Proper speeds

[overeasy]

So am I correct in stating that all Diablo style pellets will perform best generally at speeds less than 1,000 fps regardless of the caliber? So I may have a 17 cal and 25 cal that both perform best at say just as an example 865fps.

[anti-squirrel]

yes.

[fwbsport]

I use my HW95L .25 daily now with a Bushnell Trophy 4-16X SF with Match and Diablo JSB Exacts, as well as with The Eliminator .25, to find all very accurate clear out to 35 yards easy.  There is "drop" but as you pointed out sending a .25 pellet at the same speed as a .177 makes the .25 just as "flat shooting" as the .177 for all practical purposes.

My Beeman Falcon PCP will send out heavy .25s at 800 fps, the Theoben Eliminator at 705 fps, the HW95L and the HW80 are about 50 feet per second difference with the HW80 .25 going 625 fps.

As far as accuracy the larger diameter of the .25 will make "more hits" on the steel targets just for its ability to reach wider at impact or near impact.

Center to center accuracy will probably get down to the micrometers of accuracy between .25 and .177--which one actually does make tighter center to center groups.

My take on the .25 in my lowest velocity rifle, the HW95L, is that it is a Match Rifle clear out to 40 yards.  It is very very accurate--and the fact the barrel is lighter from being bored larger makes a difference in hold and vibration.  The HW95L .25 not only is Match Accurate, it is also the Quietest R9-HW95L rifle I have; and I have enough in the HW95L to say it if you look at my list.

[anti-squirrel]

I'll add some commentary here: Travis, the GTA owner, has extensively tested a boatload of airguns; he's encountered best accuracy in the 800-910 FPS range.  Does this mean that all airguns should strive for that?

Not at all.  Some can't.  Some are lower powered, like my 2400KT which can put 10 RWS Meisterkugeln wadcutters through the same hole at 25 yards using CO2 when I do my part.  Those .22 wadcutter pellets are moving barely 560 FPS.  My Lelya is equally if not more accurate.  My girlfriend has put a magazine (10 shots) in .25 Hades through the same ragged hole at 45 yards using a 1x reflex site.  IIRC, it is shooting near 880 FPS with the Hades but I neglected to write things down.  I know if I crank the speed up accuracy will start to suffer.

Above all, accuracy trumps power.  If you can't hit the target, there's no point cranking the power up.  Some airgun-pellet combinations are unpicky and hurl everything well.  Some are incredibly picky so you have to test a bunch to find what works at what speed and stick to it. 

A thumbrule for shooting is if you want lots of power but want to stick with pellets, you need to either shoot shorter distances to hold accuracy or move to a larger caliber.  The diabolo pellet shape is not the best for high-velocity shooting; that's the purview of slugs, and now is a great time to be an airgunner as we have a goodly number of slugs available in both store-bought and homebrew sizes and weights.

[overeasy]

Thank you both for taking the time to expound on a subject I’m sure has been pounded into the dirt.
Experimentation being key here.
And after all isn’t that where the fun comes in?
Again thank you!

[fwbsport]

What's being pounded into the dirt? 

What I've been pounding into the dirt all by my lonesome is the effectiveness and accuracy and ease of shooting of the HW95L in .25!

Nobody else has one!

I'd get another HW98 if it was available in .25, but with just the HW95L .25 I'm achieving better accuracy than with the HW98 .20!  I save the 95L .25 for killing things now!

[19Sheridan57]

   I will just add that not all Diabolos are the same. Like everything else in life, some are better than others . Different rifles may prefer one brand over another, too.

[Leaded]

I shoot JSB Heavy (10.34) .177’s at about 1100FPS with excellent accuracy. Maybe the cylindrical diabolo design is more stable at higher velocities?

[K.O.]

well I have a .22 Hatsan AT 44 Long... JSB 18g get spit out at 1030 fps...what surprised me is at 35 yards it is laser accurate...some time soon I will find out at what distance that accuracy falls apart... will not be surprised if it is in another 5 yards or so....I normally use  cast .22 30g BBT  in my AT.... Love the independence of it... The First shot cost ~100$ (just counting  the mold)...but the more I send rounds downrange the cheaper each shot becomes..

the Ruger 16g are very accurate in my 1322 pumpers as long as they are kept under about 750 fps... wadcutter pellets tend to like about 600-700 fps max...

oh forgot  PA has a good deal on the H&N Barracuda Hunters in the 200 count tins right now might want to give them a try... I know I ordered some...

https://www.pyramydair.com/product/h-n-baracuda-hunter-177-cal-10-49-grains-hollowpoint-200ct?p=1375

[Leaded]

I get similar good accuracies from 10yds to 75 with the JSB 10.34’s. Just haven’t done a lot of shooting beyond that other than a few NUAH targets @ 100

[subscriber]

It is generally true that there is not much to gain by driving diabolo pellets over 950 FPS.  It is generally true that their highest ballistic coefficient occurs at around 850 FPS; and that it drops like a rock when you go trans sonic.

I say, generally, because some pellets ignore these "rules".  Possibly by virtue of their specific shape; or due to the shape they acquire on firing:  If you launch a soft lead pellet with a thin skirt at pressures over 3000 PSI, the skirt balloons significantly.  The new shape may more closely resemble a cylindrical projectile in flight than the same pellet, launched at 1500 PSI, or less. 

So, some airguns seem to shoot diabolo pellets with surprising consistency, probably due to the distortion that often occurs with "magnum" airguns.

In any event, the actual ballistic coefficient, while possibly improved over the original diabolo shape, if the latter were accelerated gently to over 1000 FPS, is still probably so low that a significant amount of kinetic energy would be shed in the first 10 yards of travel.  Better to find a heavier pellet (or slug) in that caliber, to bring the velocity down to 950 FPS; or to use a larger caliber air rifle, with heavier pellets, at the same power level, for the job.

[Chris USA]

This might be of interest on the topic. Note that there are 10 parts (see links at top)

https://www.pyramydair.com/blog/2011/12/pellet-velocity-versus-accuracy-test-part-10/

[Fate]

It is generally true that there is not much to gain by driving diabolo pellets over 950 FPS.  It is generally true that their highest ballistic coefficient occurs at around 850 FPS; and that it drops like a rock when you go trans sonic.

I say, generally, because some pellets ignore these "rules".  Possibly by virtue of their specific shape; or due to the shape they acquire on firing:  If you launch a soft lead pellet with a thin skirt at pressures over 3000 PSI, the skirt balloons significantly.  The new shape may more closely resemble a cylindrical projectile in flight than the same pellet, launched at 1500 PSI, or less. 

So, some airguns seem to shoot diabolo pellets with surprising consistency, probably due to the distortion that often occurs with "magnum" airguns.

In any event, the actual ballistic coefficient, while possibly improved over the original diabolo shape, if the latter were accelerated gently to over 1000 FPS, is still probably so low that a significant amount of kinetic energy would be shed in the first 10 yards of travel.  Better to find a heavier pellet (or slug) in that caliber, to bring the velocity down to 950 FPS; or to use a larger caliber air rifle, with heavier pellets, at the same power level, for the job.

You got me intrigued, so I just fired two JSBs into a bucket of water from my D48 to see how their shape changed, a 13.43 gr and a 15.89 gr.

They both apparently touched the bucket, having a small indentation on one side (need a deeper bucket).

That aside, the recovered pellets definitely changed shape during firing. The light 13.43 gr shortened and the skirt blew out significantly, and the 15.89 gr belled the skirt but didn't get significantly visibly shorter, haven't measured either.

The changes must significantly alter their BC, as you describe. With my tuning and shooting inside at only 10 yards the BC likely doesn't come into play... but what has been interesting to me is that both these pellets make very small groups, with the lighter one grouping slightly higher than POA compared to the heavier one.

It will be interesting to see results at longer ranges, but one thing I'm fairly sure of... neither pellet will replicate the predicted trajectory of ChairGun due to the changes in the BC due to their firing-changed shapes.

In the pic the 13.43 grs are on the left and the 15.89 gr on the right, both with unshot pellets to their left. The two unshot 13.43s are first a pristine one, the middle one that I modify the shirt of to fit the loading port without falling out.

 

[Mossonarock]

I don't think this topic gets repeated enough nor do I think it gets researched enough.
Everyone keeps saying accuracy trumps power but how fast is too fast? How fast is too slow? What is that goldilocks zone where speed and accuracy are at their best? Does it change based on caliber? When I was buying my airguns, I didn't have answers to those questions. So, I bought .25 cal airguns in several power levels and different gun architectures, all springers, to acquaint myself. Of course, there were those here who thought I was just trying to go for power because "eww .25 cal." But that was not the case. So, I didn't get a lot of dialogue from other folks here that was meaningful to me. I was just trying to learn about answers I wasn't finding. So, what did I find? Maybe 700 to 800 fps and caliber didn't seem to matter. Anyone's experiences differ from mine?

[Ribbonstone]

With the idea that subjective evidence does not equal proof.


Have kept a couple of PCPs at +1040fps and thought I had some kind of "freakish-good" match up becasue they were accurate during testing all the way out to 80-100 yards.

time and use went by.

Maybe I did find a magic match up...maybe I didn't.

Getting out into the wide open...didn't shoot so well  as it had at the home range.

Eventually, realized that the home range was pretty much wind-protected over the first 20-25 yards.

20-25 yards is enough distance to bring the nearly transonic pellets to well sub-sonic before they got a fair chance at the random winds.

So had the situation where 20gr, at 1030fps was doing better at long range at 70-90 yards (wind sheltered for 20-25 yards) than 33gr. gr. starting at  800fps. at 75yards (same wind sheltered range).

BUt out in the wild open,were the wind gets a crack at them from  jump,the accuracy results reversed....the slow 33gr. were beating the fast 20gr.

Evidently the little tweaks of wind at near transonic speeds are cummulitive.  Once a pellet  it gets a lateral motiuon...it keeps it thoughout it's flight distance, and they pick up more lateral motion when exposed to wind while close to the speed of sound.

Anyway, it made me a believer of swapping to a heavier pellet (if there is one) once the chronograph starting blinkin out numbers in the middle 900's...and I've not has a reason to regret it once I get out into the wind-wild-younderlands.

[Fate]

That's good reading, Ribbon. Not exactly applicable to me with a springer, but information and insight I hadn't read before.

Who knows what lurks in the hearts of man... the PCP siren's song is always calling.

[subscriber]

Thanks for taking those pellet pictures, Jeff. 

I think that skirt bulging becomes more significant when an unregulated PCP is used to shoot the same pellets from 3000 PSI, down to 1000.  Even if the muzzle velocity were not that different due to a degree of "self regulation" at the valve, the difference in pellet skirt shape will almost certainly affect long range performance, due to the change in effective BC over that pressure range.

Obviously, a springer (that is not dieseling intermittently) will blow out the skirts on all pellets from the same can, to pretty much the same degree.  So, whatever is happening, that change in pellet shape should not drift over the next 100 pellets.  Or the next 500.  Different batches of pellets can obviously bulge to different degrees, due to different lead hardness and the exact die shaped used to make them.

Ribbonstone's observations support the general trend for projectile BC to drop off drastically in the trans-sonic speed range.  Even if the drop in energy does not matter with a lighter projectile, its lower BC means more wind drift.  And as observed, early wind drift creates an angular deviation that "points" the pellet in the wrong direction.  Then, the rest of the range to target simply amplifies the sideways deviation from the desired POI, even if the pellet were to travel straight from 25 yards on.

However, even if pellet BC generally peaks at 850 FPS, it may be beneficial to start faster because velocity drops off over range.  This is one of those things where understanding the basics is good. Then making up your own mind, based on your own situation; and your own results.   

The fact that the best pellets you could buy retain more energy at 100 yards and have less wind drift may not matter; if the pellets you have on hand still carry twice as much energy as required to get the job done, and hit the target every time, despite drifting more than the best ones money can buy.

[Leaded]

Here is a JSB Heavy 10.34 fired @ 1100fps  vs unfired from a gas ram.
Waist diameter increases, length shortens, waist to skirt transition smooths out, head to waist transition changes a bit as well but could be from impact with the water.

[subscriber]

I think Hector Medina had the most gentle pellet trap, and it was not water.  I could be confused, but I think it was a box full of cotton waste.  Will have to ask him...

I could certainly see a trashcan full of Styrofoam beads being a more gentle trap than water.

Why bother?  To be clear about which pellet distortion was from firing, and which from the sudden stop in the trap.  That said, firing distortion affects mainly the "tail end" and trap distortion affects mainly the "head end".

[Leaded]

BUt out in the wild open,were the wind gets a crack at them from  jump,the accuracy results reversed....the slow 33gr. were beating the fast 20gr.

This is interesting, the other day I was having accuracy issues at 30yds with a light to moderate crosswind so changed directions a little and was right on hitting a 3/4” group at 70yds in same wind but about 20 degrees shifted POA vs the 30yd target. Didn’t make sense at the time but maybe worth looking into with this concept (maybe certain wind conditions affect transonic pellets more).
I’ll  test in winds that cause a problem with the Heavy @1100 and compare groups to Monsters that run about 960-980 both have similar accuracies in the gun @ 30yds.