Beeman Chief - Merry Christmas to Me !!!

[rsterne]

the two important stability criteria actually become slightly worse as you get into the transonic region.  If a particular rifle were to group better at these velocities, it would in all likelihood be a result of harmonics…

100% correct, Jason.... I see no particular reason for a pellet to have a "minimum accurate velocity" up in the 900's, in fact the reverse is likely.... but certainly in one particular rifle you could see that effect, and draw that conclusion....

Gary, don't forget that in the SSG, before a rebounding hammer can store any energy in the spring, it has to overcome the preload force (in my case 4.8 lbs).... With an SSS, there IS no preload (why it works), so the spring can compress if the hammer hits it with any force.... and the harder it hits it, the more energy it can store, and then that energy can re-launch the hammer towards the stem.... Yes, it is a lot better resisting hammer bounce than a spring that is preloaded against the hammer (like most PCPs).... but takes no effort to compress it that first little bit, and is storing energy all that time.... In guns requiring a lot of hammer strike, the SSS setup can require near-impossible cocking effort.... The mass of the spring guide in a moving SSG guide setup may make some difference.... but in the case of my SSG on the Chief, the guide is stationary, and only the Delrin spring guide and the spring offer any inertia to the rebounding hammer.... It is that (4.8 lbs. of) static preload that really makes the difference in any SSG....

Ribbon, I agree, shortening that already short striker is NOT a good idea from the "tipping" point of view (cocking force on top, sear on bottom).... I thought about the idea of extending the spring guide out the rear, and using the stock spring preload system.... By threading a nut on the end of the extended spring guide, that will hit the back of the tube plug, you could use that for your "gap" adjuster.... however the preload adjuster would be buried inside the tube plug, if you used the existing allen setscrew with the hole through it.... If you used a setup like mine (10mm x 1mm bolt threaded into the plug), you would end up with a setup that LOOKED like mine, except the threaded rod would have the stop nut on the back, and would move backwards about 3/4" when you cock the gun.... It would certainly work, but might pinch your thumb if you have a habit of wrapping it over the wrist of the stock....

Bob

[rsterne]

During testing I was impressed at how stable the velocity of the Chief was, particularly after I installed the SSG, when tethered at 1800 psi.... I decided to decrease the SSG gap by a turn from the previous setting to increase the power, and shoot it both tethered at 1800, and an unreguated string starting from a 2000 psi fill.... Here is the previous chart of the SSG strings with the new one added in black....



Note that the first 5 shots are right at the sweet spot, and over 900 fps.... The total string is only 8 shots long, because the first part of the bell-curve is missing, but I expected that.... The total air use was 600 psi (ending at 1400) for an efficiency of 1.03 FPE/CI, pretty typical for a string that starts near maximum power.... It is an indication of how tight you can get the ES in an unregulated gun if you only use the top of the bell-curve.... The first 5 shots were with a range of just 7 fps (ES less than 0.8%).... I then tethered the Chief to my regulator, set to 1800 psi (pretty much right at the peak of the curve).... I shot 10 shots between 906 - 914 fps, just 4 fps above and below the 910 fps average (46.7 FPE), and a total ES of 8 fps, just 0.9%.... Basically, the gun didn't care if it was regulated at 1800 psi.... or if the pressure was dropping from 2000 psi down to 1600.... This shows excellent consistency in the hammer strike, considering the pellets were straight from the tin, with no sorting by head size or weight....

Scott (Motorhead), who does a lot of work with regulated PCPs, is always telling guys that if they are having problems with the ES on a regulated gun, they should make sure that the regulator setpoint needs to be at the peak of the bell-curve if they were shooting the gun unregulated, and tuned for that peak velocity.... This makes it VERY insensitive to variations in setpoint pressure or regulator creep.... This is a perfect example of how that occurs....

Bob

[Ribbonstone]

MAy never happen, thinking about, am pretty pleased with the way it suits my uses as it is....you've other uses, so other goals.

Your shot count isn't out of usefulness as it is.  Know I've gone on deer hunts with less than 12 cartridges ....know big-bore airgunners often go out with a shot count of 4 or 5....so with a 2K airgun rot-rodded to 10-12 shots, I think the same thing: if I can't get a grabage can raiding racoon AND HIS FAIMLY with 12 shots, then they are zombies (or I suddenly went blind).

[skorec]

But I am thinking that Monsters need more FPS for longer distances.
…
I will wait for test you at serious distances.

You seem to be holding onto a notion that ~950fps is a magical number for the JSB Monsters.   As Bob has previously explained, the two important stability criteria actually become slightly worse as you get into the transonic region.  If a particular rifle were to group better at these velocities, it would in all likelihood be a result of harmonics…in which case there is no reason to expect any two rifles, even of the same model, to exhibit precisely the same preference for a particular velocity.  So regardless of how well or how poorly the Monsters do at longer distances in Bob’s rifle, it does nothing to predict how well they might perform in yours.  This reality holds true for any pellet.  The only way to know is to test them yourself.

I agree .For now I am only persuade that my .22 JKHAN and .177 Puncher equipped with the long LW 1:17,7”  barrels prefer 950 FPS for JSB Heavy  pellets ( shot  sub MOA at 77 yd -  and day by day better  ). 
The Monsters REDESIGNED I had not taste at this speeds for now  however Kamensek  video show them to be very  accurate at higher speed from Huben K1 55cm barrel.

[SpiralGroove]

Scott (Motorhead), who does a lot of work with regulated PCPs, is always telling guys that if they are having problems with the ES on a regulated gun, they should make sure that the regulator setpoint needs to be at the peak of the bell-curve if they were shooting the gun unregulated, and tuned for that peak velocity.... This makes it VERY insensitive to variations in setpoint pressure or regulator creep.... This is a perfect example of how that occurs....
Bob

Hey Bob or Scott,
I'm being Thick Headed .... why is this so??

Because your variance is capped on the high-end, thus removing the upside ES

Kirk

[nervoustrigger]

The peak of the bell curve roughly represents the middle of usable pressure range...so if the pressure deviates slightly higher or lower, the velocity won't change much. 

Contrast that with tuning to a pressure that's somewhere on the upslope or downslope.  That means a slightly lower pressure makes the velocity go one direction and slightly higher pressure makes the velocity go the opposite direction.  Therefore a higher ES.

[SpiralGroove]

The peak of the bell curve roughly represents the middle of usable pressure range...so if the pressure deviates slightly higher or lower, the velocity won't change much. 

Contrast that with tuning to a pressure that's somewhere on the upslope or downslope.  That means a slightly lower pressure makes the velocity go one direction and slightly higher pressure makes the velocity go the opposite direction.  Therefore a higher ES.

Thanks Jason,
Yup, just looking at the bell curve should have given me a clue

[Ribbonstone]

Just to add my simple minded view.

A non regulated rifle actually has a short section where it kind of self-regulates and gives a short, really low varation, shot count.  Over that short range, it doesn't really care that the pressure changes from shot to shot, the valve just takes it in stride.

It's the same valve system in a regulated version.

So if the regulated version were set in the best spot, it would also not care about small pressure changes (as the regulators aren't perfect and the striker hit to the valve isn't perfectly the same every time). 

May not be the fasteest setting, but likely to give you the most even shot string while on regulation (as you'd have BOTH the regulator and the natural self-regulation of the striker-valve system working for you).

[rsterne]

Exactly, and why I tune to the "knee" of the curve, where this occurs.... It ends up about 3-5% below the plateau velocity at that pressure.... and when you get it just right, you can't tell you have reached the setpoint, you get a few more shots after that before the velocity falls off slowly....

Bob

[adrianm1972]

Will you be testing the effects of restricting the transfer port?  I remember reading somewhere that there is a point of diminishing returns with port volume.  Too big wastes air with no FPE increase.  I think the guy from Thomas Air Rifles said something around 60% or pellet diameter was about right.  However, that might be part of his tune to get 100 shots out of a fill for a FT competition.

[rsterne]

I am well familiar with the effects of restricting the transfer port to reduce the FPE of a PCP, pumper or CO2 gun.... Generally I have found that it doesn't have much positive effect on the efficiency, other than the air saved because of the reduction in FPE.... some but not as drastic as reducing the hammer strike has.... If you are after a BIG decrease in power, then both methods should be combined....

In terms of searching for additional FPE, increasing the port size gains FPE, right up to the point where all ports equal the bore area.... Going beyond that will lose power, because of the pressure drop before the air gets to the pellet.... as does having part of the air transfer system larger than the other.... This is because the smaller port area sets the power, whereas larger areas in other sections just waste volume.... Keeping the length of the porting system to a minimum is good, but usually not something you can change, it is part of the design....

Mike at Thomas BR uses several sizes of interchangeable transfer ports to set the FPE of his guns for different classes of FT, and for different calibers and/or pellet weights for the BR classes.... It allows him to have one basic setup, that the user is able to custom taylor for their use at the time....  My current trends for regulated PCPs (which the Beeman is not) is to use large ports and low setpoint pressure where possible, to maximize shot count.... For a pellet shooter, that generally means 75% of the caliber, with a drilled barrel port.... For a bullet shooter, where you are chasing more FPE, then full bore-area porting, which requires an oblong barrel port to avoid loading problems....

I will mention one use for smaller transfer ports, and that is to extend and flatten the shot count on unregulated PCPs.... This has been used for years by FT shooters, where they strangle the TP and lean on the hammer spring to get back the lost power.... The resulting flatter bell-curve, when done right, and on a gun that is capable of being tuned for more power than the class requires.... can results in nice long, flat shot strings....

Bob

[rsterne]

I finally got a chance to shoot the Chief today, other than just over the Chrony in my shop.... I checked the accuracy with three pellets at 50 yards, and the clear winner was the new 25.4 gr. Redesigned JSB Monsters.... Here is the group off front and rear bags, tethered at 1800 psi.... you can easily cover it with a dime....



It shot well enough with both the 18.1 gr. Heavies and the old cylindrical 25.4 gr Monsters at 50 yards.... The Heavies were shooting at 950 fps and the Monsters at 820 fps.... I cranked up the velocity on the Redesigned Monsters to 920 fps and the group opened up so that all three were shooting just over 1" at 50 yards.... I tried them at 100 yards, and got a 2.3" group with the 18.1 gr. Heavies at 950, a 2.6" group with the Redesigned Monsters at 920 fps, and about a 4" group for the old Cylindrical Monsters, but only 4 hit the paper.... This is the second gun I have tried the new Redesigned JSB Monsters in, and they shoot FAR better than the old pellets at 100 yards, although there is not a lot of difference at 50....

Since the new Monsters shot a lot tighter at 50 yards at a lower velocity I decided to back off the velocity a bit at 100, and dropped it to about 870 fps, by using the tune with 2 turns of SSG gap as in the chart above (the blue line).... This cut the group size at 100 yards in HALF, with this result.... just 1.3" C-T-C at 100 yards....



This is a 43 FPE tune, and I had the opportunity to shoot a couple of Marmots after my target session, and it really lays the hurt on them.... I took one at 58 yards and it folded like a cheap tent with a 25.4 gr. pellet between the eye and ear.... Overall, I am delighted with the results of this gun.... It is the first gun I have found that shoots better with the new Redesigned 25.4 gr. Monsters than with my standby 18.1 gr. Heavies.... which is nice because they suit the power of this gun just great.... They seem to open up over 900 fps, but in the high 800's they are deadly....

Bob

[skorec]

It is the first gun I have found that shoots better with the new Redesigned 25.4 gr. Monsters than with my standby 18.1 gr. Heavies.... which is nice because they suit the power of this gun just great.... They seem to open up over 900 fps, but in the high 800's they are deadly....

Bob

Bob, Really serious accuracy.

At my  LW barrels I have never  reached  better accuracy with the Monsters REDESIGNED ( .22 and .177 )  then the Heavies ( .22 and .177 )   but I have  tried them only at 77 yard.

https://www.gatewaytoairguns.org/GTA/index.php?topic=136516.msg1407484#msg1407484

[airpuffhunter]

Great Project and post of info thank you Bob