Matching slugs to barrels- A perspective

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rangur1

rangur1

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Jan 4, 2018
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Now the pursuit of accurate slugs that certain shooters want for their respective rifles is a real effort. Which strategy works best? Fastest? Do we use random size diameters, weights? Brands? Main consensus is grab several different weights, diameters and brands. This can get pricey and very labor intensive. I personally got sold on matching barrel diameter and matching close as possible. This eliminates 80% of available slugs and greatly reduces experimental costs and yield faster results. Others may disagree, but that’s my humble stance. Now this seems to apply to standard barrels, polygon barrels do better with smaller diameter ammo than their diameter would indicate.
 
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rangur1 said:
Now the pursuit of accurate slugs that certain shooters want for their respective rifles is a real effort. Which strategy works best? Fastest? Do we use random size diameters, weights? Brands? Main consensus is grab several different weights, diameters and brands. This can get pricey and very labor intensive. I personally got sold on matching barrel diameter and matching close as possible. This eliminates 80% of available slugs and greatly reduces experimental costs and yield faster results. Others may disagree, but that’s my humble stance. Now this seems to apply to standard barrels, polygon barrels do better with smaller diameter ammo than their diameter would indicate.
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@rangur1 Great questions and good suggestions. I love the opportunity to buy sampler packs of slugs. Griffin Airgun Ammo can put those together if you ask for a reasonably sized sample pack. Now I'm to the point of producing small batches of slugs and testing them. Slugging the barrel is probably the most efficient and one of the more affordable means of obtaining the closest slug diameter to buy in order to begin experimenting with a particular gun or barrel. The thing I don't see many people discuss is, how do you find the correct diameter slug to use in order to slug the barrel adequately?
 
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Ezana4CE said:
@rangur1 Great questions and good suggestions. I love the opportunity to buy sampler packs of slugs. Griffin Airgun Ammo can put those together if you ask for a reasonably sized ample pack. Now I'm to the point of producing small batches of slugs and testing them. Slugging the barrel is probably the most efficient and one of the more affordable means of obtaining the closest slug diameter to buy to begin experimenting with a particular gun or barrel. The thing I don't see many people discuss is, how do you find the correct diameter slug to use in order to slug the barrel adequately?
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outstanding question! I would use AVS slug sample pack only because he carries oversized slugs and secondly, his are pure lead, soft as it gets. As for reading diameter, need minimal a top quality set of calipers and measure the fins of the slug after inserting it in the barrel. You can get best slug for both choked and unchoked barrels. Just go for an obvious oversize. Say .256 for 25 cal, .2219 or.222 for 22, etc. But using pure lead is beneficial as it's relative soft nature allows the trial slug to mold to the barrel grooves for an exact diameter. Polygon design likes smaller diameter so this does not apply.
 
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Sizing the slug correctly for a particular barrel is important, but before that, picking a slug and barrel that produce a reasonable stability factor should be the primary selection criteria. Pellets are very forgiving as far as twist rate. Slugs are not. These days, I don’t usually bother with slugs that don’t give me a reasonable value when run through a stability/twist rate calculator. So most every slug I try gives at least decent accuracy.
 
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Scotchmo said:
Sizing the slug correctly for a particular barrel is important, but before that, picking a slug and barrel that produce a reasonable stability factor should be the primary selection criteria. Pellets are very forgiving as far as twist rate. Slugs are not. These days, I don’t usually bother with slugs that don’t give me a reasonable value when run through a stability/twist rate calculator. So most every slug I try gives at least decent accuracy.
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Is that basically a weight to twist rate comparision? Lighter projectile to a slower twist rate?
 
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rangur1 said:
Is that basically a weight to twist rate comparision? Lighter projectile to a slower twist rate?
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Sort of. But also affected by material density, bullet shape. Hollow cavities (hollow base, hollow point) make a difference, probably requiring a slightly slower twist, while slender spire points and boat tails probably require a slightly faster twist.

A particular shape that works well in a given twist rate will likely work well when scaled up/down in all dimensions, using the same twist rate.

It’s velocity dependent as well. Especially at and just below Mach 1. As you approach sonic, twist rate requirement spikes if you want it stable out of the muzzle.

Pellet specific barrels can have a relatively slow twist rate, so those tend to work best with short slugs, with hollow points. There can still be some BC advantage over even the heaviest pellets.

Higher power slug guns that shoot longer, heavier, high BC slugs, will have faster twist rates. Those slugs can have a significantly higher BC, so good for long range.
 
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Scotchmo said:
Sort of. But also affected by material density, bullet shape. Hollow cavities (hollow base, hollow point) make a difference, probably requiring a slightly slower twist, while slender spire points and boat tails probably require a slightly faster twist.

A particular shape that works well in a given twist rate will likely work well when scaled up/down in all dimensions, using the same twist rate.

It’s velocity dependent as well. Especially at and just below Mach 1. As you approach sonic, twist rate requirement spikes if you want it stable out of the muzzle.

Pellet specific barrels can have a relatively slow twist rate, so those tend to work best with short slugs, with hollow points. There can still be some BC advantage over even the heaviest pellets.

Higher power slug guns that shoot longer, heavier, high BC slugs, will have faster twist rates. Those slugs can have a significantly higher BC, so good for long range.
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well explained, thank you sir!
 
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rangur1 said:
Now the pursuit of accurate slugs that certain shooters want for their respective rifles is a real effort. Which strategy works best? Fastest? Do we use random size diameters, weights? Brands? Main consensus is grab several different weights, diameters and brands. This can get pricey and very labor intensive. I personally got sold on matching barrel diameter and matching close as possible. This eliminates 80% of available slugs and greatly reduces experimental costs and yield faster results. Others may disagree, but that’s my humble stance. Now this seems to apply to standard barrels, polygon barrels do better with smaller diameter ammo than their diameter would indicate.
Click to expand...
Great point @Ezana4CE made about slugging your barrel, if I had done that first would have saved me headache and money
 
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Ezana4CE said:
@rangur1 Great questions and good suggestions. I love the opportunity to buy sampler packs of slugs. Griffin Airgun Ammo can put those together if you ask for a reasonably sized sample pack. Now I'm to the point of producing small batches of slugs and testing them. Slugging the barrel is probably the most efficient and one of the more affordable means of obtaining the closest slug diameter to buy in order to begin experimenting with a particular gun or barrel. The thing I don't see many people discuss is, how do you find the correct diameter slug to use in order to slug the barrel adequately?
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To answer my own question, one of the best things I've learned to do is to read AGN threads and speak/message other owners of the same make and model guns to see what's worked for them. That's often a decent starting point. I haven't had a lot of difficulty using this method or the sample packs, but I'm curious as to what has worked for others. Ive wasted a significant amount of money just buying caliber specific projectiles based upon the caliber marketed for a specific model of air rifle.
 
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I have tried many different slugs for my .25 x600 and x700 liners @ 100 meter rings. The best results I got from boattails and ball nose shapes.
And finally I just gave up with slugs and went back to shooting pellets. Much less headache.
If I would re-tune again for slugs I know I would go resizing slugs OD not more then 5 microns "pressfit" over rifling lands. These OD dimension "sizing bushings" are not readily available from ANSI manufacturers, only to get a size smaller and diy a honing with diamond paste.
 
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Scotchmo said:
A particular shape that works well in a given twist rate will likely work well when scaled up/down in all dimensions, using the same twist rate.
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If you take a fixed design of slug and find a twist rate that suits it in a specific calibre, in order to maintain the same stability factor for larger or smaller calibre slugs of the same design and construction, you need to increase the twist rate for smaller calibres and decrease it for larger calibres, in the ratio of the calibres. So for example, if a .22 needs a twist rate of one turn in 16 inches, the identical slug scaled down to .177 would need a twist of one turn in 12.8 inches, whereas a .25 slug would require a twist rate of one turn in 18.2 inches.
 
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Scotchmo said:
Sizing the slug correctly for a particular barrel is important, but before that, picking a slug and barrel that produce a reasonable stability factor should be the primary selection criteria. Pellets are very forgiving as far as twist rate. Slugs are not. These days, I don’t usually bother with slugs that don’t give me a reasonable value when run through a stability/twist rate calculator. So most every slug I try gives at least decent accuracy.
Click to expand...
@Scotchmo Can you elaborate on the twist rate calculator? I have not used one.
 
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