GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: 11x on June 10, 2014, 07:54:40 PM
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Ok so I got a Hammerli Pneuma. my first .22 as well as my first PCP. I have done some reading about usable pressure ranges and tuning. I would like to get some advise from some more experienced PCP folks. I see where some people like a 3% variance and sum as much as 5%. I plan on hunting/pesting as well as showing off to friends with awesome acts of accuracy on occasion.
I am shooting jsb 18.13gr. as far as I know the rifle is in stock trim.{got it used}. filled to 200 bar and started slinging lead.
shot string looks like this.
783.9
784.8
788.2
791.5
790.8
794.3
795.7
801.7
807.6
809.4 ----shot 10------down to 175 bar
804.8
811.2
813.6
816.4-----shot 15
843.3 ??? fluke?
819.6
824.3
826.6
832.3-----shot 20---down to 150 bar
error
831.3
826.4
835.5
831.6-----shot 25
error
837.1
860.8--here is where things get weird. rifle seemed to get louder here
859.6
856.6----shot 30
852.3
856.3
828.9---back to normal
827.8
822.7----shot 35---down to 120 bar
821.4
error...... sun went behind some clouds and I think that had something to do with the errors from here on
827.8
error----sound of rifle got weaker from here on out
error
error
807.1
801.0
So what I would like to know is does this string look normal? Where is the sweet spot? What tuning might I try to get a better shot string. I have read about plugging some of the ports and adjusting the hammer spring. I also looked into a regulator. It is almost 100$ but I have to decide on what pressure I would like to set it at. The builder suggest 110 bar. I was thinking more like 120. Also what's up with that 5 shot group that jumped way up about shot 30?
Please feel free to make any suggestions you would like, as long as they are conducive to the conversation. I hope to start a good dialog here.
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The ES you choose depends on the maximum range you will be shooting.... a 4% ES is good to about 50 yards, at 100 yards you need 2% or less.... If you only shoot 20-25 yards you can probably get away with 10%....
I have no explanation for the high velocity shots between # 28-32, that isn't normal.... Discounting those, your string peaks at 837 fps, so 96% of that is 803, so I would discard anything less than that and look at the rest.... That means that as tuned, your fill should be to about 180 bar.... I would agree that 110-120 bar would be the place to regulate.... the higher number if your plenum volume is limited....
Bob
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thanks for the input. I have read some of your posts and they are very useful. I don't plan on taking any serious shots past 50 yds. To much room for error and I am not willing to take that much of a risk at wounding something. I think I understand what you are saying. If I disregard the abnormally high numbers and assume that they were some where between the previous normal shot and the following normal shot than that gives me 31 shots from 807.6 to 807.1 with a peek of 837.1 that would be filling to about 180 bar and shooting down to about 105 bar.
Did I get that right?
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Bob is very good at it, He took a lot of guessing and trail and era out of my game. What I would do 1st is to see where you are at? set up the chrono and a target and look for poi change as you shoot, how many shots do you get before the poi change, and that would include after the fill, and take note where the air pressure is when it is at the top of your poi and where it is when it falls off, then I would regulate as many shots as I can get at inside that range pressure. Now you have a curve that you can work for. Looking at your string I would try a curve between 820-837fps
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Assuming it’s a single shot Pneuma and not the multi shot Pneuma Elite.
Were it mine, and I wanted the power, would probably crank up the striker spring adjustment about 1 ½ turns and try another string starting at about 170-180BAR.
Depending on how turned out, might increase spring tension another ½ turn and try again.
Striker spring van be adjusted from the hole in the rear end cap. Does take a long 6mm Allen.
There is a hole in the bottom of the air tube that will line up with a corresponding hole in the nose of the striker. By slipping in a rod (or small allen key will keep the striker from rotating as you adjust the striker spring.
(http://i157.photobucket.com/albums/t50/ribbonstone/pneuma/DSCF1199.jpg)
I had to make a long allen key by cutting off a short allen key and silver soldering it to a brass rod. Much better to buy one.
(http://i157.photobucket.com/albums/t50/ribbonstone/pneuma/DSCF1192.jpg)
(http://i157.photobucket.com/albums/t50/ribbonstone/pneuma/DSCF1201.jpg)
Striker spring adjusts “OUT” (counter clockwise) to INCREASE spring tension.
If i were looking for lower power and a long shot count, would do the SAME AS ABOVE to get it running right at about 180BAR, then start plugging valve ports to lower speed/increase shot count.
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thanks so much for the advise. I may play with tuning the hammer spring. it should be a fun project. as far as poi. it seems to start off high left by about 2". as the shots progress it comes back. if I remember correctly it was at about shot 15 (816.4fps) about 160bar and stayed constant until I stopped my string (801.0fps). mind you I am only shooting at 21 yds but I can keep my groups to under .5".
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ps. thanks for the pictures. that really helps.
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thanks so much for the advise. I may play with tuning the hammer spring. it should be a fun project. as far as poi. it seems to start off high left by about 2". as the shots progress it comes back. if I remember correctly it was at about shot 15 (816.4fps) about 160bar and stayed constant until I stopped my string (801.0fps). mind you I am only shooting at 21 yds but I can keep my groups to under .5".
then that is good to know so what I did at that point was to adjust the hammer spring from a full @ 200bar and tried to get the 1st shot as close to my sweet spot as possible. and this is what I ended up with, my 1st few shots poi was acceptable, just a 1/4 from the consistent group by shot number three I was on line for the next 15 shots, I have mine set to a 15 shot string
903
903
910
913
913
908
911
913
911
913
913
912
911
906
900
901
893
888
888
883
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thanks. I plan to do some tinkering this weekend if I get time. lol I will report my results