FWB 300S needs help

[Steve Milbocker]

Hey guys I bought my 300s a couple of months ago and to say I've been impressed would be an understatement. Lots of literally 1 hole groups of 5 shots at 13 yards in my basement. Then all of a sudden a weak sounding shot and groups open up. Then a pellet stuck in the bore. After removing it the cavity looks to be filled with gunk and tiny white particles that feel like grains of sand. It has a green colored breech seal so I'm assuming it may have newer seals from what I've read but not being a tinkerer I couldn't say for sure. Can anybody shed some light on my peril? If it needs a rebuild who is the best person for the job? I've got to have this German masterpiece of a rifle shooting one hole groups again!

[Frank in Fairfield]

Motorhead in California

[Roadworthy]

Motorhead would be one option.  You could also check with John in PA.

[Buldawg76]

The grains of sand are the original white piston buffer that has degraded over time into oblivion. It is time for a rebuild. Someone has replaced the breech seal with a current FWB green seal but neglected to replace the buffer along with it. It has a steel piston ring seal so it only needs disassembled, cleaned of all old buffer residue, lubed and new buffer installed.

BD

[RawDog R1]

+1

All that has happened is the original piston buffer has failed. The piston in a 300s has a synthetic polymer piece (bumper) to cushion the blow when it rams into the front of the compression chamber during every shot. It needs replacing BEFORE you fire another pellet.

If you cannot do it, or find another Smith to do it for you, send just the action to me. I will replace it for 30$ plus the part. I do not have a green Feinwerkbau buffet here at the moment, but I do have an ARH buffer. It is flat faced vs. the slightly domed FWB.

I will return your action ready to shoot again without buggered screws or additional scarring and will sport a fresh coat of Renaissance wax.

[Steve Milbocker]

Thanks everyone for the input. Raw Dog I may take you up on that. How does the buffer stop the pressure and allow the pellet to get lodged if the pressure is built by the compression ring?

[RawDog R1]

My suspicion from experience when my OEM buffer failed is that the piston doesn’t make a full stroke, nor at full speed?
Could also be that the transfer port is being blocked by the failing, waxy type material of the buffer.

And that is just a guess.
Whatever you decide, do not shoot your 300s until it is disassembled and buffer replaced. It won’t fix itself, nor do your airgun any favors.

[Steve Milbocker]

When it quit shooting thru the same hole I didn’t want to shoot it anymore. I knew she was sick!:)

[Frank in Fairfield]

So, Ron...
In this photo it is the white stuff surrounding the green gizmo?:

[RawDog R1]

That looks normal to me Sir. Blue is the breech seal, green is the piston buffer. What appears as white is the transfer port of the compression tube?

[Frank in Fairfield]

Excellent.
Thanks

[RawDog R1]

Here is mine Frank. The white halo is simply a flash reflection off of the metal of the transfer port.

[Buldawg76]

That looks normal to me Sir. Blue is the breech seal, green is the piston buffer. What appears as white is the transfer port of the compression tube?

Exactly as RD describes.
Blue seal is aftermarket either from German supplier or ARH earlier run of material. ARH seal and buffer used to be red for last few years, but just rebuilt a friends 300 and the ARH seal and buffer I got was a purplish color. His seals can come in various colors depending on his suppliers inventory of material.

Green is OEM current FWB seal and buffer.

https://www.ebay.com/itm/Feinwerkbau-Mod-150-300-300S-Piston-Buffer-Air-Rifle/373042907929?hash=item56db170b19:g:hQsAAOSwaJ9cWZzy

https://www.airrifleheadquarters.com/catalog/item/251485/6889471.htm

BD