STO,
In re: your thoughts on fire lapping, NECO makes a kit wherein you roll the projectile in the abrasive between two steel plates, which impregnates it into the projectile. The excess is wiped off. This should mitigate getting abrasive in the breech seal, or stripping it off into the action port. Fire lapping works well in powder burners...I turned a recalcitrant Ruger #1 in 220 Swift from an improved choke to a 3/4 MOA gun by fire lapping.
There may be some concern about un-choking a choked barrel such as those found on some air rifles. I don't see this being a problem. While I don't know the Brinnell hardness of a typical pellet, they seem pretty soft and malleable...a whole lot softer than barrel steel. I think they would swage down with the choke per usual. Further, as the abrasive impregnated projectile makes its way down the bore, the abrasive is breaking down, in effect becoming a finer grit as it gets towards the muzzle end of the barrel, a situation more apt to cause choke than to remove it.
You're right about a pellet having little bearing surface. Slugs would probably be a better option. Absent that, I'd look at sizing down light pellets from the next caliber up, i.e. taking .30's down to .25. This should get us some more bearing surface.
Another thought I had that may be contributing to accuracy and/or fouling issues in air rifle barrels is the chamber itself. Anytime you cut or remove metal, you're likely gonna leave a burr, or at the very least, a sharp edge. Niether the burr or a sharp edge is our friend when we drag projectiles over it and ask for accuracy. Chamber reamers, whether they be for a powder burner or an air rifle, have a "leade", which creates what can be described as a funnel of sorts in the barrel chamber, and serves to gather the projectile up and smoothly introduce it to the rifling as straight as possible. The leade starts at a wee bigger diameter than the projectile, and tapers down. While in the leade, the base of the projectile obturates, or swells due to the forces (gases or air) pushing on its arse end, and is swaged back down at the leade/bore juncture. In a new, freshly cut chamber, this leade/bore juncture is going to be sharp, or have a burr, so as the projectile passes through it, material is going to get stripped off and gather there. This build-up could account for diminishing accuracy, and/or the appearance of excessive fouling when you clean. When we hear somebody state that their rifle/airgun took X amount of rounds to settle down and shoot accurately, there's a good chance that this my be the cause. By shooting and cleaning it, they are slowly rounding off that lead/copper shaving edge or burr.
Now some may think a soft lead pellet couldn't smooth out a burr or sharp edge. To them I say look at what running water can do to rocks.
Those of us who have toiled with centerfires have undoubtedly heard of "breaking in a barrel", wherein we shoot and clean a bazillion times to "smooth out" a barrel. Well...given my statements above, what are we accomplishing with the barrel break-in process? Is it a wonder that some rifles shoot markedly better after this process and display a decrease in fouling? Some think this process magically transforms the bore. I disagree. I think what's happening is that the bullet/pellet mangling, sharp-ass, leade/bore juncture is getting smoothed out. A lot of respected gunsmiths in the CF accuracy world think the same thing.
I have never had my bore scope in a CZ or Lothar Walther barrel, so I can't speak to the quality of their interior finish. I have had it in the big name powder burner barrel makers such as Hart, Shilen, Lilja, Krieger, Bartlein, etc., and they are beautiful. Smooth as a baby's butt, but with lapping marks. And when I chamber one, for myself or somebody else, I DO NOT do, or recommend a break-in because after I chamber and fit everything up, using a good cleaning rod and bore guide along with a snug patch embedded with lapping compound, I "short stroke"...a move I am quite proficient in...the leade/bore juncture 20-30 times, which serves to smooth that area out. Barrel is thoroughly cleaned, and break-in no longer needed. I can't help but think this process might be beneficial to an airgun barrel as well...especially one that is misbehaving.
I would LOVE to hear an actual air rifle gunsmith opine on all this.
My apologies to all if the newbie here spoke of powder burners a bit much, but I think there are happenings in the PB accuracy world that as air gunners, we should be looking at.
Justin
In re: your thoughts on fire lapping, NECO makes a kit wherein you roll the projectile in the abrasive between two steel plates, which impregnates it into the projectile. The excess is wiped off. This should mitigate getting abrasive in the breech seal, or stripping it off into the action port. Fire lapping works well in powder burners...I turned a recalcitrant Ruger #1 in 220 Swift from an improved choke to a 3/4 MOA gun by fire lapping.
There may be some concern about un-choking a choked barrel such as those found on some air rifles. I don't see this being a problem. While I don't know the Brinnell hardness of a typical pellet, they seem pretty soft and malleable...a whole lot softer than barrel steel. I think they would swage down with the choke per usual. Further, as the abrasive impregnated projectile makes its way down the bore, the abrasive is breaking down, in effect becoming a finer grit as it gets towards the muzzle end of the barrel, a situation more apt to cause choke than to remove it.
You're right about a pellet having little bearing surface. Slugs would probably be a better option. Absent that, I'd look at sizing down light pellets from the next caliber up, i.e. taking .30's down to .25. This should get us some more bearing surface.
Another thought I had that may be contributing to accuracy and/or fouling issues in air rifle barrels is the chamber itself. Anytime you cut or remove metal, you're likely gonna leave a burr, or at the very least, a sharp edge. Niether the burr or a sharp edge is our friend when we drag projectiles over it and ask for accuracy. Chamber reamers, whether they be for a powder burner or an air rifle, have a "leade", which creates what can be described as a funnel of sorts in the barrel chamber, and serves to gather the projectile up and smoothly introduce it to the rifling as straight as possible. The leade starts at a wee bigger diameter than the projectile, and tapers down. While in the leade, the base of the projectile obturates, or swells due to the forces (gases or air) pushing on its arse end, and is swaged back down at the leade/bore juncture. In a new, freshly cut chamber, this leade/bore juncture is going to be sharp, or have a burr, so as the projectile passes through it, material is going to get stripped off and gather there. This build-up could account for diminishing accuracy, and/or the appearance of excessive fouling when you clean. When we hear somebody state that their rifle/airgun took X amount of rounds to settle down and shoot accurately, there's a good chance that this my be the cause. By shooting and cleaning it, they are slowly rounding off that lead/copper shaving edge or burr.
Now some may think a soft lead pellet couldn't smooth out a burr or sharp edge. To them I say look at what running water can do to rocks.
Those of us who have toiled with centerfires have undoubtedly heard of "breaking in a barrel", wherein we shoot and clean a bazillion times to "smooth out" a barrel. Well...given my statements above, what are we accomplishing with the barrel break-in process? Is it a wonder that some rifles shoot markedly better after this process and display a decrease in fouling? Some think this process magically transforms the bore. I disagree. I think what's happening is that the bullet/pellet mangling, sharp-ass, leade/bore juncture is getting smoothed out. A lot of respected gunsmiths in the CF accuracy world think the same thing.
I have never had my bore scope in a CZ or Lothar Walther barrel, so I can't speak to the quality of their interior finish. I have had it in the big name powder burner barrel makers such as Hart, Shilen, Lilja, Krieger, Bartlein, etc., and they are beautiful. Smooth as a baby's butt, but with lapping marks. And when I chamber one, for myself or somebody else, I DO NOT do, or recommend a break-in because after I chamber and fit everything up, using a good cleaning rod and bore guide along with a snug patch embedded with lapping compound, I "short stroke"...a move I am quite proficient in...the leade/bore juncture 20-30 times, which serves to smooth that area out. Barrel is thoroughly cleaned, and break-in no longer needed. I can't help but think this process might be beneficial to an airgun barrel as well...especially one that is misbehaving.
I would LOVE to hear an actual air rifle gunsmith opine on all this.
My apologies to all if the newbie here spoke of powder burners a bit much, but I think there are happenings in the PB accuracy world that as air gunners, we should be looking at.
Justin
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