Sitting here at work stuck on a computer and pondering some shooting I did yesterday, which led me to decide to post on the subject.
As I've commented in a couple places already, I've got a Veteran Long .22 that was purchased with hopes of shooting the JSB 25.39gr Monster RDs for specific use as my long range pellet shooter. I've been playing with this gun off and on since I bought it, but the initial chrono testing and hammer tension adjusting were done with the focus being power and the 25.4s. I arrived at a pretty stable fps/hammer adjustment with the chrono in my garage, getting 900-910fps for about 46fpe.
I found out on the first attempts at 100 yards that the 25.4s were no bueno, sending flyers (spiraling as well as curve balls). I tried them at various speeds (reducing hammer tension little by little) down from 910fps and they didn't get any better. After that 25.4s disappointment, I tried the 18.1s, same day and no chrono with me. I found a place that was producing pretty good accuracy. This was the cherry picked best group from that morning, with the 18.1s- a little off center, but I think 5 shots around moa.
When I got home I was curious to see how fast they were going at that seemingly most accurate setting. Very surprised to see them going 940-950fps (for about 35-36fpe).
I've always read and been told that the true diabolo (skinny waist) pellets will give best accuracy/least wind deflection, etc in the 860-880 range.
Fast forward a couple weeks and I've been shooting this gun at pdogs and killing some at pretty crazy distances. I also took this gun and shot it at the recent Heavy Duty American Field Target competition down in Phoenix......and got skunked. I was feeling pretty confident with the gun prior to the comp but it did not go well for me. I think I was second to last, among 20 competitors. The only guy with a worse score than myself was shooting 30-32fpe. The top of the heap were shooting much heaver (and better BC) pellets up around the 50fpe range.
(I've pulled the barrel and found that it has an extremely tight choke and I think that's why it doesn't like the 25.4s, but that's a whole different ball of wax).
Back to the 18.13s though. I was amazed at the wind deflection I saw during the competition. Some of the 80+ yard shots were requiring 2 or 3 FEET of holdoff for the wind, and then the next shot, ZERO hold-off. That got me to thinking, "I wonder if the extremely poor results in the wind are because I'm shooting them so fast?" Which led to the question, "will the 18.13s have less wind deflection if they're only going 860-880 like conventional "wisdom" suggests?"
All of that got me to the testing yesterday: BC collection of the 18.13s at 870fps vs 940fps.
Using the fps at two distances method and each fps is the average of 10 shots taken at that distance. ES were pretty small for each of the 4, 10 shot groups.
BC of 18.13s @ 35.62fpe (940.5fps)= 0.0340
BC of 18.13s @ 30.5fpe (870.3fps) = 0.0358
0 and 48 yards= two distances at which fps was collected.
So, calling that 0.034 and 0.036. Yes it is slightly better, but I expected to see a much better BC at 870fps. The difference here is quite likely marginal and inconsequential. A difference of 0.0018 probably isn't going to matter much.
I also decided to shoot some ten shot groups at 870 and some more at 940 to see if any trends could be seen. (left column 870fps, right column 940fps). 81 consecutive shots and pulled a couple.
There was a slight (5-10mph) wind from the left to the right. That can be seen a little on the left column, as the groups are to the right of the center of the dime just a bit. Again, though, the groups on paper seemed pretty inconclusive, lacking a significant difference in either group size or location.
Doing some digging, I found where Robert Sterne made some comments back in 2018, specifically regarding the JSB 18.13s. Here is a screen grab of his contribution to that discussion
(entire conversation found here, if interested: https://www.gatewaytoairguns.org/GTA/index.php?topic=148410.0)
From his graph, it would appear that the difference in wind drift from the 18.13s between 850 to 950 is in the <1/4 of an inch range at 50 yards.
And there you have it, my external ballistics ponderings (sprinkled with some always helpful thoughts from Rsterne) of the morning.
As I've commented in a couple places already, I've got a Veteran Long .22 that was purchased with hopes of shooting the JSB 25.39gr Monster RDs for specific use as my long range pellet shooter. I've been playing with this gun off and on since I bought it, but the initial chrono testing and hammer tension adjusting were done with the focus being power and the 25.4s. I arrived at a pretty stable fps/hammer adjustment with the chrono in my garage, getting 900-910fps for about 46fpe.
I found out on the first attempts at 100 yards that the 25.4s were no bueno, sending flyers (spiraling as well as curve balls). I tried them at various speeds (reducing hammer tension little by little) down from 910fps and they didn't get any better. After that 25.4s disappointment, I tried the 18.1s, same day and no chrono with me. I found a place that was producing pretty good accuracy. This was the cherry picked best group from that morning, with the 18.1s- a little off center, but I think 5 shots around moa.
When I got home I was curious to see how fast they were going at that seemingly most accurate setting. Very surprised to see them going 940-950fps (for about 35-36fpe).
I've always read and been told that the true diabolo (skinny waist) pellets will give best accuracy/least wind deflection, etc in the 860-880 range.
Fast forward a couple weeks and I've been shooting this gun at pdogs and killing some at pretty crazy distances. I also took this gun and shot it at the recent Heavy Duty American Field Target competition down in Phoenix......and got skunked. I was feeling pretty confident with the gun prior to the comp but it did not go well for me. I think I was second to last, among 20 competitors. The only guy with a worse score than myself was shooting 30-32fpe. The top of the heap were shooting much heaver (and better BC) pellets up around the 50fpe range.
(I've pulled the barrel and found that it has an extremely tight choke and I think that's why it doesn't like the 25.4s, but that's a whole different ball of wax).
Back to the 18.13s though. I was amazed at the wind deflection I saw during the competition. Some of the 80+ yard shots were requiring 2 or 3 FEET of holdoff for the wind, and then the next shot, ZERO hold-off. That got me to thinking, "I wonder if the extremely poor results in the wind are because I'm shooting them so fast?" Which led to the question, "will the 18.13s have less wind deflection if they're only going 860-880 like conventional "wisdom" suggests?"
All of that got me to the testing yesterday: BC collection of the 18.13s at 870fps vs 940fps.
Using the fps at two distances method and each fps is the average of 10 shots taken at that distance. ES were pretty small for each of the 4, 10 shot groups.
BC of 18.13s @ 35.62fpe (940.5fps)= 0.0340
BC of 18.13s @ 30.5fpe (870.3fps) = 0.0358
0 and 48 yards= two distances at which fps was collected.
So, calling that 0.034 and 0.036. Yes it is slightly better, but I expected to see a much better BC at 870fps. The difference here is quite likely marginal and inconsequential. A difference of 0.0018 probably isn't going to matter much.
I also decided to shoot some ten shot groups at 870 and some more at 940 to see if any trends could be seen. (left column 870fps, right column 940fps). 81 consecutive shots and pulled a couple.
There was a slight (5-10mph) wind from the left to the right. That can be seen a little on the left column, as the groups are to the right of the center of the dime just a bit. Again, though, the groups on paper seemed pretty inconclusive, lacking a significant difference in either group size or location.
Doing some digging, I found where Robert Sterne made some comments back in 2018, specifically regarding the JSB 18.13s. Here is a screen grab of his contribution to that discussion
(entire conversation found here, if interested: https://www.gatewaytoairguns.org/GTA/index.php?topic=148410.0)
From his graph, it would appear that the difference in wind drift from the 18.13s between 850 to 950 is in the <1/4 of an inch range at 50 yards.
And there you have it, my external ballistics ponderings (sprinkled with some always helpful thoughts from Rsterne) of the morning.
I'm sorry that this barrel has not delivered what you wanted — with the tight choke and all.
— more wind if at a different angle.
Keep us in the loop on your quest for better long range precision, Franklink! 
Attachment Slug Specs Table
— I've been contemplating a power plenum for a good while now...! "I'm fighting it pretty hard, but...."