Benjamin trails morning sickness

[Windmill01]

Hello, I'm new to this forum and am seeking some advise. I have two benjamin trails one in .177 and the other .22. The .22 is a very accurate air rifle and I have put through many thousands of pellets. All I have done to this rifle is to replace the seal once. The .177 was also an extremely accurate air rifle with approx 7000 pellets through it until this problem arose. 
It seems that it has developed an issue with temperature. In the morning when it's cool it will shoot up to two inches high until about 15 pellets have been put through it when it will drop down to target. In the afternoon and if I had adjusted the scope in the morning before it had warmed up the pellets will slowly drop to about two inches below target. I have replaced the seal and swapped scopes but the problem still exists whilst the .22 remains on target. Any ideas?
Thanks

 

[Bobbed06]

I would try and lube the chamber with a couple of drops of RWS chamber lube, also do the tissue paper test to see of the breech seal is leaking. Check the stock and barrel pivot bolt for tightness and the nylon pivot washers for wear. replace the nylon pivot washers with brass washers turned down to fit in the barrel recess.

Check my thread on the rifle below by searching for details.

Crosman Nitro Venom Dusk

 

[Windmill01]

Thanks for the info, I have done the tissue test and the o ring is sealing. I learnt the lesson a long time ago with using loctite as I had a Beeman R25 (I think that was the number) and it would loosen everything pretty quickly so the stock and barrel bolts are tight. The barrel is tight when it is cocked as I tighten the screw each time I lube the seal etc.. I also oil the chamber with Abbey silicone gun oil 35 every 250 pellets. The only thing I haven't done is replace the nylon pivot washer with brass ones. I have also had a new jam spring made that works very well. Where did you obtain the washers from. I live in Queensland Australia and we don't have access to air rifle parts etc that possibly you guys have. Thanks again for your help.

 

[Bobbed06]

Hillman 5/16 in brass washers readily available online or at home building supply houses. OD has to be turned down to fit barrell recess, very easily done with a bolt and power drill with a file. This mod is the key to accuracy, along with a spotless clean lightly oiled barrell.

Video linky below

 

[Windmill01]

Thanks again for your help, much appreciated. I take it that the 5/16 is the inside measurement. I've searched on ebay but can't find the hillman washers you suggested. I will try some of our local stores in town (Maryborough) next week when we do our shop. Do you know what thickness the washers are. You are spot on with the clean barrel I have found that the 177 really likes a clean every couple of hundreds pellets or so. Once cleaned it takes about 5 or so shots to re lead the barrel for it to be accurate again. Alas it's just not happening at the moment. Anyway it's interesting working through the various issues for the pursuit of accuracy.

 

[Bobbed06]

https://www.lowes.com/pd/The-Hillman-Group-2-Count-5-16-in-x-3-4-in-Brass-Standard-SAE-Flat-Washer/3203379

specs in link /\

 

[Windmill01]

Found the specs, now the hunt. Thanks for all your help, let's hope this does the trick.

 

[laalex]

Your issue is most likely due to the lube in the chamber having to warm up. Temperatures in the compression tube get up very high for a small fraction of a second at each shot. The lube thickens when cool. I would recommend against putting "chamber lube" through the transfer port--tends to fry piston seals. The brass washers mentioned above are a must with Crosman springers. 

 

[Windmill01]

Than you, I have taken it apart two days ago gave the chamber and piston a through degrease and used much less molly on the piston as well as not using a drop of silicon oil on the side of the piston seal. It's now shooting a little better only a half inch above target for the first couple of shots and then on target after that. It was 40 degrees centre grade here the other day and the 177 was shooting consistently all over the place and up to 4 inches below. I have the impression that it is something to do with the temperature but my other trail in 22 cal shoots on target no matter what the temp. I'll keep on experimenting. Thanks again.