Bad compression tubes

[evert]

Do other people get rifles with bad comp tubes?
When working on my own springers have found a few bad tubes: some have tight/high spots in the middel of the tube, and some have ridges down at the bottom that chew up piston seals.
I'm not talking about Chinese guns, but German and British guns that are supposed to be good; a HW80 had a sharp ridge at the bottom, several Supersports seem to be oval and leak lubricants past the seal, a Tx200 with bulges, and the list goes on...

Do other people get them too, or is it just me?

[TonyL]

I've not knowingly had a gun with a bad compression tube, evert. Pretty sure I'll have had one or two, though, but been blissfully unaware. I suppose that unless a gun fails to deliver the expected power output or the force when re-inserting the piston is inconsistent, many "average" users won't be aware.

At least it'll be an easier fix on guns with sliding comp tubes.

The worst I've seen on one of mine is the Mercury S I tinkered in the Winter, where the model designation stampings are visible on the inside of the cylinder. Not too sure if this has affected anything.....piston polished, a smear of high moly content paste on the tail and some moly grease on the inside of the cylinder behind the piston when at the forward position and all seems smooth and fine.

Problems in the compression area itself will present much more of an issue, as you indicate.

[HW55T]

Do other people get rifles with bad comp tubes?
When working on my own springers have found a few bad tubes: some have tight/high spots in the middel of the tube, and some have ridges down at the bottom that chew up piston seals.
I'm not talking about Chinese guns, but German and British guns that are supposed to be good; a HW80 had a sharp ridge at the bottom, several Supersports seem to be oval and leak lubricants past the seal, a Tx200 with bulges, and the list goes on...

Do other people get them too, or is it just me?

Your jinked mate, give the sport up and go find another one that is perhaps hex free lol

Or maybe your just a perfectionist and notice more because of it ?

I've noticed a Hw35 .177 with a tight spot in the barrel about 2/5th up and a early mk2 Hw77 .177 with a choke so tight at the muzzle, I'm sure the pellets were coming out less than 4mm.

Honing comp tubes is a option, just practise on a piece of spare tube first so you can gauge how much metal your taking off with it. ;-)

[evert]

Or maybe your just a perfectionist and notice more because of it ?

Might be something in that...

Honing comp tubes is a option, just practise on a piece of spare tube first so you can gauge how much metal your taking off with it. ;-)

Problem is, my perfectionism shows up with cylinder honing too.. Those flexible hones does not correct out of spec tubes, they just follow existing imperfections.
The only really good way to hone a tube for us amateurs, is to lathe turn a brass rod to fit the comp tube and spin it in the tube covered in fine grinding paste and oil.
It works, but is a bit more tedious than using a flexible cylinder hone.

[Barryg]

Do other people get rifles with bad comp tubes?
When working on my own springers have found a few bad tubes: some have tight/high spots in the middel of the tube, and some have ridges down at the bottom that chew up piston seals.
I'm not talking about Chinese guns, but German and British guns that are supposed to be good; a HW80 had a sharp ridge at the bottom, several Supersports seem to be oval and leak lubricants past the seal, a Tx200 with bulges, and the list goes on...

Do other people get them too, or is it just me?

The only one that I can remember is a Mk 2 Airsporter.

Are the guns you are talking about new or S/H I wouldn't be surprised if AA would put the TX right.

[frogboy]

Yes.

I decided to undertake the sleeving of a HW80 to take a 25mm piston. EdBear took the cylinder and cut a piece of aircraft grade tubing to fit, Ed having made a couple of these conversions in the past, he measured the depth and referred to another tuners guide on the web as to the correct length. He returned all the bits to me saying that it was ready for me to fit together, he wasn't doing it as it was a one attempt try and if it went wrong, it would probably result in a scrap cylinder.

I checked the depth and it seemed to match the sleeving tube length. Locktite in the cylinder started to push the sleeve in and it went solid with about quarter of an inch to go, whatever I did it wouldn't move. I took it back to Ed who after much swearing at my incompetence took it away. I saw him the next week at bell target with one cylinder that he had welded a home made extractor through the cocking slot, heated the cylinder to break the locktite and removed the sleeve.
He had then measured the internal diameter and found that the last quarter of an inch was tapered, preventing the sleeve from reaching the bottom of the cylinder.
He also had fitted a new sleeve into the cylinder, allowing me with a little help from BTDT to finish the job.

So yes I have had a similar experience, and it was nearly a costly one

[mrto]

I have a BSF B55 the cylinder of which is pinched at the point the stock mounting lugs are welded to the cylinder.The gun shoots fine with a synthetic parachute seal which is flexible enough to compensate for the pinch at that point in the cylinder, following the contours of the irregularity.I don't know if this is common to all B55's.

I do know the overall build quality of the B55 does not live up to the legend!

[FPoole]

Might be something in that...



Problem is, my perfectionism shows up with cylinder honing too.. Those flexible hones does not correct out of spec tubes, they just follow existing imperfections.
The only really good way to hone a tube for us amateurs, is to lathe turn a brass rod to fit the comp tube and spin it in the tube covered in fine grinding paste and oil.
It works, but is a bit more tedious than using a flexible cylinder hone.

The brass rod thing won't be accurate either. You need a pin fitting hone. Sunnen makes the good machines here. You can buy a mandrel and use your own lathe, I suppose. I had a TX tube honed on said machine, years ago. The operator sets the thing up for the 1" bore and makes a very few seconds of strokes, to test the pattern before going all the way. Puts a beautiful crosshatch on the cylinder walls just like AA tubes have. My tube was perfect except for some marks where the bear trap notches are cut in. There is also the spot on the inside of most TX tubes opposite the cocking shoe slot, but this is never in the stroke of the seal. As long as the extreme spread for a shot string of 20 or so doesn't exceed 15 fps, I wouldn't worry. A barrel can also make the velocity spread change, so how do you know which it is?

[Shed tuner]

the ABT slot in TX tubes can sometimes cause tight spots in the tubes. Also had a tight spot on a BSA standard, but then that had a massive dent on the outside too.. took some metal off with a file, smoothed with wet n dry, power went up by 2 foot pounds. A brass mandril and some polishing paste is generally a good way to remove tight spots.. bulges are obviously harder work...

[evert]

The brass rod thing won't be accurate either. You need a pin fitting hone. Sunnen makes the good machines here. You can buy a mandrel and use your own lathe, I suppose. I had a TX tube honed on said machine, years ago. The operator sets the thing up for the 1" bore and makes a very few seconds of strokes, to test the pattern before going all the way. Puts a beautiful crosshatch on the cylinder walls just like AA tubes have. My tube was perfect except for some marks where the bear trap notches are cut in. There is also the spot on the inside of most TX tubes opposite the cocking shoe slot, but this is never in the stroke of the seal. As long as the extreme spread for a shot string of 20 or so doesn't exceed 15 fps, I wouldn't worry. A barrel can also make the velocity spread change, so how do you know which it is?

Professional honing tools are obviously the best solution, but they are not available to most of us. Many have access to a lathe, so fitting a brass lapping plug is a more likely option.

Its not only about velocity fluctuations, its about guns that tear up seals, dont make power, leak lubricants past the piston seal and burn up piston seals fast.

[hmangphilly]

Do other people get rifles with bad comp tubes?
When working on my own springers have found a few bad tubes: some have tight/high spots in the middel of the tube, and some have ridges down at the bottom that chew up piston seals.
I'm not talking about Chinese guns, but German and British guns that are supposed to be good; a HW80 had a sharp ridge at the bottom, several Supersports seem to be oval and leak lubricants past the seal, a Tx200 with bulges, and the list goes on...

Do other people get them too, or is it just me?

Seen tx tubes with high spots . Just as FPoole says , in the area of the millings . They must go in pretty hard with the tools .

Seen tapers and ovality too , It depends on what tolerances you want to measure to .

Para seals will compensate for most of these imperfections to an adequate degree for most shooters .

People using different sealing methods will demand higher degrees of accuracy in size ,roundness and parallelism of the comp tube walls .
I'm lucky to have a friendly honing company just up the road .

Cant see why your home made hone won't work if you have the patience ,even if you make a few in stepped sizes .
I've done it too , but using lengths of ground silver steel stock ( it's ground round to a tolerance ). That wears eventually ,so I don't expect you get many goes at full size from a brass lap before it then becomes the one for starting off with .

[Papa g]

I have a BSF B55 the cylinder of which is pinched at the point the stock mounting lugs are welded to the cylinder.The gun shoots fine with a synthetic parachute seal which is flexible enough to compensate for the pinch at that point in the cylinder, following the contours of the irregularity.I don't know if this is common to all B55's.

I do know the overall build quality of the B55 does not live up to the legend!

Yep I have the very same thing with a BSF 55, and a problem with an anshutz 335 mk1 where the name is stamped on the cylinder
Regards Graham

[hmangphilly]

Yep I have the very same thing with a BSF 55, and a problem with an anshutz 335 mk1 where the name is stamped on the cylinder
Regards Graham

I suppose it didn't matter so much back in the day . The floppy old seals would sort of forgive the lumps and bumps .

It's poor practice though . The design engineer must have cringed .

[mrto]

Yep I have the very same thing with a BSF 55, and a problem with an anshutz 335 mk1 where the name is stamped on the cylinder
Regards Graham

That's interesting all B55's must be like it then and doubtless some other BSF models,too.I haven't ever stripped either of my 2 Annie's,but shall try and remember what you have said about the name stamp if I ever do!

Cheers,
Mark.

[Shed tuner]

the annie compression tube problems around the stamping are well known..