Wild variations in fps JG Bar 10

Yes, it looks to be in okay condition so for testing the gun it will surely do and it may well suffice for sub 350fps use. It's all PTFE taped up in anticipation of the arrival of the new spring guide and piston. I bought the new hop because this one seemed like quite a loose fit, it was before I realised half of it was plastic.

having trouble finding a hop adjustment arm for mine as the one in it is flimsy as hell and bends when you adjust it instead of up and down movement , its a cheap acm i used for my conversion, compression etc is spot but the aim is abysmal theres meant to be a full metal after market one coming out soon, cant remember where I saw it??
unless someone has the know how and means to machine one??

Okay folks, this gets worse. VSR pistons and cylinders are not compatible with this gun, they are too wide for the cylinder.

Somone has suggested L96 spares are compatible but I don't know if it is a Well MB02 or MB03 (they look the same to me) and according to Land Warrior airsoft's website their ASPUK L96 piston does not fit an MB03.

I have found an "Mb03/MB07 Power Up Kit" on ebay (US) which could be what I need.

Anyway, the diameter of the base of the spring guide is 19mm and the length of the cylinder (exclusive of head and base) is 23cm. Any suggestions of what will fit?

Thanks

In case no one has mentioned it: Try different quality ammo.

My local site had a bad batch and they were all over the place

Different quality ammo for 100+ fps muzzle velocity variations? Really?

BTW I checked Rich's chrono against a consistent AEG and found that the results were, well, consistent so it seems to be working okay.

On those shots which weren't slam firing the muzzle velocity on the No4 was a bit more consistent with PTFE on both the hop and the cylinder head, around 240 - 280 ish and when I squirted silocon in to the nozzle it even ran about 320 for a few shots. Can't do a compression test now as it is slam firing all the time. Unfortunately I can't find a piston to fit as yet. There may even be no such thing as a replacement piston, apparently Well are known for changing their dimensions at random

Thanks for all the help so far, I will update if there is any progress.

well the silicone down the nozzle test is pretty damning for the piston seal,if its the plunger type seal then ive heard of people forcing an "o" ring into the groove on the end and super glueing it in place as a method of expanding the seal but i haven't tried it myself .

Progress today:
I was given a stock TM VSR10 spring guide which I ground down to fit in my cylinder, (APS2 guides have a different back end).

I was also given a plastic APS2 piston which seems to be the right diameter. It caught on the sear when cocked but had a 90 degree rim so wouldn't release. I ground that down to 45 degrees and it seems to work for the moment. No more slam firing

The first compression test on the nozzle was a non starter so I tefloned taped the piston head for a tighter fit and tried another. The piston popped forward, there was some resistance on the compression test and it fired a BB down the garden. I haven't chronoed yet, I will try the o-ring in the plunger and see if it helps compression first. I think the long term fix is an APS2 piston with a metal rim and get someone with the skills and equipment to accurately turn the rim down to 45 degrees on a lathe.

One problem with this gun is that the nozzle doesn't really push into the hop rubber unless the bolt is really shoved in hard and held there, if not it tends to spring back a bit and the nozzle (which is 16mm long) is about 1-2mm short of a good seal. I think a new piston head with a slightly longer nozzle is in order so my question is, does anyone know if anyone makes makes an APS2 cyliner head that has a nozzle that is longer than 16mm?

is the outer barrel screwed into the breech properly as this can lead to the hop being too far from the cylinder head,its fairly easy to not screw it in fully and only one rotation makes a big difference in seal.

No, the outer barrel slips into the receiver and is held in place with a screw through the bottom, so it is all exactly as it was made. There is a tiny bit of play when installed but not that much. I just think it was made badly. A slightly longer nozzle would sort it out. As this is a perverted chimera of VSR and APS2 designs nothing is "standard", but does anyone know the length of a stock APS2 nozzle?

Oh, and is there such a thing as a 45 degree APS2 piston? I have seen one referred to on a forum but can't see such a thing for sale.

More progress

After squeezing an o-ring in to the plunger type piston head it shoots at 310 fps +/- 4fps with a 110 spring in it. A bit low,but in the compression test the piston moved forward slowly, so it's an improvement but I'm going to try and find a fatter o-ring.

B&Q do bags of various sized O-rings...

More progress

After squeezing an o-ring in to the plunger type piston head it shoots at 310 fps +/- 4fps with a 110 spring in it. A bit low,but in the compression test the piston moved forward slowly, so it's an improvement but I'm going to try and find a fatter o-ring.

any chance of a couple of pics when you do this?

cheers
Rob

Okay, I squeezed a larger o-ring in to the piston head but it was too thick so I had to trim down the outside (not easy to do neatly with a craft knife). It's not hard but I took some pics:

Piston head & o-ring:
-- attachment is not available --
Trimmed 0-ring:
-- attachment is not available --
O-ring in piston head:
-- attachment is not available --
Now the end result is an excellent compression test on the nozzle but the pston is a tighter fit in the cylinder, so much so that it won't come out past the thread very easily so it could still possibly do with more trimming.

There is still a slight leak at the hop though, the piston creeps forward in a compression test. It's PTFE taped to hell and I fitted a brass ring around the hop bucking at the nozzle end to prevent expansion and leaking. To try and get around the apparently short nozzle I took the off-cut of the outer barrel I had lying around and made a new one, installing the hop unit a couple of mm closer to the receiver. The piston head face now sits right up against the hop unit, it can go no further, but the nozzle still only just enters the bucking, only about 0.5mm. Should this be enough? It doesn't seem like enough to me but I don't want to push the BB in too far. I have been told that the standard APS2 nozzle is 19mm, as is the VSR and the one I have is only 16mm.

Okay, the gun still Chronos at around 308 fps (not completely awful really) and while I was doing that a couple of things have just occurred to me:

1) The leak at the hop shouldn't really make much difference because in a compression test it takes well over a second for the air to leak out when I have my thumb over the barrel. If I take a shot the BB exits the barrel in about 0.01 of a second, long before that would have started to happen. Would I be correct in thinking it's not really a major factor?

2)The FPS seems low for an m110 spring: the cylinder is only as wide as an APS2 one but about an inch shorter. My memory of Boyle's laws is very vague but I would think a smaller volume of air means less pressure. Would I be right?

The conclusion I draw is that I need to put in an M120 spring to get the muzzle velocity upto nearly 350fps. Am I barking up the wrong tree?

Okay, the gun still Chronos at around 308 fps (not completely awful really) and while I was doing that a couple of things have just occurred to me:

1) The leak at the hop shouldn't really make much difference because in a compression test it takes well over a second for the air to leak out when I have my thumb over the barrel. If I take a shot the BB exits the barrel in about 0.01 of a second, long before that would have started to happen. Would I be correct in thinking it's not really a major factor?

2)The FPS seems low for an m110 spring: the cylinder is only as wide as an APS2 one but about an inch shorter. My memory of Boyle's laws is very vague but I would think a smaller volume of air means less pressure. Would I be right?

The conclusion I draw is that I need to put in an M120 spring to get the muzzle velocity upto nearly 350fps. Am I barking up the wrong tree?

balls law
the angle of the dangle is directly proportional to the lust and the thrust provided the urge remains constant..... sorry couldn't resist but yes i think you'r right.now its a stable reading try spacing the spring to add a tittle more pre-tension and see if it ups the power.

Okay time to say

Thanks for all the advice, chaps, I found a bit of brass tube in the garage, cleaned it up, popped it in and just chronoed the rifle at at about 340fps, give or take a few fps. Now I know that the hours of cosmetic fettling have not been totally wasted I can get on with finishing it. Also I know what bits to get if I need to fix it. Thanks again.

Nice...

Can I have my chrono back now?

I have a mosin to sort out!

happy happy joy joy