Ballistic Theory Same Weight Slug and Pellet - Slug Is Slower - Why?

[Billm]

If you shoot a slug and a pellet of the same weight and the slug has a significantly higher BC, why would the slug have a slower muzzle velocity by 20-30fps? Friction and/or projectile seal? Are there any other factors that might cause this? I’m mainly trying to start a technical discussion, but I am also experiencing this with one air rifle.

 

[pan60]

I am no tech on the topic but I beleave it would be to much bearing surface ( Friction ) and lack of seal.

I think thats why the hybrids do so well. they get a better seal but still suffer from to much bearing surface?

just my thoughts and only that.

 

[jlowe]

Slugs are slightly slower because the back end is not sealed like a pellet. The parachute effect that a pellets has helps at the beginning and slows them down in the end. The heavier pellets not so much.

 

[Solo1]

If you shoot a slug and a pellet of the same weight and the slug has a significantly higher BC, why would the slug have a slower muzzle velocity by 20-30fps? Friction and/or projectile seal? Are there any other factors that might cause this? I’m mainly trying to start a technical discussion, but I am also experiencing this with one air rifle.

I would blame friction just look at the difference in surface area acting against the barrel

 

[Solo1]

Slugs are slightly slower because the back end is not sealed like a pellet. The parachute effect that a pellets has helps at the beginning and slows them down in the end. The heavier pellets not so much.

If the backend of a slug is the same diameter as the grove of the barrel the seal is just as good. Pellets don’t always flair out to seal any better than a slug

 

[hameditor]

I have always felt that the cause is primarily friction. In addition I would offer the observation that slug body diameters are typically larger than pellet head diameters, although skirt diameters can be larger in some cases. This means that slugs can be a very tight fit in some barrels.

See the photo in this HAM story Big HAM Slugs Test. Muzzle Energy And Consistency For Slugs

 

[Billm]

I’m not sure if this is specific only to my newest barrel, but slugs of the same weight are slower and hit lower at 100yds than the same weight pellets. My thinking is what you guys have also stated: that length of bearing surface or smaller diameter is the main factors. I would’ve thought that the “parachute effect” would’ve made the pellets drop a lot lower than the similar weight slugs at 100yds. I haven’t been able to shoot the last couple of days due to rain and bitter cold (in the 40’s) . When I can shoot some more, I will try tapping the slugs to swell them slightly. I’m not looking for accuracy with thus experiment, I just want to know why they’re slower. How do you know if the bearing surface area is inadequate. I’m assuming that would inhibit stability and cause scattered groups?

 

[Billm]

I have always felt that the cause is primarily friction. In addition I would offer the observation that slug body diameters are typically larger than pellet head diameters, although skirt diameters can be larger in some cases. This means that slugs can be a very tight fit in some barrels.

See the photo in this HAM story Big HAM Slugs Test. Muzzle Energy And Consistency For Slugs

Just read it thanks. I have a lot of questions about this topic and appreciate everyone’s input.

 

[Solo1]

I’m not sure if this is specific only to my newest barrel, but slugs of the same weight are slower and hit lower at 100yds than the same weight pellets. My thinking is what you guys have also stated: that length of bearing surface or smaller diameter is the main factors. I would’ve thought that the “parachute effect” would’ve made the pellets drop a lot lower than the similar weight slugs at 100yds. I haven’t been able to shoot the last couple of days due to rain and bitter cold (in the 40’s) . When I can shoot some more, I will try tapping the slugs to swell them slightly. I’m not looking for accuracy with thus experiment, I just want to know why they’re slower. How do you know if the bearing surface area is inadequate. I’m assuming that would inhibit stability and cause scattered groups?

40’s

 

[Solo1]

@Billm there is not that much parachute effect as you think and are you realizing that by slug hitting lower than your pellet 0 its actually shooting flatter?

 

[Solo1]

Heres some numbers from strelock on my ghost. 30 cal aea 45 @927 fps 50yd 0 @100 703.9fps down 10.3”
30 slug 45.5 zan@976 @100 842.2 fps down 7.4”
If i change velocity of slug
45.5 slug @927 @100 808 fps down 8.4”

The slugs were 50 yd 0 too

 

[Danman]

Just read it thanks. I have a lot of questions about this topic and appreciate everyone’s input.

We are currently well below zero here lol.
Grab a 4.51dia 10.03 gr Jsb KO slug and try jamming it into your .177 TX200 barrel, i dare you ....You'll need a hammer and punch, whereas a 4.51 pellet will be too loose, i chickened out as i didnt want it to get stuck when I tried! The pellet contact area on a barrel is like the tire contact patch on a car....very tiny. I've recovered slugs and pellets after shooting them and the slugs sides are shredded by the rifling....i believe that definitely affects accuracy for long range shooting with them.

 

[PapaT]

We are currently well below zero here lol.
Grab a 4.51dia 10.03 gr Jsb KO slug and try jamming it into your .177 TX200 barrel, i dare you ....You'll need a hammer and punch, whereas a 4.51 pellet will be too loose, i chickened out as i didnt want it to get stuck when I tried! The pellet contact area on a barrel is like the tire contact patch on a car....very tiny. I've recovered slugs and pellets after shooting them and the slugs sides are shredded by the rifling....i believe that definitely affects accuracy for long range shooting with them.

I don't know about accuracy, but maybe. I do know that is proving the statements of extra friction from increased contact with rifling verses a pellet. This therefore leads to lower speed at muzzle. The higher BC just means that it is retaining more of its speed (and therefore energy) as it goes downrange.

It is interesting that same claimed diameter gets drastically different fitment. Pellet diameter is usually based on skirt if I remember correctly, I know far less on the slug side of the house.

 

[Billm]

We are currently well below zero here lol.
Grab a 4.51dia 10.03 gr Jsb KO slug and try jamming it into your .177 TX200 barrel, i dare you ....You'll need a hammer and punch, whereas a 4.51 pellet will be too loose, i chickened out as i didnt want it to get stuck when I tried! The pellet contact area on a barrel is like the tire contact patch on a car....very tiny. I've recovered slugs and pellets after shooting them and the slugs sides are shredded by the rifling....i believe that definitely affects accuracy for long range shooting with them.

I don't know about accuracy, but maybe. I do know that is proving the statements of extra friction from increased contact with rifling verses a pellet. This therefore leads to lower speed at muzzle. The higher BC just means that it is retaining more of its speed (and therefore energy) as it goes downrange.

It is interesting that same claimed diameter gets drastically different fitment. Pellet diameter is usually based on skirt if I remember correctly, I know far less on the slug side of the house.

The bearing surface on a swaged slug is uniform until you hit the ogive. It’s squeezed down through a die with parallel walls, with the ogive at the bottom and an external punch from the top to form the base. The theory on the deep lands affecting accuracy is that the protrusions made in the lead creates drag. The deeper the cut in the lead the more adverse the affect is.

 

[Franklink]

Push some slugs through the barrel and push some pellets through and note the effort required for each.

As previously alluded to, a pellets bearing surface on the head is small, so we don't displace much lead there, and the skirt is hollow, so very easy to displace the lead there. Much more bearing surface with slugs, and nowhere for the lead (displaced by the rifling) to go cuz they're solid.

What you're seeing is a very typical occurrence though, similar weighted projectiles -the slugs will go much slower than the pellet, through the same barrel with all the same settings for both projectiles.

 

[Chief 10-Beers]

I think that making sure you are using the correct diameter of slug, For instance the NSA slugs I have are .217. The same slug fits differently in the 3 different brands of Rifles I have shot them in.

 

[Billm]

I think that making sure you are using the correct diameter of slug, For instance the NSA slugs I have are .217. The same slug fits differently in the 3 different brands of Rifles I have shot them in.

That’s not usually an option with .30, otherwise I agree.

 

[Billm]

I may purchase the dies for .30 hybrid dies. The bearing surface on a .30 Ho dish base under 52gr is relatively short and basically I would guess that maybe 25% or less of the length of the slug is in contact with the barrel. Pthe contact is only in the rear of the slug. It’s conjecture, but it’s hard to believe that only rear contact doesn’t induce yaw or pitch. Not exactly in line with the thread topic, but relevant I think. The hybrids allow a larger bearing surface with a lower weight. I haven’t tried hybrid slugs, but maybe I will before buying more dies. Herein lies my issue with the Sonoran: any regulars slug over 52gr is going to be dropping below 800fps. Getting a 52gr slug to 850fps at max power is borderline. What is fast enough for .30 slugs at 100yds, I don’t really know?

 

[Billm]

Push some slugs through the barrel and push some pellets through and note the effort required for each.

As previously alluded to, a pellets bearing surface on the head is small, so we don't displace much lead there, and the skirt is hollow, so very easy to displace the lead there. Much more bearing surface with slugs, and nowhere for the lead (displaced by the rifling) to go cuz they're solid.

What you're seeing is a very typical occurrence though, similar weighted projectiles -the slugs will go much slower than the pellet, through the same barrel with all the same settings for both projectiles.

I have pushed both pellets and slugs through the barrel. They are both tighter at the breech and then open up. I need to do it again in a more controlled way.

 

[Solo1]

Bill i think your getting obsessed with this and need to just wait till you can shoot. Prepare sample slugs that you have fill the gun with air and a tank if you have and wait to shoot oh make some paper targets and mark down what was shot and how the gun was set up so you remember. Let the targets tell you whats going on