FWB 65 – low speed problem…

[ABV]

Hello. I am new to this forum, but I have been following it for a while and learning a lot from your postings. I hope you can help me with my question below. I am sorry for the long post.. thank you in advance for your patience !

I acquired a FWB 65 in fabulous condition last December. Still had the original white buffer and piston seal; only the breech seal had been replaced many years ago for one of the blue ones -in the market at that time. After spending maaaaany weeks learning about the model over the internet, I finally gain enough courage to open it up to check the internal condition, replace the piston seal and springs and do an overall maintenance session. I ordered original spares from WaffenCenter-Gotha.
Last week I finally completed my project and took the gun to the field for a trial. It all seemed to be working beautifully: coking, trigger, anti-recoil, sights, etc. But at the end I put it through the chrony… and I got very frustrated with the results…

These are the readings of a 10 shot string. The pellet I used was Gamo Pro Match, 7.56g:
- Lo: 268.8 fps
- High: 319.1
- Average: 290.8
- Extreme Spread: 50.35
- Standard Deviation: 13.82

Terrible results. Even more considering that 1) I replaced the piston ring with a “Tuning” one and 2) my model has the dual spring set. I’m not looking to get more than the 450 fps average that the gun is supposed to deliver, but with these ‘enhancements’ I was sure I would have no problem getting to that mark at least.
I could think that such a large extreme spread is due to the brand new springs –and the cheap ammo maybe?-, but such a low speed is, I think, a symptom that something is not working the way it should.

I have been thinking about these 3 possible reasons:
1 – it seems that the chamber is not reaching its full closing position by 3 or 4 millimeters. I actually have to apply a bit of force to the cocking arm in order for it to lock. And I think the reason is the breech seal… I expected the material to be more like a flexible rubber (like the old blue ones) , but it is hard plastic. I think it is a bit long and not fitting the cone of the loading port perfectly because it is slightly denting it (the cone denting the seal, I mean). Does the fit get better after some rounds?
2 – I slightly polished the piston and the chamber. Very little really, only up until their surface was a bit shinier and smoother again. Is this perhaps preventing a good air compression?
3 – I noticed that the spring guide fitted better in one end of the spring than in the other (odd really… means that the spring then is not perfectly symmetrical??). At the end I placed the guide in the end with the easier fit. I am referring to the outer, thicker spring. Could this ‘tightness’ be slowing down the spring when it is released?

I am not new to airguns, and I am fairly experienced in servicing them. The fact that the gun is working well mechanically leads me to believe that it was not an error from the disassembly-reassembly process.

What do you think the problem could be?? Many many thanks for your advice!

- Alex

[kevinweiho]

ABV, did you change all the old seals with new seals? The newest seals are green in color except for the buffer which is black.

Can you explain what "tuned" piston ring was used? If the old ring is still in good shape and not cracked, it is not necessary to replace it. When assembling, did you slightly lubricate the piston and springs and if so, with which lubricant?

When I changed the seals on my FWB80, (did'nt change the springs, they were still good) I also felt that closing the compression chamber was a bit difficult, but after shooting the pistol for a time, the breech and buffer seals had broken in and was easy to close.

Did you notice any grinding sound between the two mainsprings when cocking the pistol? What is the current shot count, as new seals and springs need a break-in period to achieve maximum velocity.

[ABV]

Thank you very much for your response.

Yes, I changed the 3 seals. Indeed, breech and piston seals are green, and the buffer is black –Feinwerkbau originals.
I am attaching an image of the “Tuning “ piston ring. It has two over-lapping edges at the crack of the ring so –supposedly- not a single bit of air can scape in between, which generates better compression and thus a few additional fps.

I did lubricate the spring guide and both springs with a very thing/light coat of high grade Moly paste from Air Venturi. I did not lubricate the piston… I read many comments –including the instructions manual - where they recommend not to do so.
I cannot hear any strange noise when cocking; only the clinking sound of the bear-trap mechanism being activated. The cocking cycle feels pretty normal. Rather hard though, because the springs are brand new, but no alarming feel or noise.

I have put 70 shots through the gun so far.

I didn’t chrony the gun before the maintenance job. When I got it I noticed that the buffer was practically gone, and I didn’t want to risk chopping off the metal piece that goes in front of it. It is important to note though, that I found both the original springs and ring in good condition. But I thought that since I was going to open up the pistol and order spare parts anyway, I’d go ahead and replace them also since I didn’t know exactly how worn they really were .

- Alex

[kevinweiho]

I still recall many years ago when I reassembled the piston back to the compression chamber and at the same time, I had to squeeze the piston ring with my thumb and index finger. I found out it was a tight fit. I was curious to see if there was any air leakage, so I proceeded to do a test by covering the breech hole with my index finger and using my other hand to pull back on the piston like if it was a syringe. I felt resistance, that proves the ring was still good.

The manual tells you not to use any lubrication on the piston because the pistol had been “permanently lubricated” (with Moly) from the factory. When I got all the gunk off from the old seals, I cleaned and polished the piston and compression chamber, only applying a small amount of moly onto the groove of the piston ring. The remaining grease that oozed out was then smeared over the exterior of the ring.

I guess if everything is working, you’ll have to break-in your pistol (around 500 to 1.000 shots) to see if there are any changes in velocity. Are you getting good groups from the low velocities and have you tried lighter pellets that weigh 7 grains?

[Gwhite]

Another issue may be the age of the "new" seals. Depending on the age, material and storage conditions, rigor mortise may have set in. They may require a bit of breaking in if they are stiff.

[ABV]

Thanks again

Kevin – I am getting OK groups.. definitely not what the model can do. But then again, with such a large extreme spread velocities, achieving a tight group is physically impossible at this point. Also, we are both getting used to each other, gun and I : ) so I am sure the outcome will improve overtime.
I have not tried lighter pellets. But really, how much speed can a 0.56g lighter pellet deliver? +30fps? +50fps?? It would still be 100fps below expected average.
I guess you are right, the gun might need a long break-in period… everything else is working fine, the trigger is a dream and overall the pistol is a pleasure to shoot. I will keep shooting and chrony it every 150-200 shots to monitor progress

Let me ask you… when you replaced seals and serviced your gun, did it go back immediately to its previous performance? Did it also need a break-in period?

Gwhite – good point, it could be that too. Yet another reason to give it a chance and allow a few hundred rounds to see how she does.

[PFribley]

I have a 65,80 and a 90. When they needed work I sent them to our host. Pilk guns. Fast turn around time. Quality work. And reasonable fees for their service. The best part about it is. When I get them back they work as new. No grief!!!

[Misny]

I have a 65,80 and a 90. When they needed work I sent them to our host. Pilk guns. Fast turn around time. Quality work. And reasonable fees for their service. The best part about it is. When I get them back they work as new. No grief!!!

I've had the same experiences with Pilkguns. My old 65 shoots like new and I can't tell you how much they did for my Morini. Pilkington is tops in my book, too!

[ABV]

I don't doubt it. The problem is that I live abroad ... and unfortunately over here that kind of quality service is not available. You have to learn, try and hope for the best : ( You are very very lucky to count with such a reliable resource!

[kevinweiho]

Let me ask you… when you replaced seals and serviced your gun, did it go back immediately to its previous performance? Did it also need a break-in period?

Alex,
When I replaced the seals, my gun wasn’t back to its peak performance until I could easily latch up the cocking lever. I did a couple bag rested, five shot groups and was amazed that the gun was able to group them into a single elongated hole. I had tested with various pellet brands (Gamo, H&N, and RWS) and weights, and found the 7 gr. pellets to be the most accurate. By the way, remember to add some blue loctite on the pivot lever screw, as it will work itself loose over time.

May I ask where you’re living abroad? In Costa Rica, there are very few gunsmiths who will work on match airguns, and will cost you an arm and a leg to get them fixed.
That is one of the reasons why I decided to service my own guns.

[ABV]

Thanks for the tip Kevin. And which pellet in 7.0g have you found to work best with your gun?

I live in central Mexico. We do have gunsmiths that can deal with a standard spring gun, but I don't trust them with a precision instrument like the 65. Just like you, I have learned by researching and trying. That is why forums like this one are truly invaluable.

[kevinweiho]

My gun is the most accurate with RWS Meisterkugeln pistol pellets. The Diabolo Basics are accurate as well, but your results may vary.

Yup, the same here. Smiths can do service for simple spring guns; some are butchers when dealing with finer and more sophisticated guns.

Are the current Mendoza spring rifles still considered as “mierdozas” ?. I have a ten year old RM-800 that has taken down a good number of pests throughout the years.
There was a rumor in the internet that rifles with quality control are being exported, while “defective” rifles are being sold in Mexico.

[ABV]

Hahaha Well, here's the deal with the Mendozas... I believe that expectation is the mother of frustration. The Mendozas are very basic springers, good for plinking, that you can find here for about us$160. The problem is that people expect them to perform like Anschutz and when that doesn't happen the norm is to blame the brand. Some of them are actually good looking rifles. I have one as well, a RM 600, and she is a consummated can killer at 30-40 meters : ) lots of fun ...
But you know, I have actually learned a lot from her. Trying to squeeze a decent performance from a basic springer significantly sharpens your shooting technique.

[kevinweiho]

Shooting springers accurately with open sights is very challenging and really helps to reinforce and perfect your “follow through”; they have the slowest “lock time” among the airgun powerplants.

My gun came with a factory test card, but I was unable to reproduce a similar tight grouping probably due to the dieseling design of the rifle.