I Did Some Work On The Gsx100

[Jonjon79 13,340]

After a recent round of pellet testing with the Impact GSX100, I got some rather disappointing chrono readings - JSB Heavies (10.34gn) gave me an average of 685fps/10.78ftlb with 13fps variance over 17 shots.

 

I'm not one that wants to chase 11.9999999999 ftlb but, I do want a decent level of power and consistency so that I've got the best chance of killing cleanly when I hunt.

 

I've never really done any work on a PCP so, I thought it over for a few days until, a power adjuster for a Mk1 Rapid came up for sale.

 

I bought the adjuster and started to have a serious think about my rifle.

 

There was an antitamper in the back of the block - again, I've never removed one of these. I could have cut a groove with a Dremel and unscrewed it but, I wanted it intact in case the adjuster had a different thread.

...... It was suggested that I try superglueing something to it. A wingnut worked perfectly, it came out nice and easy.

Also, the threads were exactly the same.

 

The 2 spings and plastic guide are very close to back of the actual block - when I fitted all 3 parts of the adjuster, there wasn't enough room left to pull the bolt back fully and cock the rifle so, back to head scratching for a minute......

 

I compared the main body of the adjuster and the antitamper plug - they were both recessed in the back to take the rifles spring guide, the adjuster part being 1 or 2mm deeper.

 

I had a look at the screw-in bolt fror the adjuster - when fully wound in, it gave around 7mm of new preload behind the hammer spring (discounting the pin section on the end).

 

Decision made - I did away with the brass tophat from the adjuster and, chopped the end off the bolt section.

 

I gave the 2 springs and guide a quick clean and, after using some fine sandpaper wrapped round a biro to make a cut out in the back of the stock, it was all back together.

[Jonjon79 13,340]

I'd be lying if I said that I hadn't considered how much use a JSB Heavy at 900fps would be when hunting at night but, I've got no FAC and, my little 'un wouldn't be impressed if I got caught.

 

Besides, that's not what I'm looking for from this rifle.

 

After a few tests with a few different pellets, I'm very happy with the results.

 

With the adjuster bolt taken out completely, JSB Heavies are giving an average of 668fps/10.22ftlb with an 8fps variance.

 

With the adjuster fully wound in, it's now an average of 710fps/11.53ftlb with a 10fps variance.

 

I reckon with a little more tweaking, I can get the variance down and, set this pellet at around 715fps.

...... I'm really looking for the flattest trajectory possible, with as much punch as possible for hunting.

 

The real surprise came at the target end......

The first picture is 10 shots at 30yrds at the lower power.

The second picture is 10 shots with the adjuster wound in - these pellets really seem to like the extra fps - longer range testing will be interesting.

[Bunnyblatter 1,012]

That is some impressive groupings from both settings mate.

[just-A-snap 1,269]

Be safe and be happy.

All the best

[Jonjon79 13,340]

That is some impressive groupings from both settings mate.

Cheers mate

 

They were done indoors rested but, I was surprised how it tightened up with a bit more velocity.

[Jonjon79 13,340]

Be safe and be happy.

 

All the best

Will do Renos,

 

Atb mate

[Bunnyblatter 1,012]

Little bit more oomph and they do look good.

[mark williams 7,549]

Doesn`t get better than that Jon

 

 

atb Mark

[Jonjon79 13,340]

Doesn`t get better than that Jon

 

 

atb Mark

Cheers Mark

 

I've just arranged to take it out tomorrow night. Hopefully it'll get me my first rabbit of 2017.

[tomburras 2,721]

Nice little modification!

[villaman 9,979]

Nicely done , but how would you stand if the police took it in with the stock cut out by the anti tamp ?

[mattwhite 1,992]

That's pretty close to perfect jon?

[moxy 617]

Nicely done , but how would you stand if the police took it in with the stock cut out by the anti tamp ?

As long as it's running within the legal limit then everything is fine.

[villaman 9,979]

 

Nicely done , but how would you stand if the police took it in with the stock cut out by the anti tamp ?

As long as it's running within the legal limit then everything is fine.

 

Yes i know moxy but if they see it has been modified to allow a easy adjustment ,then who knows what would happen

[Jonjon79 13,340]

Nicely done , but how would you stand if the police took it in with the stock cut out by the anti tamp ?

Cheers mate

 

My understanding is along the same lines as Moxy - I think the police may get twitchy about an external power adjuster and, would probably destroy the rifle if it could be easily pushed over power.

 

While testing it, I tried to put it over to see if was possible but, with this set up, it physically won't do it - if I put any more preload behind the hammer spring, the rifle won't cock. The highest reading I managed was 719fps/11.89ftlb with JSB Heavy. The only other pellet to come close was Bis Mags but, they were still lower

 

Rightly or wrongly, I considered that there's some sub 12 air rifles on the market with variable power so, it should be fine.

 

........ I just hope I'm correct if it ever comes to the crunch

 

Atb