Smaller longer ports for softer shot feel ?

[eyebull]

For absolute accuracy, the short port, lightening fast guns are awesome Have you had a play with a sorted springer in the 70-75mm stroke range ?
I was surprised by the LGV; it is quite nice to shoot, but it doesn't come close to the stroked TXs for me...

No I haven't as yet - perhaps I will get to have a play with one at the meet if I make it? While I wouldn't say it has been short-stroked, my LightSport (or Sportning? ) BSA frankenstein shoots quite snappily (but sub-12) with a .177 V-Mach kit, and seems to be improved in all ways by the quicker action. I suspect the longer .22 supersport barrel is also minimising surge which the original XL suffered from greatly.

I do have a 95k that could perhaps do with the short stroke treatment, at the moment it is rather twangy and not particularly nice or easy to shoot, so perhaps a candidate for a bit of tweaking? As much as possible within my limited abilities of course. Perhaps I'll start another thread on the best course of action for this one?

[TheWilding]

I know people have played with bearing arrangements at both ends of the spring for this reason. But many say not worthwhile and the bearings get hammered too much. I think the idea of "plain" bearings would be preferable...So, at each end of (properly finished and polished) the spring, how about a polished steel washer, Delrin in the middle and another polished steel outer?

I fitted a similar arrangement to my Diana Model 50, 3 polished steel washers at either end of the spring, of which the spring ends where polished aswell, I used to fit a similar arrangement to high powered Airsoft rifles, it gave no torque twist at all and the fps variance was down to 2fps over a 20 shot string.


I only removed the system as it cut the size of spring I could fit, and as the TP is so long, plus a mahoosive bucket of a load tap at the other end, I need all the spring I can get to keep the fpe above 8


On the TP size thing, again in the Model 50, I made a 2 stage sort of TP sleeve as I was experiencing piston bounce and had no suitable way to add weight back into the piston.... its 26.5mm over all not including the the load tap, for the first 10mm I drilled the sleeve out to 3mm, then for the remainder I drilled it to 2.5mm, the lead-in on the 3mm end was dressed out to a trumpet shape...... fpe remained the same but the piston bounce was gone making the shot cycle nicer.... far easier to keep on target on follow through etc.


Also a top tip for those looking to fill up lost volume on the seal face that haven't gone to the effort of making a O ring head.... I used to use this on Airsoft guns of all types for the same reason as I use it in Air guns, including full auto guns, so I know it takes a hell of a lot of punishment and not fail....... fill the screw slot, lug depression etc with several coats of liquid electrical tape, available from all good www sale sites, applied with the tip of a screw driver and left to set for a day or two it cures soft and pliable, and quite thin so can be built up to a fair depth, yet hard/strong enough to take the hammering that your average piston face goes through, if the surface is cleaned with spirits it stays stuck pretty much indefinitely and the best thing is if you need to remove the seal again for any reason it just, peels off with some help with a knife.... just thought I'd pass that on


ATB


Sean

[Artfull-Bodger]

Sounds cool, got a link?

Try this Jon--

http://www./itm/10Pcs-AXK1528-Thrust...item27d79a0d51

[Shed tuner]

Try this Jon--

http://www./itm/10Pcs-AXK1528-Thrust...item27d79a0d51

Ta..!

[TonyL]

Try this Jon--

http://www./itm/10Pcs-AXK1528-Thrust...item27d79a0d51

Linky no worky for me.

[Artfull-Bodger]

Dang, just search for "needle roller thrust bearings" on Fleabay.

They took a while to arrive but there's ten in a pack, complete with hardened washers.

[Shed tuner]

I just put the item number 171120921937 from your link into that well known auction side and job done

[bigtoe01]

If the piston rotates you should not need a bearing within the piston...im all ears if it makes a difference however.

when i built my 80's i noted it took 12 shots for the piston to rotate 360deg...

[TheWilding]

If the piston rotates you should not need a bearing within the piston...im all ears if it makes a difference however.

when i built my 80's i noted it took 12 shots for the piston to rotate 360deg...

Don't ask me why I know this, but I do..... on Airsoft repeater rifles, even when fitted with a ball roller, thrust bearing, with guide plates, at the guide end, the piston, which are fully rotating as standard, still rotate when cycled... Last time I rebuilt and did any testing on one I counted an average of 30 to 35 shots to rotate 360 degrees.

And bear in mind the springs on Airsoft guns are ALOT softer than anything used in an Air rifle, even the high fps ones I used to use, so if its happening to them it must be happening to our Air rifles aswell if we only fit a bearing at one end.


Like I said above.... bearing at both ends... good.... at one end.... not so good, but still of benefit.


I think Soleware do a needle roller bearing for the Hatsan 55S & 60S as part of their tune-up kits, its advertised as being used to reduce torque turn, which if reviews are correct, they suffer with quite badly, but I have also read that they tend to collapse due to the high stress impossed by the spring.

Taking you fleetingly back to my Airsoft experiences even their ball thrust races used to collapse, most commonly was the cage holding the bearings would fall apart..... And these are not cheap crap, alot of them are brass or folded steel cages and high grade steel plates, with bearing tracks ground into their faces.

I prefer the idea of flat plate bearings, as they will take the spring compression load better and the larger surface area should be less frictionally challenged once the suction has broken, rather than the increased friction of the applied pressure on a dozen or so high points of the rollers..... one is harder to get going but gives less compression friction once it is moving, the other is easier to get moving but compression friction will be higher, but constant..... Then again I could be talking complete b0!!0x


ATB


Sean

[bigtoe01]

Sean

hardened thrust washer in nose of piston, same on rear guide, ertalyte tx tophat, same for a slip washer on the rear guide. 10x stronger than delrin and slippier than ptfe...

you do not need bearings that will break up when smashed with the forces an air rifle spring places on them.

add a rotating piston and you will never feel the torque twist

[DoctorBoudreau]

Machined to precise fit for the piston and stem. No top hat or spring guide required. A double start model won't even deflect!

http://heli-cal.com/cm/Products/Mach...ings/Home.html

I emailed them a few years ago and the owner actually replied. He agreed it would be a great application but I blanched at the cost. If money was no object .....

More data http://www.heli-cal.com/Library/PDFs...svsWire-14.pdf

[TheWilding]

Sean

hardened thrust washer in nose of piston, same on rear guide, ertalyte tx tophat, same for a slip washer on the rear guide. 10x stronger than delrin and slippier than ptfe...

you do not need bearings that will break up when smashed with the forces an air rifle spring places on them.

add a rotating piston and you will never feel the torque twist

Gah, I really need to get a lathe!!! Then I could make half of these things!


Thing is my garage doesn't have the space and I actually LIKE my wife, so its probably a good thing I don't


ATB


Sean

[Artfull-Bodger]

Sean

hardened thrust washer in nose of piston, same on rear guide, ertalyte tx tophat, same for a slip washer on the rear guide. 10x stronger than delrin and slippier than ptfe...

you do not need bearings that will break up when smashed with the forces an air rifle spring places on them.

add a rotating piston and you will never feel the torque twist

The concept behind this is that you reduce the torque effect without the need for a rotating piston, aimed squarely at HW rather than AA etc, the spring keeps the bearing under constant compression through preload, its at it's greatest obviously when the rifle is cocked, but at no time should there be any impacting forces upon the bearings, now if you consider a delrin, brass or aluminium top hat or preload spacer survives the forces the spring exerts, hardened steel rollers sitting between hardened steel washers and lubricated should survive without any problem, there's simply not enough compression to crack the needle rollers, the cage is unloaded and practically no rotation to build up temperatures through friction that can cause failure (main cause of bearing failure).

To fit, all you need to do is turn up a new spring guide with a seat for the bearing to locate accurately on, so far in testing it's working, but I will be putting a lot more shots through the Mercury test mule before I am satisfied!

[TopDog]

Hi guys

Some very interesting stuff here which I enjoyed reading since I don't usually frequent this area.

Some while ago, I got interested in resolving the "quick"; "lazy", "gentle nudge" etc etc etc subjective terminology and decided to develop a means of measuring the recoil accelerations (and vibrations of course!) throughout the entire action cycle. This can be done relatively easily and economically using mems accelerometers fitted to the test subject. I generally use adapted scope mounts to secure the measuring device to the scope rails to ascertain the accelerations produced in the action.

Original thought was to have a portable device for resolving issues at the range but have moved on since then although still possible if you don't mind lugging around LapTop and PC scope unit as data capture devices.

One can generate all the data one needs this way and then spend ages relating the actual shocks and vibration to what is felt by the shooter! The argument about much happening after the pellet has left is OK provided the rifle is used by a robot since then the second shot would not be influenced in any way by the first! People aren't like that and the "shooter feel-good factor" will play an important part in the overall accuracy achieved.

A couple of results are shown in the ref

http://freepdfhosting.com/1823926ecc.pdf

By using such techniques one can characterise a rifle initially and then track the action performance details for every change and compare with those before the change both quantitatively and subjectively and thereby build up a matrix to help to home in on whatever one considers optimum!

Tools of course, are just tools and the value of them comes from what one does with them.

This is, however, great fun and long may it be so!

atvb
David

[Shed tuner]

David, very very interesting....

I was having a conversation with BlackBeard about the graphs / models, the basis of which was "what should be we looking to achieve" ?

e.g. minimal velocity of the gun at the time of the pellet exit, or minimal displacement or minimal acceleration etc.
I think you have a system now where we can measure guns, and potentially use this to identify the specific characteristics of the ones we subjectively "like".

I'm also amazed how many little bounces there after before the gun comes to rest - cleanly in the first the piston is still moving, but not sure of the others are just the spring moving around.