Short stroke 80 Loud!

[maximus]

Hi, my 177 60mm stroke 80 shoots nice, good power, low recoil but seems to have quite a crack with it on firing. What would do the BBS tuners think the causeof this could be? TP is about 3.5 btw. Bit slammy from too much spring perhaps?

[Shed tuner]

they are louder.. higher barrel pressure at pellet release...

Shoot it with different weight JSBs and see what energy differences you get.. gives an idea of it's got too much preload, e.g. 7.9s and 8.4s ?

[TonyL]

As Jon says, give it a try with those different pellets.

That's quite a short stroke you're running. Different rod or head? To my mind, you're having to work that reduced volume a little too hard and a short stroke / wide bore won't be as efficient as a longer stroke / narrower bore set-up with the same swept volume. I think a stroke value in the region of 66 to 70mm will provide a softer feel? Playing with piston weight may help, too.

[john79]

Does it have a silencer on it? my 177 80 had a v-mach kit fitted and it had a silencer ...it was very quiet

[maximus]

Thanks for the replies lads. It is fitted with a steel vmach Silencer but they are not the quietest, just look the coolest. I'll do a bit of chronoing and post the results. The piston is lightened by having holes drilled in it but I added weight back with a steel top hat. Accuracy is good with 8.4 job's. Will chrono with the 7.3s and see. Probably did when I was setting it up but can't remember the Results.

[Mach 1.5]

I think the piston may also be the problem. Try one without holes drilled in it. Too many causes a drag factor with the airflow. Mach 1.5

[maximus]

Right, I've had a faff about with it this afty. Initial chrono was 780 with 8.4 and 862 with 7.3 a bit high with the light ones and .7ft lbs difference. Took it apart and it had a steel top hat and a 2mm brass washer and 2mm plastic washer in front of the top hat plus a 3mm plastic washer on the guide. First iteration was to remove the two plastic washers which gave 745 with the 8.4 and 805 with the 7.3. Bit low. I then added a 2mm steel washer in front of the top hat and got 755 and 815. Finally I removed the steel washer (2mm) and replaced the 3mm guide washer this gaining 1mm of pre load plus a rear thrust bearing. Power is now 766 with 8.4 (just over 10.9) and 830 with 7.3 which is just shy of 11.2. These seem good numbers to me so am leaving it at that. Still goes off with a grunt but not as bad as before. Can't test accuracy now thou due to rubbish weather but hopefully it will still group as good as it did before!

[Shed tuner]

yup, perfect, now leave it alone and enjoy it

The big 30mm bore does need a decent amount of piston weight to conteract the back pressure, so I wouldn't go very much less than stock, even with that shorter stroke.