Tuning Where are the "sweet spots" in air gun velocity?

[GunshipGuy]

Question: Where are the "sweet spots" in velocity when tuning a.177 or .22 air rifle?

Back story: While I'm "mechanically challenged," I'm trying to tune a .177 RTI Prophet Compact. The last owner used it for shooting slugs. I'd like to use it for pellets. (JSB 8.4s would be ideal.) I've had good results by adjusting my .22 rifles to shoot around 880-890 fps. At one time I owned a .22 Vixen that shot accurately at around 700 fps. And I assume that the high power rifles must shoot accurately at velocities above 890. So--generally speaking, are there multiple sweet spots in velocity, is there only one ideal velocity when tuning a rifle, or does it vary from rifle to rifle and barrel to barrel? Thanks in advance for your help.

 

[Stubbers]

Varies based on pellet shape, such as diabolo will have a different ideal velocity over wadcutters, and so on.

It's always best to spend the time to get intimate with your gun and how it groups based on both pellet (from brand to weight), to velocity.

For diabolo pellets 800-900 tends to be in the range for the sweet spot, however as you said, this can vary depending on barrel, caliber and pellet selection, so only use that as a starting point.


-Matt

 

[airgunmike56]

I agree 800 - 900 fps , You can squeeze a little more out of a 177 900 - 980 sometimes, You did not say what Prophet you had , 1-2-or 3
If its been shooting slugs make sure the barrel is clean,
On my Prophet II compact 177 barrel installed , I have my reg, setting at 90 bar and shooting JSB 10 gr at 960 fps .
Mike

 

[shambozzie]

You want the 177 anywhere fron 850 to 900 with jsb 10.3. I have mine @ 850 with jsb 10.3 and reg @ 105 with plenum install. Will shoot small clover leaf @ 70 yds. Prophet 1 performance compact. 177.

 

[JimD]

I like to see velocity between 800 and 900 too but I see a lot more change in accuracy from use of different pellets than I do from changing velocity. A couple of my PCPs will not shoot the pellet they like best over 800. That does not seem to affect their accuracy. I have one that is more accurate at 920 than it is at 880. So I think the process is to find a pellet your gun really likes and then see if you can tune it for a velocity you like.

Some examples may help. My P35-177 really likes H&N Baracuda FT pellets. It's best 30 yard challenge score with them is a 197. That was at a velocity of 880. I initially shot them over 900 fps just because the gun was tuned for a little heavier pellet. I did not shoot as high a score at a higher velocity but I don't know if the velocity is the reason, I may have just shot better when it was tuned a little lower. It shot quite well over 900.

My P35-22 really, really, likes 21 grain H&N Baracuda Match pellets. It has twice put three in exactly the same hole at 25 yards and gave me a 200 on the 30 yard challenge last year. I have not messed with the regulator on this gun but have tweaked the hammer spring. The velocity is about 830 fps. It cannot do a lot more than that.

My P35-25 really likes JSB Heavies MKII preferred. In the summer I can occasionally get them over 800 fps but usually it's more like 750 fps. These little guns are hammer spring limited to under 150 bar on the regulator and the barrel is 450mm long. They are small and light but not super powerful. I've shot a 194 with this gun on the 30 yard challenge. I do not know if more velocity would help the accuracy. I tend to think it wouldn't make much if any difference.

My Caiman X likes H&N Baracuda 18 pellets. With it's 100 bar reg setting it can shoot them 940 fps. I shot it a lot at 880 fps but it seemed to be too slow for the regulator setting. I am pretty sure I shot at least one 199 on the 30 yard challenge with it at 880 but I shot a 200 with it at 920 fps. My guess is I could turn the regulator down to 90 or 95 bar and tune for 880 fps and it would be at least equally accurate there. I might sometime but I am not in a rush, it shoots great at 920.

I've also tried to make guns like a pellet I wanted to shoot by changing velocity and been totally ineffective in doing this. I also tried tuning the P35-177 at several points between 800 and 900 fps with it's former favorite, the H&N Baracuda Match. Didn't seem to make much difference in accuracy.

I've seen reports of instability, especially in wind, from velocity over 900 fps. But others report great accuracy there and my Caiman experience has shown no signs of instability but I have not shot it at long range yet. But to be safe my target is usually 880. I do not think there is a magic velocity. I think some reports of better accuracy at different velocity are probably more related to the tune than the velocity. I think it is important to get the hammer spring adjusted appropriately for the regulator setting (typically about 5% under peak velocity). If that doesn't give you your target velocity I would change the regulator setting. But if you gun seems to really shoot well a little faster or slower than your target, I tend to just leave it there and enjoy it.

 

[MongooseV8]

Generally speaking, 800-880fps is the sweet spot for a pellet. Each pellet design and weight will act differently and can vary quite a lot from that range, but that is not the norm. Pellets are aerodynamically challenged and dont like to be pushed too hard or too fast; they start doing all kinds of crazy things in flight. My Impact M3 shoots Hades pellets just over 1000fps very well up to about 50-60yds then they get unpredictable. If I slowed them down my accuracy would improve and hold for a longer range.

Slugs can be used well in a bigger range, ~750-1050fps due to their much better trajectory characteristics. The problem is many of the pcps on the market will not play well with slugs, and they have proven difficult or impossible to nail down for most users. I have found a few slugs that do well in my setups at about 1005-1050fps but that is not the norm either.

Either way you will ultimately find yourself velocity capped the closer you get to the sound barrier. So any air powered setup with probably forever be limited to ~1050fps at sea level.

 

[EPG]

Question: Where are the "sweet spots" in velocity when tuning a.177 or .22 air rifle?

Back story: While I'm "mechanically challenged," I'm trying to tune a .177 RTI Prophet Compact. The last owner used it for shooting slugs. I'd like to use it for pellets. (JSB 8.4s would be ideal.) I've had good results by adjusting my .22 rifles to shoot around 880-890 fps. At one time I owned a .22 Vixen that shot accurately at around 700 fps. And I assume that the high power rifles must shoot accurately at velocities above 890. So--generally speaking, are there multiple sweet spots in velocity, is there only one ideal velocity when tuning a rifle, or does it vary from rifle to rifle and barrel to barrel? Thanks in advance for your help.

Hi Gunshipguy,

I think you are going to be challenged tuning a Prophet P1 Compact for 8.4g pellets.

I realize you have a Compact, but the P1 is a high powered PCP originally designed around shooting the .22 25.4g JSB MRD pellet at 1,000fps using a proprietary slow twist rate barrel - objective was 100 yard benchrest accuracy.

As such, you should have a 34 gram hammer in your P1 rifle. You may struggle to get consistency with that heavy hammer and hammer spring preload turned way down for a 8.4g pellet.

Likely, a 10.3 or 13.4g pellet will work better. I’ve had great success with my P1 using these two pellets when I have it set up as .177. I have the full size P1.

 

[GunshipGuy]

Wow! Thanks for all the great info. This is just what I needed. I'm waiting on some breech seals right now, but I look forward to tuning the Prophet.

I believe what I have is a Prophet Performance Compact--the original rifle.

 

[Stubbers]

Don't mind if I do....

Oh wait, you said breech seal, not beach seal....my bad!

-Matt

 

[bchannell]

I get pretty good results at 100 yards or slightly further, with pellets at 900-950 fps, using JSB 18.1 gr pellets. I've shot just over 1" groups with my Cricket Carbine at 946 fps avg. I had expected it to be too fast, but it's great. I'm experimenting with a few rifles to see just where the limit is. My Brk Sniper is set at 850fps with 18gr and shoots very well at 100yds. My DreamTac is set at far less, something like 780fps and it will do less than 2" at 100 yds.
When I get my Impact .22 up and running, I'll definitely crank it up til it destabilizes the pellets to see what max is, but so far the speed is slightly higher than most think. My guess is 1000fps is just about too much, with 1080 fps or so being supersonic. I'm also going to go to heavier pellets when I get time.
That's the cool thing about airguns, there's always new directions to go.

 

[Caliber 22]

I think it is not the speed the pellet flies best at, but the riffle / barrel vibrations like with a PB rifle and air turbulence as the pellet leaves the muzzle. I saw some air rifles shooting good at 870fps, not so good at 900fps but good at 930fps. I contribute that to the barrel vibrations / harmonics more than the pellet aerodynamics. Shooting at MV of 930fps, the pellet will slow down through 900fps but it is still shooting good, but at 900fps MV the group open up.

My pcp shoots H&N B 18 best at 940 - 950fps up to 100 meter. But JSB 18gr not good at all from a slow 700 to 970fps. Then recently I increased the reg pressure and installed a stronger spring and found the JSB 18gr to shoot good at 1020fps MV but not over 75 meter distance. Also Rifle Premium 18.6gr is shooting best at 1050fps MV up to 50 meter but not at lower speeds. I can mention a few other pellets as well but you get the drift.

My wife's pcp shoots both JSB and H&N 14gr best at 780fps.

So, the conclusion is that every rifle & pellet combination has it's own speed it shoots best. I don't subscribe to the idea that a certain pellet shoots best at a fixed speed from every rifle it shoots best from.

Others will have different experience.

 

[Stubbers]

I think it is not the speed the pellet flies best at, but the riffle / barrel vibrations like with a PB rifle and air turbulence as the pellet leaves the muzzle. I saw some air rifles shooting good at 870fps, not so good at 900fps but good at 930fps. I contribute that to the barrel vibrations / harmonics more than the pellet aerodynamics. Shooting at MV of 930fps, the pellet will slow down through 900fps but it is still shooting good, but at 900fps MV the group open up.

My pcp shoots H&N B 18 best at 940 - 950fps up to 100 meter. But JSB 18gr not good at all from a slow 700 to 970fps. Then recently I increased the reg pressure and installed a stronger spring and found the JSB 18gr to shoot good at 1020fps MV but not over 75 meter distance. Also Rifle Premium 18.6gr is shooting best at 1050fps MV up to 50 meter but not at lower speeds. I can mention a few other pellets as well but you get the drift.

My wife's pcp shoots both JSB and H&N 14gr best at 780fps.

So, the conclusion is that every rifle & pellet combination has it's own speed it shoots best. I don't subscribe to the idea that a certain pellet shoots best at a fixed speed from every rifle it shoots best from.

Others will have different experience.

I personally subscribe to this theory as well, but, I would add that pellets themselves will have optimal velocities based on shape to both minimize wind drift and for the flattest trajectory, however that doesn't mean your rifle will like that speed without some type of muzzle/barrel tuning devices.

Just my 2c added into the pile of penny thoughts.

-Matt

 

[Caliber 22]

I personally subscribe to this theory as well, but, I would add that pellets themselves will have optimal velocities based on shape to both minimize wind drift and for the flattest trajectory, however that doesn't mean your rifle will like that speed without some type of muzzle/barrel tuning devices.

Just my 2c added into the pile of penny thoughts.

-Matt

Some time ago I wanted to buy a barrel tuner to test but the guy at the shop said it will not work with my rifle because of the barrel shroud, they tested it, so he said. I still want to try it. It works perfectly on some of my PB's including my .22LR with tuning silencer, shooting 15mm groups at 100 meter with it and 30 - 50mm without.

Later I thought about it that FX has some barrel tuners on their shrouds that actually works. I saw some videos where a guy used a M3 that was not tuned for presision for the particular pellet and with the tuner in action it shot some presice groups.

 

[Spartan]

The magic number that appears most often for me is 890 fps.

Across many (but not all) guns, barrels, and pellets.

I do not know why this is, but I have learned to both accept it and embrace it.

 

[Emu]

Golden rule: 880-900 fps.

Truth: Go to the range and "feel" your rifle and look the pellet how it flys at diverse speeds..

My Vulcan 2 .25 Cal shoots the JSB's 25.4 grain at 953 fps like a real champ.

 

[Racing]

Hm. A while back i went ape on the cheapest POS i could find, in 177cal.
In the end i came to settle on H&N´s 20 grain hollowpoints and the thing tossed them well into supersonic with no ills observed (just shy of 1300fps)
I bet this could be juiced up even more will be but..

What i´m saying is that for slugs out of THAT aspect all bets are off.
Then true. The trans sonic area around the speed of sound can eff anything up, no argument, and what´s more it´s at least my opinion that airguns have no place being super..
That is however not the same thing as that it can not be done, with absolutely retained accuracy.

 

[Peashooter]

I would not go to that light pellets, shoot some of the 10.4-5-6 grain pellets out there.
and i will agree on the sped 800 - 900+ fps
For the same tune you could probably shoot 10 grain slugs too, i shoot those to 134 yards, and they do A LOT better than any pellet i have tied to shoot to 100 yards.
10 grain JSB KO mk 3 have been really good to me, better than 10 grain Zan.