Relationship of FPS to Accuracy?

[GadgetX]

Helping a friend out with his Daystate .25 cal Safari. 

He is shooting JSB 25gr pellets.  He said it was TERRIBLE on high power, but grouped at low power, get this, at 3/4" at a 108yard outdoors.  His FPS 940 on low power.  I shoot MKIIs at high power which I get dime size groups at 60 yards.  My FPS is ~950fps.

I think this open up my eyes on FPS being extremely important for accuracy.  And the reason MKIIs work best in all my Daystate airguns is because I like to shoot on high power...  I may go down to low power with JSB 25gr and smile when I get 200+ shots on a fill.

Thoughts??

M

[Rat Sniper (AKA: PaulT58)]

900 to 975 sure seems to be the optimal FPS for pellets, regardless of caliber.  Be it .177, .22 or .25, I generally shoot for between 925 and 950 FPS and get very satisfying results! 

[PikeP]

Staying outside of the transonic region of velocity is quite important when shooting. You either want your projectile to stay super sonic during its entire range of flight (and be designed around super sonic flight) or you want your projectile to remain sub-sonic for its duration of flight. Hitting just the edge of the region isn't detrimental, but the deeper into it you go, the less stable your projectile will become. HTH

-Matt

[Ribbonstone]

Why some rifles shoot well faster than others (with the same pellets) pretty much eludes me....they just do.

Generally, when velocity starts reaching 925-970fps, will more often look for the next heaviest pellet and give that a try....moving up in weight if adjusting/tuning gets me back to that speed.

Some times I get trapped....nothing else heavier, and there is still more speed to be had...so I'll just have to keep tuning for faster if I'm looking for power(or stop adjusting and live with what I got).

I now have no dobuts about the wind at close range screwing up long range when speed gets to 4 digits. Can shoot great when calm,does really stupid stuff when the wind hits the pellet early in it's flight.

So I'd much prefer something like 30gr. at 875fps than  20gr. at 1075fps.

[rsterne]

In addition to the stability of the pellet possibly changing at different velocities.... the barrel harmonics can also affect the group size.... As you change the velocity, you change at what point of the barrel vibration the pellet arrives at the muzzle.... Have it arrive near the end of a swing, when the barrel is pausing, and the group size can shrink dramatically....

Bob

[Mod90]

Bob beat me to it.
Barrel harmonics can change at HV vs. LV, altering your POI. This is due at least in part to our airguns barrels not being as stiff as firearm barrels since they're usually made of a somewhat milder steel. A loose fitting shroud can also cause harmonics issues.
As a counter, if the shroud fits and works as designed and its indeed a barrel harmonics problem, some folks are float the barrel with some success. Tensioning the barrel is another way some go.  If those are not an options one is  willing to try, and if the muzzle is threaded, then adding some weight to the muzzle (air stripper, a muzzle brake, s heavy moderator, I've even seen a guy use metal collars once) can help as well. Adding some weight helps counter the inclination of the muzzle to flip upward during the shot as the projectile the barrel, by either directing and dispersing the blast in the case of an air stripper, or with weight alone if using a heavy brake or moderator.

Hope this helps.

[anti-squirrel]

I challenge everybody to find wadcutter pellets that group at a much-closer 50 yards when muzzle velocity exceeds 900 FPS.  I'm in the same camp as Mister Dean (Ribbonstone)

I've found the most accurate velocity for most domes to be right ~ 880.  Mind you, if you find 920 is even more accurate than 880 then good on you, but this has not been my limited experience.  OTOH, Travis has mentioned similar results and he's had pretty much everything under the sun. 

[PikeP]

I challenge everybody to find wadcutter pellets that group at a much-closer 50 yards when muzzle velocity exceeds 900 FPS.  I'm in the same camp as Mister Dean (Ribbonstone)

I've found the most accurate velocity for most domes to be right ~ 880.  Mind you, if you find 920 is even more accurate than 880 then good on you, but this has not been my limited experience.  OTOH, Travis has mentioned similar results and he's had pretty much everything under the sun.

Quite a few variables go into this...form factor (18.1's and redesigned 25.4's wont obey that same fps rule to the T...) and your barrels twist rate, all have compounding effects on ultimately what fps is best...one pellet may do best at 750, where as another does best at 850, and another at 950...really can't generalize all domed pellets being best at 880 IMO...although if one were required to give one number, and one only, then 880 is probably not a bad one to give...

[GadgetX]

Thanks for all the input.

After reading replies and shooting airguns for 30 + years, IMHO I think a 34ish gr pellet at 920 fps is my best shot at hunting.  This has opened my eyes up shooting 25gr at 900ish at low power for target shooting is the "Cats Meow".  200+ shots per fill (nearly a tin).

Thanks for all the replies.

M

[Ribbonstone]

Anti squirrel:

Do think there is more going on with WC's than just weight/diameter...somthing hooked up with base drag vs.head drag with increased speeds.

Even at 25-30 yards and match rifles/low speeds, very often find RN pellets doing better than WC's.

GAgetX:

No complaint....could have picked anything from 860-920fps  and I'd just nod.

[Nomadic Pirate]

I try set up my guns to shoot in the -/+ 900 fps regardless of pellet weight, power, caliber.

[anti-squirrel]

Anti squirrel:

Do think there is more going on with WC's than just weight/diameter...somthing hooked up with base drag vs.head drag with increased speeds.

Even at 25-30 yards and match rifles/low speeds, very often find RN pellets doing better than WC's.

GAgetX:

No complaint....could have picked anything from 860-920fps  and I'd just nod.

I'm just a huge fan of wadcutters, and they Do Not Like going fast.  I wish we could obtain .25 and .30 wadcutters easily.  I'd have jumped to .30 the millisecond they were available.  Even at 450 FPS I bet it would be awesome for pesting.  I may be lucky in that the gun I shoot the most, my 2400KT, has a decided preference for RWS Meisterkugeln.

[GadgetX]

Wow quite pest you have there.  .30 required...

M

[K.O.]

Anti squirrel:

Do think there is more going on with WC's than just weight/diameter...somthing hooked up with base drag vs.head drag with increased speeds.

Even at 25-30 yards and match rifles/low speeds, very often find RN pellets doing better than WC's.

GAgetX:

No complaint....could have picked anything from 860-920fps  and I'd just nod.

I'm just a huge fan of wadcutters, and they Do Not Like going fast.  I wish we could obtain .25 and .30 wadcutters easily.  I'd have jumped to .30 the millisecond they were available.  Even at 450 FPS I bet it would be awesome for pesting.  I may be lucky in that the gun I shoot the most, my 2400KT, has a decided preference for RWS Meisterkugeln.

 

well how about .410..    https://www.ebay.com/itm/410GA-wad-cutter-pellet-bullet-mold-AS-Lyman-style-/292198322361

https://www.gunpartscorp.com/products/595510A     

https://www.gunpartscorp.com/search#query=.410%20barrel

[K.O.]

a related thread...

https://www.gatewaytoairguns.org/GTA/index.php?topic=174899.0

[tor47]

From 850, to 920 is like 8 persentage faster. Not much.

[tor47]

From 850, to 920 is like 8 persentage faster. Not much.

The reason I said that is that some refer to shooting at the 800 range as low power, while shooting higher than 900 as high power, while the persentage difference is not that much. So if a gun does not shoot good at 950, but do at 880, the it probably does not make much practical difference, except the one shooting at 880 probably will have more shots on a fill.

[tor47]

From 850, to 920 is like 8 persentage faster. Not much.

The reason I said that is that some refer to shooting at the 800 range as low power, while shooting higher than 900 as high power, while the persentage difference is not that much. So if a gun does not shoot good at 950, but do at 880, it probably does not make much practical difference, except the one shooting at 880 probably will have more shots on a fill.

[AlanMcD]

It may be only 8% faster, but energy is is a function of the speed squared.  So moving from 850 to 920 FPS increase the FPE by a little over 17%, not just 8%.

Of course accuracy is most important - 17% more FPE in a missed shot does no good.  But speed and energy are not the same.

[PikeP]

Good point Alan. I also don't think 8% of anything is 'minor' or negligible...that is quite a large margin in any change...