Benjamin Optimum velocity

abstruse said:

At this point, my guns are a marauder and air Venturi bullpup, both in 25 caliber. I have enjoyed getting to know them and shooting them. Pretty soon, I need to start doing some tuning. With that in mind, is there any optimum velocity one should aim for if accuracy is the main concern?

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MOST pellets like to be in the 800 - 900 fps range out of a PCP. I suggest starting on the low end and see how the groups are and go from there.

There are a lot of videos on the subject. I would start there first so you do not reinvent the rifle tunes.

Like max trouble said, 800 to 900 on diabolo pellets, you may be able to stray higher or lower but if it's like my gen 1 mrod 25 you won't get too far past 900. Ironically the exact king is the only one that will go. As fast as 850 out of my gun but at that speed it's very very accurate and consistant. Mines old as heck and is a gm barrel version.

Excellent advice. 850 is where I usually start and go up to whatever is good.
Barrels are different and even different barrels from the same place will shoot differently. Some of mine really like high velocities, even approaching 950 -960. I do know that at long distances of 75-100+ the spin in ~17 twist bbls is too high at those speeds. FX slow twist and RTI LR barrels can do it though.

This is a fascinating subject to play with.

some of my best pellet results came from my old dreamline tac with the .25-600 1:16 liner installed. the 25.3/25.4's were gyroscopically unstable due to the twist rate being too fast. But the 34gr pellets were lethally accurate, you could really reach out with them. I Reverted back to the 1:24 superior because 25.4gr at 895-900 is ample energy to end any squirrel or bird, and .75-1.25moa at 100 is more than acceptable. Also 90-95 shots is "mo betta' than 55-60

It depends on the type of pellet. I found that in my .22s JSB jumbos like to fly a bit faster at 900fps while the standard pellets like to go 850-890fps.

SciueraPlumbea said:

some of my best pellet results came from my old dreamline tac with the .25-600 1:16 liner installed. the 25.3/25.4's were gyroscopically unstable due to the twist rate being too fast. But the 34gr pellets were lethally accurate, you could really reach out with them. I Reverted back to the 1:24 superior because 25.4gr at 895-900 is ample energy to end any squirrel or bird, and .75-1.25moa at 100 is more than acceptable. Also 90-95 shots is "mo betta' than 55-60

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I'm using a 380mm pellet liner and I'm shooting the 25.4 kings accurately out to birds at 110 yards thus far. My mrod just falls apart almost exactly at 75 yards no matter the velocity, weather, wind, or angle. The pellets start to big spiral like magnus is getting them.

gxs said:

It depends on the type of pellet. I found that in my .22s JSB jumbos like to fly a bit faster at 900fps while the standard pellets like to go 850-890fps.

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In 22 my buddies gun was the most precise at 930 fps with hades pellets. It was a confounding thing.

Barrels and ammunition are the deciding factor in selecting a velocity.

My Prod will not shoot it's favorite pellet (copper plated FTTs) more than 750 fps but is quite accurate with that tune. My Caiman X likes H&N Baracuda 18s the best of any I've tried and likes to shoot them about 910 fps. My P35-22 really likes 21 grain H&N Baracudas but can only shoot them about 820 fps. My P35-25 is the most modified and shoots 25.4 grain FX pellets very accurately at about 925 fps. I've tried the often recommended 880 fps in the guns that will reach it but it is not as accurate in my guns. I rarely shoot past 35 yards only because that is what I can do at home. I have shot the P35-22 at 100 yards and less but I don't think I've shot the others this far. It was reasonably accurate with a little under 2 inch 5 shot group in some wind.

I do not believe there is a "best" velocity for different pellets or even guns. You need to find a pellet your gun likes and the velocity it likes to shoot that pellet. You may need to try different pellets at a couple different power levels. With a 32 fpe tune, my P35-25 was pretty accurate with H&N 20 grain FTTs. But with power up to 45 fpe or so, it prefers JSB 25.4s and 34s. It is really inaccurate with the light weight H&Ns. Might be a speed thing I guess. But over a reasonable range of velocities I have not found a guns "favorite" pellet to shift. The P35-25 got a new bigger plenum to get to the higher power level and I think that changed it's dynamics.

Like @JimD says there is no concrete list of rules. It's trial and error, but i would start somewhere around 800 and work my way up till groups fell apart or the gun starts talking (getting wasteful) for pellets if you can send them that speed... Which you should be capable of. One of my guns is happiest below 500 fps being an old pistol with the jsb 18 grain pellets. My impact when it shot pellets seemed to show its best precision at about 900 fps with those.

Just let your rig speak to you, there are signs when they're happy. Do you know whose barrel your mrod has, and is it regulated or not?