Velocity Jump on new barrels

[Doug Herold]

All barrels respond differently to a cleaning regiment so I try to find out what the barrel likes first.

My experience has been that a clean barrel is the most accurate. At some point a barrel fowls to the point that it becomes very consistent and this is what most match shooters look for because they cant clean after each relay. If you leave the barrel fouled, load development should be done in this condition not in a clean condition.

I have followed the progress of custom barrels from the first shot on
and found that as the barrel broke in it got faster.until break in was complete. Then it settled in to a consistent velocity and as it became fouled velocity dropped very little but accuracy became worse as the barrel fouled. This normally occurred at 4 to 7 rounds from clean depending on the barrel itself. (I think this is the reason that it is hard to shoot a great 5 shot group) because it always seems like a flier happens on the last round. (It could also be shooter stress because he tries so hard to place that last bullet in the center of the group and not mess up a beautiful group.

Once you get through the point that fouling effects the consistency,
you may fire several hundred rounds before the bore has to be cleaned due to accuracy issues.

My match rifles had to be used fouled, because they would be required to fire 100+ rounds during the match with no time to clean.

My hunting rifles only require 1 shot (Hopefully) and cleaned after several hunts (3 or 4 shots). I work up my hunting loads by cleaning after each test load so they are all tested in the same conditions to evaluate each load fairly.

So to sum this up, I have different cleaning regiments for hunting and match shooting based on accuracy requirements needed under the conditions.

As to checking if your barrel is clean or not, Some solvents done turn the patches green and some do, so to find out, try some of your Butch's in the bore and if it doesn't turn green, your cleaning is going OK.

Fouling is an interesting beast. During brake in it prevents uniform break in (The reason you clean after each shot) once a barrel is broken in It tends to protect the bore from wear even though it may hurt accuracy at some point (This is one of the reasons that factory barrels come fouled from test firing).

I clean all of my firearms frequently because fouling can damage the bore after while because powder residue can attract moister and cause corrosion, Clean and oiled cant. everyone has there opinion on cleaning frequency and the amount of time and quality of the cleaning, but having worked on many firearms that were not taken care of or cleaned often or not at all and compared to the ones that were meticulously maintained, there was a total difference in there condition.

I don't recommend any bore solvent that has abrasives because they shorten barrel life and should not be necessary. In my opinion, It is counter productive to worry about barrel life and then use an abrasive cleaner of bullets in the bore. There are to many good solvents available that only address the fouling.

Sorry for the long explanation.

J E CUSTOM

J. E., Thanks for your input. I appreciate the long explanation

 

[Doug Herold]

I've been blessed to be able to afford a couple of GA Precision rifles. When I asked George Gardner about barre break in, he said just shoot it and clean it at the end of the day the first 2-3 times. Then expect to see velocity increase by 75-150 fps after somewhere between 100-200 shots. Velocity will stay at that new speed until the throat starts to go, then you should check the distance to lands and readjust. After those changes, once the barrel starts to lose velocity again, it's time to rebarrel.
FWIW Both of mine were built with Bartlein barrels.

Thanks, Kimber
That has been what I have found with that gun. I exaggerated a little on the degree of velocity increase, but it has been significant >100fps. Appreciate ur input.

 

[Doug Herold]

I agree with most of what has been typed in the thread. One thing I did not see mentioned is the fact that sometimes once fired brass will cause more pressure therefore more velocity than new brass. You mentioned 100 rounds. Did that happen to be how many pieces of new brass you had?

Yep, that was with the 100 rounds of new head stamped Hornady for the GAP.

 

[J E Custom]

Here is a test I performed to answer some of these questions.

https://www.longrangehunting.com/threads/new-barrel-break-in-and-cleaning-methods.160450/page-2

Look at post #20

J E CUSTOM

 

[Doug Herold]

Here is a test I performed to answer some of these questions.

https://www.longrangehunting.com/threads/new-barrel-break-in-and-cleaning-methods.160450/page-2

Look at post #20

J E CUSTOM

Wow ! Great data !...

 

[NZ Longranger]

There are such widely expressed views on forums about cleaning, break-in and barrel life etc, and I can't help but wonder how many are actually based on fact rather than widely ranging unsubstantiated beliefs.

A few simple facts for you to ponder over.
1. Velocity increase always comes with a commensurate pressure increase. The pressure comes first, and the velocity is just a byproduct of it.
2. Pressure increase without a change in your load or powder/rifle temperature is always due to either increased friction, or/or decreased bore size due to changing surface structure or fouling buildup.
3. Unless you use a quality bore scope, you have no real idea of what is going on in your bore, cleaning or throat wise.

To give some cred to what I'm saying, we have an Oehler Ballistic Laboratory and measure pressure and velocity all the time, and we use a Hawkeye borescope with superb resolution - always. We also regularly slug our barrels to get an idea of bore dimensional changes that you can't see with a borescope. We build custom rifles in a range of cartridges including some very large wildcats that would be considered seriously overbore. We specialise in getting both good performance and relatively good barrel life out of these chamberings.

Velocity increase after about the 50 rounds onwards point in a new barrel well cleaned with solvent is always due to the throat getting rougher increasing friction, and also due to a dimensional change caused by the metal structure changing - surface platelets standing up and leaning down barrel if you can picture what I'm getting at here - and also depending on powder used, a hard carbon build up. No amount of solvent cleaners will change this, but it is easily kept on top of with sensible use of abrasive cleaners in the first 6 inches of the bore. Anyone who says you should not use abrasive cleaners in barrel break-in has never looked at the throat after even the most careful chambering job with the sharpest reamer and best lube - let alone the average factory barrel chambering job. The throat always has a lot of burrs on the downwind side of each land - sometimes even melted metal swaged into the downwind groove from a blunt and badly lubed reamer, and often some very deep annular grooving. Again, the quickest and often the only way to sort out these throats is with an abrasive or something like David Tubb's system.
We always break-in firstly by abrasive cleaning the throat to remove as many of these burrs and polish it as much as possible, and then with carbon solvents and abrasive cleaners, and keep on top of carbon and dimensional changes with regular abrasive cleaning of the throat. Since we started doing this, we no longer see the 50 to 100 round count pressure/velocity increase, and keep constant velocities right through the life of the barrel, and also hardly have to chase the throat at all. Contrary to what you may think, abrasive throat cleaning prolongs accurate throat life extensively.
So, so much more I can say on this subject, and proper cleaning/break-in techniques, but this should be enough to start some discussion!

 

[dfanonymous]

Just going to say, I've seen more people ruin barrels cleaning then I have not cleaning.
That means using things like sweets for to long or even gashed the throat with a cleaning rod and caused a burr that created hard extraction.

 

[NZ Longranger]

Yep, bad cleaning is worse than no cleaning.
No one else want to debate, comment on what I said?

 

[Gamesniper19]

This year I had a Proof barrel put on a custom gun I had built. After @ 100 rounds through the gun, I got a 150fps increase in mv. Is this common only with the Proof???... or do other barrels jump their velocity after break-in?

Yes, it is common with PROOF barrels. My discussions with the barrel engineers at PROOF is because of the grade of steel they use, tolerances of the barrel, and performance optimization once shot; their barrels can take as little as 80 and as many as 150 rounds to find their sweet spot

 

[Gamesniper19]

There are such widely expressed views on forums about cleaning, break-in and barrel life etc, and I can't help but wonder how many are actually based on fact rather than widely ranging unsubstantiated beliefs.

A few simple facts for you to ponder over.
1. Velocity increase always comes with a commensurate pressure increase. The pressure comes first, and the velocity is just a byproduct of it.
2. Pressure increase without a change in your load or powder/rifle temperature is always due to either increased friction, or/or decreased bore size due to changing surface structure or fouling buildup.
3. Unless you use a quality bore scope, you have no real idea of what is going on in your bore, cleaning or throat wise.

To give some cred to what I'm saying, we have an Oehler Ballistic Laboratory and measure pressure and velocity all the time, and we use a Hawkeye borescope with superb resolution - always. We also regularly slug our barrels to get an idea of bore dimensional changes that you can't see with a borescope. We build custom rifles in a range of cartridges including some very large wildcats that would be considered seriously overbore. We specialise in getting both good performance and relatively good barrel life out of these chamberings.

Velocity increase after about the 50 rounds onwards point in a new barrel well cleaned with solvent is always due to the throat getting rougher increasing friction, and also due to a dimensional change caused by the metal structure changing - surface platelets standing up and leaning down barrel if you can picture what I'm getting at here - and also depending on powder used, a hard carbon build up. No amount of solvent cleaners will change this, but it is easily kept on top of with sensible use of abrasive cleaners in the first 6 inches of the bore. Anyone who says you should not use abrasive cleaners in barrel break-in has never looked at the throat after even the most careful chambering job with the sharpest reamer and best lube - let alone the average factory barrel chambering job. The throat always has a lot of burrs on the downwind side of each land - sometimes even melted metal swaged into the downwind groove from a blunt and badly lubed reamer, and often some very deep annular grooving. Again, the quickest and often the only way to sort out these throats is with an abrasive or something like David Tubb's system.
We always break-in firstly by abrasive cleaning the throat to remove as many of these burrs and polish it as much as possible, and then with carbon solvents and abrasive cleaners, and keep on top of carbon and dimensional changes with regular abrasive cleaning of the throat. Since we started doing this, we no longer see the 50 to 100 round count pressure/velocity increase, and keep constant velocities right through the life of the barrel, and also hardly have to chase the throat at all. Contrary to what you may think, abrasive throat cleaning prolongs accurate throat life extensively.
So, so much more I can say on this subject, and proper cleaning/break-in techniques, but this should be enough to start some discussion!

NZ. I agree with much of what you said although I would have to review the data on your point around "a velocity increase always comes with a commensurate pressure increase" before I agree 100%. For the rest of my comments, I am not including factory barrels...the build with them is so inconsistent I dont think it is even fair to hold them accountable to a custom barrel application. I agree with what you said about how they are built and if we are talking full custom rifles with high quality barrels, factory barrels are a non-issue.

Yes, the rationale you stated, especially barrel fouling and increased friction can cause increases in pressure. We do need to clarify what is an increase in pressure. Some normal increases are due to the cocktail we choose to run. According to military testing with 308, a change of pressure from 4 different component mixes, using the exact same bullet and powder weights, saw chamber pressure differences from 45000 CUP all the way up to 53600 CUP. In some cases, the velocity difference across all the metrics reviewed was as little as 15 fps and as much as 30 from step to step (50 to 100 points of pressure). Hardly a pressure increase of note. We saw the same with 264 win mag with chamber variations from 51000 and 2914 fps to 64000 cup and 3048 fps. Again with very low changes in overall pressures due to any fouling.

A barrel would have to be fouled to the point of danger to have a huge affect on pressures that would cause signifiant issues. Would velocity change, perhaps, if the fouling were so constricting to change the overall bore of the barrel. That may affect fps but I have no data to show that 100 rounds would cause that. IF that were the case, PRS and military shooters would clean their barrels every 100 rounds to stay accurate which they do not do.

That said, not all metal acts the same, and not all barrels act the same, especially carbon fiber barrels. We cannot use 100% metal barrel mentality 100% of the time with carbon fiber barrels. They act differently due to their stiffness and their ability to move heat. I am happy to discuss this at any length with anyone who would like to.

Question, What scope are you utilizing to see metal platelets?
There is data to show that barrels get smoother the more they are shot for the very reason you mentioned, continued friction and heat at such high nodes, the metal of the barrel is re-tempered at a microscopic level every time we shoot. This is what would cause the barrel molecules to "go in one direction" but it would take a 400X microscope to see that. This is also a huge factor in cleaning and barrel break in...the more you shoot, clean to bare metal, and shoot, the smoother the barrel is and the performance should subsequently be more consistent, until the barrel and chamber reaches a fail point from wear.

I am very fortunate to have first hand knowledge of the PROOF barrel testing and personally knew Jeff Lawrence, the brains behind their barrels. (PROOF bought Jeff Lawrence barrels as part of their conglomerate). According to Jeff and the research done by SOCOM, they saw increase in fps without significant pressure increases at about 80 rounds of 300 WM with PROOF barrels. (the key to that statement is what we define as significant pressure) This was seen with a clean bore, and a dirty bore. The corresponding fps increase was around 48 fps average and stabilized after about 80 rounds and was consistent through 1500 rounds.

The stated 140+ fps increase seems a bit out of range. My ask of Doug would be what measuring tool was used? Magneto speed? Have you ensured that whatever measuring tool you used, it is calibrated and reading correctly? Test it on a rifle you know is consistent to be sure.

Barrel break in is a VERY SUBJECTIVE thing. The metal of the barrel has a lot to do with it, the type of solvent and the way it is cleaned has a lot to do with it, and the abrasive/lack of abrasives have a lot to do with it. There IS NO ABSOLUTE rule for cleaning a barrel. Too many variables, was it button rifled, who lapped the barrel before and after, was it lapped at all, was it cut rifled, what grade of steel was used, how well is the reamer made and how was it chambered? For instance, Blaser uses a grade of steel so hard, they dont lap them...incorrect lapping can hurt a barrel even worse. So if that happens and you dont know it, and you use abrasives, you can make the barrel even worse.
Furthermore, if you use abrasives and aren't super careful to be very even with your cleaning, you can oval a barrel and case huge pressure and accuracy issues. When all else fails, ask the barrel maker what they recommend and go with that as your rule.

Abrasives actively remove metal in larger quantities than can be actively controlled by the vast majority of people. Professionals who lap barrels do it by feel first and visual confirmation, the average person could never achieve that so I do not recommend abrasives to the average shooter, ever.
First hand data and first hand review of bore integrity has shown me is; if your throat, specifically the first 3 to 6 inches is degraded, then you will lose accuracy. Additionally, if the last 1 to 3 inches is degraded, you will also lose accuracy. Generally, a barrel will be "burned out" in the first 6 inches and more acutely in the first 2 inches. This is one of the reasons many shooters "chase the threads" to increase barrel life.

I do not recommend the regular use of barrel abrasives unless there is a specific reason to address a specific section of your barrel (fouling, beginnings of rust or pitting). Cleaning to bare steel is what we want and you don't have to use abrasives to do that in a well made barrel. NO, you don't. Additionally, in all the barrels that I have seen, no PRS shooter that I know, no military shooter that i worked with, and the barrel makers that I talk to tell me no abrasives.

Ok....here we go

 

[dfanonymous]

NZ. I agree with much of what you said although I would have to review the data on your point around "a velocity increase always comes with a commensurate pressure increase" before I agree 100%. For the rest of my comments, I am not including factory barrels...the build with them is so inconsistent I dont think it is even fair to hold them accountable to a custom barrel application. I agree with what you said about how they are built and if we are talking full custom rifles with high quality barrels, factory barrels are a non-issue.

Yes, the rationale you stated, especially barrel fouling and increased friction can cause increases in pressure. We do need to clarify what is an increase in pressure. Some normal increases are due to the cocktail we choose to run. According to military testing with 308, a change of pressure from 4 different component mixes, using the exact same bullet and powder weights, saw chamber pressure differences from 45000 CUP all the way up to 53600 CUP. In some cases, the velocity difference across all the metrics reviewed was as little as 15 fps and as much as 30 from step to step (50 to 100 points of pressure). Hardly a pressure increase of note. We saw the same with 264 win mag with chamber variations from 51000 and 2914 fps to 64000 cup and 3048 fps. Again with very low changes in overall pressures due to any fouling.

A barrel would have to be fouled to the point of danger to have a huge affect on pressures that would cause signifiant issues. Would velocity change, perhaps, if the fouling were so constricting to change the overall bore of the barrel. That may affect fps but I have no data to show that 100 rounds would cause that. IF that were the case, PRS and military shooters would clean their barrels every 100 rounds to stay accurate which they do not do.

That said, not all metal acts the same, and not all barrels act the same, especially carbon fiber barrels. We cannot use 100% metal barrel mentality 100% of the time with carbon fiber barrels. They act differently due to their stiffness and their ability to move heat. I am happy to discuss this at any length with anyone who would like to.

Question, What scope are you utilizing to see metal platelets?
There is data to show that barrels get smoother the more they are shot for the very reason you mentioned, continued friction and heat at such high nodes, the metal of the barrel is re-tempered at a microscopic level every time we shoot. This is what would cause the barrel molecules to "go in one direction" but it would take a 400X microscope to see that. This is also a huge factor in cleaning and barrel break in...the more you shoot, clean to bare metal, and shoot, the smoother the barrel is and the performance should subsequently be more consistent, until the barrel and chamber reaches a fail point from wear.

I am very fortunate to have first hand knowledge of the PROOF barrel testing and personally knew Jeff Lawrence, the brains behind their barrels. (PROOF bought Jeff Lawrence barrels as part of their conglomerate). According to Jeff and the research done by SOCOM, they saw increase in fps without significant pressure increases at about 80 rounds of 300 WM with PROOF barrels. (the key to that statement is what we define as significant pressure) This was seen with a clean bore, and a dirty bore. The corresponding fps increase was around 48 fps average and stabilized after about 80 rounds and was consistent through 1500 rounds.

The stated 140+ fps increase seems a bit out of range. My ask of Doug would be what measuring tool was used? Magneto speed? Have you ensured that whatever measuring tool you used, it is calibrated and reading correctly? Test it on a rifle you know is consistent to be sure.

Barrel break in is a VERY SUBJECTIVE thing. The metal of the barrel has a lot to do with it, the type of solvent and the way it is cleaned has a lot to do with it, and the abrasive/lack of abrasives have a lot to do with it. There IS NO ABSOLUTE rule for cleaning a barrel. Too many variables, was it button rifled, who lapped the barrel before and after, was it lapped at all, was it cut rifled, what grade of steel was used, how well is the reamer made and how was it chambered? For instance, Blaser uses a grade of steel so hard, they dont lap them...incorrect lapping can hurt a barrel even worse. So if that happens and you dont know it, and you use abrasives, you can make the barrel even worse.
Furthermore, if you use abrasives and aren't super careful to be very even with your cleaning, you can oval a barrel and case huge pressure and accuracy issues. When all else fails, ask the barrel maker what they recommend and go with that as your rule.

Abrasives actively remove metal in larger quantities than can be actively controlled by the vast majority of people. Professionals who lap barrels do it by feel first and visual confirmation, the average person could never achieve that so I do not recommend abrasives to the average shooter, ever.
First hand data and first hand review of bore integrity has shown me is; if your throat, specifically the first 3 to 6 inches is degraded, then you will lose accuracy. Additionally, if the last 1 to 3 inches is degraded, you will also lose accuracy. Generally, a barrel will be "burned out" in the first 6 inches and more acutely in the first 2 inches. This is one of the reasons many shooters "chase the threads" to increase barrel life.

I do not recommend the regular use of barrel abrasives unless there is a specific reason to address a specific section of your barrel (fouling, beginnings of rust or pitting). Cleaning to bare steel is what we want and you don't have to use abrasives to do that in a well made barrel. NO, you don't. Additionally, in all the barrels that I have seen, no PRS shooter that I know, no military shooter that i worked with, and the barrel makers that I talk to tell me no abrasives.

Ok....here we go

I'm sure I missed it but why do "we" want to clean down to steel again?

When copper and foul builds up it will have a plateau for awhile where things will stay consistent. When using factory ammo, as long as you pay attention to changes in velocity curves, you can get hundreds doped and on target.

Cleaning down to bare steel every time before a shooting session just seems harder to be consistant with good dope, especially as the throat erodes over time...and the barrel throat ALWAYS errods

 

[Gamesniper19]

I'm sure I missed it but why do "we" want to clean down to steel again?

When copper and foul builds up it will have a plateau for awhile where things will stay consistent. When using factory ammo, as long as you pay attention to changes in velocity curves, you can get hundreds doped and on target.

Cleaning down to bare steel every time before a shooting session just seems harder to be consistant with good dope, especially as the throat erodes over time...and the barrel throat ALWAYS errods

Cleaning down to steel is the only way to ensure barrel integrity, completely. Any left fouling, copper, dirt, excess anything can have a long term affect. If you are planning on shooting 100 rounds today, and another 100 tomorrow, there may be no need to clean at all, although many shooters clean after the leave the range as a point of fact no matter how many round have been shot or how long between sessions. Clean to bare metal and ensure you have a consistent barrel. If you are not planning to shoot again soon, condition your barrel and then, clean to bare metal before you go the range next time.
Then easy, when you go back to the range the next time, your first round is a fouler. You then have a warm dirty barrel similar to the one you shot last time and zero should be similar, if all other conditions are the same.

There is quite a bit of data to support, the most accurate ladders and DOPE start with a clean barrel...

You have a fine piece of equipment, that has been built to exact specifications down to the thou or even 10th of thou. Take care of it.

 

[NZ Longranger]

Awesome post JM!
We're about to head into the mountains for a week, so unfortunately I won't be around to discuss this for much longer but a couple of quick comments on your interpretation of what I said.

Guys who are seeing a velocity increase as they fire more shots down the barrel with no changes to the load or conditions, will be seeing a pressure increase if only they could measure it. That was my point. If you were loading up to a max pressure at the start of your 50 to 100 rounds, and then see a 100fps or whatever increase in velocity after 50 to 100 rounds, your pressure will have increased commensurately, potentially into a higher pressure zone than you intended. We have proved this so many times over and over across the Oehler Ballistic Lab.

Any chambering job will benefit from a careful abrasive cleaning of the throat area (only, not the whole bore) before commensing break-in.

Certain over bore cartridges and powders will develop a carbon ring and a tightened throat area diameter from a surface structure change with repeated shooting. The ball powders like US869 (awesome powder though it is at producing velocity for pressure) are a given for this carbon ring, and hot pressures and temps affect the surface structure. You can feel this surface change easily on a tight cleaning patch once you think you have your bore clean. You can push the patch down the bore with no noticeable change in friction, but then try pulling it back and you'll feel a quite noticeable increase in the area just ahead of the throat due to the fact you're now going "against the grain". No amount of solvent use will remedy this, only the correct use of a mild abrasive cleaner like KG2 applied in this exact area.

High volume competitive shooters are really unlikely to encounter this, due to the cartridges and powders they are using. And in some extreme overbore cartridges you need to clean too regularly to keep this bore restricting from affecting accuracy to be useful in these disciplines, and their barrel life is too short anyway. But for a long range hunting rifle that may only ever be shot a handful of times between cleans, abrasive throat cleaning is the best way to keep consistent accuracy and velocity over the life of the barrel - in our humble opinion of course!
So in this case, this means cleaning to bare, polished in the throat area, metal.

 

[Gamesniper19]

Awesome post JM!
We're about to head into the mountains for a week, so unfortunately I won't be around to discuss this for much longer but a couple of quick comments on your interpretation of what I said.

Guys who are seeing a velocity increase as they fire more shots down the barrel with no changes to the load or conditions, will be seeing a pressure increase if only they could measure it. That was my point. If you were loading up to a max pressure at the start of your 50 to 100 rounds, and then see a 100fps or whatever increase in velocity after 50 to 100 rounds, your pressure will have increased commensurately, potentially into a higher pressure zone than you intended. We have proved this so many times over and over across the Oehler Ballistic Lab.

Any chambering job will benefit from a careful abrasive cleaning of the throat area (only, not the whole bore) before commensing break-in.

Certain over bore cartridges and powders will develop a carbon ring and a tightened throat area diameter from a surface structure change with repeated shooting. The ball powders like US869 (awesome powder though it is at producing velocity for pressure) are a given for this carbon ring, and hot pressures and temps affect the surface structure. You can feel this surface change easily on a tight cleaning patch once you think you have your bore clean. You can push the patch down the bore with no noticeable change in friction, but then try pulling it back and you'll feel a quite noticeable increase in the area just ahead of the throat due to the fact you're now going "against the grain". No amount of solvent use will remedy this, only the correct use of a mild abrasive cleaner like KG2 applied in this exact area.

High volume competitive shooters are really unlikely to encounter this, due to the cartridges and powders they are using. And in some extreme overbore cartridges you need to clean too regularly to keep this bore restricting from affecting accuracy to be useful in these disciplines, and their barrel life is too short anyway. But for a long range hunting rifle that may only ever be shot a handful of times between cleans, abrasive throat cleaning is the best way to keep consistent accuracy and velocity over the life of the barrel - in our humble opinion of course!
So in this case, this means cleaning to bare, polished in the throat area, metal.

NZ - you and I could talk for a long time and learn from each other. Your post reminded me of something I saw on the 7mm-300 Norma improved I built last year. We did see the carbon rings you mentioned and this overbore cartridge is INCREDIBLY finicky and any issues can cause pressure and accuracy issues. Cleaning to bare metal is vital.
In this particular case, cleaning with an abrasive may be appropriate for that particular spot, and I did agree with that in my statement, although I would still say and I hope you agree, very few people should ever use abrasives if they don't know how. They should not be used as a regular cleaning routine.

I agree, an initial chamber polishing with abrasives can help increase accuracy, as long as the abrasive polishing does not take the chamber out of tolerances. Again, this takes someone knowing exactly what they are doing. This should NOT be done again after the rifle is broken in unless there is an issue.
This is the same for a good barrel, in fact some barrels are made a 10th tight so that a good hand lapping can make the diameter exactly what the barrel maker wants in spec. Some are left a 10th tight at the muzzle for all copper bullets to ensure contact in the last 3 inches. Yes, abrasives are used. Again, no average shooter should ever use abrasives on their barrel as an everyday process to clean to bare metal unless they know EXACTLY what they are doing. If they don't that is a sure way to ruin a barrel at worst, and lessen barrel life at the least.
I agree with you, that for LR hunters and normal shooters, under normal every day conditions, they will never come to this need and that is why I recommend they ONLY cleaning with solvent to the bare metal. I would not recommend abrasive cleaning to someone who doesn't know what they are doing. Solvent and a good brush is enough for 99% of all shooters.

What I do like about this sport and this community, is that success can be seen with various processes. A 1/4 minute gun is a 1/4 minute gun and if we are talking microscopic data, like barrel life variances of 10% or pressure variances of 1000 CUP, then it is less of a barrel cleaning process and more of a heat and number of rounds issue.

Hope you have a great mountain adventure and come home safe.