Preferred Velocities?

[tentman]

Hello from a Newbie to the airgun world (I'm a refugee from a very long apprenticeship in the 22 RF accuracy world)

From my reading there seem to be "preferred velocities" in the PCP guns to run certain projectiles at e.g. 890's for pellets and 930's for slugs.

Are these preferred velocities a function of projectile performance (oburation maybe, or skirt deformation or ???) or are they a consequence of barrel harmonics or something else ?

Cheers

 

[bdzjlz]

Pellets approaching 1050 or greater become unstable. Very generally speaking the .22 jumbo monster redesigned and .25 King Heavy pellets shoot best somewhere between 890 and 960, and every rifle/pellet combo will be different.

With spring rifles, due to harmonics, I have rifles that shoot best in the upper 600s or 700s but most pcps willl shoot the .177 pellets well in the 800s and 900s, and even into the low 1000s occasionally. One just has to have a good chronograph and do significant testing to find the best match between rifle and pellet. There is no other option.

 

[corny]

It’s very subjective. If you’re looking for 3/4-1” groups at 50-60y yeah, 880-890 will do that in most modern barrels.
If you looking for the absolute best accuracy a gun can give, you’re going to have to dig deeper.

My most accurate gun holds a casual 3/8-1/2” group at 50y. With a simple forearm bag. 860fps

Got a little prod pistol with the same ammo (18gr jsb) with hold its own with 655fps.

I guess I’m trying to say..don’t be afraid to try different speeds.

 

[dizzums]

depends on what youre doing ..ultimate accuracy for paper punching is much like firearms and reduced velocity gives less turbulence on projectile exit and usually more accuracy .. in the real world its a compromise of power and accuracy, and of course gun design and quality is going to affect performance also .. generally speaking, 900ish works out best for most pellet guns as a good compromise of speed/ accuracy keeping the trajectory characteristics consistent across platforms .. depending on what youre doing, you can experiment from there on what works best for you .. for me i like them faster with a flatter trajectory and more punch, 950-1000+ if accuracy stays acceptable .. but i could care less about punching paper, i want to explode fluffy butts organs lol..

 

[MikeAllen]

As a newbie to our airgun world I'd suggest you watch some of the AEAC (Airgun Exploration and Advancement Channel) on YouTube, especially some of the interviews that Steve Scialli has done with winning shooters. Personally, I'm pretty happy with my current tune at 872 fps.

 

[Long_Gun_Dallas]

880 is about the magic number. I don't claim to understand all the ins and outs, but this is roughly the speed that the least amount of wind drift occurs at. Personally, I shoot more around 950fps in my hunting rifle. But most of my guns shoot around 600fps give or take. Less noise, less ricochet, less air use. Still enough to take small game.

 

[Hateful McNasty]

Ya, for common dome type and weight pellets 850 - 880+/- , but for odd shaped like wads/ flatheads , pointed , ect my sub 600 stuff handles them so much better.

 

[starlingassn]

for pellets 880fps (below the transonic region) seems to be the magic area if you want the utmost accuracy.

slugs seem to like to go faster,
but even launched at slower speeds,
they will still experience less drop at distances than the same weight pellet,
be less affected by wind drift,
and retain more of their energy downrange than a pellet.

 

[MEC17670]

Out of my Crown mk2 600mm barrel .25 with a 29gr neilson likes 970fps. With the 25.39gr. jsb , 890 + - 5 fps seems to be the sweet spot out of the 1:24 twist barrel.
I still working on the 1:16 liner.

 

[JimD]

I've convinced myself that I cannot make my guns "like" a pellet by shooting it faster or slower. I've tried, it didn't work. I haven't spent enough time trying to get pellets that shot well from my guns to shoot better or worse by changing velocity. I'm willing to accept that there could be a gain but I think velocity is a much less important factor at the velocities I use (generally under 900 fps).

I'm not sure going lower in velocity hurts accuracy in most cases but it makes the trajectory worse. If you go too fast, the pellet can be unstable. I've read that happens more when it's windy. I try to find a velocity between 800 and 900 fps that the gun shoots accurately and call it good enough. It can mean adjusting the regulator. I have not had good results trying to change velocity much with the hammer spring. The hammer spring definitely affects accuracy but has only limited effect on velocity in my guns. I've also had odd velocity on the first shot of the day when the hammer spring was not close to the setting that maximizes velocity at that regulator setting. So I find the hammer spring setting that maximizes velocity and go up and down a little on the hammer spring from there trying to find a setting that maximizes accuracy. My Avenger likes a little higher hammer spring setting but usually the best point is a little under the maximum velocity setting.

 

[TheBeardedGunsmith]

When I first made my .50 air rifle, I couldn't wait to share it with the airgun Facebook groups that I belong to because of its insane performance. It pushes 325 grain slugs at 1587fps. I had people in the groups tell me that it wouldn't have any accuracy unless I installed an air stripper because of the huge blast of air behind the projectile. They must not be used to a perfectly cut target crown because that rifle will hold moa to sub moa groups st 100 yards. I prefer the most speed that I can get but I'm also used to powder burners.

 

[DirtyGator]

When I first made my .50 air rifle, I couldn't wait to share it with the airgun Facebook groups that I belong to because of its insane performance. It pushes 325 grain slugs at 1587fps. I had people in the groups tell me that it wouldn't have any accuracy unless I installed an air stripper because of the huge blast of air behind the projectile. They must not be used to a perfectly cut target crown because that rifle will hold moa to sub moa groups st 100 yards. I prefer the most speed that I can get but I'm also used to powder burners.

Phenomenal! And I agree, there is magic to be had out there. I don't know much, but can say that I have a pcp that shoots pellets +1150 easily and has above average accuracy. Not sure I could explain it and certainly didn't discover it. Ever since I stumbled on that, I systematically test not only projectiles, but velocity as well. I don't think i can tell a gun and projectile combination what it needs to like.

 

[Trucker3573]

I have found in some guns velocity matters for a particular pellet. My .25 cal avenger didn’t seem to like hades at normal pellet speeds. That was a bummer then I saw the AEAC video on the gun and he turned the speed down on his to get them to shoot. That worked like a charm. At 840 fps they were excellent where they weren’t in the 880’s. Same with my fx streamline .22. Always hear the original ST barrel only likes jsb pellets. Not true. Won’t shoot a crosman 14 gr worth crap at normal speeds. Turn them down to 750-800 fps and they are excellent.

 

[Berserkeley Mike]

Is it possible that in some guns velocity/power level matters _for the gun_ too, in addition to the particular pellet? I ask because I have a multipump (Seneca Dragonfly .22) that shoots every pellet the best at 6 pumps. Not 5, not 7, not 8 but 6. Sure, some pellets shoot much tighter groups, but for each, 6 pumps gives the best group for that pellet, and that is from light (10gr.) to heavy (20gr.) pellets. I'm trying to figure out why and so far am thinking that the velocity may be the most consistent at that pump level, but need to measure a lot more velocities for different pellets to be sure. Or maybe at 6 pumps the air pressure balances the hammer strike?

 

[bigHUN]

I don't want to initiate a drama but the pellet optimal speed is more related to a rifling twist rate. For my Impact MK2 I have couple liners with 1:15, 1:24, 1:27, 1:32 in 600 and 700 lengths. I did a lot of testings, I preset the Reg and the Dwell to a given tune and just swapping liners only got different size grouping. For a number 880 fps for example every each liner if I raise or lower the speed by 10 fps increments, the groups show different personality. Also a pellet speed is a ballpark only if you shoot in the morning or noon, still need that little excersise +/- 10 or 20 or 30. The best to search for perfect tune in smaller increments up or down...

 

[JimD]

I shoot Crosmans in my Prod sometimes and they shoot pretty well. Copper plated H&N FTT shoot better but Crosmans shoot well. It's velocity with either is around 750 fps. Maybe that's a good velocity for Crosmans.

I thought I had tested different velocities for my 25 caliber cast pellets trying to get them to group but I just looked through my notebook and I see a lot of tests of different casting temperatures but none for velocity. I would really like to get them to shoot so maybe I better cast up a few (at least 100) and do a little shooting with the Avenger. I will need to degass it and set the regulator pretty low, like maybe only 1200 psi and work my way up and see how it shoots. The regulator came set to 2900 but the benefits fall off pretty quick as you go over 2000. Testing at different regulator settings will inherently test different velocities. I don't like using the hammer spring to adjust velocity, it sometimes makes the regulator act up so I just balance the hammer spring to the regulator setting it close to the maximum velocity for that regulator setting. I;'ll probably have to use "junk pellets" to get the hammer spring set or I'll have to do a bunch of casting. Maybe I'll have some data in a week or two.

What I've previously done is to match the weight of the pellet to the regulator setting of the gun to get 800-900 fps. I guess it might not be a coincidence that my best shooting gun is set to about 835 fps, a lower velocity than most of my rifles. The Avenger is currently set to shoot FX 25.39 grain at 930 fps. It is quite accurate at that velocity for the FX (made by JSB) but that doesn't mean it's the right speed for my cast (NOE hunter mold). I don't really want to shoot at under 750 fps or so for trajectory reasons and would really like to keep it over 800 but the biggest factor is where (and if) I can get some accuracy.

 

[tor47]

I shoot Crosmans in my Prod sometimes and they shoot pretty well. Copper plated H&N FTT shoot better but Crosmans shoot well. It's velocity with either is around 750 fps. Maybe that's a good velocity for Crosmans.

I thought I had tested different velocities for my 25 caliber cast pellets trying to get them to group but I just looked through my notebook and I see a lot of tests of different casting temperatures but none for velocity. I would really like to get them to shoot so maybe I better cast up a few (at least 100) and do a little shooting with the Avenger. I will need to degass it and set the regulator pretty low, like maybe only 1200 psi and work my way up and see how it shoots. The regulator came set to 2900 but the benefits fall off pretty quick as you go over 2000. Testing at different regulator settings will inherently test different velocities. I don't like using the hammer spring to adjust velocity, it sometimes makes the regulator act up so I just balance the hammer spring to the regulator setting it close to the maximum velocity for that regulator setting. I;'ll probably have to use "junk pellets" to get the hammer spring set or I'll have to do a bunch of casting. Maybe I'll have some data in a week or two.

What I've previously done is to match the weight of the pellet to the regulator setting of the gun to get 800-900 fps. I guess it might not be a coincidence that my best shooting gun is set to about 835 fps, a lower velocity than most of my rifles. The Avenger is currently set to shoot FX 25.39 grain at 930 fps. It is quite accurate at that velocity for the FX (made by JSB) but that doesn't mean it's the right speed for my cast (NOE hunter mold). I don't really want to shoot at under 750 fps or so for trajectory reasons and would really like to keep it over 800 but the biggest factor is where (and if) I can get some accuracy.

My guns also are usually most accurate between 800-850 fps. The factory tunes are usually higher like 880 or so. It could simply be that most guns are tuned higher from factory, to allow a wider range of pellet choises for the customers, and not nesesarry because it is the most accurate speed? Since I ,mainly use jsb 10 grains for my .177 guns, I see no need to shoot them faster, if low 800`s turns out to work best.

 

[qball]

Hello from a Newbie to the airgun world (I'm a refugee from a very long apprenticeship in the 22 RF accuracy world)

From my reading there seem to be "preferred velocities" in the PCP guns to run certain projectiles at e.g. 890's for pellets and 930's for slugs.

Are these preferred velocities a function of projectile performance (oburation maybe, or skirt deformation or ???) or are they a consequence of barrel harmonics or something else ?

Cheers

For optimum accuracy the preferred speed isn’t any different compared to PB subsonic projectiles, at or blow Mach 0.8 or around 900fps depending on temp and slower. Keep in mind people’s definitions of accurate is different, example is hunting via bench rest accuracy.

If a slug won’t shoot well except at 1000fps then it’s not properly stabilized. Pellets have more complicated shapes to creat more turbulence so definitely lower than Mach 0.8.