Weird pellet flight at 100yd

[Bramezy]

Fx Crown MK2 600mm shooting .22 25gr pellets 920fps at 100yd benchrest. Had some crazy flights. It would travel most of the way to the target in a nice arch then the last second it would spin off crazy to one direction or another by several inches. It was very erratic. Didn’t happen everytime. Only a handful of times but it was enough to cost me points.
Im shooting the stock setup and liner. Wondering if the speed needs to be higher or slower as maybe it’s destabilizing then? No issues at 50yd, stacks em.

 

[igolfat8]

I’m certainly no expert at that distance, or any for that matter. By what you are describing it sounds like the pellet is stable most of the way then destabilizes so I might think that more velocity might help? However, I would defer to others with more knowledge and experience.

 

[Motorhead]

Slow em down @ 20-30 fps & try again. ( IMO the most likely )
That don't work or gets worse ... can always try faster, but that just increases the RPM of them & the forward speed will still degenerate faster than spin does & pellet will again wobble / spiral at some point.

 

[JimNM]

Rather than destabilize, I suggest that the pellet is over stabilized. Like when you drive your bike too fast and get the dreaded front wheel wobble o' death.

I agree with Scott/Motorhead.... Just a touch too fast rotationally. Slow it down a little bit and see it that helps. A different pellet will act differently, too. Change speed or change pellet to correct the issue.

For those who are numbers nerds, run the math on the rotation speed. It will blow your mind how fast a 1 in 16 barrel spins a pellet. Make it easier, do a 1 on 18...1.5 feet to a rotation.

920(fps)/1.5(twist ratio)*60(sec to minute)
36,800 rpm

Easy to see how as the forward speed decays due to BC, the ratio between rotation and linear speed can get out of balance.

 

[Bramezy]

Thanks. Ill try that.

 

[nervoustrig]

Overstabilized as a starting condition, which then becomes unstable downrange.

 

[Centercut]

It seems like the key is “only a handful of times”. If it was over stabilization resulting in instability would this happen all the time? I think you need to increase the speed to between 960 and 980 fps. Worst case it will delay the instability distance… Could be a bad batch of pellets. .22 RD Monsters are notorious for poor quality and throwing flyers. Some will tell you it’s always the barrel and never the pellets, but I don’t buy that….

 

[Airgun-hobbyist]

... when you drive your bike too fast and get the dreaded front wheel wobble o' death.

Off topic for a safety concern...

@JimNM Check the preload tension on the steering stem bearing nut. A lot of times the head shake wobble comes from the loose steering stem and neck bearings unloading and changing the front end geometry. The bearings become scalloped within the race over time because they don't turn very far. Depending on the bike design, an easy way to tell if things are loose is to grab by the steering neck and stem nut with your left hand and pump the front brakes a couple times real hard while traveling fairly slowly. If the neck is loose you will likely feel the slop there when the front tire bucks and pulls inward, rolling the stem and handlebars forward (unloaded) and then back (at rest, cruising).

 

[airgunmike56]

Off topic for a safety concern...
Very very good, I have always jaked the front wheel up and pulled on it foreword and backward any slop or movement is a no go,,

Mike

@JimNM Check the preload tension on the steering stem bearing nut. A lot of times the head shake wobble comes from the loose steering stem and neck bearings unloading and changing the front end geometry. The bearings become scalloped within the race over time because they don't turn very far. Depending on the bike design, an easy way to tell if things are loose is to grab by the steering neck and stem nut with your left hand and pump the front brakes a couple times real hard while traveling fairly slowly. If the neck is loose you will likely feel the slop there when the front tire bucks and pulls inward, rolling the stem and handlebars forward (unloaded) and then back (at rest, cruising).

 

[JimNM]

Have had the wobble a few times on my bicycle as a kid. Thanks thougu, all the same.

The interaction between the drag stabilization and the spin stabilization is dynamic, changing at a constant and predictable rate. I am not a calculus guy, geometry is more my speed. Stabilization is a relative term - the pellet follows an arcing path while in flight - but some how does not strike the target (usually!) in a nose high attitude. Hmmm, some point along the path, it must somehow (drag effect) orient the nose of the pellet along the flight path. The pellet continues to wobble a tiny bit as the drag and the spin forces remain somewhat in balance. When the drag force declines due to loss of linear velocity, the spin stabilization overpowers the drag stabilization, resulting in deviation from flight path in unpredictable and exciting directions.

At least that is how I understand some of the science. I am wrong twice a day, and it is still early.

 

[Raider03]

Fx Crown MK2 600mm shooting .22 25gr pellets 920fps at 100yd benchrest. Had some crazy flights. It would travel most of the way to the target in a nice arch then the last second it would spin off crazy to one direction or another by several inches. It was very erratic. Didn’t happen everytime. Only a handful of times but it was enough to cost me points.
Im shooting the stock setup and liner. Wondering if the speed needs to be higher or slower as maybe it’s destabilizing then? No issues at 50yd, stacks em.

I have heard multiple times, 970fps for the 22cal 25grain MRD in an FX.

 

[stanginthe11s]

I'm gonna use the excuse of out of balance pellet. question though, if this happened only a hand full of times and I'm guessing on the same day could it not be atmospheric condition related? swirls that can't be seen? turbulence at a given spot? etc.

 

[Raider03]

I have heard multiple times, 970fps for the 22cal 25grain MRD in an FX.

 

[JimNM]

To clarify, I am not insisting that over speed the the main or only contributing factor to the wild pellets. It CAN be a factor, and with localized weather and wind gusts, pellet variances and gun variables all in the mix, elimination of a single controllable variable may be beneficial to the cause.

Shoot'em good!

 

[Bramezy]

I have heard multiple times, 970fps for the 22cal 25grain MRD in an FX.

Ill need the slug power kit installed for that

 

[Bramezy]

I'm gonna use the excuse of out of balance pellet. question though, if this happened only a hand full of times and I'm guessing on the same day could it not be atmospheric condition related? swirls that can't be seen? turbulence at a given spot? etc.

It was dramatic and last second. Had a nice arch going to target then last second it would crazily spin a random direction several inches.

 

[igolfat8]

What is your barrel length?

Do you have the same thing happen at other ranges? It could be our goofy swirling winds? It eats my lunch a LOT.

 

[JimNM]

Push the target another 20 yards ... I bet you see more of the wild pellets.

 

[JoePolanco]

Wondering if the speed needs to be higher or slower as maybe it’s destabilizing then? No issues at 50yd, stacks em.

Two things to consider but they're not mutually exclusive. During the height of the pandemic we noticed a change/variation in the skirt depth of JSB Monster 25.39 redesigned pellets. This 1mm increase in depth, although tiny, makes a significant difference in the way the pellets behave at various speeds. I suspect differences in the laminar flow coming off the skirt is what is responsible for the destabilization issue. Check your pellet tins for differences in inner skirt depth and sort them as deep/shallow accordingly. Then begginning around 860fps, try increasing the avg fps by increments of 10 for each until you've eliminated the destabilization.

 

[Tomiboy]

Ill need the slug power kit installed for that

or a 700mm barrel