Air Gun Home :: View topic

rsterne · Moderator

I finally got all the bits and pieces that I needed to assemble my 850 on HPA (I never even bought a CO2 cartridge for it).... I'm a very curious guy, especially when it comes to a new platform.... so I decided to go right back to basics.... The first tests were done with the stock valve and hammer spring.... I used JSB Exact Jumbo 15.9 gr. pellets as they will also be suitable at higher energies as well.... and I have a good supply of them....

I set up the regulator so that it was jammed open and whatever pressure was in the bottle would also be in the gun.... I then pressurized the tank to 1200 psi and did a shot string and recorded each velocity.... Once I determined the peak velocity, I discarded anything less that 90% of that number and graphed the rest using Excel.... I also recorded the pressure after each clip and graphed the pressures as well (every 100 psi)....

I then disassembled the gun and replaced the valve with a flow-modded one I got from Roald at "The 850 Store".... Unfortunately, the valve leaked air out the barrel.... I shot a couple of clips through it and it settled down but it was still losing about 100 psi every 5 minutes or so.... I pre-loaded 4 clips (all I had) so that I could shoot as quickly as possible and repeated the first test, but with the modded valve.... The shape of the curve is accurate.... but it is undoubtedly shorter than it would be had the valve been sealing properly.... Here is the graph:

As you can see, the stock valve was in partial lock above about 1050 psi.... The velocities were eratic above that pressure, and there was a sudden increase in velocity at about 1030 psi.... However, velocities remained within 10% of the maximum achieved up to 1200 psi and down to 680 psi with the peak velocity of 670 fps reached at 900 psi.... The velocity was within 5% of the peak from about 820 psi to about 1030 psi.... There were 66 shots within 90% of the peak velocity and 31 shots within 5% of the maximum (ie between 637 and 670 fps).... If you were trying to achieve the flattest shot string with a stock valve and hammer spring.... I would recommend a regulator pressure of 900 psi....

The results with the flow-modded valve are typical of what I have seen in my 22XXs when you improve the flow through the valve.... As the energy increases, the shot string becomes more curved, and the peak velocity moves to a lower pressure (with no other changes).... It is interesting to note that this valve exhibited a much smoother bell-curve than the stock valve.... with no eratic behaviour.... All 26 shots from 1100 psi down to 600 psi were within 10% of the peak velocity of 722 fps which was reached at 850 psi.... There were only 16 shots within 5% of the peak (ie between 686 and 722 fps), however, and they all fell between 700 and 1000 psi.... If you were trying to achieve the flattest shot string with a flow-modded valve and a stock hammer spring I would recommend a regulator pressure of 850 psi....

Roald's flow-modded valve increased the peak velocity in my rifle from 670 fps to 722 fps.... a gain of 52 fps using the 15.9 gr. JSBs.... It didn't take me very long to shoot the string.... but if the valve hadn't been leaking the string would certainly have been a bit longer.... I'm sure the leak is something very minor and easily corrected and that this is NOT typical so please don't take this as a criticism in any way.... sh!t happens....

The next step will be for me to take the gun apart and install the heavier hammer spring I got from Roald (and find the valve leak).... After testing that, then I will modify the barrel port and lead-in as per the thread on the 850 forum.... It will be interesting to see how the performance changes with those additional modifications.... Stay Tuned !!!

Bob

Lipoly · Veteran Member

First off, thanks Bob for your very exhaustive testing; it really is a service to the sport. Secondly...when you post these behemoths, I'd love to see you do a small paragraph summarizing your results so those of us w/o your knowledge can have better confidence we are actually understanding all the data you are giving us. Good job...I really enjoy your tests. I understand it may be hard to distill all that data to a small paragraph, and you'd obviously be leaving details out, but I think it would be beneficial nonetheless. After we understand the overall results, it will be easier for us to digest the finer details.

broommaster2000 · Moderator

Hi Bob!

What kind of a set up are you using? A small buddy bottle or straight from the tank? Neutral

I have been thinking about this in the past, but never really got around to doing so.

Over here you can now get the 850 in .25 too, but it's branded as the Walther 1250 Dominator. Mr. Green

rsterne · Moderator

I am using an 18 ci. tank with a Ninja regulator and an adapter from the 88gr. airsource thread to the paintball threads on the regulator.... The tank sits with the regulator hidden but the tank in front of the permanent section of the forestock.... The forward, removable section of stock that normally covers the 88gr. is gone....

The 1250 Dominator uses a different system to the 850.... It has a 300 Bar (4350 psi) removable reservoir and it has a regulator built right into the front of the valve.... I think the regulator pressure is about 120-130 Bar (~1800 psi) but I'm not sure about that.... It seems that smiilar performance can be obtained with an HPA converted 850 for significantly less money than a Dominator.... Not as clean a look, however....

Bob

broommaster2000 · Moderator

AirGunEric · Site Admin

I just wanna know- how many SCUBA tanks does Bob own? Mr. Green

rsterne · Moderator

One.... and it only has 1500 psi in it right now.... Evil or Very Mad

Bob

broommaster2000 · Moderator

You'll need an air-pump. Mr. Green

rsterne · Moderator

I have now conducted the next two test sessions.... I am using a long B&A adapter drilled out to 5/8" ID for a depth of 1.7" which adds 8.5 cc to the volume between the valve and the regulator.... I did this because in my 22XX testing I found that extra volume added performance.... I am running an 18 ci. tank (same physical size as a 9 oz. CO2) and a Ninja regulator to which I added a shim so that the pressure was higher than what I comtemplate using.... It turns out to be about 2000 psi.... The front of the tank is further back than a 22 ci. tank in the normal location so the balance of the rifle is unaffected.... The regulator is completely hidden by the stock with the gauge sitting in the square notch in the bottom front of the stock.... I installed the heavy hammer spring I got from Roald prior to these tests....

The first test was done with the flow-modded valve I got from Roald.... I got the leak fixed, it was a bit of dirt under the valve as I expected.... no problem there.... I was very pleased with the results.... I only started my shot string from 2500 psi (my SCUBA tank is only at 1500 and I didn't feel like hand pumping to 3000).... After recording and graphing the results I pulled the gun apart again, removed the barrel, and modded the lower port and lead-in as per Roald's instructions.... I then repeated the test with the new setup.... The results (including those from the initial testing) are shown below:

As you can see, the flow-modded valve and heavy hammer spring netted an average of 969 fps (32.9 FPE) with the JSB Exact 15.8 gr. pellets above the regulator setpoint.... At 1800 psi, the velocity was down to 940 fps (31 FPE) and at 1600 psi it was down to just above 900 fps (28.4 FPE).... I tried a few shots with JSB Exact Heavy 18 gr. pellets (above setpoint) and they averaged 936 fps (35 FPE)....

When I ported the barrel, I gained about 20 fps.... but the interesting thing is that the air usage did not increase.... I got the same number of shots from 2500 psi down to 1500.... but at higher energy.... The JSB 15.8 gr pellets averaged 988 fps (34.4 FPE) above setpoint.... 963 fps (32.5 FPE) at 1800 psi.... and 920 fps (29.7 FPE) at 1600 psi.... Once again, I tried a few JSB 18 gr. pellets.... and they averaged 951 fps (36.1 FPE) above setpoint.... It is significant that porting the barrel significantly increases the EFFICIENCY of this platform on HPA.... ie the amount of FPE produced per cu.in. of air used.... You get about 1.5 FPE extra per shot, at no cost in air usage....

The maximum performance numbers are a bit above what I want.... I am aiming for ~900 fps with the JSB 18 gr. Heavies (~32 FPE).... It looks like I should be able to achieve that at about 1800 psi.... or maybe a bit less.... I am thinking about shaving down the end of the hammer spring guide to reduce the preload slightly as it is obvious that the current spring is capable of handling at least 2000 psi.... Has anyone done this?.... Do you know how much to remove so that the valve would be right at the peak of the velocity curve at 1800 psi?....

Bob

Dust · Member

34 to 36 fpe isn't bad at all. That's Marauder territory

rsterne · Moderator

I have spent the last while refining the settings on this gun.... It was actually a little hotter than I wanted and in the interest of more shots per fill I reduced the regulator pressure and the hammer spring preload somewhat.... I am now running ~1670 psi regulator pressure.... Judging by the shot string, the ideal setup would be even less preload on the hammer spring (and if necessary a slightly higher regulator pressure).... but I have already machined off most of the base portion of the spring guide that Roald supplied with his heavy hammer spring setup.... I shortened it by 4mm (0.160").... It would appear that using the drilled out long B&A adapter to get the extra 8.5 cc volume between the valve and the regulator was key to improving the efficiency of this platform.... Although I am only running an 18 ci. tank, I am getting similar (or higher) shot count to the standard 22 ci tank and short adapter setup at these energy levels.... Here is a full shot string (9 clips) from 3000 psi down to 1600 using JSB Exact Heavy 18.1 gr. pellets:

You will note that the string starts out at ~920 fps and gradually loses ~10 fps as the regulator output drifts downwards as the tank drains.... As soon as the regulator hits setpoint, the velocity drops below 900 fps.... the average velocity over the 68 shots above setpoint was 913 fps (33.5 FPE) with a high of 923 and a low of 906.... That represents a total velocity variation of under 2%.... which will cause less than a 1 pellet diameter vertical shift in the POI at 50 yards.... certainly better than I can shoot.... The efficiency is the best I have ever achieved at these power levels.... 68 shots at 33.5 FPE is a total of 2278 FPE.... 1300 psi / 14.5 = 89.7 Bar times 18 ci. equals 1614 ci. of air at 1 Bar.... That works out to 1.41 FPE/ci.... which is 11.6 Barcc/FPE for those who use that measure of efficiency....

I have fitted the gun with a Leapers 3-9 x 40 AO Scope in medium height Leapers rings.... one of my favourite setups for airguns.... the gun weighs 8 lb. 4 oz. complete and balances about the middle of the forestock, just behind the swell designed for your hand.... I find that quite nice.... The only modification I had to do to the stock was remove the forward portion that covers the 88 gr. CO2 cartridge and drill one hole in the side for the male Foster fill fitting.... The Ninja regulator is short enough that it is hidden by the stock, and the gauge sits in the square notch in the bottom of the forearm.... I really like the 8-shot rotary magazines.... They index reliably when you function the bolt, and can handle pellets up to and including 28.4 gr. EunJin Domes....

I tried a variety of pellets (1 clip of each) with the following results:

JSB Express 14.3 gr: 987 fps / SD of 2.0 / 30.9 FPE
JSB Exact 15.8 gr: 943 fps / SD of 3.0 / 31.2 FPE
JSB Heavy 18.1 gr: 913 fps / SD of 2.6 / 33.5 FPE
H&N Baracuda 21. 0 gr: 832 fps / SD of 3.3 / 32.3 FPE
JSB Monster 25.2 gr: 747 fps / SD of 2.6 / 31.2 FPE
EunJin Domed 28.4 gr: 711 fps / SD of 1.0 / 31.9 FPE

It turns out that my favourite pellets end up with the highest energy in this gun.... and their velocity is right where I want it.... any higher and the BC would be falling quickly and the gains would be lost in the first few yards anyway.... This has been a very interesting and rewarding project.... My thanks to Roald for all his help and advice.... and the first rate parts, of course....

Bob

fritz · Silver Status Member

Information... overload.

Bob, you could charge us for this information. You really need to start making custom airguns. What kind of accuracy are you getting out of it?

Dust · Member

Is drilling out the B&A adapter a standard mod, or something that you came up with while playing with it? I would like to get my 177 850 as effecient as possible, but not that worried about big power.

sniper · Silver Status Member

if bob has any humanity he will be donating his brain to science. Laughing

bob, you need to get an ad deal going with airgun makers

as a outside sales rep in conjunction with joe.

you 2 are the reason i own a pcp. Razz

rsterne · Moderator

Accuracy: Only tested inside as yet.... one ragged hole at 20' as it should be....

I came up with the idea of drilling out the long B&A adapter.... I took one look at the lack of volume between the valve and the regulator and figured it was a no-brainer.... It looks like I was right.... The 850's that Roald sells are about 72-80 shots at just over 900 fps with 14.3 gr (~26 FPE).... He makes a hotter version (on request from what I understand) that gives "about 60 shots" at 31 FPE.... (~940 fps with 15.8 gr. Exacts).... His guns all use a 22 ci. tank with an 1800 psi regulator and the short B&A adapter.... He will also detune the gun to under 20 FPE for FT work.... more shots, of course....

I have a feeling he will be surprised at how many shots I am getting with the 18 ci. tank.... I know I was.... I was hoping for about 50.... Shocked

I get a real hoot out of playing with PCPs.... Not only can you get better performance.... but when I can do it with an increase in efficiency it REALLY turns my crank.... Mr. Green

Bob