I hate seeing claims without proof and here I am doing just that, oh well, take it or leave it. 
So, I have been on a quest for .177 slug nirvana. I bought an Impact from douger to dedicate for that cause; it was shooting .22 very consistently, so yeah, a great base.
I tried the 500mm, and the 600mm barrels and they were great with pellets, but just ok with slugs, and not great with slugs past 60 yards. The only promising slugs were the JSB knock outs and the NSA 15.5s, but the NSAs are no longer made, so no joy there. The JSB 13.43 were tried after viewing Viking Airgunner's videos, thank you Pete - kudos to you!.
Then after searching high and low, viperjoe offered up some 700mm .177 superior barrel kits, which I have been waiting on and have been on back order forever elsewhere- thanks viperjoe!
So, I was shooting the JSBs at 875 fps, #4 on the HS, range 50 yards, which is where I always start. I saw no change (at 50 yards) #4 and up, so why waste air, I thought. Well today, after some plinking on a calm and windless day, I just happened to shoot at a madrone 101 or so yards away and figured out my holdover. I ended up adjusting from #4 to Max for less drop. Then, after establishing holdover, I shot at my first impact point, which disappointed me because I could not see where it hit. So I shot again, same thing. Then I shot again and noticed a small change in the original point of impact.
I then got out the spotting scope and could not believe what I saw- I was hitting well within an inch of the aim point. Those .177s are sure small at that range. I walked up the hill with a tape measure but the impacts were 15 feet up the tree, so I had to do an estimate, which based on the size of .177s, were well below an inch, actually closer to just over the width of my thumb.
That's my story and I am sticking to it.
I will set up targets and get photo proof on another day.
[edit] I forgot to mention, the overcast day yielded all errors on the chrony That too will come next time.
So, I have been on a quest for .177 slug nirvana. I bought an Impact from douger to dedicate for that cause; it was shooting .22 very consistently, so yeah, a great base.
I tried the 500mm, and the 600mm barrels and they were great with pellets, but just ok with slugs, and not great with slugs past 60 yards. The only promising slugs were the JSB knock outs and the NSA 15.5s, but the NSAs are no longer made, so no joy there. The JSB 13.43 were tried after viewing Viking Airgunner's videos, thank you Pete - kudos to you!.
Then after searching high and low, viperjoe offered up some 700mm .177 superior barrel kits, which I have been waiting on and have been on back order forever elsewhere- thanks viperjoe!
So, I was shooting the JSBs at 875 fps, #4 on the HS, range 50 yards, which is where I always start. I saw no change (at 50 yards) #4 and up, so why waste air, I thought. Well today, after some plinking on a calm and windless day, I just happened to shoot at a madrone 101 or so yards away and figured out my holdover. I ended up adjusting from #4 to Max for less drop. Then, after establishing holdover, I shot at my first impact point, which disappointed me because I could not see where it hit. So I shot again, same thing. Then I shot again and noticed a small change in the original point of impact.
I then got out the spotting scope and could not believe what I saw- I was hitting well within an inch of the aim point. Those .177s are sure small at that range. I walked up the hill with a tape measure but the impacts were 15 feet up the tree, so I had to do an estimate, which based on the size of .177s, were well below an inch, actually closer to just over the width of my thumb.
That's my story and I am sticking to it.
I will set up targets and get photo proof on another day.
[edit] I forgot to mention, the overcast day yielded all errors on the chrony
That too will come next time.
