FWB 300SU with Gehmann Irises on the iron sights

[dtdtdtdt]

Discussion of peep sight use on air rifles got me to thinking about the wonderful sights that came with my FWB300SU that I bought used 20 years ago.  I dug them out of the possibles sack and looked them over.

I found the original invoice for the rifle in 1978 (214 pounds) and for the upgraded sights FWB Model 650 (53 pounds).  At the time the exchange rate was about 3 dollars to the pound. I paid $350 for the whole set up rifle, sights, glove etc  including shipping in a rifle case from the UK to Chicago. (That's another story in itself - the Postal Inspectors and ATF, got involved!!)

The sights have Gehmann D75 adjustable irises and colored filters on the rear sight and an Gehma nn D75 adjustable iris on the front sight.  It also has a second shorter front sight and at least two sets of regular inserts.  There is also a riser attached to the sights for use with the higher front sight in offhand shooting.  The shorter set along with the shorter cheek piece appear to be for prone shooting.  The colored filters give the option of red, blue, yellow, gray, and two open/clear.

I went to the Gehmann site and found the D75 is not made any more but that there is a another model with 750 in its name that appears to have the same properties with the addition of polarizing filters. 

All this is wonderful BUT the iris adjustment dials on both front and back sights won't move!  I guess they are stuck.  I can't find a screw or any evidence of a locking device to keep them where they were set.  I don't want to get vigorous and damage them so am proceeding with caution.  The Gehmann sight specifically states that NO oils, greases, cleaning agents other than "pure" alcohol should be used on the sights.  (I found a comment from someone on another site that he was soaking his in KROIL!!!)

Has anyone else had a similar problem and know what to do?

[MDriskill]

You might try gently warming them up, and just keep working the dials. Then maybe try that drop of alcohol as a persuader if needed?

Some of my older ones are kinda stiff, but I've never had one lock up completely. You are correct, there is no sort of lock screw on them.

[dtdtdtdt]

Thanks for the suggestion on the alcohol.  I found a discussion somewhere else by a person who had the same trouble.  He took the Gehmann Irises off and put them in a small flat-bottom dish and filled with alcohol to above the iris mechanism but below the colored filters.  A few hours of soaking freed the rotating ring.  Sounds like Gehmann used some kind of lubricant that eventually dried out.  Mine are 42 years old (Bought in 1978!) so expect that is the problem.

One other piece of advice from that person, don't try to loosen them from the sight unit with wrenches other than the spanners that Gehmann makes. Since I didn't have them, I found a guy on eBay Canada that had the spanners and bought his LAST ones.  They are due in next week sometime.   

I will let you know what happens!!

[dtdtdtdt]

Final update on Gehmann iris release! 

I ordered the Gehmann wrenches and torque wrench from a shop in Canada selling on EVIL BAY.  Ordered May 8th, shipped Mau 10th, Arrived in Canada Customs May 11, LEFT Canada Customs JUNE 10th, arrived at my USPS on June 20th!!!!  Sad to say that USPS was the better of the two.  My feedback suggested that he look for a different shipping method!!

Anyway, 

I soaked the iris assemblies for the front and rear sights in isopropyl alcohol.   

The front sight iris released after about 2 hours in the alcohol.  After twisting it back and forth over the full range of motion, it loosened up nicely and works perfectly now.

The rear sight iris that also has filters of different colors to aid in sight adjustment.  The filters were working when I started.  The iris adjustment remained stuck after 3 hours in the alcohol.  I got out my ultrasonic cleaner and let it run for about 10 minutes.  The iris remained stuck and the white paint that let you see the setting came off.  A couple more minutes in the ultrasonic and I thought I could see some movement.  I wrapped the front edge with masking tape and gently applied a channel-lock wrench to the big end and the FWB wrench to the little end.  Gentle turning with slowing increasing pressure, it came loose and as above twisting back and forth over the full range of motion is functioning perfectly.

I will replace the white paint in the lettering with some of my wife's nail polish.  Not done yet will do it in the morning.

A successful conclusion.  By the way, used selling prices of the sights with the Gehmann irises exceed the whole price I paid for the rifle by 50%. 

[Yogi]

Final update on Gehmann iris release! 

I ordered the Gehmann wrenches and torque wrench from a shop in Canada selling on EVIL BAY.  Ordered May 8th, shipped Mau 10th, Arrived in Canada Customs May 11, LEFT Canada Customs JUNE 10th, arrived at my USPS on June 20th!!!!  Sad to say that USPS was the better of the two.  My feedback suggested that he look for a different shipping method!!

Anyway, 

I soaked the iris assemblies for the front and rear sights in isopropyl alcohol.   

The front sight iris released after about 2 hours in the alcohol.  After twisting it back and forth over the full range of motion, it loosened up nicely and works perfectly now.

The rear sight iris that also has filters of different colors to aid in sight adjustment.  The filters were working when I started.  The iris adjustment remained stuck after 3 hours in the alcohol.  I got out my ultrasonic cleaner and let it run for about 10 minutes.  The iris remained stuck and the white paint that let you see the setting came off.  A couple more minutes in the ultrasonic and I thought I could see some movement.  I wrapped the front edge with masking tape and gently applied a channel-lock wrench to the big end and the FWB wrench to the little end.  Gentle turning with slowing increasing pressure, it came loose and as above twisting back and forth over the full range of motion is functioning perfectly.

I will replace the white paint in the lettering with some of my wife's nail polish.  Not done yet will do it in the morning.

A successful conclusion.  By the way, used selling prices of the sights with the Gehmann irises exceed the whole price I paid for the rifle by 50%.

Good news!

Your wife has white nail polish?

-Y

[dtdtdtdt]

She thinks so! 

Not sure as she gets her nails sharpened professionally twice a month!!!  When we go up to bed this evening, I'll check.  Otherwise, I will stop at Wally World tomorrow and buy a cheap bottle.

Always something!!! 

[spevie]

The Markal paint stick is designed to fill the engravings with white paint. I don't think nail polish will work as well. The Markal product is used on things like Leica cameras, P08 pistols, various microscopes, etc...not expensive, and anything Gehmann deserves the best?

[dtdtdtdt]

Thanks for the suggestion.  I'll see if I can find it.  Google says a Fastenal store about 3 miles away sells them.  Quick Robin to the BATmobile!!!

Welcome to the site by the way!!!

[dtdtdtdt]

Spevie:

Thanks for the suggestion.  Found paint pen, different brand, but just as you suggested it worked great.

The paint filled the engraving perfectly and made the numbers visible but not "glowing".

LOOKS GREAT.

Thanks again
Dave

[dtdtdtdt]

Boo hiss!!! 

Two days after the "loosening" it's stuck again but not as bad. 

I suspect whatever was gumming them up re-precipitated when the alcohol evaporated.  I will just leave well enough alone for now since I am not using them anyway!

On the good side the white paint suggested worked a treat. 

Dave