HW77 springy underlever

[AC all day]

Questions for the educated.....
I have just been given an old 25mm 77.....it's rust free and also finish free, not sure which way to go yet....leave as is, have reblued or wrapped....but that's not the question....
When I got it the underlever required a slight pressure to return it closed( it's fitted with a ball catch silencer) and frequently pops open. I had this before when lead swarf built up in the breech area, it's not that....also the breech seal is flatter than a flat thing( now removed no change). I have stripped it down and wondered my next move, could the cocking link be short and causing this? or looking at the face of the piston sleeve it is not dead flush with its sides, can and has this moved? Do I try a new sleeve?
Over to you guys??

[T 20]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

[piggy589]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

I had a 97 with the same problem,yes indeed, a cocking arm like a dog's hind leg

[TonyL]

Check the cocking arm or lever isn't slightly bent, which would cause your problem

I had a 97 with the same problem,yes indeed, a cocking arm like a dog's hind leg

Yep, agree.

Also, guessing it's a Mark 1, check that the sides of the foresight unit / underlever retaining recess aren't damaged and also that, if the unit has ever been removed, it's securely fastened (Loctited) in its rearwards most position.

[Rickenbacker]

Barrel bent upwards would give the same symptom.

[AC all day]

Thanks guys.....things to check for sure!

[AC all day]

OK I have checked the arm and linkage and the barrel all appear straight. I have placed a machined straight edge along them and can see no gaps. I tapped the silencer and the u/l now holds closed but is still springy.
Is there any difference between models on these guns?
Could it be the piston outer being too long?
Time to check out the bay, for parts!

[T 20]

Is there any difference between models on these guns?
Could it be the piston outer being too long ?

Not enough difference to cause the problem you have.

The piston shouldn't come into this as the cocking linkage only acts on the cylinder --- does the underlever fail to catch when both cocked and uncocked ?

[Geezer]

I presume that is a vintage slip-on suppressor held on by a grub screw (and maybe - my preference - a thin bras shim or -others - glue, loctite). It could be that it has moved a tad forward and now isn’t holding properly. Have you tried moving the suppressor back to increase the lock-up?

[AC all day]

I presume that is a vintage slip-on suppressor held on by a grub screw (and maybe - my preference - a thin bras shim or -others - glue, loctite). It could be that it has moved a tad forward and now isn’t holding properly. Have you tried moving the suppressor back to increase the lock-up?

Spot on exactly....it is a slip on silencer.
I have given it a gentle tap and yes it does hold the underlever but iirc from previous 77s you should just return the U/L and it snuck into place....there is slight springiness in this.
Currently there is no breech seal or mainspring in this and it's springy. As said before the crown of the compression tube is slightly raised by a mm or 1.5....
I have also just looked and 25mm tubes are rare so will 26mm fit??

[T 20]

Spot on exactly....it is a slip on silencer.
I have given it a gentle tap and yes it does hold the underlever but iirc from previous 77s you should just return the U/L and it snuck into place....there is slight springiness in this.
Currently there is no breech seal or mainspring in this and it's springy. As said before the crown of the compression tube is slightly raised by a mm or 1.5....
I have also just looked and 25mm tubes are rare so will 26mm fit??

A 26mm cylinder/piston assembly will fit.

I'd try putting a pellet in the barrel but leaving it's tail hanging out then closing the lever --- if the pellet is pushed fully into the barrel it tells you if the transfer port is hitting the barrel.

If the pellet remains proud of the barrel then the crown could be the problem --- easiest solution is to machine the crown on the cylinder back.

[Geezer]

Spot on exactly....it is a slip on silencer.
I have given it a gentle tap and yes it does hold the underlever but iirc from previous 77s you should just return the U/L and it snuck into place....there is slight springiness in this.
Currently there is no breech seal or mainspring in this and it's springy. As said before the crown of the compression tube is slightly raised by a mm or 1.5....
I have also just looked and 25mm tubes are rare so will 26mm fit??

Pleased to be of help. I have 3 of them with slip-ons, and two need occasional tightening to avoid the lever dropping down when fired. The other one is glued on really tight.

T20 has given you the other necessary advice on the innards.

These are great guns.

[AC all day]

A 26mm cylinder/piston assembly will fit.

I'd try putting a pellet in the barrel but leaving it's tail hanging out then closing the lever --- if the pellet is pushed fully into the barrel it tells you if the transfer port is hitting the barrel.

If the pellet remains proud of the barrel then the crown could be the problem --- easiest solution is to machine the crown on the cylinder back.

Now that is a really clever idea!!

Thanks for that.....I'll give it a try

[Daveo]

Did you sort this?
Could it be the anti bear trap?

[FPoole]

Sounds like you are saying the end of the compression tube sticks out from the walls of the compression tube. That would make the breech area hit the end of the barrel and try to pop the under lever back out. Not sure what holds the plug in the head end of the comp. tube, but maybe it has been "modified" for a tighter lock up. Machining the end of the tube flush won't help because it's the recess for the breech seal that's hitting the barrel.