PTW BB chopping

[Mike581]

Was warned about chopping bb's when I first got the gun and it did it yesterday.... I stopped firing and changed mags straight away and all other mags are fine.
So I'm sure this is down to the mag rather than the cylinder, my question is, what do I need to do to the mag to sort it? It's only recently been opened up and cleaned etc.
Cheers

[Razur]

Re: PTW BB chopping

From google

When you open the receiver there is a round block in the end of the lower receiver covering the hole the stock tube creates. You need to add some of the special SystemA PTW cylinder shims (hope it came with some) in behind this to get it to stick out further so the cylinder is pressed into the hopop unit harder. The upper and lower receiver should be incredibly hard to get apart. You should have to hit the stock with your hand so hard it hurts to open the receiver.

This fixes most times the chopping BB problem shows up but not always. There where a couple cases on ASC where no matter what an experienced PTW gundoc did it would still chop.

A second possible cause is the mag feed lips are too close together and are holding the BB's too tightly. As a result the mag holds onto the BB's too hard and the nozzle doesn't knock them free as it should, it cuts them. Why SystemA decided to go with a sharpened knife edge steel nozzle I will never know; it makes absolutely zero practical sense. Even if it does fire right it can dent the BB's and totally screw up the flight path.

[Mike581]

Re: PTW BB chopping

Cheers mate. I saw that one this morning, I know it's the mag and why it does it but need to know the fix for it. I read on one site to put a cleaning rod down the mag then move it back and to? Can't see what that would do though?
Anyone had this happen?

[The Reptile House]

Re: PTW BB chopping

Rodding the mags works for me. Basically, what happens is that as the mags get used the lips get slightly deformed and exert too much grab on the BB. Rodding opens up the feed lips.

Edit: Also, what BBs are you using? Chopping is very often due to incompatible BBs. I go with Green Devil if I have to use bio and Madbull Match Grade if not (both in 0.25 flavour). I know your other mags are fine, but it's worth pointing out.

[Mike581]

Re: PTW BB chopping

I'm using excel .25s mate, all PTW users at my site swear by them.

Ok... Bit of an update, I tried the rodding idea and probably due to me being an idiot, I've now got the rod jammed in the magazine.

So my next question, how do I strip down the magazine?
Do I need to knock out the 2 roll pins through the mag?

[The Reptile House]

Re: PTW BB chopping

I've done that before with the rod - it did come out, eventually

Yes - you need to punch the pins out first.

[guard-sniper87]

Re: PTW BB chopping

as TRH said mate, rod the mags and also try shimming them if they are vanaras mags etc

the standard ptw mags ie steel casings just need bedding in and will work fine,

also there is a youtube guide about how to strip down the ptw mags, the ptw forum users made it

[Mike581]

Re: PTW BB chopping

Ok, mag stripped, cleaned and put back together ok...
Firing fine now but...
Noticed this before I took it apart and still doing it, one of the retaining tabs is sticking down and not springing back up, it's letting the followers release up into the gun.
Spring is fine, filed it a little, bit of silicone on it but still doing it whenever it's fitted up into the gun. Any ideas?

[[email protected]]

Re: PTW BB chopping

I have experienced the same with Revolution gearboxes-the piston/cylinder head and piston head assembly although not enclosed in a casing/cylinder are the same as those in the PTW. In their latest batch Systema have started providing O-RINGs to slide onto the barrel and up against the hopup unit so as to push it back tighter to the box-in effect the same as the shims do in the PTW as Razur referred to-this has helped somewhat but an odd one still breaks so you need to be vigilant.Would agree with the comments regarding the steel noozle also-has anyone else experienced this problem and have any other ideas for a fix?