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Cold Bore - possible cause

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barronian

Sergeant of the Hide
Full Member
Minuteman
Jan 18, 2019
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Irrespective of which of my guns or which ammo i use my first shot (cold bore) is invariably 'hot' - normally between 40 and 100 f/s faster than the other shots.

This has been bugging me so i've been trying to ascertain the cause of it.
Ive looked at keeping ammo warm/cooling it overnight to ambient/letting the gun cool/cleaning/not cleaning/different shoulder pressure/etc.
For a while i had a working hypothesis that the chamber and barrel dimensions change(expand) when heated by the first shots so that subsequent shots are slower.

However today i think i have come a major step towards isolating the cause :)

This was an easy test to do and it proves to be highly repeatable with 100% correlation (so far!)
so... today i had confirmed again that cleaning the barrel before shooting the first round (today it was Hoppes 9) didn't stop the cold bore 'hot' shot. (Eley Match at 1131 f/s instead of 1084 f/s. ES 46, exclude the first shot and ES = 5).

so i tried blowing through the barrel until i got condensation out the magwell (its cold and wet here so that didnt take long).
1003 f/s cold bore ! 1086 max, ES 83. exclude the first shot and ES =6.

repeated this several times and got very low velocities for each cold bore shot,

fired a new clip without 'blowing' and had no cold bore anomaly.

blow again before a new clip and ... cold bore anomaly.

dont blow - no anomaly.

So, what i think is normally happening is that my guns come from inside a very dry gun safe ( RH <25% ) and the first shot is 'hot' but the water in the combustion products 'wet' the barrel so subsequent shots are 'normal'.

Whether all of the effect described above is due to excessive condensation retarding the combustion or due to increases in the friction in the barrel i don't know - either could give the lower velocities. However, i believe most ammo is produced in an environment with a RH of 40-50%. it's also a known that changes in the humidity of the propellant affect the burn rate, and hence the velocity of the bullet.
So its not inconceivable that higher humidities such as the ~90% in my 'blown' barrel are retarding the combustion while lower humidities are making it burn marginally faster ?

This might also explain why people who live and shoot in 'nice' climates often say that they don't see any Cold Bore effect ?

Comments ?
 
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I just wrote to 6x5 thread about trying the blowing trick!

Good to know it works, I need to try it too. Today I tried if working a boresnake many times gives any different results, it does not indeed.

Your point makes sense because cartridges make a lot of vapor and it condensates to barrel surface. The next cartridge then has to change the earlier cartridge's condensated water back to vapor.

The first cartridge will get to pass the bore without any puddles stealing its energy.

However it is, this trick will let me shoot without any cracking noises on the first shot!
 
Get a piece of silicon tubing that's long enough to fit into the chamber while allowing you to blow into it without having to go through all types of body gyrations.

This reminds me of the "blow tubes" we used to use while shooting black powder cartridge rifles in an effort to keep the fowling soft.
 
Blowing from the muzzle end without cleaning will send quite much dirt to the bolt/magazine.

I can already picture how people are going to think I am weird... putting the barrel on my mouth on a public range.

"Are you gonna blow your head?"
-"No, I am blowing the barrel."
 
barronian said:
Irrespective of which of my guns or which ammo i use my first shot (cold bore) is invariably 'hot' - normally between 40 and 100 f/s faster than the other shots.

This has been bugging me so i've been trying to ascertain the cause of it.
Ive looked at keeping ammo warm/cooling it overnight to ambient/letting the gun cool/cleaning/not cleaning/different shoulder pressure/etc.
For a while i had a working hypothesis that the chamber and barrel dimensions change(expand) when heated by the first shots so that subsequent shots are slower.

However today i think i have come a major step towards isolating the cause :)

This was an easy test to do and it proves to be highly repeatable with 100% correlation (so far!)
so... today i had confirmed again that cleaning the barrel before shooting the first round (today it was Hoppes 9) didn't stop the cold bore 'hot' shot. (Eley Match at 1131 f/s instead of 1084 f/s. ES 46, exclude the first shot and ES = 5).

so i tried blowing through the barrel until i got condensation out the magwell (its cold and wet here so that didnt take long).
1003 f/s cold bore ! 1086 max, ES 83. exclude the first shot and ES =6.

repeated this several times and got very low velocities for each cold bore shot,

fired a new clip without 'blowing' and had no cold bore anomaly.

blow again before a new clip and ... cold bore anomaly.

dont blow - no anomaly.

So, what i think is normally happening is that my guns come from inside a very dry gun safe ( RH <25% ) and the first shot is 'hot' but the water in the combustion products 'wet' the barrel so subsequent shots are 'normal'.

Whether all of the effect described above is due to excessive condensation retarding the combustion or due to increases in the friction in the barrel i don't know - either could give the lower velocities. However, i believe most ammo is produced in an environment with a RH of 40-50%. it's also a known that changes in the humidity of the propellant affect the burn rate, and hence the velocity of the bullet.
So its not inconceivable that higher humidities such as the ~90% in my 'blown' barrel are retarding the combustion while lower humidities are making it burn marginally faster ?

This might also explain why people who live and shoot in 'nice' climates often say that they don't see any Cold Bore effect ?

Comments ?
Click to expand...

Wow this is awesome... so now I just need to figure out how much blowing to get the exact avg velocity instead of shooting slower :). Are you going to keep testing until you get your first cold bore shot to be ~1086?
 
@littlepod i suspect it will depend a bit on the RH of the air on the day... I don't compete so cold bore really isn't a problem for me i just 'needed' to understand what was going on. I can happily shoot 5 rounds before i settle down to a 6x5 or whatever :)
 
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The combustion is not affected by the outside humidity, the enclosed powder supplies everything it needs to burn, both oxygen and fuel.

Upon ignition, everything is sealed between the bullet and the case until the bullet leaves the barrel.

You are changing the barrel surface in FRONT of the bullet, either the lube layer or moisture in the bore.

Without blowing........On a clean bore (no lube), the first shot is harder to push down the bore, thus increasing pressure (ie, more velocity) subsequent shots are sliding on a layer of lube. Cold lube also increases pressure (and velocity) on a cold bore.

Adding moisture puts a different lube (water) that is a little slicker than the bullet lube...... less pressure, (ie less velocity)
 
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@Hellbender I'm far from expert but im not sure that your logic is correct.

My understanding is that more friction will increase the pressure - due to a DECREASE in the velocity of the projectile. I think of two end members :
1) a bullet with no mass and no friction - this would ride the leading edge of the expanding gasses, no pressure buildup other than that due to the viscosity of the expanding gasses, and
2) a stuck bullet - zero velocity and extreme pressure buildup.

I'm also assuming (again no experimental knowledge here) that since the bullets are designed with a lubricant that the bullet slides on the lubricant - which would imply that some lubricant is left behind the bullet as it passes down the barrel. This lubricant and whatever moisture film is on the barrel will be burnt along with the burning gasses ?

Initially i thought that the amount of moisture in the lubricant film would be so small as to be inconsequential but here is my thought exercise :
.22 lr charge is approx 0.085g.
water content about 1% = 0.00085g
from what i can find on the reloading forums it looks like raising the humidity of the powder by 1% may reduce the bullet velocity by approx 5%, this is in the same order as the observed effect.

if im not messing things up, 0.00085g water in a 710mm barrel would be a film about 7 nm thick. I tried to do some research on humidity films on various steel types .... now feeling more ignorant than i was before i started :-( Anyway if i understand what i found then a humidity film at 80 % humidity could be about 4 nm thick - and that this thickens dramatically (by about 8 orders of magnitude !) as you go towards 100% RH.

At some stage i will need to do another experiment, with de-greased ammo to check that it isn't the wax/lube that is affecting the burn rate. It might be that in the 'wet' barrel less wax/lube is retained by the barrel after the passage of the bullet, and the wax may be an accellerant ? Or the wax/lube isn't as effective as an lubricant on 'wet' barrel walls (higher friction = lower velocity) ?

soooo much still to understand ! :eek: :ROFLMAO:
 
I know it seems counter intuitive about the friction and pressure, but you are both right and wrong (as was I in my post above when I implied there was NO difference in the added moisture).

As long as the powder IS BURNING (14-18" approx. in a 22LR) higher friction loads in the barrel will INCREASE velocity because of increased pressure (ie, a "tight bore" centerfire barrel will have a higher velocity than a "normal" bore diameter barrel (with same loads), this is a known and proven fact and can even be proven in interior ballistics programs such as Quickload).

AFTER BURN, in a longer barrel, then you are correct, increased friction will slow the bullet down.

You are also correct in the higher moisture content could slightly reduce velocity, but not anything like the almost 130 fps spread you are seeing, I don't know if it's possible to calculate exactly, but I would expect closer to 5-15 fps (within normal deviation).

I have several cans of IMR powders over 30 years old (some are marked $6.99) and their velocities are still identical to the new IMR powder I buy today.

I also have many old boxes of .22 match ammo (Tenex and Winchester) that have been stored poorly (I live in MO with high humidity) and their velocities have not changed appreciably from 25+ years ago. The bullet is loose in many of these rounds, Tenex is the worst. I've had a chronograph since the early 80's.
 
Well lets try lubing the barrel before the cbs next time.

I was thinking of CLP or just plain synthetic motor oil.

But blowing is the easiest task to do, you do not necessarily have oils and means to lubricate the barrel at the range.
Did you notice that the cbs was more accurate too after blowing? They tend to be more or less fliers usually.

Could it be that blowing straight towards the chamber end could have more sudden changes to cbs, as that is where the extra friction/water should help the most.
 
Don't use anything with Teflon in it, this can cause weird stuff to happen and is VERY difficult to remove.

Dip the tips of the bullets in different lubes to try , there are many threads on this if you do a Google search.
 
Hellbender said:
Don't use anything with Teflon in it, this can cause weird stuff to happen and is VERY difficult to remove.

Dip the tips of the bullets in different lubes to try , there are many threads on this if you do a Google search.
Click to expand...
I thought about dipping them but I find it a bit finicky. Greases magazines etc.
I could do it just before chambering the round but it is not complete enough.
After all it is just to test if it is only the lubrication that causes the cbs or not.
I guess I will run oiled cloth on a brush a couple times through.

I already like the blowing trick a lot, I doubt I can forget to bring my lungs with me so it is foolproof.
 
Last edited:
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Hi Folks, really appreciate all the input ! Unfortunately i wont be able to test anything at all for the next three months - temp relocation to BC, Canada - without my guns. Will be back home at Easter.
 
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I was planning on driving up to Whistler in a few weeks, and wanted to swing by IBI so they can play with my rifle, but it looks like getting it across Customs will be a bitch, so that probably won't happen...
 
Yep, i didn't even try bring mine in.
Whistler is great. board or skii ?
 
@Cuzz ROFL !
@littlepod Boarding for us too :) Whistler is just expensive in general ! but the boarding is great and its easy for us to get to - takes 22 hours but it is 'easy' :eek:
 
I think he refers to the air tube.

I tried the oiling trick last time at range.
Oiled quite heavy, then took another cloth and left just a thin film around.

But forgot to bring the chrono.
But still, the first shot made it thunder, it just smelled very bad.
 
This is interesting but it does not explain the different cold bore shots of different rifles or why we still have CB deviations even when it is warm and dry out. I have a Rem 540XR that is very accurate but the first 10 shots are high to the right gradually having less and less deviation until it settles in on shot 8, 9 or 10. I have a Savage B-mag in 17WSM which has no cold bore deviation that I can measure whatsoever. It makes it a great hunters rifle. My Anschutz 54 and Win 52 are in the middle. Both take between 3-5 shots to settle down and start printing X's. I have another Annie model 1451 whose coldbore is extreme with the 1st shot being as much as 1.5" high using Lapua CX. It does settle quickly after 2-3 shots. Hard to see how water vapor alone would cause such wide spread deviation. The water condensation may indeed be part of the equation but like most things in real life there are other variables in play.
 
JG26_Irish said:
This is interesting but it does not explain the different cold bore shots of different rifles or why we still have CB deviations even when it is warm and dry out. I have a Rem 540XR that is very accurate but the first 10 shots are high to the right gradually having less and less deviation until it settles in on shot 8, 9 or 10. I have a Savage B-mag in 17WSM which has no cold bore deviation that I can measure whatsoever. It makes it a great hunters rifle. My Anschutz 54 and Win 52 are in the middle. Both take between 3-5 shots to settle down and start printing X's. I have another Annie model 1451 whose coldbore is extreme with the 1st shot being as much as 1.5" high using Lapua CX. It does settle quickly after 2-3 shots. Hard to see how water vapor alone would cause such wide spread deviation. The water condensation may indeed be part of the equation but like most things in real life there are other variables in play.
Click to expand...
To be honest there is not much other variables than the barrel surface that can be the cause behind CBS.
I doubt it is all about vapor but adding some may clearly help with the symptoms.

I first had cbs to top and top left, but then they moved to right and down.

One was even over 1" down and 1" right.
 
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Near miss said:
To be honest there is not much other variables than the barrel surface that can be the cause behind CBS.
I doubt it is all about vapor but adding some may clearly help with the symptoms.

I first had cbs to top and top left, but then they moved to right and down.

One was even over 1" down and 1" right.
Click to expand...

My factory Tikka barrel was down 1" and down 1" right on Cold Bore at 100 yards. That was one of the reasons why I thought getting a thicker bull barrel would help. But now it looks like I have the fast first shot as I'm shooting off a super dry barrel that's been sitting in the safe. Though my factory barrel would actually cool down after 30 min and require a few shots to settle in every 30min. The new thick barrel just needs that first shot of the day to lube up and then it shoots consistently until it goes back into the safe.

For center-fire rifles, especially thin barrels, the heating up of the barrel does cause a shift. That's why thin barrels don't do well over long strings. I'd assume that heat up from being cold would deifnitely have a cold bore shift too.
 
JG26_Irish said:
This is interesting but it does not explain the different cold bore shots of different rifles or why we still have CB deviations even when it is warm and dry out. I have a Rem 540XR that is very accurate but the first 10 shots are high to the right gradually having less and less deviation until it settles in on shot 8, 9 or 10. I have a Savage B-mag in 17WSM which has no cold bore deviation that I can measure whatsoever. It makes it a great hunters rifle. My Anschutz 54 and Win 52 are in the middle. Both take between 3-5 shots to settle down and start printing X's. I have another Annie model 1451 whose coldbore is extreme with the 1st shot being as much as 1.5" high using Lapua CX. It does settle quickly after 2-3 shots. Hard to see how water vapor alone would cause such wide spread deviation. The water condensation may indeed be part of the equation but like most things in real life there are other variables in play.
Click to expand...

Actually i think it might explain some of the different responses in different guns.

Assuming all your guns are stored in exactly the same dry conditions:

possible model 1 - combustion retardant.
in this model i would expect the different barrels to have different rugosity and hence retain different levels of 'wetting' possibly taking different number of shots to reach their max retainable 'wetting'. ?

possible model 2 - water in combustion products is responsible for 'wetting' the barrel changing the friction for subsequent shots.
same explanation as model 1 ?

This might explain why many of the hand lapped custom barrels appear to have little cold bore deviation ?
 
Near miss said:
I think he refers to the air tube.

I tried the oiling trick last time at range.
Oiled quite heavy, then took another cloth and left just a thin film around.

But forgot to bring the chrono.
But still, the first shot made it thunder, it just smelled very bad.
Click to expand...

Yep been there done that. I've tried with different oils and cleaning agents with no good correlation to the results. So far the only thing ive seen a correlation with is the humidity of the inner surface of the barrel.
Cleaning with a desiccant (alcohol) produces a large CB anomaly but it also removes the lubricant film so i dont know which causes the effect.
 
barronian said:
Actually i think it might explain some of the different responses in different guns.

Assuming all your guns are stored in exactly the same dry conditions:

possible model 1 - combustion retardant.
in this model i would expect the different barrels to have different rugosity and hence retain different levels of 'wetting' possibly taking different number of shots to reach their max retainable 'wetting'. ?

possible model 2 - water in combustion products is responsible for 'wetting' the barrel changing the friction for subsequent shots.
same explanation as model 1 ?

This might explain why many of the hand lapped custom barrels appear to have little cold bore deviation ?
Click to expand...
Do we have custom barrel shooters that can confirm this?
This is my belief also, that custom barrels have less CBS effects than factory barrels do.
 
My Vudoo has none that I can discern shooting RWS R50, but I haven't shot it under 50 deg. or so for groups.

If I scrub it to bare metal, then it takes about 3-4 shots to settle in, but none are out more than 1/4-3/8" at 50 yd.

My Anschutz 64 needed about 5 shots to settle in (out 1/2" or so @50).

40X (factory heavy bbl) needed about 3-5 ( same as Annie).

Good ammo makes a lot of difference (better lube coating in bbl. stays more consistent when cold)

Have you guys tried any Biathlon ammo? The propellant and lube is optimized for cold weather.
 
@Hellbender Ive tried Lapua Polar Biathlon and SK biathlon Sport both of them before the freezing temps arrived. I haven't tried them at temps below freezing yet.

Have you looked at your barrels with a good bore scope ? Is the barrel on your Vudoo more polished than the others ?
 
The Vudoo (Ace bbl) looks very smooth compared to all my other factory bbl's, all my other customs are centerfire, and the Ace bbl is comparable to Bartlein and Kreiger.
I no longer have the Annie or 40X, and did not have a bore scope at the time.
 
Hellbender said:
The Vudoo (Ace bbl) looks very smooth compared to all my other factory bbl's, all my other customs are centerfire, and the Ace bbl is comparable to Bartlein and Kreiger.
I no longer have the Annie or 40X, and did not have a bore scope at the time.
Click to expand...
My Vudoo is much more polished than my 64 annie. And like Helbender , my v-22 throws first cold clean shot 1/4 to 3/8”, My Annie will throw 2 shots an inch off center if cold and clean.
 
Last edited:
I have had several 22lr’s with custom barrels and many many more with factory barrels. All the rifles with the custom barrels have shown little to no cold bore shift. That is clean cold or fouled cold (true cold bore shots also, at least 24 hours since the last time they were fired). I’m not even going to try to speculate as to the reason, I have some thoughts but they are purely speculation.
 
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so if the custom barrels that don't show a CB effect or have reduced CB effect have a more polished surface than 'mere mortal' barrels then possibly they develop less of a humidity film and hence show less sensitivity to the CB effect ?
 
barronian said:
so if the custom barrels that don't show a CB effect or have reduced CB effect have a more polished surface than 'mere mortal' barrels then possibly they develop less of a humidity film and hence show less sensitivity to the CB effect ?
Click to expand...
I surely don’t have anything to back this up but i don’t see how a polished or unpolished bore would gather or hold more or less moisture?
This is however a very interesting and worthy subject!
 
as far as i understand it the rugosity (roughness) of the surface has a direct effect on the formation and thickness of a humidity film. It is a non-linear relationship so its not as simple as smooth = little/thin and rough = lots/thick. Something to do with surface tension, electrostatic forces and molecule size...
 
barronian said:
as far as i understand it the rugosity (roughness) of the surface has a direct effect on the formation and thickness of a humidity film. It is a non-linear relationship so its not as simple as smooth = little/thin and rough = lots/thick. Something to do with surface tension, electrostatic forces and molecule size...
Click to expand...
I just talked with vudoo, mine has the middle sized molecules.
 
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I see it:

Rougher surface = more surface area.
More surface area = more contaminants
More contaminants = more stuff in the way of the bullet
More stuff in the way of the bullet = more stuff to go south.
 
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