Ah!now this is useful info!
I knew about breaking a bore in but never heard of fouling shots before.
I didn't have any idea about fouling shots before I joined the Marines and would up getting trained for 'Long Range Marksman'.
Every rifle will have it's own 'Fouling' amount.
For my heavy .308 it's close to 10 rounds before it pulls in for good groups,
With my .300 Weatherby bench rifle, it's 4 or 5 fouling shots before it's ready to go, and that's about average for most 'Hot Bore' shooting.
I have a little bolt .223 Rem. that it only takes 2 rounds before it's ready to go.
If you are hunting, you want zero your rifle for a 'Cold Bore' shot.
It's time consuming, becuase you have to sit and wait for the rifle to cool down before you can fire the next round in your group!
I usually take two or three for 'Cold Bore' sight in shots, so I can fire one, clear it off the table and set up another rifle, and then another rifles...
That helps pass the time waiting for the barrel to cool for the next round...
If you sight in all in one afternoon, then you expect your rifle to hit something with a 'Cold Bore' the next day, you WILL miss!
Cold, clean bores NEVER shoot where you think they are going to unless you actually take the time to let the barrel cool down between shots!
I only use aluminum or brass rods in my guns,coated if I can find them or a "bore snake"made of nylon.
Aluminum can rub off in the bore,
I stick with a highly polished stainless steel once piece rod,
Or a coated one piece rod.
'Micro' polished one piece rod doesn't have anyplace to 'Bite' the muzzle...
You have to keep up with the coated rods, solids that can be abrasive can embed in the coating and scratch things.
I've usually got a rag wrapped around mine to clean it off every stroke.
The easy way to save your muzzle crown is to clean from the breech.
I learned to polish a dark bore some years ago using pearl drops toothpaste,an oversize bore brush and a electric drill,they always shot well afterward,would that break in a bore?
No. All polishing does is buff out the HIGH or TIGHT spots.
What fire lapping or break in does is polish the nicks, scratches, ect. out of the LOW, or spots that are over sized.
A scratch, pit, tool mark, ARE BY DEFINITION, "OVER SIZE".
Although Over Size, they still have sharp edges, still get copper and powder forced into them.
Clean & Sharp, they carve up the bullet, gouging it or removing weight from its outer jacket, making it fly stupid or making it impossible for it to cut the air properly.
If you clean like crazy between shots, making sure there is no copper or powder residue there to hide the sharp edges or fill in the pits, scratches, ect.,
Then firing, cleaning, firing, cleaning, firing, cleaning will smooth all those sharp edges down and remove the burrs left by machining.
The process of smoothing out the scratches, pits, tool marks, ect. is called Burnishing... And it should be part of the break in process for center fire rifles.
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As for pearl drops and drill,
You can polish a rusty chamber that way, but the bore where the rifling is, you need to polish that with an 'In & Out' stroking motion so your polishing pad moves with the rifling.
Rotary tool in the rifling will wear the rifling ridges (Lands) down more than the rest of the bore,
And it will take the sharp edges off the rifling.
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How we used to hone out a tight spot in the rifling,
And early hammer forged barrels had tight spots fairly frequently,
Where the barrel would under size the bullet, then the bullet would 'Rattle' down the barrel from the tight spot to the muzzle and that barrel would never be accurate the way it was...
SO,
We would take a bore brush, put that in the barrel,
Pour some molten lead in around/through that brush,
And as the lead hardened, it would set up around that brush and make a barrel size plug connected to the brush/rod.
You could add an abrasive (I've used toothpaste, car paint rubbing compound, valve grinding paste, ect.) and stroke the tight spots out of the bore with that lead covered brush.
It's called HAND LAPPING a barrel.
I almost forgot, your rod should have a ball bearing handle on it, so the brush can follow rifling...
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With modern pull through button rifling, there aren't any tight spots, you would have to find an older hammer forged barrel to find tight spots.
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There are a couple of products you can use to 'Fire Lap' your barrel.
One is bullets impregnated with an abrasive,
You fire progressively finer abrasive bullets down the barrel, and as you do, it's supposed to polish the barrel.
I don't much care for that idea.
I'm sure the pressure behind the bullet is distorting that bullet, and I'm also equally sure that distortion is grinding away at parts of my barrel that don't need it...
Like the edges of my rifling!
There are pastes you can apply to your own copper jacketed bullets.
I think this is a bad idea for the same reason.
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Usually, if you don't have an old military firearm,
You won't have problems with 'Tight' spots in the barrel.
The days of the singular hammer forging creating the rifling alone are long gone.
Some barrels are hammer forged into general shape,
Then button rifled for an EXACT fit, but most are just CNC drilled blanks that are pull through rifled, and that particular process doesn't allow for 'Tight' spots.
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