Murat Gulkan (no login) from IP address 212.156.163.140
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First, a correction on earlier measurments of 650-680 fps: I took those measurements at approx. 8yds from the muzzle, as is the custom when measuring firearms. I noticed that this was an issue when I saw the large drop-off between MV and V at 10 yds in the Straighshooters.com velocity tests.
Corrected velocities, with 14.5grn RWS Superpoints, are: M48=695, M52=695, M54=710 fps. All guns have stock parts and altitude is sea level with temperature of approx 25 C.
The 48 has new parts with about 200 pellets thru it. The 52 belongs to a friend and has probably seen 1000+ pellets. The 54 is brand-new with about 110 pellets, most of them shot today.
I replaced the JM GSI kit on the 54 back with factory parts because it was, as posted two days ago, definitely much weaker than normal. The same guy installed and uninstalled the kit, bringing the 54 back up to par with the other two guns, so I assume he is ok.
An inquiry to JM produced some logical (and prompt, I might add) replies about potential leaks etc., but no obvious remedies.
Straightshooters velocity tests with exactly the same pellets put the 52 at 783fps and the 54 at 756fps, so I am well below those figures with all three guns.
This raises the question of whether or not these guns are of the "controlled velocity" variation. My undertanding is that some RWS guns in Europe are limited to 700fps (230 m/s), but the fact that the 54 is above that makes me unsure of these guns.
Does anyone know how to identify velocity-controlled guns, and / or how velocity is in fact controlled? I have so far heard 3 different answers. My gunsmith here says that they use a special steel washer to limit the airflow. I remember reading something similar in this forum a while ago (btw, these guns don't have that washer). Someone earlier wrote that they use a weaker mainspring, but don't identify it as such. Finally, an e-mail from the JM site (not written by JM himself) only says that the changes made to controlled guns are "deep and irreversible."
All suggestions and opinions are welcome. Should I give up and resign myself to life at around 700 fps? I plan to use the guns for hunting so velocity is important.
I also plan to contact RWS with the guns' serial numbers to find out their status. The dealer here doesn't know. All in all I am bummed though.
The German controlled version should have an "f" stamped on it somewhere I believe. As far as I know the only difference is the mainspring, because that's what they identify the export springs with as I had reported earlier on your previous post. They donot mention any other part for export models.
Contact DIANA directly in Germany, as they are the only ones to know if your rifle's serial number was for export or controlled German use http://www.diana-airguns.de/DIANA_Catalogue.pdf
M.
It seems strange that all the guns you mention....
June 28 2005, 7:05 PM
are shooting slow. At first, I would have said go for a new appex piston seal and a new breech seal but when the others you've mentioned are shooting the same, well that's a hard one to figure out. Is there any chance that the chrony you are using if reading wrong?
Anyway, there are things you can try, but before, let's get some things straight:
"Pentagon F" mark in German guns means they develop less than 6 ft-lbs. Definitely not your case.
The way German guns are made free (that's what the F stands for, free from permitting or licenses or documentation) is by using a different spring. That is straightforward. What is less known is that there are other changes to make the guns BREAK if they are tried to push beyond the legal limit. For example, the pivot where the lever pulls in the Pentagon F mark carries a different heat treatment process that should allow the piece to break if it was made to cock a 17 ft-lbs spring. And that is a reasonable power level to expect from a normal gun. Which would mean 726-727 fps for 14.5 grs. pellets. Other guns I've seen have a smaller transfer port. Still others have a controlled leak. So manufacturers anywhere try to take precautions against someone purchasing a 6 ft-lbs gun and turning it into a 17 ft-lbs beast; while in the proces mocking the law.
We've said this before, and I will say it again. Airguns kill with accuracy, not with power. Your gun is yielding 15.5 ft-lbs, plenty of power with a well placed shot for animals up to 30 lbs. weight.
If you want speed, change caliber. Go to 0.177" and you will get plenty of speed.
For the moment try chronoing with heavier pellets, some pistons simply behave better with heavier pellets. Until the piston is well burnished and the piston's skirt is as smooth as a baby's butt, you can get that level of difference in MV's. I would not suspect a leak, but I would suspect overlubrication and a new piston in a new gun. You can also try just a dab of some moly lube in the piston skirt, or try buttoning the piston's skirt.
Simply use the guns, have fun and learn to shoot them well. As they age, they will improve and so should all of us.