Proper speeds

[Chris USA]

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".

I remember seeing a 4" PVC pipe with cap at one end and stuffed with pillow stuffing. About 4' long and packed not too tight and not too loose. As I recall,... it worked quite well. I have not done it, nor water.

[Ribbonstone]

What comes out isn't exactly what went in.

Smack them in the rear hard enough and pellets will obturate(expand their skirts) and scrunch down (shorten). 

Soft catch....the rifling marks show that what happened,had to happen in the bore.



Balistic media catch,so the nose is useless...but the base shows the obtration of this softer pellet.



Oversized pellets can get some scallop marks at exit....."fins".




For bolt probe loading rifles.  IF the bolt is wobbly or the probe bent, can end up seating the pellet a little cock-eyed.  Recovered pellets can show where the bolt probe contacted deep down in the hollow base.

[HectorMedina]

@ Chris USA;

That's right Chris, Good memory.

4" Dia. pipe, whether cardboard or PVC, doesn't matter. Dacron pillow stuffing, VERY loosely packed, 2' long should be enough to stop gently up to 24 ft-lbs 0.22" pellets. If you want to play it safe, use 3' and no cap at the end.

Upon recovery of pellets, look at the head with a mag glass. If there are strands, or prints of strands, then you are packing the pillow stuffing too tightly.

To ALL.-
You can read this:  https://www.ctcustomairguns.com/hectors-airgun-blog/at-the-moment-of-firing-and-fit-of-pellet-to-the-rifling

And, there is a good discussion here:  https://airgunwarriors.com/community/airgun-talk/ah-buhleeve/#post-38463

Truth is that we tend to group together things that are not that much alike: Waisted pellets are different from "column" pellets that are different from slugs.

Pellets are flange stabilized, not drag, not spin, not fin. FLANGE stabilized; for the most part. But NOT ONLY flange stabilized, so the real physics behind a waisted pellet with rebated secant ellipsoidal head are completely different from the domed head, two cones waisted pellet, and those are different from the column style (2nd Generation/current JSB heavies). Yes they are all pellets, BUT, they are all morphologically (shape-wise)  different.
You need to throw in the fact that the last swage die in the life of the pellet is the barrel itself, plus the fact that the most detrimental of all  motions to a flange stabilized projectile are the natural motions of precession, nutation, and yaw, that happen even to the most elementary top or dreidel.
Whenever a pellet starts spiralling, for all intents and purposes of the air-flow around it, changes its shape drastically.

MV affects ALL these factors, from the aerodynamics (surface pressure on different points of the pellet), to gyrodynamics (how stable the pellet is in its rotation), to the shape the air flow "sees" that is NOT the physical shape of the pellet, however pristine/deformed that may be.

Even Wikipedia consigns the fact that pellets are, GENERALLY, most accurate between 800 and 900 fps:
https://en.wikipedia.org/wiki/Air_gun

Last thing to consider is that, at the energy level we use, specially in spring-piston airguns, WE the shooters, take a role in the dynamics of the shot cycle.
In a 6.5X68 Vom-Hoffe (one of my favourite cartridges of all  times and dating back to the 1930's), the role of the shooter is just as an aiming mechanism. The gun/cartridge combination is either accurate or not. Little will 60 lbs of flesh and bones (weight of torso) can do for the shot cycle of a cartridge that yields a smidge under 3,000 ft-lbs. at the muzzle.

Now, 60 lbs out of 20, or 12? it's a different proportion altogether.

THAT is what is so fascinating about airguns. WE as shooters CAN, and DO, contribute to the shot cycle. Not so much in PCP's, but still a little.

Trying to come up with a general rule that applies to ALL airgun projectiles is not only humanly impossible, but scientifically incorrect.
Distinctions need to be made and all the principles understood, and we are FAR from that.

Best thing then, is to test. But test, knowing WHAT you are testing, and WHY.

Testing can be as simple as shooting groups at short range just to discard those pellets that are a HORRIBLE fit to your gun, to long range testing to determine what will be your "competition system", to very elaborate firings with instrumented sleds to record the shot cycle characteristics of a spring-piston airgun, to extremely expensive controlled firings of pellets with radar trackers to understand the exterior ballistics.

And, believe me, WE ALL CAN contribute to the knowledge base.

I am always learning from posts here. The diversity and the powers of observation of airgunners is always remarkable.

Keep well and shoot straight!






HM

[fwbsport]

The inside temperature of the springer keeps the mechanism DRY unlike PCP's, one good reason to use one--but how hot is the pellet that is sprung from a springer compared to a PCP?

I have a .25 Falcon PCP I never use; it has the accuracy and the power but the "fill up the tank again" thing and regulation v non-regulation and hammers and such doused me out of the PCP world.  I found the speeds of .25 caliber around 500-600 fps to be deadly accurate in the HW95L--more so than in .177 or .22.  The .20 has the ability to be shot just under 900 fps with good results clear down to R7 levels, and the same thing happens for me using the springer HW95L .25.

Then there is the size and length of the springer like the HW35E v HW95L v R1 v HW77K v HW97K v HW50.  I find the HW35E springer to be the most FASCINATING springer of all!  In .177.

I find calibers that work in certain rifles better; and rifles that will shoot ALL with precision (been shooting HN Pistol Match, JSB lites, HN Crow Magnums, and HN Match in the HW35E .177 and it doesn't care what I use I get the same fine accuracy I'm looking for at 25 yards)!

The proper speed can vary, then, on everything put together here.  Oh, and another word about that Falcon PCP, I can't keep up with the number of pellets I can shoot out of the barrel of a springer while using ANY PCP; that TANK has to be "reloaded" as well!

 

[overeasy]

This site is such a wealth of information and helpful and generous folks that we should all thank our lucky stars that such a place exists!
Dave

[Ribbonstone]

weird mix of post ideas....but have a "don't give a ship what happens to it" springer (about 16-17 foot pounds).

Lets see what it does if I induce it to not so good in co2 rather than air.

[K.O.]

here(at bottom of post) is a CFD result I found about a shotgun pellet @ mach .9 (about 1000 fps)... it can represent a JSB pellet in that they have true hemispherical heads... 

I drew some lines using paint... first line is at 2 calibers... second is at 2.5... and the line ends at 3 calibers... Thought it might help visualize how the skirts of different length JSB (and similar near hemispherical nose) round nose pellets ride in a low pressure zone... for example a .22 JSB 18g is about 1.4 calibers long and a .177 Sniper Mag is about 1.7 calibers long... so can imagine that with the flared out skirts also... so maybe gyroscopic stability assumes a bigger role at middle and high trans-sonic speeds... 

But... then take a look at a 15g bullet at the same length same .5 caliber nose... I reduced density for the missing mass...but can not control where  mass is missing from and mass towards the outside diameter  is more important to gyroscopic stability... so twist probably would need to be just a touch faster than shown... 

http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=inches&weight_unit=grains&bullet_name=.338+air&re_calculate=yes&boundary_layer=L%2FT&diameter=.177&length=.311&nose=.088&meplat=.001&drive_band=.177&base_diameter=.177&angle=0&boat_tail=0&secant_radius=&weight=15.4&density=8.7 

http://www.geoffrey-kolbe.com/cgi-bin/barrel_twist.cgi?diameter=.177&length=.31&nose=.088&meplat=.001&base_diameter=.177&angle=&boat_tail=&b_twist=17.7&secant_radius=&unit_length=inches&temperature=59&humidity=0&local_pressure=29.92&pressure=29.92&altitude=0&density=c_d&custom_density=8.7

so the sniper mag stand in slug shows about .94 for a stability factor from a L.W. barrel (17.7 twist)at 1000 fps... 1 is unstable so most likely it shows it needs enough flare stabilization going on to make up the difference...also  you will notice that the drag curve is pretty flat to about 600-700 fps and then at 1000 fps it is at about 7 times the drag... and that can give an idea/correlation of the length of the low pressure area that the skirt is riding in... now with the skirt vs the slug the drag actually rises at lower speeds instead of being flat as with a with a slug... more of a smile type drag profile...wonder just how  closely all this would match up with actual Labradar doppler results... 

would also love to see how different result would be with JSB with blown out skirts at say 600-700 fps  out of say an Mrod (3000 psi) and hopefully not blown out skirt of say a disco/maximus(2000 psi)... you can bet there is a difference in the drag curve...thus showing the need to do your own drop charts rather than just trusting a tool like chairgun... Chairgun does give a rough idea of what to expect tho... 

It is good to live in times that we have the tools to help shed more light on the whys and have a better understanding of how different pellets work... and how they can work out of different rifles and barrels... for instance send the above .177 round out of a barrel that is choked down to .172 groove and the round grows in length to .326...slight differences but there none the less...


http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=inches&weight_unit=grains&bullet_name=.338+air&re_calculate=yes&boundary_layer=L%2FT&diameter=.172&length=.326&nose=.088&meplat=.001&drive_band=.172&base_diameter=.172&angle=0&boat_tail=0&secant_radius=&weight=15&density=8.7 

http://www.geoffrey-kolbe.com/cgi-bin/barrel_twist.cgi?diameter=.172&length=.326&nose=.088&meplat=.001&base_diameter=.172&angle=&boat_tail=&b_twist=17.7&secant_radius=&unit_length=inches&temperature=59&humidity=0&local_pressure=29.92&pressure=29.92&altitude=0&density=c_d&custom_density=8.7