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THEOBEN ELIMINATOR .22 (CM III). LEAD/LUBRICANT DEPOSIT IN THE BORE AFFECT ACCURACY: HERE HOW I’VE SOLVED THIS PROBLEM.

Posted by ROBERTO on July 31, 2000

    What all the Eliminator owners knows is that this rifle tend to lead the bore after a couple of tenth shots, these lead/lubricant deposits affect the accuracy, resulting in open groups.
I’m use to clean barrel by using a cleaning rod and some MP5 oil, but I’ve noticed that on the Eliminator this method only removed partially these heavy deposit, because after some few tenth shots they were again there, harder than before.

    Thanks to Airgunletter, I’ve discovered JB Bore Paste, and after this treatment the bore was again mirror-like and the groups sub-inch at 50 meters (premiers).
The only problem is that this treatment last hundred shots, more o less... then again this deposit start growing.
Because JB paste is a little abrasive, I didn't like use it so much frequently, so I started thinking on a solution.

    My opinion is that lead deposits are due to the fast peak of pressure, typical on springers, that opens the rear cavity of the pellet, "splatting" it in the bore, increasing excessively the friction between the barrel and the pellet skirt.
On Airgun World, Feb. Issue, an article say the Premiers are suitable up to 25 FP.. and this is the low power end for an Eliminator..
Also the lubricant used by Crosman to lube the Premiers have a part in this game. I was thinking it was not suitable for high powered spring guns.
I’ve e-mailed THEOBEN regarding this problem; this is the answer: “ ..... We know that Crosman Premier do lead up the bore. I understand Crosman are looking into the lead/antimony mix to improve the situation....

    In order to solve or reduce this problem I start thinking to wash carefully the pellets and relube them, may be using some hi-tech lubricants such as Dupont Krytox (PTFE dispersed in solvent) o micronized moly based lube, that I know are giving good results on many experiment conducted by some bullets and barrel manufacturers.
For this purpose THEOBEN gave me the following advice: “...The pellet lube we recommend is made by Lubro-Teknik. It comes in a 100ml pump spray bottle. It is really the best thing we have found. “

    At the moment I don't have this lubricant available, but I’ve ordered it and will report after tested.
Before starting my test I’ve selected many products currently available on the Italian market, but after had a very informative talk with a Dupont technician I’ve decided to proceed only with two brands:
- CRC Penlub: Penlube is clear, light, not grease, not flammable and contains molybdenum disulphide particles. This moly particles remain on the pellets surface when the others components are evaporated;
- Saratoga PTFE: this is a substitute for the Krytox, that I will have soon as a sample directly from Dupont. However this is based on PTFE molecules too, only little bit bigger than the original Dupont Krytox. PTFE is dispersed in a solution with volatile solvent, not flammable.
For the test I’ve used exclusively Crosman Premiers (are absolutely the best in terms of accuracy, ......and the worst for barrel deposit...) . The rifle was settled at +/-25 FP.

    Here the procedure:
1. wash the pellets using some nitro solvent and a brush;
2. put the pellet under fresh water to eliminate all traces of nitro solvent;
3. dry them by a soft cloth and an hairdryer;
4. light spray of lubricant on the pellets;
5. eliminate the excess of lubricant by using a clean cloth and air blow.
Clean the barrel using JB Bore Paste, following the procedure reported on Airgunletter (June issue). Remember to repeat this step if use pellets lubed with different product!
I’ve made 10 chrono sessions for each kind of lube, here a typical string (sorry, but measurement are in m/s ).

PENLUB PTFE
1 265,0 257,0
2 267,0 263,0
3 266,0 266,0
4 270,0 265,0
5 268,0 264,0
6 273,0 265,0
7 267,0 262,0
8 270,0 266,0
9 269,0 259,0
10 268,0 259,0
average 268,3 262,6
dev std 48,1 94,4
D s % 17,9 35,9
max 273,0 266,0
min 265,0 257,0
diff 8,0 9,0

    As preannunced from Dupont technician, the moly lubed pellets have an higher average speed (268,3 vs. 262,6 with PTFE), it means that moly, in this particular case, produce lower pellet/bore friction than the PTFE, it has also a better effect on consistency, in fact the DS % is 17,9 vs. 35,9.
In terms of friction, molybdenum disulphide shows superior qualities for pellets launched at high velocity, with high pressure between pellet skirt and bore. PTFE is well suited for lower velocity (I know some airgun manufacturers are experimentation Krytox for ten meters rifle/pistol..).
Now some more helpful details...

    During the test, and later in the week-end I’ve shot around 5-600 shots WITHOUT CLEANING THE BARREL AT ALL. All the accuracy tests resulted ALWAYS around 1” and 1.5” at 50 meters.
After all these shots the bore is still clean, and no traces of deposit are visible.
Yesterday, during a field trip, I’ve used Premiers lubed with both products alternatively (... just because things are not enough complicated.....), checking the impact point on a tree 40 meters far: the difference was unnoticeable.

    All this long report (hope not too boring..) is to share my conviction that accuracy troubles in the Eliminator are due to lead/grease deposit inside the bore and the solution could be wash and relube the pellets (please, don't tell me I’ve just discovered the hot water...). So now we have just to find the best lubricant (I will report again when I will have the Dupont Krytox and the Lubro Technic).
Hope this helps all the Eliminator/Crow Magnum owners (but also the owners of other powerful spring guns: I’ve made the same treatment on my 52 cal .177 - 20 FP Venom tuned- with great result!).
Robert

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