FPE from slugs versus pellets-an example

[Franklink]

@JungleShooter.....

For everybody else, this came up in a recent discussion here on AGN....how much fpe loss do we typically see from slugs? Well, it depends. lol.

Gun is a Vet Long in .22 with a 23inch 6 groove polygonal LW with a 1:32 twist rate, choked. Yes, an RTI "LR" barrel that a friend cut for me to fit a Veteran.

Didn't do any tuning or tweaking for these #s, same reg pressure and hammer tension and hammer spring for all of them. (replaced orings in the reg recently and it's settled into a bit higher fpe than what it was the last time I shot it, about a week ago)

All five lubed with Gunzilla.

.22/25.4gr Monster RDs: 934.5, 928.7, 925.5 --> average of 929.6 = 48.75fpe
.218/22.5gr Varmint Knocker: 968.9, 974.1, 971.1 --> average of 971.4 = 47.16fpe
.218/24gr Varmint Knocker: 934.3, 937.5, 938.5 --> average of 936.8 = 46.78fpe
.218/26gr Varmint Knocker: 907.1, 912.8, 909.3 --> average of 909.7 = 47.79fpe
.218/28gr Varmint Knocker: 863.8, 872.6, 875 --> average of 870.5 = 47.13

Honestly VERY surprised at how little fpe is lost when using slugs versus pellets from this barrel. Typically, the difference is much larger. Couple things that may be at play here though....the bore on the LR barrel is VERY smooth.....it's a poly, but it's even smooth for a poly.......and the choke isn't obnoxiously tight.

Again, all the other times I've tried this (other guns or other barrels), the slugs cost multiple FPE versus the same "tune" with pellets.

The only "rule" that I've found slugs follow, is that they don't follow any of the "rules" that we read about on the forums, or personal preconceived notions, even when based on previous slug experiences.

Quite interesting, and thought you (and others) might think so as well.

(For anyone curious, the top three weights showed promise, even though they're going slower than most would say they should be shot, AND being shot through a choked barrel, AND being shot through a pretty slow twist rate. The 24grain were the most promising. Basing that on how they shot at 100 yards).

 

[JungleShooter]

Frank,

thanks for the write-up and heads-up.
I'm glad this time things worked in your favor.
Very interesting.

AND:
Maddeningly unpredictable slugs....!!

Matthias

 

[Clifton]

You don't loose FPE with slugs. They have a better BC and carry speed longer. At 30 yards you will have significantly higher fpe if starting at the same fpe from the muzzle v pellets. Polymags and Hades loose even more than domed pellets at 30 yards. The further the distance, the greater the loss of fpe for pellets V slugs.

Others have posted BC for various pellets and slugs.

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[dizzums]

thankfully though, most pesting is under 30 yds. and 50fpe isnt needed on rats .. for medium to large game a case can be made for slugs ... sparrows and rats no, not really, no .. targets at 1000yds in wind, ok, maybe, if thats your thing ..

 

[nervoustrig]

You don't loose FPE with slugs.

Franklink was speaking of internal ballistics, whereas you are speaking of external ballistics.

 

[Franklink]

Franklink was speaking of internal ballistics, whereas you are speaking of external ballistics.

Yep, simple muzzle velocity here.

BC and downrange retained speed (and therefore fpe at impact) is a different ball of wax.

 

[Vetmx]

Choke with slugs is generally a speed killer. Or an oversized slug. Or what a slug is made out of. The recipe.

 

[ctshooter]

The VKs are definitely a softer lead to retain that amount of fpe. With the NSA I generally lose a good amount more.

With the same power setting on my RW 177:
Daystate Howlers (NSA) 12.6gr @ 920 fps = 23.69fpe
JSB Redesign 13.43gr @ 940 fps = 26.36fpe

I'm seeing approx 10% loss of power with a lighter slug.

 

[nervoustrig]

To muse on this topic just a bit…there are a few things going on at once that contribute to different muzzle velocity / muzzle energy between a slug and pellet, even when variables are controlled as much as they reasonably can be.

For example, _ideally_

1. both the slug and pellet weigh the same
2. both the slug and pellet produce equal friction in the bore
3. both the slug and pellet seal equally well to the bore

And of course no change to the airgun’s state of tune…same pressure, same valve lift and dwell. If all 3 things were possible, we could expect something pretty close to equal muzzle energy for the slug and pellet.

Regarding #1, there are some examples of commercially available slugs and pellets of equal weights (e.g. 10.3gr JSB Knockouts and Heavies). But that’s pretty much where the apples to apples comparison begins and ends.

Because numbers 2 and 3, friction and sealing, are mutually exclusive. To get a slug’s friction down to anything approaching that of a pellet, it would need to be barely skating along the lands. But if it’s skating along the lands, sealing is compromised and air is spilling out through the grooves.

Likewise, the reverse is true. If the slug seals completely, its friction is likely substantially higher than that of a pellet which is contacting only in a small ring at the skirt and an even smaller one at the head.

Granted there is some middle ground to play in, like the use of driving bands or knurling to produce a better seal without contributing so much friction. But in the overwhelming majority of (if not all) cases, there’s going to be a small to modest loss of muzzle energy when going from a diabolo pellet to an equal weight slug. In my experience, it even holds true when the AG is tuned way up on the velocity plateau for the pellet. In other words, when there is excessive lift and dwell the pellet can’t use but the slug can use.

 

[Scotchmo]

...

For example, _ideally_

1. both the slug and pellet weigh the same
2. both the slug and pellet produce equal friction in the bore
3. both the slug and pellet seal equally well to the bore

….

Seating depth might be another small factor. When using a pin probe. At least it is for me.

 

[Scotchmo]

I did some testing today to see how chamber depth affects this difference.

Before, pellets (.30 caliber, 44.75gr) seated with light resistance on the cocking lever. A similar weight NSA (43.8gr) took more force to seat than I felt comfortable with.

Pellet 975fps
Slug 960fps max but inconsistent and often much slower.

Another slug, the 44.5gr FX Hybrid was so tight in the lead-in, that it was almost impossible to seat and half the time, the shot would not even make it out of the barrel.

I recut the chamber significantly deeper. Pellet seats with a little less drag but still a friction fit at the skirt. 43.8gr NSA drops in with about 0.1” of “jump” remaining after closing the lever.

Pellets 975fps
Slugs 995fps

Big improvement for the slugs.

I’m going to try the FX Hybrids next time as they should work now as they have 0.05” inches of “jump”. Later, I’ll try to decide on a good compromise in the lead-in. Maybe reduce the lead-in a little from this latest setting. Possible with this gun since it uses a thimble.

This is another instance where I’m trying to shoot both pellets and slugs using the same gun/same barrel/same tune. Pellets or swaged slugs. It’s easier to setup when dealing with one particular pellet or one particular slug.

I’ve had better success with dedicated higher power airguns with cast slugs only. Sized as bore riders with a single driving band in the back half that seals into the grooves.

 

[Vetmx]

Seating depth might be another small factor. When using a pin probe. At least it is for me.

Velocities jumping all over the place with a barrel with conventional rifling is generally always too short of a leade. Doesn’t matter the probe. And I agree, a better launch yields better velocity in most cases. None of this applies to FX.

 

[Scotchmo]

Velocities jumping all over the place with a barrel with conventional rifling is generally always too short of a leade. Doesn’t matter the probe. And I agree, a better launch yields better velocity in most cases. None of this applies to FX.

True, same issue with any type of probe. Except, when also using projectiles that are not flat base (deep pellets), the pin probe has one more variable that we need to take into account.

 

[Vetmx]

True, same issue with any type of probe. Except, when also using projectiles that are not flat base (deep pellets), the pin probe has one more variable that we need to take into account.

Yep, even less seating depth without even realizing it. I‘ve heard guys say that pin probes won’t seat a slug concentrically. That can only happen if you have way bigger problems. I don’t like pin probes for other reasons. Fortunately with the power of guns that should be shooting slugs, the 10 or so fps gain of a pin probe is meaningless. Just bump the reg and save some aggravation. My RTI has a pin probe and I use a FX barrel on it for .30 slugs. Not flat base. I had to machine the barrel adapter to set the liner a little closer to the transfer port so the slug would be seated flush with the pin probe.

 

[Nattboy]

Thank you all. Great lesson.

 

[heavy-impact]

If I ever have a squirrel stuck to the muzzle of my airgun I'll be sure to utilize that 1 extra ft/lb from a pellet.

For the 99.99999999999999997% of game not clinging to the muzzle I prefer the far greater energy delivery of slugs.

People spend thousands on airguns and accessories, pay $5 for a cup of coffee but can't justify using slugs that cost slightly more than pellets.

What am I missing here? Maybe I'm stoopid.

Before anyone gets upset with me... I'm just clowning around. We're all free to pursue our interests and I promise not to touch your pellet hoard that cost slightly less than slugs and delivers more energy before it leaves the barrel because internal ballistics are important too.

 

[Scotchmo]

I adjusted the chamber depth and am now getting:

JSB 44.75gr@978fps $0.147/pellet 95fpe
NSA 43.8gr@990fps $0.107/slug 95fpe

That is in an unchoked barrel.

If you get the 4 for 3 from Pyramyd air, the pellets are almost as low cost as the slugs. Both are accurate. The pellets are often a little more accurate, at least out to about 70yards. After that, slugs are generally better, especially when shooting under difficult conditions.

.177 is a good caliber for pellets. The only reason I even shoot pellets in my larger caliber airguns is because I shoot in a lot of airgun competitions and some of them require Diabolo shaped pellets, even when the Diabolos can cost more and perform worse. Outside of competition, I prefer slugs.

Unless you are shooting a low FPE airgun, slugs are a more efficient use of lead.

 

[Franklink]

Another example from my shooting today.

Same barrel/reg pressure/hammer tension/hammer weight that produces 805 with .20/13.73 pellets (19.8fpe) produces 580fps with .20/18.9 slugs (14.1fpe).

I didn't play with the ballistic apps to find out how far it would take, but with that starting deficit, it's gonna be out there a long ways (and single digit fpe) before the slug catches up to the pellet in this example.

 

[JungleShooter]

Another example from my shooting today.

Same barrel/reg pressure/hammer tension/hammer weight that produces 805 with .20/13.73 pellets (19.8fpe) produces 580fps with .20/18.9 slugs (14.1fpe).

I didn't play with the ballistic apps to find out how far it would take, but with that starting deficit, it's gonna be out there a long ways (and single digit fpe) before the slug catches up to the pellet in this example.

Thanks, Frank, to have real world data to overthrow some wrong assumptions and generalizations.

On my last outing I had a Prophet 2 Compact tuned for Polimags (26.00gr) at 955fps = ME 52.6FPE.
On a whim I sighted it in for JSB Heavy's (39.95gr) that should have resulted in 835fps — but they thundered out the muzzle with 884fps = ME = 59FPE!
I was happily surprised = a 6.4FPE gain!!

Based on that, in your recent example I would have expected that because the slug (18.90gr) was heavier than the pellet 13.73gr) — it would at least make up for the added drag in the barrel and have about the same amount of muzzle energy (ME).

But nope, the slug lost 5.7FPE — wow, that's just terrible.


➠ I just hope the ATP slugs will do well in the RTI barrels (CZ and RPB)....! They are so crazy heavy, I need every foot-pound my short little shooters can squeeze through their transfer ports!

Matthias

 

[Franklink]

➠ I just hope the ATP slugs will do well in the RTI barrels (CZ and RPB)....! They are so crazy heavy, I need every foot-pound my short little shooters can squeeze through their transfer ports!

Matthias

I tried some of the .22/32.3 gr "ATP Smooth" from a 12 land and groove, unchoked LW barrel (standard 1:17.7 twist rate) and was thoroughly UNimpressed.

My understanding is that the RTI/RPB LW is essentially the same barrel as what I tried, with the only difference being a 1:16 twist rate.

The ATPs from my barrel were tried at various speeds.....870 seemed bout the best, but even then it was throwing some that would miss a 9x11 sheet of paper at 100yards.

I hope your barrel shoots them better than mine.