⁍⁍ Did someone say: "We need BETTER PROJECTILES" ??

[JungleShooter]

In another thread @Triglav observed that in powder burner research & development the emphasis has shifted away from simply adding more gun powder in ever increasing cartridges.

And then he said:
"Same principle applies to airguns:
WE NEED BETTER PROJECTILES, not more air through the port, or a larger caliber."


Well said.

We have NSA blazing the projectile trail with lowering the price of the formerly very expensive slugs.


We have Altaros blazing the projectile trail with doubling the BC for slugs.


We heard FX announce "the replacement for the airgun pellet" — that particular exaggeration was published a year and half ago.

➧ I am quite sure that we will NOT follow the advice of their misguided marketeers and "say goodbye to pellets."

However, I am convinced that a good many of us would have use for a hollow point projectile that:
▪ has an amazing expansion in flesh upon impact, and that
▪ has a high enough BC in order to keep up its impact velocity out to 40 or 50 or more yards — so that that amazing expansion can actually happen!
➔ I'd suggest a true (not fudged) *BC of 0.050*.

➔ Incidentially, a BC of 0.050 would also limit the range and impact of the projectile when used for angled shots into the trees:
At this BC the impact energy of the projectile returning to earth is rather low, cf. graph below.




Besides better projectiles I have others repeatedly call for barrels that are much better adjusted to the projectiles — and that are more consistently made (one true diameter, not a "nominal" diameter/caliber).
Sounds right!




These are great times to be an airgunner!
Let's see what the Shot Show, IWA, & Co will bring this year. I hear that Niels at NSA is working on a new projectile that will have great expansion.

Matthias



Graph:
Impact energy upon return to earth — of a 18.13gr projectile with 0.050 BC — shot at various inclination angles:

 

[delooper]

Altaros is going in an interesting direction.

In powderburners we're starting to see a lot more monolithic copper projectiles. High BC, with various internal geometries.

I imagine Altaros is experimenting with it, but slugs like their high BC units where they've been hollowed-out somewhat on the inside, that could be really interesting.

 

[MrP]

I recall seeing Griffin had lead slugs formed around a plastic core.

 

[JEFFPPC]

The name of the game in centerfire br in both short and long range is......barrels and bullets. No reason it should be different here.

 

[N2 Shooter]

Almost every hunting attribute you mention is present in the FX Hybrid Slugs, one of my favorite slugs for small game. Phenomenal expansion at reasonable velocities due to the hollow core design.

I've shown this image before, but this is a full pass through on a groundhog at 60+ yards that I recovered after reviewing the video. The groundhog was standing on its hind legs, and was completely dead before falling face down in the grass. Shot with the FX Maverick VP .30cal at 930 fps.

 

[JDGriz]

I vote for lead-free Altaros slugs, to cover the middle power range (30-60 fpe).

 

[Ballisticboy]

The projectile in my avatar had a measured BC of 0.056 for a 14.5 grain .22 round, the actual round pictured. In .177 form, it had a BC of .041 for a 10.5 grain round. These were made and tested 30 years ago.
The current shape for slugs is very similar to many subsonic bullets, which are known to have some accuracy problems. Similar problems were encountered with military bullets when the US army asked for improved rounds for their standard infantry weapons. A large and expensive research programme had to be initiated to find out what could be done and how.
As for lead free slugs, increased barrel twist rates will be needed in many cases, especially for rounds with boat tails etc. This thread https://www.airgunnation.com/threads/a-first-look-at-possible-lead-free-slug-problems.1280218/ looked at the problems.
I still think that many of the popular boat tailed slugs have much too big an angle, with much longer than required boat tails. Boat tails are a classic case of bigger is not always better. Bob Sterne incorporated my suggestions in his latest designs, which showed improved performance.

 

[JDGriz]

@Ballisticboy The alternative to using a lighter alloy is to drill a hole in the back - which Altaros could probably do since they are machined. This would also keep the second moment of inertia almost as high. One possible downside is that this might lead to over-leading the barrel, as the pressure compresses the slug outwards.
Also maybe there is still a twist rate that would work for both lead and non-lead slugs; if say 13"-15" twist is enough for a lead-free slug, this would also work for the normal slugs - only pellets would suffer a bit (the actual number does matter, whatever it is).

 

[Ballisticboy]

@Ballisticboy The alternative to using a lighter alloy is to drill a hole in the back - which Altaros could probably do since they are machined.
This would also keep the second moment of inertia almost as high.

It would also move your centre of gravity forward, which would change your aerodynamic moments and may increase group sizes as a consequence. Things don't always work out the way you want.

 

[JDGriz]

It would also move your centre of gravity forward, which would change your aerodynamic moments and may increase group sizes as a consequence. Things don't always work out the way you want.

That depends on depth of the hole and front ellipse-shape "sharpness". CoG should be easy to keep where needed, or close to original.
I would still prefer lead-free if it can be made to work - it's just simpler and there's nothing to gather debris or dirt etc.

 

[JungleShooter]

I'm not sure I would require Altaros slugs to be "lead free" (that's a whole different thread on environmentalism ).


But I sure would like to see Altaros (or any other manufacturer) to offer something with a dream BC of 0.2 ➔ but a bit lighter than the ATP 49.5gr (.25) slugs.


Because I like compact guns — which makes it hard to get heavy projectiles up to speed.
(But then again, that's just me and my compact obsession. I will probably get at least one comment from you guys telling me to get a life and get a dedicated slug gun with a proper 700mm barrel. And you're probably right. )


Matthias

 

[JDGriz]

@JungleShooter Yes, that depends on what is more aerodynamic; shorter or less dense, given the same weight. But I suspect less dense, for a meaningful decrease in weight at those original lengths and weights.

 

[Ballisticboy]

That depends on depth of the hole and front ellipse-shape "sharpness". CoG should be easy to keep where needed, or close to original.
I would still prefer lead-free if it can be made to work - it's just simpler and there's nothing to gather debris or dirt etc.

Unfortunately, shortening the nose will move the aerodynamic centre backwards towards the CG, making things worse, not better as far as group size is concerned. It will change the moments of inertia, which may or may not improve what you are trying to achieve. The overall shape and length have to be balanced with the available twist rate to achieve the desired performance.

 

[JDGriz]

@Ballisticboy How about making the nose (relatively) pointier?

 

[Michael]

I've seen a few articles that may support this (or rather focus attention on the projectile over the barrel type):

TacomHQ
Why rifling has minimal effect on BC, a bullet’s drag.
The following images exhibit Schlieren photography, commonly used to capture fluid dynamics. In general (depending on the imaging technique) darker the line, greater the fluid density.
We can visually appreciate the position of the grooves cut by the lands are often within the primary and secondary shockwave thus yielding little effect, but this obviously can change depending on bullet design.
While this offers a simple, visual representation, Applied Ballistics LLC shot over 1200 Berger .375 cal 407gr Solids through their 375 EnABLER to formally quantify the effect of rifling, fire cracking, etc.
The top plot consists of points that represent 5-shot groups that change color every 100-rounds to identify a bore clean. The bottom plot trends the deviation in BC to round count where we see the loss equates to only 1-2% on a “shot-out” barrel.
Consequently, imperfections and non-uniformity in the grooves cut by rifling have minimal effect on the projectile itself compared to other variables like CG, principal axis tilt, the barrel, and muzzle exit.

Applied Ballistics LLC
How much do riflings affect BC?
Based on Doppler radar testing, the number and type of riflings have a very minor effect on the measured BC.
As a barrel firecracks and becomes rougher over its life, there is a measurable drop in BC - about 2% - which is more of a difference than we've measured for different rifling types (of the same twist rate)

 

[JungleShooter]

Talking about wanting high BC.... — I noticed that benefit of BC is not a linear progression (or however the math whizzes would word that, I probably said this wrong).

What I mean is this:
Let's assume a projectile of constant weight (18.13gr) and constant muzzle velocity/energy (33FPE).
Now, let's increase BC in even steps (say, 0.025) of that projectile.
However, the the gain in velocity/energy at target (say, 100y) does not increase in even steps.

See the chart below, showing the velocity at 100y of 4 projectiles, each with a BC increased by 0.025 (0.025 ➔ 0.050 ➔ 0.075 ➔ 0.100):

.025BC* = RED curve
.050BC = BLUE
.075BC = GREEN
.100BC = PURPLE





The same is true for wind drift reduction — it does not decrease in even steps (wind at 90⁰ with 8mph [13km/h]).
See chart below, showing the wind drift at 100y for each of the 4 projectiles.

.025BC* = RED curve
.050BC = BLUE
.075BC = GREEN
.100BC = PURPLE




➠ My layman's conclusion:

For practical, every day shooting of a majority of shooters the greatest benefit will come if the manufacturers can increase the BC at the low end, i.e.:
▪ Getting a hollow point with 0.020BC up to 0.030.
▪ Getting a dome with 0.030BC up to 0.040.
▪ Getting the larger caliber pellets with their low-BC-for-weight-BC into the 0.050's and 0.060's.


Cheers,

Matthias


*Yes, I know that technically BC is a number that does not have a unit of measure, like distance has "miles" and temperature has "Fahrenheit." — But, to me it's seems to be a clearer way to write it.

 

[Ballisticboy]

@Ballisticboy How about making the nose (relatively) pointier?

Moves the aerodynamic centre further back again. Of all the nose shapes, conical has the furthest aft centre of pressure. The curvier they are, the further forward it tends to get.

 

[Ballisticboy]

Talking about wanting high BC.... — I noticed that benefit of BC is not a linear progression (or however the math whizzes would word that, I probably said this wrong).

What I mean is this:
Let's assume a projectile of constant weight (18.13gr) and constant muzzle velocity/energy (33FPE).
Now, let's increase BC in even steps (say, 0.025) of that projectile.
However, the the gain in velocity/energy at target (say, 100y) does not increase in even steps.

See the chart below, showing the velocity at 100y of 4 projectiles, each with a BC increased by 0.025 (0.025 ➔ 0.050 ➔ 0.075 ➔ 0.100):

View attachment 430943
.025BC* = RED curve
.050BC = BLUE
.075BC = GREEN
.100BC = PURPLE





The same is true for wind drift reduction — it does not decrease in even steps (wind at 90⁰ with 8mph [13km/h]).
See chart below, showing the wind drift at 100y for each of the 4 projectiles.

View attachment 430944
.025BC* = RED curve
.050BC = BLUE
.075BC = GREEN
.100BC = PURPLE




➠ My layman's conclusion:

For practical, every day shooting of a majority of shooters the greatest benefit will come if the manufacturers can increase the BC at the low end, i.e.:
▪ Getting a hollow point with 0.020BC up to 0.030.
▪ Getting a dome with 0.030BC up to 0.040.
▪ Getting the larger caliber pellets with their low-BC-for-weight-BC into the 0.050's and 0.060's.


Cheers,

Matthias


*Yes, I know that technically BC is a number that does not have a unit of measure, like distance has "miles" and temperature has "Fahrenheit." — But, to me it's seems to be a clearer way to write it.

We really need to be getting away from BC's and use purpose drag laws more if we want to see how to improve things. We need detailed drag breakdowns of all of the separate parts of the projectile, otherwise we may spend all our time trying to reduce the drag of something which is relatively unimportant. For example, we may concentrate on the nose of a pellet but, unless we are shooting at 1000 ft/sec or above, a round nose contributes very little to the overall pellet drag. Base drag is a much bigger component. For a wadcutter it is different, there the nose has a large contribution to the drag, unless the edges are slightly rounded off when the nose drag will plummet.

 

[weevil]

I'm not sure I would require Altaros slugs to be "lead free" (that's a whole different thread on environmentalism ).


But I sure would like to see Altaros (or any other manufacturer) to offer something with a dream BC of 0.2 ➔ but a bit lighter than the ATP 49.5gr (.25) slugs.


Because I like compact guns — which makes it hard to get heavy projectiles up to speed.
(But then again, that's just me and my compact obsession. I will probably get at least one comment from you guys telling me to get a life and get a dedicated slug gun with a proper 700mm barrel. And you're probably right. )


Matthias

Can you settle for a BC of 0.18 and 56fpe?

FX - Wildcat compact 22 and Altaros slugs👍

Another winter tinker that could be a long winded story but I’ll cut to the chase. It concerns my FX Wildcat, which has served duty in many configurations from 177 to 30 in compact (500mm) and sniper (700mm) form. It started out as a Mk3 tubed version and was converted to a BT through the...

www.airgunnation.com

 

[Engg.Ken]

I feel that a pellet or slug which is consistently made over its production lifecycle is better than the rest.