Rimfire Bore Erosion
- Thread starter crb
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G
Gerry
Guest
rimfire bore erosion
It's usually at 6 o'ctock due to the priming compound and the powder being in the bottom of the chamber.
The priming compound is like ground gass and erodes the barrel like sand blasting.
It's usually at 6 o'ctock due to the priming compound and the powder being in the bottom of the chamber.
The priming compound is like ground gass and erodes the barrel like sand blasting.
B
BottleBaby
Guest
Gravity.
Hello, the bullet makes at least one full rotation as it goes down the bbl. Why doesn't it carry the grit to the top ? If the bullet passing over [ or pushing ? ] the crud was the culprit the damage should be consistent over the full 360 degrees of the bore.
Now if the twist was 0 [ zero ] then I could see the bullet pounding the bottom of the bore with the crud.
I'm not doing a Calfee here and asking esoteric questions that I already know the answers to. I don't know what the deal is with the 6:00 bore wear.
I do know the standard 'It's gravity'. The problem is that if you really think about it the standard answer doesn't add up.
Now if the twist was 0 [ zero ] then I could see the bullet pounding the bottom of the bore with the crud.
I'm not doing a Calfee here and asking esoteric questions that I already know the answers to. I don't know what the deal is with the 6:00 bore wear.
I do know the standard 'It's gravity'. The problem is that if you really think about it the standard answer doesn't add up.
Proper method
You will get various suggestions, but you will have to decide for yourself. As for my barrels, I will always run a dry patch after I'm through for the day. This will push most all the corrosive crap out on the barrel. You could also just clean and store. As the throat to most affected, you might just brush that area in front of the chamber and just wet patch the rest of the barrel. This way you will not remove the lub from the bore. It will reduce the amount of foulers need before you start a target.
You will get various suggestions, but you will have to decide for yourself. As for my barrels, I will always run a dry patch after I'm through for the day. This will push most all the corrosive crap out on the barrel. You could also just clean and store. As the throat to most affected, you might just brush that area in front of the chamber and just wet patch the rest of the barrel. This way you will not remove the lub from the bore. It will reduce the amount of foulers need before you start a target.
I am wondering if the junk left behind each bullet is actually corrosive? Even though it only sits there for maybe a minute or two at most I wonder if it is attacking the metal.
My new Hart had about 2 boxes of ammo through it, was brought home and cleaned within a couple of hours of the last shot. When I borescoped it I could already see the faintest beginnings of the 6:00 deterioration.
Normally I clean within minutes of the last shot on each target but the first shots through the Hart were at a silhouette match where it is not real convenient to clean plus it was raining.
ETA- Also what I am seeing does not have the look of grit being drug across polished metal. It's more like sandblasting.
My new Hart had about 2 boxes of ammo through it, was brought home and cleaned within a couple of hours of the last shot. When I borescoped it I could already see the faintest beginnings of the 6:00 deterioration.
Normally I clean within minutes of the last shot on each target but the first shots through the Hart were at a silhouette match where it is not real convenient to clean plus it was raining.
ETA- Also what I am seeing does not have the look of grit being drug across polished metal. It's more like sandblasting.
O
Outback
Guest
The glass type particles from the priming compound are smashed into the bore surface - just like an object on the road - you smash into it - generally ride over the top of it - depends how large it is as to the damage it has done
Any damage done to the lead causes the lead to be out of balance and causes it flight path to be eliptical on the way to the target - you can see this when shooting at night with a good scope on .22 and good light overhead
One of my rifles has the firing pin on the bottom and front locking - this rifle leaves a finer residue in the barrel - the residue is spread more evenly all around the bore - these observations are enhanced with the continued use of the Hawk Eye Borescope - this rifle has the ability to shoot more shots before accuracy decreases - barrels are lasting longer with this firing pin set up
With cleaning after a match, a by-product of ignition is water and with a scope you can sometimes see small droplets forming - not long before rust forms with the help of sulphur residue and a steel barrel especially - as said before, an oily patch after shooting is cheap insurance
Any damage done to the lead causes the lead to be out of balance and causes it flight path to be eliptical on the way to the target - you can see this when shooting at night with a good scope on .22 and good light overhead
One of my rifles has the firing pin on the bottom and front locking - this rifle leaves a finer residue in the barrel - the residue is spread more evenly all around the bore - these observations are enhanced with the continued use of the Hawk Eye Borescope - this rifle has the ability to shoot more shots before accuracy decreases - barrels are lasting longer with this firing pin set up
With cleaning after a match, a by-product of ignition is water and with a scope you can sometimes see small droplets forming - not long before rust forms with the help of sulphur residue and a steel barrel especially - as said before, an oily patch after shooting is cheap insurance
T
Tom C.
Guest
interesting observation. outback. how many rounds do you shoot out of
a barrel before the accuracy falls off from erosion, wear, etc.
a barrel before the accuracy falls off from erosion, wear, etc.
F
Fred K
Guest
Some bore damage is done when one runs a dry patch through after shooting. It is always best to run a wet or moist patch through after shooting. A dry patch just pushes the grit along on the bore surface. The grit does little damage when shooting because it is blown out ahead of the bullet.
Fred K
Fred K
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Fred,
Due to the boundary layer effect, I wonder how much of the grit does get blown out of the bbl before the bullet gets to it.
Outback, tires roll over glass in the road. Bullets ain't rollin'. Now the junk in the bore may roll as the bullet passes over it and this may explain some of what we are seeing. Also the bullets are highly embeddable.
Due to the boundary layer effect, I wonder how much of the grit does get blown out of the bbl before the bullet gets to it.
Outback, tires roll over glass in the road. Bullets ain't rollin'. Now the junk in the bore may roll as the bullet passes over it and this may explain some of what we are seeing. Also the bullets are highly embeddable.
O
Outback
Guest
Some setups will take much longer to foul where accuracy will fall off - asually with a general set up around 40-50shots
The type of chamber, head space, firing pin has an effect on how long before a barrel will go off. Just like the combustion chamber of an engine, the higher combustion pressures the more damage may be done - building a rifle with a lower peak presure is important to abrasive wear - especially to the distribution of the barrel residue and its size
The type of lands and the internal size of the barrel also effect this - some barrels are more self cleaning and less prone to this problem
I was testing at Eley factory, where the group size can suddenly open up - clean with brush and patch and accuracy returns
Experimenting with AN2000 actions and head space and chamber type is nearly a science on its own - a tight chamber and tight headspace is will cause problems to the barrel and accuracy
The Hawk Eye Scope and shooting at night benchrest, with a high power light above and shining to the 50m target, are essential tools in rifle development. The scoped .22 rifle lets you view the path of the projectile to the target. If the setup causes the path to yawn or skew, then accuracy falls off. Good shots stay behind the dot in the scope - wild shots are so obvious - some barrels you can spend many hours on them and they are never any good as the bore has not been driled straight - whether this is due to impurities in the Stainless or the manufacturer did not sharpen the flutes on his drill correctly
The type of chamber, head space, firing pin has an effect on how long before a barrel will go off. Just like the combustion chamber of an engine, the higher combustion pressures the more damage may be done - building a rifle with a lower peak presure is important to abrasive wear - especially to the distribution of the barrel residue and its size
The type of lands and the internal size of the barrel also effect this - some barrels are more self cleaning and less prone to this problem
I was testing at Eley factory, where the group size can suddenly open up - clean with brush and patch and accuracy returns
Experimenting with AN2000 actions and head space and chamber type is nearly a science on its own - a tight chamber and tight headspace is will cause problems to the barrel and accuracy
The Hawk Eye Scope and shooting at night benchrest, with a high power light above and shining to the 50m target, are essential tools in rifle development. The scoped .22 rifle lets you view the path of the projectile to the target. If the setup causes the path to yawn or skew, then accuracy falls off. Good shots stay behind the dot in the scope - wild shots are so obvious - some barrels you can spend many hours on them and they are never any good as the bore has not been driled straight - whether this is due to impurities in the Stainless or the manufacturer did not sharpen the flutes on his drill correctly
O
Outback
Guest
CRB
As you said, some junk gets picked up and some rolled into barrel - some old pitted barrels rely on this junk build up to fill the holes - why when you clean some old barrels and they take a lot of fouling shots to develop accuracy again
As you said, some junk gets picked up and some rolled into barrel - some old pitted barrels rely on this junk build up to fill the holes - why when you clean some old barrels and they take a lot of fouling shots to develop accuracy again
Yours sir, is an astute observation. It would be quite interesting to be able to match 2 similar actions with the pin variations and measure the residue from both systems. Might I inquire which action you have the modified pin in?
O
Outback
Guest
Pete,
With the AN2000 rifle it is a easy task to reset a barrel - with a cone chamber it is a good idea to rotate the rifle barrel after around 2000 rounds to get more even wear on the lands - remember the worn edged bottom land in around 8 inches is at the top where there is little wear - the top land does the same in reverse - this means the lead's groove meets a changing land as it proceeds down the barrel - there would have to be some instability involved here and maybe setting up particular vibrations that may distort the lead
The finer and more even the barrel residue is, the greater chance you have of achieving a more consistent higher score - it is an experimental game to achieve this - the ability to do a barrel change in around 5 minutes with the AN2000, lends itself to the rifle where you can gain practical knowledge on different set ups
Over the years, taking notes from this forum and building rifles, has lead to gaining some valuable knowlege and competition success
Outback
With the AN2000 rifle it is a easy task to reset a barrel - with a cone chamber it is a good idea to rotate the rifle barrel after around 2000 rounds to get more even wear on the lands - remember the worn edged bottom land in around 8 inches is at the top where there is little wear - the top land does the same in reverse - this means the lead's groove meets a changing land as it proceeds down the barrel - there would have to be some instability involved here and maybe setting up particular vibrations that may distort the lead
The finer and more even the barrel residue is, the greater chance you have of achieving a more consistent higher score - it is an experimental game to achieve this - the ability to do a barrel change in around 5 minutes with the AN2000, lends itself to the rifle where you can gain practical knowledge on different set ups
Over the years, taking notes from this forum and building rifles, has lead to gaining some valuable knowlege and competition success
Outback
O
Outback
Guest
Tim
The rifle referred to is the Swiss rifle - Bleiker - Small front locking bolt - pin at 6 - part of the chamber is set into the action (it is still a normal type chamber, just there are 2 parts to it) - this results in a small expansion area as the primer end is a little larger in diameter - just pick up a spent case from the latest model, "Challenger" - in finals in Olympic SmallBore, these are the leading rifles at present - and yes this rifle has a finer residue and spread more evenly
Outback
The rifle referred to is the Swiss rifle - Bleiker - Small front locking bolt - pin at 6 - part of the chamber is set into the action (it is still a normal type chamber, just there are 2 parts to it) - this results in a small expansion area as the primer end is a little larger in diameter - just pick up a spent case from the latest model, "Challenger" - in finals in Olympic SmallBore, these are the leading rifles at present - and yes this rifle has a finer residue and spread more evenly
Outback
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T
Tom C.
Guest
thanks for stopping in ob have a good evening.
O
Old Gunner
Guest
Yes at least they used to do so.
Some older single shot target pistols didn't have a throat, the bullets were pushed in to engrave to the rifling before firing. When people run across these old pistols they think they are .22 short chambers.
Atomized glass if imbedded in the bullet acts as a fine lapping compound, to polish the bore like a slow fire lapping process rather that eat away at it visibly as the gas driven particles do at the throat.
PS
Most old centerfire rifles and Shotguns I've examined showed more pitting on the upper surface of the bore. I'd figured this was due to gravity pulling oils away from the top while on a rack for years at a time.
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So you are saying that the gun is making it's own lapping compound but this lapping compound is selective and only works on the bottom of the bore ? Even though the lap [ aka the bullet ] makes a full revolution in the bbl this selective compound only etches the bottom 2/3 of the bore.
That has not been my experience with lapping a large number of poppet valves. You can put one small spot of compound on a valve and lap the seat and when you clean the lapping compound off the parts you will have a nice lapped surface for the full 360 degrees.