Slug speed

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Turbo911

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Feb 25, 2022
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Worcestershire, United Kingdom
Hi for someone trying to understand the physics of pcp air rifle shooting can someone explain the optimal slug travelling speed,
for instance from all the info i seem to be reading watching 920-950fps seems to be the ultimate but why not 1050 -1080 fps ?,
i can pretty easily get my my M3 or Huben K1 up to these higher speeds in .25 cal which i would think higher speed = more power + flatter trajectory would = better accuracy, So what am i failing to see or understand ?
i,m learning so go easy on me……
 
I don’t think it’s about optimal speed. Some slugs do better slower, some faster. The important thing to know when shooting slugs (and not the only thing to know), is that wasted air from a tune is more detrimental to slug accuracy than almost anything else in an air rifle. Sure speed and twist rates are also very important, but if any wasted air is behind that slug when it leaves the barrel, the turbulence in the air alone will cause the slug to do odd things with its trajectory. If you can make those faster speeds possible without blowing a bunch of wasted air down that barrel, then I think you’ll see decent accuracy at many different velocities.
 
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With a slug, you go where it takes you. You can’t make it do anything. You can’t set speed parameters in your head and try to stick to them. The only thing you might want to concern yourself with as you follow some slug/barrel/slug combinations higher and higher trying to find accuracy is this. Did the engineers that designed your gun design it to be shot at the pressures you are now shooting at. Airguns are designed by manufacturers to handle the volume that airgun shooters shoot at normal settings. How long will your gun last with you pounding on it? How long will it remain consistent? I have two guns that with the slug that agrees with their twist, choke, and leade can be shot in the 800-900fps range out to 100 yards accurately without leaning on the gun real hard. A pokey slug out of an airgun going in the mid to upper 900’s will drop 8-9 inches at 100. If it’s going 1,050 it will be 6-7 inches. Nothing flat about that. Either way you have to make a precise adjustment to hit what you’re aiming at. That’s why you focus on nothing other than accuracy and consistency. And that’s if you ever even find it. The speed will be what it is.
 
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I've read that 950-975 is about the upper end of the typical subsonic safe zone, depending on atmospheric pressure & humidity. Designs with optimized ballistic coefficients can be pushed to 1,000 FPS and faster before transonic effects ruin accuracy. Increasing velocity to transonic, or coming out of the barrel supersonic but slowing to transonic before arriving at the target is likely to have a negative impact on accuracy.
 
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Vetmx said:
With a slug, you go where it takes you. You can’t make it do anything. You can’t set speed parameters in your head and try to stick to them. The only thing you might want to concern yourself with as you follow some slug/barrel/slug combinations higher and higher trying to find accuracy is this. Did the engineers that designed your gun design it to be shot at the pressures you are now shooting at. Airguns are designed by manufacturers to handle the volume that airgun shooters shoot at normal settings. How long will your gun last with you pounding on it? How long will it remain consistent? I have two guns that with the slug that agrees with their twist, choke, and leade can be shot in the 800-900fps range out to 100 yards accurately without leaning on the gun real hard. A pokey slug out of an airgun going in the mid to upper 900’s will drop 8-9 inches at 100. If it’s going 1,050 it will be 6-7 inches. Nothing flat about that. Either way you have to make a precise adjustment to hit what you’re aiming at. That’s why you focus on nothing other than accuracy and consistency. And that’s if you ever even find it. The speed will be what it is.
Click to expand...
Geeze i,m even more confused now than before i posted the thread or am i ?, as reading your reply over and over i am beginning to understand things thanks …..
 
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Just remember this. You don’t buy a Peloton and instantly look like the guy in the commercial. Same goes for slugs. You have just been watching slug commercials. Can you look like a Peloton or Bowflex guy? Yes if you have the right genetics, put in the work and eat sticks and twigs. Can you have success with slugs? Yes, but in some cases it would be easier to look like the Bowflex guy. It just depends on many factors. Some guns do pretty good right out of the box, others keep you chasing your tail. It also depends on your standards. If you have firearm standards, then you’re borderline delusional and really have your work cut out for you.
 
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Pellets are fairly simple to tune to.
Slugs? Welllllll not so much. My FX M3 22 loves Zan .218 23 gr shot at 970-980 fp. It shot them pretty well at 1050 too. By all the written word I should be able to shoot them very well out of an STX liner. Nope would not do that. Shot them out of a heavy slug liner and they are laser like.
Set my wife’s M3 up and her STX liner shot them better than a heavy liner. Neither liner shot them as well as my gun did at any velocity. Bumped her up to NSA .218 24.8 gr @ 960 and viola!!! We have a winner. There is no standard barrel or standard slug that performs well together.
The search and tinkering is what we lovingly refer to as the “rabbit hole” It ain’t for everybody but if you like to tinker, experiment and study slugs are great entertainment. If you aren’t that person you will get frustrated and swear slugs were invented to drive people crazy.
 
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Chukar60 said:
Pellets are fairly simple to tune to.
Slugs? Welllllll not so much. My FX M3 22 loves Zan .218 23 gr shot at 970-980 fp. It shot them pretty well at 1050 too. By all the written word I should be able to shoot them very well out of an STX liner. Nope would not do that. Shot them out of a heavy slug liner and they are laser like.
Set my wife’s M3 up and her STX liner shot them better than a heavy liner. Neither liner shot them as well as my gun did at any velocity. Bumped her up to NSA .218 24.8 gr @ 960 and viola!!! We have a winner. There is no standard barrel or standard slug that performs well together.
The search and tinkering is what we lovingly refer to as the “rabbit hole” It ain’t for everybody but if you like to tinker, experiment and study slugs are great entertainment. If you aren’t that person you will get frustrated and swear slugs were invented to drive people crazy.
Click to expand...
Well, I'm taking a side trip down the rabbit hole, ordered a couple of power kits from Huma for my Mavericks, 1 ea. .22, .25 pellet/slug, I'm sure I'll be spending more money somewhere down the line.
 
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madeintheuk said:
I don’t think it’s about optimal speed. Some slugs do better slower, some faster. The important thing to know when shooting slugs (and not the only thing to know), is that wasted air from a tune is more detrimental to slug accuracy than almost anything else in an air rifle. Sure speed and twist rates are also very important, but if any wasted air is behind that slug when it leaves the barrel, the turbulence in the air alone will cause the slug to do odd things with its trajectory. If you can make those faster speeds possible without blowing a bunch of wasted air down that barrel, then I think you’ll see decent accuracy at many different velocities.
Click to expand...
Yes, the extra air really affects the accuracy of the slugs. It is very evident at far distances. Below in the first picture is 3 lines on the Impact valve and the second picture is 1 line on the valve at 200 yds. All other settings on the gun were the same and one group was shot right after the other. The extra air on the first picture was with the valve opened just a little longer, which destabilized the slug.

IMG_20220924_145333595.jpg


IMG_20220924_145325945.jpg
 
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rappert said:
Yes, the extra air really affects the accuracy of the slugs. It is very evident at far distances. Below in the first picture is 3 lines on the Impact valve and the second picture is 1 line on the valve at 200 yds. All other settings on the gun were the same and one group was shot right after the other. The extra air on the first picture was with the valve opened just a little longer, which destabilized the slug.

View attachment 308290

View attachment 308293
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That’s an amazing change and an awesome 200y group! I’m still an Impact newbie… is the valve you are referring to the one above where the bottle attaches?
 
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I bought it because it can be a .177 through .35 caliber in one gun with the ability to adjust it to shoot pellets or slugs in any weight. Before I buy a powder burner, I usually have all the components to reload for it and many of my guns have never had a factory round shot in them. The Impact is as close to that as you can get!

The only experience I can relate to “dirty air” to is cast bullets in powder burners. A really fast powder like Bullseye can work well up to a certain charge and then accuracy goes to crap in a hurry. It’s hard to believe, even seeing it happen, that a group can go from 1“ to 4” with a grain of powder. A slower powder will increase speed through the length of the barrel with a lot more room for adjustment. So two different powders, same bullet, same fps but drastically different group sizes.

Is this a case of ”how you got this speed” that causes the dirty air?
 
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Turbo911 said:
Thanks for the reply’s i,m allready half way down the rabbit hole and enjoying learning.
i have recently set myself a range up at 50 & 100yds but been so windy here not had chance to spend a few hours playing with settings.
Click to expand...
Turbo911, you have plenty of data here to help and get you on your way. Be patient and make as few adjustments as you can.

Patrick
 
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Ultimately, everyone has different goals with their different air rifle setups. Some hunt, some do pest control, some shoot at different levels of competition. All airgun people are individuals, as are the guns/barrels/pellets/slugs they shoot. It is not as easy as just turning up the power and sending slugs down range. If you want a flat shooter for hunting and or long range shooting, here is my suggestion. First, set the gun up to shoot as powerfully as you can. Then, find a slug through testing that shoots as accurately as possible, with the smallest groups. Then, slowly adjust the setting downward (also trying a barrel tuner that M3) and see if the groups get smaller. Once you get the best slug/barrel/tune combination you can either stop, or keep going down the rabbit hole to perfection. Pretty good groups and perfect shooters are not easily had.
 
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hardairmagazine.com

The External Ballistics Of Slugs In Airguns - Hard Air Magazine

For the most part slugs in airguns act in a similar manner to pellets. But there are some subtle differences as we will see in this post.
hardairmagazine.com hardairmagazine.com

interesting to say the least . (Thanks to Bob Sterne)
950-1000 fps seems to be the sweet spot for slugs in pcp’s 290-305 m/s till about 200 meters . On even longer distances a 1050 fps could work well
 
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