Groups sizes versus distance. Proportional?

Guess #1) When you change ranges, you need to adjust side focus on your scope for paralax. In a perfect scope, the cross-hairs will perfectly track. Most scopes don't have perfect tracking, so depending on where you visually set the focus for paralax, the cross-hairs might not be exactly centered.

Guess #2) For "ideal conditions", you'd need an indoor range that does not have air circulation. Wind generally is not a constant for the entire length on your further shots. Wind direction changes, gusts, swirls..and all impart directional forces.

Guess #3) Borrowing a term from archery..Parachute Drag..you can have great groups up close that deteriorate as distance increases. Essentially, if your projectile has too much drag, then that drag has a greater negative effect the further the projectile travels and the more it slows. More drag equals more slowing equals group deterioration..

https://www.castlearchers.com/archery/v/10-bow-tuning-guide-by-easton/

On Page 9.

Excessive drag will cause the arrow to become unstable due to the rapid decay of its forward velocity. When forward velocity drops too quickly, instability occurs. This unstable flight causes poor grouping at long distances and extreme vulnerability to wind drift. On light weight arrows, it is very important to reduce drag to a minimum to maintain maximum downrange velocity. This can be done by reducing the size (height and/or length) of the fletching or by reducing the angle of the fletching, or both.

Click to expand...

Skirted pellets probably just have too much drag. Great at close range..not so good as the velocity decreases. In archery, you see the drag created by fletching size and the amount of offset. Close range hunters use huge 5" vanes or feathers with helical or lots of offset (degrees from 0)...for stabilization. FITA shooters (90meters) use 1.5" vanes with little or no offset. Sounds like skirted pellets and slugs..right?

While the drag theory sounds plausible, it has been demonstrated that pellet BC can actually improve as distance increases. Much of this is due to the speeds they are being shot.


I would agree that it’s probably just wind. It’s extremely difficult to predict the effects of wind at 25m....let alone 100y. I was looking for a place to shoot indoors at 100y and after thinking about it more I realized that it would be highly unlikely that I could find still enough air in a large building to make any productive use of the testing. My results indoors at 25m can be influenced by just opening a door. The wind effect squares with distance so the influence at 100y is 16x the influence at 25.

Mike 

Mike are you talking about air rifles specifically or all fire arms? From my experience with fire arms under ideal conditions the group sizes are some times proportional. Everything has to be totally right with the world but it can happen. 

I think at the extreme limits of a cartridge/bullet combination perhaps when they fall below a certain velocity the proportionality falls apart. Instability of the projectile maybe ( certainly see this with pellets)

There are lots of variables and it's hard to eliminate all but one making it difficult to determine what is having the results on target.

I know for me shooting pellets beyond 75 yards can get frustrating. Shooting heavier pellets at higher velocities extend the range.

Where I work I can easily shoot Indoors to a 100yd and beyond, but it proved pointless!, just as you said, probably worse because of thermals I had to deal with? I might as well tested outside, I was flustered, but it was an experience!

Where I work I can easily shoot Indoors to a 100yd and beyond, but it proved pointless!, just as you said, probably worse because of thermals I had to deal with? I might as well tested outside, I was flustered, but it was an experience!

Click to expand...

I've had the same experience. I was expecting an indoor range to be a real advantage for testing. Didn't happen. 

Might also include holding your aim steady as 2x the distance ,just a little variance or movement makes a big difference in poi. 

Another thought on drag.

Drag is a function of velocity squared. A small change in velocity will create a different drag. The faster you push something the more drag it has. More drag equals quicker deceleration, all other things being equal.

Since most airguns don't shoot "DUP"s over the chronograph for a given series of shots, it would be safe to assume there will always a drag difference.

A group size difference at longer distances would be something you'd almost expect to be the "norm", given shot to shot FPS variations in most airguns.

Yes wind, 

as an experiment wind flags were placed at 5 yard increments from 20 yards out to 90 yards. about 15 in total, spaced in a stagger pattern so as to not get any tails caught in any flags or stands

they were placed at 3. 4. 5. feet high. at various times during the day and pictures taken in 2001

also various tail material was tried, 2 variations of sail tail weight were the best and for the most part in short range benchrest they still are. 


what was taken as fact was to watch the wind swoop in between 15 yard increments

we then placed flags 2 yards apart in a similar staggered fashion. neat stuff as wind does not always push like a blanket but can push in one foot intervals or less



so from 50 yards out to 100 there may be as much or many as a dozen wind currents of different intensities, direction and duration


i like 6-8 flags from 15 yards to 85 yards and most times I watch for the flags not like the others to see when to pull the trigger



fascinating to watch and then learn

when you are done this introductory discussion in wind and wind flags, 

then perhaps you are ready to move onto the more difficult discussion



wind probes and lastly 





WAIT FOR IT



uppy downy flags, yes that is what they are called and were manufactured by brflags .com. a friend rick graham who still shoots in Tacoma Washington but has sold his flag making business



JEFF

In my decades of testing dozens of 50 and 100 yard capable airguns, my best 100 yard single groups and my best average group sizes are reasonably close to proportional with powerful .22 and .25 caliber air rifles; however .177s do not hold proportional accuracy to 100 yards.

Examples- the best single 100 yard groups I've ever shot with air rifles measured .55 " center-to-center (with my .22 Brocock Bantam Hi-Lite) and .60 " center-to-center (with both my .25 Sam Yang Sumatra and .22 Shin Sung Career II 707). And the best single 50 yard groups I've achieved measured .17" c-t-c (with a .177 Shin Sung Career II 707) and .20" c-t-c (with a .177 Falcon FN-19)).

The best average 100 yard groups I've achieved calculated to 1.06" and 1.17" c-t-c (in both cases with aforementioned .22 Shin Sung Career II 707) ; and the best average 50 yard groups have calculated to .43" c-t-c (with both my first .22 FX Tarantula and aforementioned .177 Falcon FN-19).

INTERESTING (to me) is that none of the guns mentioned above were/are regulated PCPs; all are unregulated.

INCREDIBLY INTERESTING (to me) is the fact that in assembling the information above it occurred to me that none of the air rifles I've used in field target competition warranted a single mention here at (even) 50 yards. That's despite the facts two of them captured multiple State Champion titles (in three states; an HW100 and my RAW TM1000), and one captured an AAFTA Grand Prix National Champion title (the HW100). Go figure!

The players-



The .22 Career II 707 (.177 looks identical).





The .22 FX Tarantula.





The .22 Brocock Bantam Hi-Lite.





The .177 Falcon FN-19.

Thought I would post this as a pictorial refute of a comment made earlier.

Was retuning my rifle with the RD monsters. Took about 10 shots over the chrono. ES was 3...SD of 0. 


Mike 

That's PHENOMENAL, Mike!

I might have to pick up my Lucifer hotline , and sell my soul... again! (This time for a Thomas) 

Naw... I wouldn't even get enough for a down payment.

Haha....Don’t think it’s worth it Ron. You have enough guns, you could sell a few and probably not even miss them. How many guns can one guy shoot, anyway?Lol

Thought I would post this as a pictorial refute of a comment made earlier.

Was retuning my rifle with the RD monsters. Took about 10 shots over the chrono. ES was 3...SD of 0. 


Mike

Click to expand...

I assume you did not sort these pellets at all, Mike, correct?

No, no sorting. Just from the tin.

Mike....can you feel a difference in the gun at the top of the fill vs the bottom? I see the velocity is steady, but since you are working with different pressures...it must use more dwell as the pressure drops. Much like a well tuned unregulated mechanical gun. 


Mike

I see...I believe we are saying the same thing just different ways. You need less hammer strike with a lower pressure...but you have to hold the valve open longer to make up for the lower pressure. It’s a balance of volume...so to speak. 


Mike 

Thought I would post this as a pictorial refute of a comment made earlier.

Was retuning my rifle with the RD monsters. Took about 10 shots over the chrono. ES was 3...SD of 0. 


Mike

Click to expand...

Mike, with all due respect, I think you’re making my point. Your specific airgun is exceptional. It is also not representative of “most” airguns. Most airguns are lucky to get 2 or maybe 3 dup readings in a row..let alone getting them on a consistent basis.