Pellet corkscrewing

[LDP]

Everyone has covered lots of stuff to check so I wont get into more of that. 800 fps isnt slow for 100 yd shooting. Its not used as much as 875+ but its still viable. You have more drop and more wind drift than running 900 fps but thats why scopes can be adjusted. I have my 380mm .25 barrel set at 725 fps with 25 gr. JSB on one of my crown mk2’s for pesting and hunting when I need a short platform and stupid quiet. I shoot it at 100 yds and its deadly accurate still and has 17 fpe at 100 yds. Starlings, house sparrows, collard doves or anything similar will be toast. I have no doubt it will knock ground squirrels flat with head shots at that distance. I run my .30 and longer barrel .25 Just above 900 if I need that power or need help with wind drift at 100 but 800 fps with the 25 gr. JSB is still very potent at 100 yds. I dont know what your target at 100 yds is so you may need more power than 800 fps.

 

[Bobbybeef]

Also you said it was an FX barrel. I know I’ve seen post were people had issues with diagonal pellet drops. They ended up having to index the barrel. I wonder if this is more likely the issue.

My daystate revere spiral also

 

[qball]

The slug liner indeed has way too much twist rate for pellets but I had awesome accuracy with the slug liner shooting pellets but it is far more tune sensitive.

I can almost bet money you regulator is at 90 bars or less, turn your regulator to 120-130 and find 940 fps with valve at 4 lines then turn down the valve till you reach 900-920 and it will be a laser beam.

 

[bigHUN]

My custom .22x500mm poly barrel for Leshiy2 spiralled the 25.4 MRD's so bad, I re-crowned - cleaned - washed - polished the barrel, weight and size sorted the diablo, tried all speed testing between 800 and 970, and still. I bought five other brand and weight pellets, and still I cannot get a 1" group @50.

 

[bigHUN]

Regarding what to look & feel for, here's a DIY guide I drafted up a while back.

Barrel troubleshooting and accurizing how-to - Airguns & Guns Forum

Barrel troubleshooting and accurizing how-to, Air guns, Airgun Forum

www.gatewaytoairguns.org

I always forgot to ask you about the "Knock down the sharp transition between the leade and the bore"
Is the "lead" length or dept to call it - dimensionally critical? I assume not really because we have shorter and longer pellets, only to make the transition smooth ???

 

[nervoustrig]

For the most part pellets are not particularly sensitive to the leade length and geometry. Consider an extreme example like the original Smooth Twist barrels where the pellet doesn’t encounter the rifling until it’s almost to the muzzle. Still it achieves very good accuracy, albeit having a distinct preference for JSB pellets.

Speaking more generally, we want the pellet seated so at least its head is supported in the rifling so it is does not have an initial yaw when the pressure pulse hits it from behind. The skirt can be in the rifling or not...it is oversized, meaning the back end of the pellet is supported even if it is in the freebore section.

Granted there are some benchrest guns fitted with an adjuster to fine tune the seating depth. It’s not a magic wand of course. Guns without such an adjustment win all the time. It’s just one more thing in the toolbox.

Meanwhile slugs are a different animal. Here the goal is usually a very gentle taper into the rifling, and there is usually some experimentation involved in finding the optimal depth.

 

[Vetmx]

Chamber a pellet then pull the barrel out of the gun. Take a peek into the transfer port and you might have your answer.

 

[TDK]

From a big picture, it has to be one of three categories:
1. Damage to the pellets done by loading, firing (Vetmx suggestion above) or barrel damage
2. Barrel twist rate too fast
3. Bad batch of asymmetrical pellets.

I would guess it is probably a combo of 1 and 2. There is some damage occuring and the fast twist rate is exacerbating the spiraling. Looking at liner twist rates, old Slug A is 1:20, new Superior Heavy is 1:18. New Superior standard is 1:24, and that is already a compromise to try and support FX hybrid slugs. The old Pellet liner A was 1:27. A 1:20 twist is going to be heavily biased towards the slug side.

Not quite apples to apples, but in .30 cal, the superior standard (1:22) is known to have less accuracy with pellets at longer ranges

 

[bigHUN]

I did the math simulation for the 700mm liner (type of barrel) and there is not much of a difference between 1:15 and 1:30 twist rate ones the pellet catches the RPM. The only difference is in the very first 2-3" of a "moment of inertia" and ones the pellet start travelling=following along the rifling, the remaining length is ""stable RPM"".

 

[SkeeterHawk]

I had this same problem on a 2240 that I modified. The barrel wasn't lining up with the breech exactly. I basically had to re-crown the breech side of the barrel to alleviate the problem. I'm not saying that you would have to re-crown an FX barrel as I'm sure that they have that part figured out, but as @nervoustrig and others have mentioned, this could be the issue. Perhaps when you took your barrel out or something, there is something misaligned, or even some debris behind the barrel that is "scratching" the pellets on the way in. Anyway, I don't know how much this helped, but that's my $0.02

 

[Feinwerk]

@Ginuwine1969 ,
Did you find the cause of the spiralling?

 

[Ginuwine1969]

Yeah swapped the 600 mm barrel for a 700mm and it stopped.

 

[Feinwerk]

Glad you got it fixed. Wonder what was wrong with that 600mm barrel.

 

[The Codger]

 

[Ginuwine1969]

Yeah, got tired of messing with it. It was my slug A liner barrel, I but figured everyone else was shooting 700mm for 100 yard or more bench so that is the route i went and it stopped.