle, like running between centers in the olden days, is literally hit & miss. The best match gunsmiths have adopted Gordie Gritters method of chambering and consistently produce rifles capable of amazing precision.

 

[Doco Overboard]

"I would think a top barrel maker would straitened a barrel before even reaming it prior to rifling it."

Top barrelmakers don't "straighten" barrels.

When I think barrel, I think barrel making from raw materials start to finish.
From a top barrel maker like SA , BSA, Savage or even HS maybe.
I can machine a barrel blank at my house if I wanted to. Theirs even guidance for shape diameter etc that’s proven by record. And instructions for constructing cutters broach’s reamerers etc. Guidance for cutting bullet seat and leade that’s old as hell from guys like Newton.
How I can measure stress after two or more after being straitened / during production I need help to understand.
Otherwise you have a custom barrel and no record, or even a proof for that matter.
When you find two that shoot the same or can even read sight graduations in on a micrometer or vernier scale
Or even two shooters that can shoot the same for that matter.
The guy posed a question for cold bore shooting. With a 22 you know the answer to that and the original question was broad and not specifically stated in the first place. Does a cold bore shot act in a manner that can be predicted.
Well not in a 22 that’s for damn sure.

 

[lazarus]

Thanks, Outrider. I forgot about the clean versus fouled barrel. I remember E. Shell talking about cleaning the barrel only when accuracy starts to degrade.

Q

What’s cleaning?

In all seriousness rifles I rarely clean barrels. Maybe once a year. Pistols I clean somewhat more frequently because I tend to shoot them more with dirtier stuff and if POI is effected, it’s less than any offhand accuracy variance I’ll introduce all on my own.

I notice almost no cold bore deviation versus a follow-up shot on any of my guns. Clean versus dirty, there is.

Barrel profile does determine walk. My Sako Forester .308 shoots into a quarter at 100 with premium hunting or match ammo for 3 shots. If I don’t let it cool for 10 minutes the next one is going to move up and right about a third of an inch. Rinse and repeat until it’s walked 1.5” to the up and right.

My Howa 20” heavy barrel 6.5 Grendel moves towards the 8 o’clock starting around round 10 or 12 in less than 5 minutes. But it’s real slow. But it’ll shift over the next 10-15 rounds about a total of 3/4” and doesn’t really move from there.

My Howa 22” standard profile .223 moves towards the 11 or 12 o’clock, depending on the ammo, starting around round 6-8 within about 5 minutes and will also shift about an inch over 10 rounds. Sooner and with generally fewer rounds than the Grendel as well as just slightly more shift.

The Grendel returns to cold bore within about 15 minutes in the shade if it’s cool out. The 223 is more like 20 minutes in the shade in cool weather.

Either I can keep shooting them hot and they’ll stay in the same point of impact. Groups open slightly when hot, but I’d say less than 20% increase in group size. But I also don’t care to put the kind of wear on them shooting them roasting hot does. Plus the heat mirage is usually getting pretty bad by then.

I am willing to buy it’s me and not the gun. Except on the Sako. Its barrel is not floated and I am positive it’s the barrel pressing on the stock when it’s warm/hot. I’ve just never wanted to inlet the forearm more to prevent it from happening, because it’s a hunting rifle only for me and a hand-me-down at that.

 

[antco]

Cleaning? Don't clean until accuracy degrades or the gun stops operating. Excessive cleaning kills more barrels than bullet wear does.

Cold bore is a misnomer. Rename it to clean bore. Already discussed above by experts.