Stripping my s/h 0.22 Remington Express Compact

[CapitalBee]

This isn't plagiarism as I have taken this from Venoman's post on UKCAF from back in 2014 (so quoted my source). It concerns the Express Compact:

"Dont think this is a express with a carbine barrel, its based on the express but the cylinder is shorter. The stock is also shorter and the length of pull to the trigger. When you cock it the barrel stops at about 90deg, on the box it claims the power is 7ft lbs. I test fired three .22cal rifles , firing 12 shots to clear the oil the tested it on the chrono, all three rifles fired 10/10.25 ft lbs with Superdome and AirArms pellets. If this will drop time will tell, the gun looks like it aimed at the junior shooter , but i find you need more effort to cock it than the express."

Looks like spring compression / strength has been played with to overcome lack of swept volume (15mm shorter). This may be why the reduced spring is having a marked effect on power?

[Mr.Fixit-Norm]

This isn't plagiarism as I have taken this from Venoman's post on UKCAF from back in 2014 (so quoted my source). It concerns the Express Compact:

"Dont think this is a express with a carbine barrel, its based on the express but the cylinder is shorter. The stock is also shorter and the length of pull to the trigger. When you cock it the barrel stops at about 90deg, on the box it claims the power is 7ft lbs. I test fired three .22cal rifles , firing 12 shots to clear the oil the tested it on the chrono, all three rifles fired 10/10.25 ft lbs with Superdome and AirArms pellets. If this will drop time will tell, the gun looks like it aimed at the junior shooter , but i find you need more effort to cock it than the express."

Looks like spring compression / strength has been played with to overcome lack of swept volume (15mm shorter). This may be why the reduced spring is having a marked effect on power?

You could well be right. I was a bit surprised at an average drop of 20ft/sec but this could easily be rectified if I wanted. I think I’ll put maybe a tin of pellets through it and then see what it’s like. The piston is still quite stiff in the cylinder and as has been said earlier in the thread, a tight piston will reduce the power.
The cocking effort is more acceptable ( to me ) now so I won’t do anymore tweaking till it’s been run in further. Interesting to read that info though, thanks.

Norm

[evert]

I'd get a good seal fit before you start cutting the spring... That often means a lot of seal sizing and shooting, as someone mentioned earlier, its easy to go too far.
I like my seals to be a "medium" fit, so not so loose that pistons fall under their own weight. Never measured seal resistance, but a guesstimate would be about 0.5kg to push the piston.

[Mr.Fixit-Norm]

I'd get a good seal fit before you start cutting the spring... That often means a lot of seal sizing and shooting, as someone mentioned earlier, its easy to go too far.
I like my seals to be a "medium" fit, so not so loose that pistons fall under their own weight. Never measured seal resistance, but a guesstimate would be about 0.5kg to push the piston.

That’s interesting evert, I wonder if there’s an optimum seal resistance ? If when I’ve got it apart I could push the piston back to its ‘at rest’ position, remove the spring, find a steel tube that fits over the piston rod then fit a plate to the top on which I could place weights. Weighing the tube and plate I can then mount the cylinder vertically in a clamp and start adding weights til the piston moves.

Might be an interesting experiment

[evert]

That’s interesting evert, I wonder if there’s an optimum seal resistance ? If when I’ve got it apart I could push the piston back to its ‘at rest’ position, remove the spring, find a steel tube that fits over the piston rod then fit a plate to the top on which I could place weights. Weighing the tube and plate I can then mount the cylinder vertically in a clamp and start adding weights til the piston moves.

Might be an interesting experiment

That experiment will give some useful insight. It would be interesting to se how power changes with different seal resistance.
I'd guess that there's different "best" seal resistance for different types of seals and guns. Some seals have thin sealing lips that expand when pessurized, this probably causes a lot of friction that you cant detect with the sliding test.
I prefer to try different seals from different makers before sizing.
You can often find one that fits and does what you want without removing any material if you have several to choose from.
But that big box of seals costs a bit of money.....

[Mr.Fixit-Norm]

Yes it would be quite expensive to experiment with seals from different sources ! The new one I bought was from the Chambers air gun spares site and was listed as 28.6mm, and is identical in size, colour, price and part number to the Diana 34 seal !

Maybe a Diana 34 seal from a different manufacturer would be worth a go ?

The thing is the cylinder measures 28.0mm maximum and I was wondering if 28.6mm is too big to even wear in ?

I sized it down to approx 28.4mm thinking this would be safe ( the old one that came out was 28.2mm.), but are there any guns with a seal at 28.2 or 28.4 as std ?

Something else I was wondering, both the HW35k I recently worked on and the Remington have similar internal setups and both have springs with top hats and rear spring guide, both have slip washers and new piston seals and are lubed with ‘bumslide’

The Remington has absolutely no twang whatsoever and if you didn’t see it shoot but heard it, you’d think it was a precharged gun or gas ram
The 35 on the other hand still has a slight but noticeable twang ? The only thing I could think of that could be making a difference is that the Remy has an external metal spring guide between the spring and the inside of the piston, could this be creating additional twang dampening ?

Norm.

[Shed tuner]

the Remy has an external metal spring guide between the spring and the inside of the piston, could this be creating additional twang dampening ?

Norm.

yes, which is why lots of us fit them

[TonyL]

That’s interesting evert, I wonder if there’s an optimum seal resistance ? If when I’ve got it apart I could push the piston back to its ‘at rest’ position, remove the spring, find a steel tube that fits over the piston rod then fit a plate to the top on which I could place weights. Weighing the tube and plate I can then mount the cylinder vertically in a clamp and start adding weights til the piston moves.

Might be an interesting experiment

That experiment will give some useful insight. It would be interesting to se how power changes with different seal resistance.
I'd guess that there's different "best" seal resistance for different types of seals and guns. Some seals have thin sealing lips that expand when pessurized, this probably causes a lot of friction that you cant detect with the sliding test.
I prefer to try different seals from different makers before sizing.
You can often find one that fits and does what you want without removing any material if you have several to choose from.
But that big box of seals costs a bit of money.....

That would, most definitely, be a most interesting investigation, chaps. As evert says, I think there would be different optimal resistance with different types of seal. Generally, we've just gone by "feel" previously.

[Mr.Fixit-Norm]

That experiment will give some useful insight. It would be interesting to se how power changes with different seal resistance.
I'd guess that there's different "best" seal resistance for different types of seals and guns. Some seals have thin sealing lips that expand when pessurized, this probably causes a lot of friction that you cant detect with the sliding test.
I prefer to try different seals from different makers before sizing.
You can often find one that fits and does what you want without removing any material if you have several to choose from.
But that big box of seals costs a bit of money.....

Hi Evert,
Sorry but due to the issues I had with the piston sleeve / spring and time constraints, I didn’t really have time to start fabricating a resistance checking device but if it gets stripped again I definitely will

Norm

[Phil Russell]

Re: seal resistance.
That would make fascinating readings. I suspect that optimal seal resistance will also be influenced by the power being generated by the spring and also, of course, by any lubrication on the seal that influences its resistance against the cylinder wall.
Cheers, Phil

[evert]

Looks like spring compression / strength has been played with to overcome lack of swept volume (15mm shorter). This may be why the reduced spring is having a marked effect on power?

What is the stroke length? This rifle is beginning to sound interesting...

[Shed tuner]

add a steel top hat around 15g. should give you back most of the power you lost with minimal cocking effort increase

[Mr.Fixit-Norm]

add a steel top hat around 15g. should give you back most of the power you lost with minimal cocking effort increase

Thanks, I’ll give that a try, a good excuse for more workshop time, although it’s going take me more time to make than the delrin one !

[Mr.Fixit-Norm]

What is the stroke length? This rifle is beginning to sound interesting...

That’s the one thing I didn’t think to measure, once I’ve made the steel top hat that Shedtuner suggested I’ll measure it

[TonyL]

What is the stroke length? This rifle is beginning to sound interesting...

Wonder if anyone has the stroke length for the standard Express? I've never worked on one but, just from shooting them briefly, they would seem to be quite a sizeable beast with the ability to make plenty of power easily? Guessing more than generous stroke length? Therefore I'd have to have a guess that this smaller version, with its 15mm shorter stroke, shouldn't present too many problems?

I think it's the tightness of the seal (which, if not silly tight, I'd just allow to bed in) and I think that Jon's idea with the increased piston weight has much merit, increasing preload, momentum and sectional density.

Or, as power isn't high on the list of priorities, and if Norm's happy with the way it shoots / cocking effort etc., just shoot it, let it run in and enjoy?