I lucked out and was able to buy a totally trashed HW80 barrel on ebay. LOL. The guy's description sounded apologetic, he knew it was not salvageable. But it has been perfect for my purposes, so I should thank him.
The issue is that both of my HW90's have barrel droop. About 0.5 degrees at the barrel to receiver joint. I think Weihrauch builds in some droop. According to an English HW35 review at https://www.gunmart.net/gun-reviews/airguns/air-rifles/history-of-the-hw35
The purpose of this project was to see if it's possible to eliminate droop caused by barrel block to receiver misalignment. I had been looking for a expendable Weihrauch barrel so the old HW80 barrel made a perfect experimental subject. The HW80 barrel was rusty and seriously bent. The guy said it spent time in an old tool box. I noticed the pivot hole had a spider web in it.
I mounted the barrel in my spare HW90 receiver and checked straightness on an old iron tablesaw wing that I use as a surface plate.
The barrel also had considerable sideways bend.
I had decided to skim some material from the barrel block stop pad. That would allow the barrel to swing just a little farther. I considered skimming the opposite surface in the receiver. But that would require a milling machine and a long shank carbide end mill to reach between the yokes. So that's out.
But how much material should be removed? I used basic right angle trig.
The formula is height = hypotenuse * sine (angle). The hypotenuse is the swing arm distance from the axis hole to the pad. That was 26mm + 3.5mm, = 29.5mm. Converted to inch yields 1.16 inches. I had measured barrel droop at 0.5 degrees. So the final value for height = 1.16 * sin (0.5) = 0.010 inches.
And how much material can be safely removed? Too much swing would allow the barrel block to hit the receiver. The gap measured 0.009".
The distance from the axis hole to the top of the barrel block was 22mm, or 0.870 inches. So the ratio between Hypotenuse A and B is 0.870/1.16 or about .75. So removing 0.010" from the pad would reduce the gap by .75, or 0.0075". That is mighty close to 0.009". What the heck, it leaves about .0015" gap.
This would be extremely easy with a milling machine. But I don't have a mill so the alternative is filing by hand. To support the file and keep it flat, I cut a block from old oak flooring. The slot is wide enough for the barrel block, plus a couple of pieces of double sided scotch tape.
Here's the support piece mounted on the barrel block. Note that I put a piece of double sided scotch tape on each side of the barrel block before mounting the oak piece. They are probably not necessary, but I wanted the oak piece to be absolutely immovable.
I filed the pad with my trusty smooth sided file. It has no teeth on the edge, to protect the part.
It took just a few strokes to remove 0.010". I actually dismounted it and tested in the receiver a couple of times. Slow is safe!
Then I mounted the barrel in the receiver and cycled it a few times. The pad shows a nice, even witness mark where the receiver stop pin contacts it. That means the oak piece kept the file flat during filing.
The barrel lockup seems unaffected by removing 0.010". It is not noticeably harder to 'break' the joint. So I think that is not an issue. A more important consideration is the receiver gap, which now measures about 0.001". I checked it with light.
The barrel block and receiver are now within 0.1 degrees of each other. Originally it was 0.5 degrees. I regard that as a success.
But we still have 0.6 degrees droop caused by the flat spot on the aft of the receiver. If you use a scope, you'll still have to use a drooper mount.
So this can be done. Would I do this to a good barrel? No, probably not, for several reasons:
However, for the lucky folk who have a Beeman RX, can you check for barrel droop? I have a theory that Beeman ordered RXs from Weihrauch with no barrel droop. If that's the case, it was probably accomplished by mounting the receiver stop pin a little lower. I'm curious.
The issue is that both of my HW90's have barrel droop. About 0.5 degrees at the barrel to receiver joint. I think Weihrauch builds in some droop. According to an English HW35 review at https://www.gunmart.net/gun-reviews/airguns/air-rifles/history-of-the-hw35
The purpose of this project was to see if it's possible to eliminate droop caused by barrel block to receiver misalignment. I had been looking for a expendable Weihrauch barrel so the old HW80 barrel made a perfect experimental subject. The HW80 barrel was rusty and seriously bent. The guy said it spent time in an old tool box. I noticed the pivot hole had a spider web in it.
I mounted the barrel in my spare HW90 receiver and checked straightness on an old iron tablesaw wing that I use as a surface plate.
The barrel also had considerable sideways bend.
I had decided to skim some material from the barrel block stop pad. That would allow the barrel to swing just a little farther. I considered skimming the opposite surface in the receiver. But that would require a milling machine and a long shank carbide end mill to reach between the yokes. So that's out.
But how much material should be removed? I used basic right angle trig.
The formula is height = hypotenuse * sine (angle). The hypotenuse is the swing arm distance from the axis hole to the pad. That was 26mm + 3.5mm, = 29.5mm. Converted to inch yields 1.16 inches. I had measured barrel droop at 0.5 degrees. So the final value for height = 1.16 * sin (0.5) = 0.010 inches.
And how much material can be safely removed? Too much swing would allow the barrel block to hit the receiver. The gap measured 0.009".
The distance from the axis hole to the top of the barrel block was 22mm, or 0.870 inches. So the ratio between Hypotenuse A and B is 0.870/1.16 or about .75. So removing 0.010" from the pad would reduce the gap by .75, or 0.0075". That is mighty close to 0.009". What the heck, it leaves about .0015" gap.
This would be extremely easy with a milling machine. But I don't have a mill so the alternative is filing by hand. To support the file and keep it flat, I cut a block from old oak flooring. The slot is wide enough for the barrel block, plus a couple of pieces of double sided scotch tape.
Here's the support piece mounted on the barrel block. Note that I put a piece of double sided scotch tape on each side of the barrel block before mounting the oak piece. They are probably not necessary, but I wanted the oak piece to be absolutely immovable.
I filed the pad with my trusty smooth sided file. It has no teeth on the edge, to protect the part.
It took just a few strokes to remove 0.010". I actually dismounted it and tested in the receiver a couple of times. Slow is safe!
Then I mounted the barrel in the receiver and cycled it a few times. The pad shows a nice, even witness mark where the receiver stop pin contacts it. That means the oak piece kept the file flat during filing.
The barrel lockup seems unaffected by removing 0.010". It is not noticeably harder to 'break' the joint. So I think that is not an issue. A more important consideration is the receiver gap, which now measures about 0.001". I checked it with light.
The barrel block and receiver are now within 0.1 degrees of each other. Originally it was 0.5 degrees. I regard that as a success.
But we still have 0.6 degrees droop caused by the flat spot on the aft of the receiver. If you use a scope, you'll still have to use a drooper mount.
So this can be done. Would I do this to a good barrel? No, probably not, for several reasons:
- It only corrects for droop caused by barrel to receiver lockup.
- It's limited to about 0.4 degrees. Because you need some gap.
- It's too easy to screw up
- Weihrauch may have intended it to have droop.
- Droop doesn't affect gun function.
- Drooper mount still required for scopes.
However, for the lucky folk who have a Beeman RX, can you check for barrel droop? I have a theory that Beeman ordered RXs from Weihrauch with no barrel droop. If that's the case, it was probably accomplished by mounting the receiver stop pin a little lower. I'm curious.
