Smaller longer ports for softer shot feel ?

[Shed tuner]

Just built a new toy - 80mm x 25mm cylinder, 12mm x 3mm port, .177, 11.5 FPE.
Shoots nice, and really quite soft.
My softest shooting TX is also the one with the longer, small port (3.5mm x 7.5)
About to build another TX with same port to see if it's fluke...

What do you reckon ?

I'm not talking crazy long ports like HW35 or LGVs (but those LGVs do shoot quite soft, right ?)

I'm thinking the smaller port reduces flow (from cylinder) after the piston has bounced, when it's on it's second forward stroke, so there's more air to dampen it's final crash into the cylinder. But why long ? Simply to get the SCR to a reasonable number, otherwise the piston will bounce too much/too early. Incidentally the aforementioned softer shooting TX has a little lost volume in front of it's seal too, so behaves like it has a longer port.

Incidentally soft shooting is / may not everyone's absolute goal, as I'm still convinced shorter ports are more efficient (easily proven) but they just feel different. I'd so short port, high efficient, fast for HFT, and something soft (longer, small port) for benchrest.

Might try just sleaving a stock 10mm long ported TX comp tube down to 3.2 and see how it goes...

Still thinking.. Blackbeard ?

[slugger]

my short stroked tx was still at a prev 4.0 mm port [standard length] fast, and nice. i was wondering if it was a tad snappy [hence me asking you to do a shot cycle vid] anyways, now that it has the standard port once again and the standard seal, i know its not uber efficient [as you lot keep telling me] but the truth is its now perfect in my eyes , really stable shot cycle , not snappy or jumpy [my prosport looks like a bucking bronco by comparison] so im not so sure the end-goal is all about maximum eficiency tbh..
sure if you were building a full-on fac rig and wanted the best velocity possible with minimal 'spring' then sure.... but for sub 12 im thinking too much eficiency / perfection isnt always the best thing to aim for maybe

[TonyL]

I have been wondering about this very thing for some time.

May have even asked on another thread some time ago, but maybe not picked up as it was going off at a bit of a tangent.

It seems we all accept that a shorter port is more efficient, but I have been wondering for ages if the longer port can contribute to a better shot cycle. So, maybe a little more spring required to get to the same power; thus giving a little more first stage recoil (?) , but, maybe, potentially better controlled surge (and surge is more detrimental for accuracy / hold sensitivity).

Will watch with interest........

[Shed tuner]

I don't think this is a surge issue - for that the larger port is better - I think it's the third phase, where the piston comes to rest after bouncing.

But I'm really just guessing...

[T 20]

Hi Jon

I take it you didn't have a play with the really rough looking HW35 of mine --- I can't even remember if I had it with me at the Bash.

This gun has a 30 X 71 bore and stroke and an O ringed piston head, I've sleeved the transfer port on this one down to 2.3mm over it's full 26mm length --- the firing cycle is really nice and is similar to that of an LGV but it has a little torque twist.

The firing cycle on this one is the reason I bought a 35E to play with, I'm going for the same 71mm stroke on this one but with a rotary piston --- the other reason I bought the E is this :-

http://i1138.photobucket.com/albums/...ps2a3a9fa9.jpg

http://i1138.photobucket.com/albums/...pse954facd.jpg



All the best Mick

[eyebull]

As Jim was saying in one of his articles a few months back, accuracy also has to be considered (it is the main goal after all!) when tuning rifle for a better 'feel' of stroke. The short stroke may be more snappy and efficient but is that accompanied by an increase or decrease in effective accuracy...? That information is not always posted but arguably is the most relevant factor.
The LGV has a longish stroke and, on paper, a less than optimal set up with regards to lost volume etc. but it is easy to shoot accurately....we can't lose sight of what the goal is here. It's quite possible that the 'ideal' set up is not necessarily going to be the most efficient on paper, or even the best by feel.
I would like to know the comparative accuracy and hold sensitivity of these various stroke set ups, as part of the available data...

[slugger]

tx200 full length >
walnut stock [lighter than beech]
stroke set to 83mm
port diameter and length standard [standard port radioused on entry side]
piston lightened a little
delrin tophat and guide
titan spring for mk2 tx cut to length and finished/polished [roughly 25mm preload at a guess]


admitedly theres lost volume a plenty with the stock seal [altho i have made the piston rod protrude into the seal-hollow with a domed profile]
and the 10mm long standard port-length is hardly optimal... but the shot cycle and accuracy is better than all my other springers [sfs 98....... prosport.........25mm conversion 97k........and not that its really relevant but i shall add my theoben evo to the list]
infact the only gun i posess that is more accurate [and only just] is my seriously modded hw100

[slugger]

i would like to add [it should go without saying really in present company] but i will for the benefit of the non techy readers who may stumble upon this thread
when i say my tx is more accurate and has a nicer shot cycle than the others mentioned its all relative obviously........when at the club [25yd range with target/score cards] the scores i get with the others are very good with the tx only being a couple of point higher on average........for example if i were to average 95 with the hw 98 / hw 97 and prosport then the tx will net me an average of say 97.........and this is an average based upon say 10 targets each , so, as you can see they are all good, all close, but the tx just pipps them all
also when i say the hw100 is better still "but only just" i would guess im averaging a 98 / 99 type score these days.. so again not a million miles apart in terms of ultimate accuracy........

in truth a good marksman will outshoot me with a bog-stock out-of-the-box tx or hw97 or hw98 even if im using my short stroked tx.........but like i say, its all relative.......im not the best shot in the world by a looooong way, but a well settup springer [in this case my tx] gets me higher scores, which is [no matter which way you look at it] improving accuracy
i would also like to point out that my snappy theoben evo can be ridiculously accurate too, but [and its a big "but" in my humble oppinion] i have to be on form, i have to get my hold perfect every shot, hand position/tightness of hold/posture/breathing/trigger technique/follow-through etc etc which as im sure most of you realise just doesnt happen ALL the time........
what im trying to say i guess is > there are dozens of accurate rifles out there, but very few that allowe you the flexibility of changing hold/balance and are forgiving of being "on form" versus "having a bad day" and will still give you a good score [accurate shot placement] my tx is one of them

[TonyL]

I've sleeved the transfer port on this one down to 2.3mm over it's full 26mm length --- the firing cycle is really nice and is similar to that of an LGV but it has a little torque twist.

The firing cycle on this one is the reason I bought a 35E to play with, I'm going for the same 71mm stroke on this one but with a rotary piston --- the other reason I bought the E is this :-

http://i1138.photobucket.com/albums/...ps2a3a9fa9.jpg

http://i1138.photobucket.com/albums/...pse954facd.jpg

All the best Mick

Lovely, Michael. Absolutely lovely.

Re the torque twist...A couple of months ago I had the pleasure of having a few shots with Kieran Turner's LGV. Kieran had stripped, degreased and sparingly re-lubed with the Napier grease. Big scope on too.

Very, very nice to shoot. Extremely accurate. At one point we screwed on a HW silencer and the thing was nigh-on silent. An absolute joy.

But.....Now maybe this might be down to the fact that the thing was so nice and refined and smooth...and we're definitely nit-picking here, but torque twist was definitely evident. As I say, maybe because the thing was so subdued made this stand out more, but stand out it did.

Actually makes me wonder if rotating piston is the way forward or not? Maybe better to contain the torque INSIDE the piston? 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?

Also, to say the 35's such an old design and with its big, heavy, 30mm piston, it doesn't do too bad, really. I think a lot of it is due to the stock design / weight distribution.

Just think, lightened piston, polished, the plain bearing arrangement and properly matched spring. This would result in a very refined old girl.

[TonyL]

As Jim was saying in one of his articles a few months back, accuracy also has to be considered (it is the main goal after all!) when tuning rifle for a better 'feel' of stroke. The short stroke may be more snappy and efficient but is that accompanied by an increase or decrease in effective accuracy...? That information is not always posted but arguably is the most relevant factor.
The LGV has a longish stroke and, on paper, a less than optimal set up with regards to lost volume etc. but it is easy to shoot accurately....we can't lose sight of what the goal is here. It's quite possible that the 'ideal' set up is not necessarily going to be the most efficient on paper, or even the best by feel.
I would like to know the comparative accuracy and hold sensitivity of these various stroke set ups, as part of the available data...

Quite right.

As Jim has pointed out on a fair few occasions, achieving better accuracy has to be the main goal.

Shot cycle is subjective. Jon had three TXs at the Bash, all with different strokes / set-up. Different shooters preferred different set-ups.

We're all suckers for a nice, smooth cocking cycle and a smooth firing cycle with no resonance. But, ultimately, accuracy should always remain the #1 goal.

[Shed tuner]

Hi Jon

I take it you didn't have a play with the really rough looking HW35 of mine --- I can't even remember if I had it with me at the Bash.

This gun has a 30 X 71 bore and stroke and an O ringed piston head, I've sleeved the transfer port on this one down to 2.3mm over it's full 26mm length --- the firing cycle is really nice and is similar to that of an LGV but it has a little torque twist.

The firing cycle on this one is the reason I bought a 35E to play with, I'm going for the same 71mm stroke on this one but with a rotary piston --- the other reason I bought the E is this :-

http://i1138.photobucket.com/albums/...ps2a3a9fa9.jpg

http://i1138.photobucket.com/albums/...pse954facd.jpg





All the best Mick

Hi Mick, nah, didn't see that one - only the LGV 35 and an E you has just bought from Solware... looks liek that stock will come up nice with a bit of TLC

Seems like there may be a pattern here....

[Artfull-Bodger]

Lovely, Michael. Absolutely lovely.

Re the torque twist...A couple of months ago I had the pleasure of having a few shots with Kieran Turner's LGV. Kieran had stripped, degreased and sparingly re-lubed with the Napier grease. Big scope on too.

Very, very nice to shoot. Extremely accurate. At one point we screwed on a HW silencer and the thing was nigh-on silent. An absolute joy.

But.....Now maybe this might be down to the fact that the thing was so nice and refined and smooth...and we're definitely nit-picking here, but torque twist was definitely evident. As I say, maybe because the thing was so subdued made this stand out more, but stand out it did.

Actually makes me wonder if rotating piston is the way forward or not? Maybe better to contain the torque INSIDE the piston? 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?

Also, to say the 35's such an old design and with its big, heavy, 30mm piston, it doesn't do too bad, really. I think a lot of it is due to the stock design / weight distribution.

Just think, lightened piston, polished, the plain bearing arrangement and properly matched spring. This would result in a very refined old girl.

I am running a test at the moment on a BSA Mercury, I located a supply of 15ID 28OD 2mm thick needle roller thrust bearings, I turned up a spring guide which fits in the cylinder end cap that has a locating step, the greased bearing race sits between two hardened steel washers on this step, and the spring on this, so far I have put a couple of hundred shots through the rifle and once it's done approx. 1000 I will strip it and check the bearings for damage, when you consider the rollers are hardened, lubricated and not subjected to any excessive rotation and therefore thermal loads I can't see the pressure applied by the spring being sufficient to cause damage?

Testing back to back from the FT sitting position I noted how much the rifle came off target over ten shots, fitted the new guide and bearing and repeated the ten shot test, There is no doubt the rifle exhibited less movement laterally with the bearing fitted, the recoil felt more rearward with less twist or pull of to one side, I am going to continue to test with and without the bearing fitted and with different shooters to try and judge how much benefit there is to having the spring free to rotate at one end.

[Shed tuner]

As Jim was saying in one of his articles a few months back, accuracy also has to be considered (it is the main goal after all!) when tuning rifle for a better 'feel' of stroke. The short stroke may be more snappy and efficient but is that accompanied by an increase or decrease in effective accuracy...? That information is not always posted but arguably is the most relevant factor.
The LGV has a longish stroke and, on paper, a less than optimal set up with regards to lost volume etc. but it is easy to shoot accurately....we can't lose sight of what the goal is here. It's quite possible that the 'ideal' set up is not necessarily going to be the most efficient on paper, or even the best by feel.
I would like to know the comparative accuracy and hold sensitivity of these various stroke set ups, as part of the available data...

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...

[Shed tuner]

I am running a test at the moment on a BSA Mercury, I located a supply of 15ID 28OD 2mm thick needle roller thrust bearings....

Sounds cool, got a link?

[Shed tuner]

So thinking more generally on this.... the smaller ports defo need a heavier piston (unsurprisingly), and the converse is true... the stock 10mm x 3.8mm TX port is too big, so everyone tuning them back to m1/2 strokes ~ 82mm lighten the piston, or makes an ally piston. I did that too, and it works well.

However my 7.5 x 3.5 ported gun is much softer and more pleasant to shoot, and runs a shorter stroke too (75mm)

Just been playing today with 5.3 x 3.5mm port, and getting too much piston bounce - with a piston that had previously been lightened to around 200g. Adding 20g of weight helped, but it needs more... So I need to find a full weight piston to see if there's any mileage in shorter and smaller ports with heavier pistons... I also need to find an LGV/U seal for it, as the old HW seal currently installed is far too prone to expand under pressure, making the problem worse...

My PTXE is shooting really nice with it's 3mm x 12mm port, full weight (230g) TX piston and HW seal. Not quite as soft as the softest TX, but nice.