Slug speed?

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Franklink

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Sep 3, 2017
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In theory, does a given slug need to be doing at least a certain threshold of fps to be accurate? Or is it more a matter of certain barrels don't like certain pellets (or certain slugs)?

Bought some 23gr NSA slugs for my .22 Veteran Short lately and wasn't greatly impressed with the accuracy. Two inch groups at 55 yards. Going into it I kinda figured that a max 32fpe gun probably wouldn't have the juice necessary but thought I'd give it a try. 

Surprisingly, the "one full revolution in from 20fpe setting" that does about 27fpe with most pellets was a little more accurate than the "two full revolutions in from 20fpe setting" that normally does 32fpe with most pellets. 

As an aside, they fit very tightly. There was enough resistance with the first slug that it made me think it had tipped and was going into the leade sideways. 

I'm leaning towards the thought that the gun just isn't powerful enough, but the better groups at lower power is making me scratch my head. 

(Nothing against the slugs here, very nice looking projectiles.)
 
I have shot various NSA and VK slugs in my Impact 700 slug barrel at 740 through 980fps and they were sub MOA at 100 yards. Yes, they do need to go a certain fps probably to get the needed spin to be stable. Most guns are choked to tight to shoot slugs accurately. You will need to find a slug that fits your barrel well and then tune the gun well to get good results with slugs. If you do these things you will be rewarded with airgun nirvana.

Yes, they do fit tight in the gun. I tried to push one through my barrel with a cleaning rod once and it wouldn't go. I finally put the barrel back on the gun and shot it out. That is crazy tight!
 
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Slugs offer more drag and are more sensitive to the barrels true size it's one of the issues that bullet casters pull their hair out over. The biggest issue is the rifling twist rate, slugs needs a higher twist rate than pellets do. 

I've talked to hunters supply quite a bit about this very topic, one thing she suggests it to take your gun to a gunsmith and let them size the barrel this will help in deciding what size slugs to buy.

This is an issue with all airguns but using my Texan as an example even though it's labeled as a .45 it is a .457 if I shoot .450 they go everywhere, if I shoot 458 I lead my barrel
 
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Buy a sizing die and try sizing and testing your slugs with different diameters. For my .25 caliber I bought a .2485", .249", .2495. Most .25 caliber slugs are made at .250" so I can size them down perfectly. This works great for FX liners that have a choke. I need to do more testing, I had just started when I had major gun problems. I'm up and running again, will test in depth this week. 

Stoti
 
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In theory, does a given slug need to be doing at least a certain threshold of fps to be accurate? Or is it more a matter of certain barrels don't like certain pellets (or certain slugs)?

Bought some 23gr NSA slugs for my .22 Veteran Short lately and wasn't greatly impressed with the accuracy. Two inch groups at 55 yards. Going into it I kinda figured that a max 32fpe gun probably wouldn't have the juice necessary but thought I'd give it a try. 

Surprisingly, the "one full revolution in from 20fpe setting" that does about 27fpe with most pellets was a little more accurate than the "two full revolutions in from 20fpe setting" that normally does 32fpe with most pellets. 

As an aside, they fit very tightly. There was enough resistance with the first slug that it made me think it had tipped and was going into the leade sideways. 

I'm leaning towards the thought that the gun just isn't powerful enough, but the better groups at lower power is making me scratch my head. 

(Nothing against the slugs here, very nice looking projectiles.)
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Try a shorter slug that isn't a tight fit. FPE /velocity or different weight slugs can't fix a bad seat. 
 
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The twist rate of the barrel's rifling, matched to the weight of the slug, at a known and consistent fps, is what determines the proper match up of speed, spin, and weight for maximum accuracy in powder burners. Why would this be different in pcp's?



Hoot
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I think the difference is with a powder burner the “ fire” expands the bullet into the lands and groves somewhat negating the issue of bullet diameter. Air guns not so much . NOW that’s my thinking not necessarily a fact. More of a question What do you think Kevin? 
 
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One of the biggest areas a lot of people miss about slugs is the softness of the lead itself if it's too hard then you would have to shoot an undersized slug to get any kind of speed and it may not engage the rifling properly. Vice versa if it's too soft it deforms and will not shoot accurately virgin lead with a small amount of alloy is best. 

This is one of the reasons why recycle lead can be such a pain in the butt its hardness is variable you'll never know the exact hardness of the bullet,

Another factor that can affect a slug or pellet for that matter is properly mixed alloy if the pot is not hot enough then the mix process may not be complete the result will be an unbalanced slug this is most expecially true when shooting and Big Bore with larger and longer slugs.

The slugs design itself plays a huge factor in how it's going to react and its accuracy the BC of the design plays a direct role in the balance of that bullet and for a proper balance the twist rate will also affect it.

it's all on a sliding scale depending on the weight of the bullet caliber of the bullet the length of the bullet The twist rate of the barrel the speed of the bullet everything has a effect in if one variable is changed then the other variables may need to be changed also.

Casting is a pretty in-depth process with a lot more science and metallurgy then many people think it's not about just throwing some lead in a pot melting it and pouring it into a mold.

I'm not an expert at this but I I'm not so sure that the feet per second and corresponding twist rate has an effect on each other. To clarify, if the barrels twist rate is enough to support a slug the the fps will not effect that rate. Consider a football it doesn't matter if it's passed a short ways or clear across the field just as long as the person throwing it puts the twist in the throw. And barrels twist rate is set it doesn't change just because the bullet is traveling slower or faster, 


 
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If they were going in that hard try cleaning and polishing the bore and seeing if that makes a difference. It would open it up a little bit, and polishing seems to work better for slugs because they have more surface area touching the lands and grooves. Also, after the cleaning and polishing, shoot silicon lubed slugs to help keep it moving and cleaner.
 
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"I'm not an expert at this but I I'm not so sure that the feet per second and corresponding twist rate has an effect on each other. To clarify, if the barrels twist rate is enough to support a slug the the fps will not effect that rate."

Also not an expert but I have to disagree with this. My experience has been more with powder burners than air guns for this but it suggests they are directly related. Seems higher FPS would have to mean higher spin rate in the same barrel ASSUMING that the rifle has enough power to propel the slug to the needed velocity and ASSUMING that the lead (pure lead=softer) isn't deforming/scraping off in the barrel. Faster twist rate should require more energy to propel the slug down the barrel and might result in more "scraping".
 
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