Specna SA-S03 tinkering

[Floperator]

A bit bored yesterday so I decided to pull apart my Specna and see why exactly it's so inaccurate (notably less accurate than my Lancer m4). View attachment 88712Yes this is pissing in the wind somewhat trying to mod a crap rifle, but I might as well kill some time until TAC-41s are back in stock, and I might get a half decent shooter out of it, at least something I can lend a friend if they come skirmishing with me.

Think I've figured out what the issues are though. Firstly a crap loose o-ring for a piston seal. Easy fixed.

Then it looks like the 'buffer' at the end of the piston has loads of lost volume, and through the holes in the buffer I can see what look like holes in the piston itself.

View attachment 88713

Again should be a straightforward fix. Loctite and glue gun should do for that.

The third thing is a bit out of my wheelhouse and what I could do with some help with. Looking down the barrel, the hop rubber looks distorted and asymmetric on full or 3/4 hop, and I suspect it's that that's causing the windage innaccuracy.

View attachment 88716

View attachment 88717

Is there an aftermarket replacement for this? If there are a few types available, what are the relative benefits of different brands/hardnesses?

Is this rifle a copy of another gun?

Other than these issues everything else seems to be in reasonable order. Trigger is OK, barrel is clean. Bolt pull is already a little stiff so I'll stock with the stock spring.

I'm not going to throw good money after bad but I think I can stretch to a new hop rubber.

Any advice appreciated.

 

[EDcase]

The piston O-ring is meant to be loose. As it travels forward the air is forced in the holes and expands the O-ring to make tit seal.

There shouldn't be any holes in the piston itself though.

 

[Floperator]

The piston O-ring is meant to be loose. As it travels forward the air is forced in the holes and expands the O-ring to make tit seal.

There shouldn't be any holes in the piston itself though.

Yeah I've just had a look and you're right, the holes in the face of the piston vent underneath the o-ring.

This is...sub-optimal.

For a tiny little system that's already operating with a mouses fart of swept volume, I don't think it needs this kind of lost volume and inefficiency. I think I'm going to proceed with sealing the end of the piston and putting a proper well sealing o-ring on.

 

[EDcase]

Erm, good luck with that...

 

[RostokMcSpoons]

Won't that make it harder to move the piston when your cocking the gun?  That's the whole point of the o ring system as it is now.  And you think the bolt pull is stiff already... ?

 

[Floperator]

I'm used to tuning spring piston airguns and in comparison to even a cheap and nasty break barrel, this system, if you could call it that, is so LUDICROUSLY inefficient that I'm amazed it manages to queef a bb out the end at all.

I won't be making the o-ring super tight obviously and it's going to be properly lubed, the extra friction of an o-ring that actually *fits* won't be noticeable when cocking in comparison to the spring resistance, and should be easily overcome by the spring on firing. 

Any input on the hop rubber?

 

[Floperator]

Well, it seems to have done the trick.

The noticeable piston slam seems to have gone, and if anything it's easier to cock in that it's not getting hung up on the forward stroke of the bolt like it sometimes was before. Filled the holes in the end of the piston with hot glue, and put a smaller o-ring under the original o-ring to give it some support. 

In the absence of any compatible aftermarket hop rubbers that I can find, I did manage to twist the barrel in the hop housing so it sits straighter, which has stopped the shots veering off to the side.

Going to wait until I get some .4s to chrono it, heaviest weight I have atm is .3s, but power looks like its slightly up.

And accuracy has definitely improved.

Also gave it a very basic little camo job

View attachment 88721