Slug weight vs length for accuracy

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elh0102 said:
With most air rifles, this can present a safety issue. I there is air in the gun, I'd remove the barrel before pushing the pellet out from the muzzle to breech.
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You are correct and in fact this should always be done every time you change to a different pellet. It is called slugging a barrel. In PBs it is done with a soft lead ball. For the purpose of sizing a barrel. In an airgun ideally you want the least amount of barrel friction with sufficient rifling bite not to strip lead from the pellet. It is the reason most pellet manufacturers make their pellets in different sizes. Just .001" in diameter can make a big difference.

I'm a touchy/feely guy and I like to feel the resistance of the pellet or slug passing through the barrel and I usually do not remove the barrel when I do it. After a while with experience, you will feel the difference between tight and loose. Viewing the depth of the styrations is a pretty good clue.
 
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Matt Drubber has a great, but long video on this. One key point that I haven't seen anybody touch on is too much air, THAT will destabilize slugs. I've been playing with FX/RMR hybrids in both .22/.2173 and .25, still getting the .22's to play well but it's a process, even though they're good enough for 100+ yard Ground Squirrel splats.
 
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TheShooter (aka Seeker) said:
Do you aim at the bore diameter +0.01mm as an ideal slug diameter?
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Roachcreek has said size your slugs .0005 to.001 larger than your groove diameter. That's why anybody shooting slugs needs to slug their barrel then measure the diameter in at least 2 places to find that dimension. Remember, over the counter slugs are going to vary in diameter. Always size them to get the most consistency which along with weight equals accuracy. Also the longer the slug the more twist rate you'll need to stabilize it.
 
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DesertSilver said:
Roachcreek has said size your slugs .0005 to.001 larger than your groove diameter. That's why anybody shooting slugs needs to slug their barrel then measure the diameter in at least 2 places to find that dimension. Remember, over the counter slugs are going to vary in diameter. Always size them to get the most consistency which along with weight equals accuracy. Also the longer the slug the more twist rate you'll need to stabilize it.
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you mean bore diameter? how can you shoot something bigger than groove diameter in an airgun?
 
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Guys, why not doing a very gradual leade so that just a tiny bit of a slug after chambering is in the full rifling but still the rest of it is also kept by the tapered rifling? Like below.

IMG_20231025_170135~2.jpg

IMG_20231025_170135~3.jpg


I don't think there is anything better than that.
 
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I watched a guy onYT mess with a barrel on a BSA 12 , bad performer, several issues one being when chambering the pellet it was not engaging the rifling at all,he made a longer pellet probe to overcome the issue,it also had a crown problem ,when both were corrected the rifle shot very much better.Having shot a lot of cast bullets over many years found the most important thing was bullet fit in the chamber ie throat. Cheers Mal in au.
 
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shotmaniac said:
you mean bore diameter? how can you shoot something bigger than groove diameter in an airgun?
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In order to create a barrel to projectile seal, all projectiles (bullets, slugs or pellets) are always larger than the barrel ID. This does two things, first the projectile is swaged to conform to the barrel size creating a gas seal and secondly to cause the rifling in the barrel to grip the projectile in a manner tight enough so the rifling bites into the projectile and does not slip. Slipping creates lead debris fouling the barrel. Yet the fit must not be so tight that excessive resistance exists as this limits velocity and creates heat that can melt the lead creating even more deposits in the barrel. It is a careful balance. All barrels have two diameters, the land diameter and the groove diameter where the groove diameter is largest by about .006". Airguns can be different where some airgun barrels also use a choke at the end of the barrel. This was very common in the past, but today not too many manufacturers still use them. You may also note that airgun pellets should also have two diameters, one at the head and a slightly larger one at the skirt. The difference being about .010" where the head diameter should exactly match but not be bigger than the barrel land diameter. Please also note that the Diabolo pellet form is used in airguns to prevent excessive resistance in the barrel by only allowing the skirt to bite into the barrel rifling because the Diabolo form stabilizes the pellet flight primary through skirt drag and secondly through spin. Airgun slugs limit resistance through a tapered form unlike bullets that have little to no taper. Slugs are flight stabilized through spin only and are sensitive to rate of rifling rotation because of that.
 
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