Srs Leaky Piston?

[38super]

Hi All

Just put my new Silverback SRS together and this is what I get with my finger over the muzzle.

On the vid you can hear air coming out behind the piston.

Any thoughts on improving the cylinder air seal? Or is this what I should expect?

View attachment 73734

 

[alxndrhll]

Potentially stupid question to ask before dipping into advice if there is a leak (it'll tend to be from the hop if there is one), are you covering the end of the inner barrel itself rather than the end/whatever device you have at the end of the outer barrel? It's damn near impossible to do this type of compression test if you're not covering directly over the inner barrel, it's seemingly hard to explain what I'm trying to say with words. I can try and throw together a shit example on paint if I'm making zero sense.

Edit:

I went ahead and did my shit paint drawing to try and better illustrate my question.

View attachment 73738

Yellow is the inner barrel, black is the outer barrel.

If you're currently covering the end/cap of the outer barrel as shown above by the red arrow you'll be losing air out of the inner barrel... hence appearing to be a leak. If you're covering the end of the inner barrel as shown above by the green arrow (I'm assuming requiring the removeal of the end cap) then you're likely leaking fro your hop chamber. It'll vary depending on what bucking you're using, I believe you had a FAST hop you were putting in it? Historically I found Silverback buckings in the FAST hop needed a very small amount of *whispers very quietly* PTFE tape to ensure a seal.

There are a few of them out there, but this is probably the best 'how to put an SRS back together' video I've seen. There are some aftermarket parts which he has but the method is largely the same irrelevant of what you're running.

 

[38super]

I did the test with the barrel end cap off. You can hear air leaking out of the back of the cylinder. Same thing happens if I take the bolt out and hold my finger over the nozzle.

I've watched that video and his was the first method I tried, just using a little silicon oil. When that didn't work I tried other methods I've seen used such as a thin layer of silicone grease. No luck.

Update.

Cleaned it all out and started again with just silicone oil. No different. Definitely not getting 100% seal in the cylinder.

(Note: This is with the original hop. I haven't fitted the Fasthop yet.

 

[alxndrhll]

Can't say it's something I've heard before, granted it looks like they may have changed the design of the piston again. Only real way of testing to see if it's making much of a difference is to get a chrono out and see what the consistency is like. By my understanding the main reason air seals are seen as so important is largely down to consistency. The worse the air seal, the more variance there is in the amount air sending the BB down the barrel, and such the consistency of FPS/joules per shot is worse... though this is very much me piecing together why it's important, truthfully I've never really looked into why from anyone better informed than myself. (If this is incorrect please let me know, I'll happily edit it to prevent the spread of misinformation)

If it's consistent when you're chrono'ing it then I suspect it's by design because across all the bolties I've used over the years it's not something I've ever experienced. Leaks have always been from the hop unit/where the nozzle meets the hop unit, a bit of lube on the inside of the cylinder and a bit of lube around the edge of the piston head has always ensured that's all air tight for me. Might be worth 'working' the piston head (assuming it's still the 'cup' design) just to loosen it up a bit. Just massage (for lack of a better word) the edges of the piston cup, if the piston cup is too stiff they may not be creating the proper seal against the cylinder. I remember this being an issue with some of the earlier WASP pistons so could well be a similar case here.

 

[38super]

Accuracy is fundamentally the pursuit of consistency. Getting the gun to do exactly the same thing every time. Especially important for sniper guns.

From what I've read the SRS is supposed to be very good for air seal.

I have noticed this. I don't know how perfectly circular the edge of the piston cup needs to be.

View attachment 73741

View attachment 73742

 

[alxndrhll]

Aye, very much been there done that. But there are a whole host of things which ultimately contribute to accuracy. The reason I tend to find bolties somewhat infuriating is you can get them shooting absolutely perfect, and then everytime you take them apart to do maintainence (and you should at the very least be properly cleaning the barrel after every outing imo) chances are it won't be as perfect as it was.

Just the nature of the platform, everything needs to be well lubed and clean to get that consistency... but to ensure everything is well lubed and cleaned you have to take them apart alot. It's a weird vicious cycle, I'm sure many would echo the frustration of having your RIF shooting exactly as you want and knowing you need to tear it down at some point... and be forever be chasing 'how it was' ?.

Just looks like a bit of 'flash' from the moulding process, wouldn't be enough to disrupt anything imo... largely because it looks to be on the bottom edge of the piston cup. It's hard to say really, given they're made in batches and seem to iterate on the design/manufacturing of components for each run outside of general advice of what usually works it's difficult to provide much else.

Given yours is from the most recent batch I'd say the best bet if none of the standard stuff seems to be working would be to jump into a SRS Facebook group and see what other owners of RIFs from the same batch have to say. They'll likely wind up asking exact what parts are in there, so brace yourself for the irritation of having to explain that it's irrelevant what hop chamber you're using because the leak seems to be from the cylinder/piston. I don't tend to advise anyone toward Facebook groups (outside of the Wolverine MTW Owners group because the folks in there are genuinely helpful regarding that platform), but I'm not sure how useful historical/general information on prior models of the SRS is at this point.

 

[38super]

Something to look forward to there then. AEG's seem pretty straightforward in comparison. I know cleaning the barrel is essential.

For the sake of £5 and 2 minutes work I'm going to get a replacement piston cup and see if it looks or behaves differently.

I've already got a Mousefart piston head on the way so I'll be able compare.

Some people on an SRS fb page say it looks OK but I'm getting 330 +/- 7 fps on .3's with no hop. Ideally I'd like better consistency.

 

[Oneshotscott]

That air seal doesn't look good at all.  Any deformations on any surface which contacts to create the air seal will have an affect. (whether its the seal or the inner surface of the cylinder)

If you have bought the RIF new then contact the retailer regarding this and it should be covered through warranty. 

 

[38super]

That air seal doesn't look good at all.  Any deformations on any surface which contacts to create the air seal will have an affect. (whether its the seal or the inner surface of the cylinder)

If you have bought the RIF new then contact the retailer regarding this and it should be covered through warranty. 

Some people on fb have said it looks OK to them but I'm not convinced as I've definitely seen better.

I've raised it with the retailer and sent the vid direct to Silverback. Waiting on a response from either.

 

[38super]

Update.after fitting new piston cup.

Before:

331 +/- 9 fps

Finger over the muzzle test - 9 seconds

Audible air leak from back of cylinder

After:

337 +/- 3 fps with around 1 shot in 10 dropping to 331 fps.

Finger over the muzzle test - 40 seconds plus

No audible sound of air leaking.

Next task is checking the hop unit.