Tuning the precihole SX 100

[chinmay1986]

Hi fellow IFGians,

what m trying to do here is take a fair amount of knowledge from the experienced IFGians to supertune a precihole sx100 which of friend of mine has graciously donated to me for experimentation as he has now graduated to a Diana 350 .

So here's the simple facts that I think I know.

It's a Pegasus model so give about 12ftlb of muzzle energy..whioch is good enough but I want to turn it into a magnum air rifle now that I have the option.

The heart of any AR is the spring and the piston. so m planning to replace the following original parts with after market parts

The spring : to be replaced by a Diana 350m spring : Wire Diameter 3.2 mm
Coil OD 21 mm
Coil ID 14.6 mm
Total Coils 37.5
Full Compressed Length 120 mm
Free length 316 mm

Piston seal : to be replaced by APS seal for Diana. here's the link to it
http://target-tune.in/international/pro ... DIANA.html

Straight rod piston: here's the link to it
http://target-tune.in/international/pro ... -T01-.html

Spring guide: if required.

Now what I want to know is:
Firstly : what is the dia of the precihole piston receiver and can it take a 28mm seal.

Secondly: can the receiver take a 21 mm dia spring.

I know doing all this voids the warranty and stuff...the AR is already an yr plus old so doesn't matter it has seen it's hey days already.. :p
And is this tuning even possible to do...

I would love to have comments from all the experienced IFGians.

[brihacharan]

Hi fellow IFGians,

what m trying to do here is take a fair amount of knowledge from the experienced IFGians to supertune a precihole sx100 which of friend of mine has graciously donated to me for experimentation as he has now graduated to a Diana 350 .

So here's the simple facts that I think I know.

It's a Pegasus model so give about 12ftlb of muzzle energy..whioch is good enough but I want to turn it into a magnum air rifle now that I have the option.

The heart of any AR is the spring and the piston. so m planning to replace the following original parts with after market parts

The spring : to be replaced by a Diana 350m spring : Wire Diameter 3.2 mm
Coil OD 21 mm
Coil ID 14.6 mm
Total Coils 37.5
Full Compressed Length 120 mm
Free length 316 mm

Piston seal : to be replaced by APS seal for Diana. here's the link to it
http://target-tune.in/international/pro ... DIANA.html

Straight rod piston: here's the link to it
http://target-tune.in/international/pro ... -T01-.html

Spring guide: if required.

Now what I want to know is:
Firstly : what is the dia of the precihole piston receiver and can it take a 28mm seal.

Secondly: can the receiver take a 21 mm dia spring.

I know doing all this voids the warranty and stuff...the AR is already an yr plus old so doesn't matter it has seen it's hey days already.. :p
And is this tuning even possible to do...

I would love to have comments from all the experienced IFGians.

Hi Chinmay,
> Your plan to tune your PH SX100 appears very ambitious
> This may perhaps give you an additional 2fpe.....
> The seal in SX100 is synthetic & comparable with APS Diana
> SX100 piston does not have a 'Piston Rod' - its read end is machined to act as a sear to lock with the trigger sear - hence the Diana type piston will not fit as the SX100 trigger mechanism is different....
> The only way out is to bung in a more powerful spring - but as I mentioned it will only produce an extra 2fpe
> Unlike other Indian made ARs - PH ARs are precision made & any alteration may come in the way of its smooth functioning.
> Please bear in mind "Its not the power in the AR that matters - Its how accurately it shoots"
Briha

[chinmay1986]

@ briha:

Thanks brother...
well 2fpe does feel menial for wht m planning to do. Nyways m gonna replace the spring with a magnum one.

Sad to know the straight piston wouldn't work but happy atleast the Diana seal would.

Would also like to know whether I shud keep the original synthetic spring guide or shall replace with a steel one for the stronger spring?

[Basu]

Dear chinmay,
The stock main spring or the springs of PH guns are meant to give shooting pleasure and somewhat decent power.
So their springs are not supposed to give power only.
The spring which you propose to use ,may not fit with the ID of piston.
I read some where that Gsmith 27 spring suits well with ID of piston but there you need to reduce the OD of spring guide by sanding it so that it fits snugly with spring.
Since I did not do the above so it is simply an information ,nothing beyond that .
But one thing I can say for sure that harder spring will surely increase vibration to a noticable extent.
Briha expects 2fpe ,seems quite ambitious .
The piston seal is quite good and I do not see any reason to change it. Any change of seal will change the firing sound , if not anything else.
I expect max 1fpe than a PH new spring but with Gsmith , power will sustain longer.

Basu

Note : I doubt wheather TTI is operational.

[AnandNair]

You will not be able to convert it into a magnum springer just by changing the piston and spring.
the diana piston will not fit because the precihole piston rear is machined to engage the trigger sear and no piston rod.
replacing the spring with a magnum one will only increase the cocking force required and increase in vibration and noise.

[chinmay1986]

nyone got any idea what's the seal size in a PH SX100...

[Basu]

I can not give you a straight data.
I have used PH seal in my gun whose receiver has a ID of 27.8 mms. So seal dia should be a shade more than that.

Basu

[ganeshn]

@chinmay1986 pls keep us posted about your tunig for sx100, have you made any headway.eagerly watching this space.

[bennedose]

I do not believe that a springer's power delivery can be increased significantly without increasing the stroke volume of air that is moved when the rifle is fired. Increasing the volume is key to power delivery. That would require major re-engineering. Other things are just "adjustments" that remove inefficiencies

However the exercise of opening up an air rifle, doing various things, putting it all back together and then being disappointed at the loss of performance is part of the game. I must also point out that as a community, most of us in India do not own Chronys which are vital for measuring power delivery. We simply use approximations - which is fine for amateur air gunners - but if a doctor used the sort of approximations in giving medicine dosage - people would die. Unfortunatley cheap chrony's are unavailable to us in India - so I personally find it very difficult to believe muzzle velocity estimates made by approximate methods.

I think what we need in India is for someone to design and sell a chrony that anoyne can own rather than the current situation where it is as difficult to access a chrony as it is to get a weapon licence.