Tumbling (pellet)?

[z324u]

I've been doing a bit of pellet testing with the wildcat (.25) the last few days. I have noticed something about the heavier pellets, and was wondering if it could possibly be tumbling? I know I've seen this before with firearms where the projectile is destabilized due to improper twist.... I really need to get a camera setup to see what i'ts doing in slow motion.

So far I get the best groups with Air Arms 25g with JSB 25g just behind it. From what I've searched on here and other places the 33g pellets should be a bit better, but that's not the case here. Looking at my barrel there isn't much that stands out. If anything, it looks better than most of the ones I see posted as far as clean machining of the rifling at the end of the barrel.

For what I'ts worth, even the 33g pellets are pretty accurate (to me). The furthest I've stretched it out is 100yds, and it's about 3.5-4" 
At 50yds it's almost pellet on pellet with the 25g, and maybe 1/2" with the heavier stuff. 

These are at 75yds below. You can really see the sideways punching of the paper on the bottom pic (33g).

25g JSB

33g JSB MKII

 

[fe7565]

Assuming your pellets are intact and not damaged....I would start with checking (chrono) your pellet velocity. Certain pellets are stable within fairly narrow velocities, especially past 50 yards. Usually between 850-920fps it's a safe bet that the pellets are stable.

Next check if there is anything clipping...albeit unlikely if you get pellet on pellet at 50 yards.

Check your shooting technique and/or your shooting rest.

Pellet head check/sizing may also help if you barrel likes a certain pellet head size. This is the most difficult to measure and may only give marginal/if any results unless your rifle is way off the standard pellet head sizes i.e. 5.52mm. The AAs are already one of the best, may want to try JSBs too and some Barracudas with slightly different head sizes for comparison.

 

[z324u]

I did chrono check each pellet before testing - I should have added that.

25 JSB - 902 ave
25 AA - 904 ave
33 JSB - 802 ave 
33 JSB II - 800 ave 

My regulator is still set to 140 bar as far as I can tell.

 

[fe7565]

Nothing else obvious stands out to me based on the info, except cleaning the barrel. Hope someone else can chime in.

 

[Ginuwine1969]

I'm seeing more and more JSB 34 grain pellets START to spiral further down range 75-100 yards, the first part of there flight is solid and the second have begins to open up, so it may be something with them slowing down then spiraling. Don't know for sure, i'm do know that my Tactic is shooting MKII's at 790 at the muzzle 680 @ 75 yards and 640 @ 100 yards.

 

[z324u]

Update - after resealing the gun, my velocity has moved up to an average of 915fps for the 25g and 789fps for the 33g. The 33g groups tightened up a bit, but the 25g JSBs and AAs seem to be the preferred pellet.

I am going to stick with the AA pellets, and order several tins today. From what I've seen (maybe just coincidence) there are far fewer bent pellets in the AS tins and the groups are about the same. Not to mention the AAs are 1$ cheaper per 350! 

 

[fe7565]

Great to hear that it improved. Reminds me that after I replaced the pellet-probe o-rig (external) on my Airwolf accuracy restored immediately. Apparently the air was blowing by during some shots.