Recommended speed of 109 yards for JSB KnockOut .251?

[SvilenP]

Hello colleagues, in May I did my first tuning in life, and in addition to cleaning, I put a power plenum, a new combat spring (both from Talon) and pushed a little with Dremel transfer port. As a result, I can now increase the speed / power more than the factory possible.

The rifle is Taipan Veteran long .25, which has a barrel LW 550mm with shock, 17.7 "twist.

I decided to start the tests with JSB KnockOut .251. At 50 m (54.7 yards) at an average speed of 271 m/s (~ 889 fps) and my current setup and opportunities I liked the result. / By the way, I lost 10 m/s (32.8 fps) due to the difference between slugs and pellets, barrel shock /

Then I decided to try the 100m (109.4 yards). At top speed, I didn't like the result. I decided to increase the speed and made it at an average of 281 m/s (~ 922 fps) but I also don't like the result.

/ I apologize for the "decoration" but that's what it is./

Of course there are things that are a fact - on the one hand it is 25 caliber and can not be compared in accuracy with 22 (here some people will not agree for sure but this is my opinion). On the other hand the rifle is a bullpup and tying this to my setup at the moment, as well as the bad from the wind place where I shoot, it's a bit debatable if the result is bad (in my opinion) because of the speed, slugs, barrel, setup, me as a shooter or all together ...

But assuming the problem is speed, what speed would you recommend me to try with these slugs?
Thanks in advance!

PP. Since I ran out of the above slugs, I will now try H&N slugs - in both subcalibers (I took two sets of one of the two subcalibers), and then I have some VK slugs to sample. However, if someone advises me for a specific speed for the upper slugs, it will be useful for other slugs!

 

[Reidy]

From what I've seen, small adjustments in the hammer spring tension can make big differences at long distance. 

You say it has a plenum so I'm assuming it's regulated? Again, from what I understand if you're putting out more air than needed after the slug has left the barrel, it causes unstable air behind the slug. Reducing your hammer spring tension will release less air but still at the same pressure. 

I've seen this work well with people using FX rifles. 

 

[mercado]

I didn't find any slugs to be accurate in that 1-17-7 twist...I found it in the 177cal and. 22cal ..but not even 1 in .25..the only thing close to "acurate"..was a cast bullet..from mp molds but then I didn't have power enough to push it at least at 850fps .. bullet cast at 47g...I once use a tj 1-22 twist in a talon ss and pellets were more stable even at full power than my .25 taipan or cricket...I'm trying now to find a machinists to machine me one of those tj 1-22 for my .25 cricket..

 

[SvilenP]

Thanks for the answers colleagues. I'm still not that deep in the tuning of the rifle, and also my English is not so good, I use Google Translator for writing, so I will try to describe in more words what I understand from your posts:
1.Reidy:
The rifle has a regulator set at 150 bar (2175.6 psi). As far as I understand what you are telling me, I have to reduce the tension of the combat spring at which the valve will close faster and a small "portion" of air will be supplied. In other words, to lower the speed of the projectile a bit, something in between my two specified values ​​- for example 275 m/s (~ 900 fps)?

2.mercado:
Theoretically, I've read information about the twist rate, but unfortunately only for firearms. It was a question of using a longer or heavier bullet using a "slower" barrel, or in other words, for example, for AR-15 it was about 1:10, and for a lighter bullet - "faster" barrel: 1:7, 1:8.
However, I personally don't know about air weapons ... Obviously there is no analogy with firearms if you want to use a "slower" barrel?

Personally, if I could get one, I would try a polygonal tube without shock, but for now, alas. If anyone has information, from his own experience, in addition to Knockout, he can give me advice on other types of slugs, namely H&N and VK.
Thanks in advance!

 

[dannya1a]

look into NSA (Neilson Specialty Ammo). his slugs are really good.

 

[Reidy]

1.Reidy:

The rifle has a regulator set at 150 bar (2175.6 psi). As far as I understand what you are telling me, I have to reduce the tension of the combat spring at which the valve will close faster and a small "portion" of air will be supplied. In other words, to lower the speed of the projectile a bit, something in between my two specified values ​​- for example 275 m/s (~ 900 fps)?

It's not about reducing the speed of your slug, though that will be a small side effect, it's about reducing the amount of wasted air that's behind the slug that can destabilize it after it exits the barrel. If your barrel has a 'slow' twist rate then you need the slug to be moving quickly, so it spins faster to stabilize it correctly. It's about trying to use the air efficiently. Enough air to get your projectile going at the speed you need but only just enough air that it's done most of its useful expanding before the projectile leaves the barrel so that what is left over does not buffet the tail of the slug, pushing it off target. 

 

[SvilenP]

look into NSA (Neilson Specialty Ammo). his slugs are really good.

Thanks colleague, and I will get to them, but I have some considerations about the NSA. The point is that NSAs are not available in Bulgaria compared to JSB Knockout and H&N slugs and this will lead to a serious increase in the cost of supplying NSAs to me. However, I will try them later.

It's not about reducing the speed of your slug, though that will be a small side effect, it's about reducing the amount of wasted air that's behind the slug that can destabilize it after it exits the barrel. If your barrel has a 'slow' twist rate then you need the slug to be moving quickly, so it spins faster to stabilize it correctly. It's about trying to use the air efficiently. Enough air to get your projectile going at the speed you need but only just enough air that it's done most of its useful expanding before the projectile leaves the barrel so that what is left over does not buffet the tail of the slug, pushing it off target.

Thanks for your answer, I understand your idea, but I don't know how to achieve this? The idea is also good in terms of the fact that this will lead to more shots, but what I know at the moment and if we do not talk about replacing parts with others made specifically for this purpose, rotates or to reduce the pressure of the combat spring at which the valve spring will close faster or replace the valve spring with a stronger one which in practice seems the same to me, as an effect with the previous version or am I mistaken? Maybe it's not a bad idea for a strong valve spring?