Revenge of Low FPS on Jing Gong AUG A3

evilrobotshane

I am hungry and fed up. The hop-up unit on my shooty-stick was a little bit broken and glued back together, and my nice new metal one arrived today, with a 6.04mm barrel, Guarder silicone hop bucking and unrelated goodies. I installed all that, and clocked it at around 140fps. Screw.

So I learned about gearboxes and shimmings and tappets and timing and pistons, took it apart (first time!) and didn't see anything obviously wrong, and put it back together again. There seems to have been a slight improvement, it's now a bit under the 200fps mark, but I'm running out of ideas.

It's been like this since the start, and although I brought it back to Eirsoft and clever dude there (Masada?) said he'd sorted it and it was up to 280fps, it hasn't been any time I've chronoed it (although I did break the hop-up unit installing a new rubber immediately after). Everything I could think to check is seated properly, there's a good seal in the cylinder. I'm pretty baffled.

It's all stock parts except the new barrel and hop-up stuff, and anything that was done in Eirsoft. What's left to try? The spring? Why? What is it if it's stock, and what would I replace it with? Argh.

Shiva

Where are you chronoing it ? What kind of chrono ? Any chance the chrono is at fault ?

And naturally, it could also be the hop up problem.

If you want to bring it back we'll chrono it again for you, and show you the results, and fix it while you wait if needed.

bullets

I dont trust Chronos at the moment.

Recently got very contrasting results between
between two different chronos on the same AEG.
One reading on a borrowed Chrono had the AEG under the limit, arrived to a skirmish site an hour later and it was showing slightly over the limit.

~B

evilrobotshane

Previously I've chronoed it at The Warehouse and repeatedly at Hit & Run Tactical Airsoft (advance Jebrovia fair!), but today I'm using a chrono borrowed from a Multicam goon of my acquaintance, that says Xcortech X3200 on it and has a fancy interface and only gives a reading about a third of the time. I can tell it's not up to scratch though anyway, from watching the flight path.

My brain refuses to accept that the hop-up can any longer be at fault - the whole lot has been replaced and upgraded.

Thanks for the offer, I may be able to get in this week. I'd really like to know what's going on though, everything seems top-notch.

mle1324

Yes i once got .55j on one chrono and on another which was beside it i was getting 1.00j so that more less says it all....

Puding

use both the Xcortech X3200 and the Madbul, always found them to give reliable constant matching results in the same test environment, testing one indoors and then testing the other outdoors in bright sun for example can cause problems for example, also had a chrono where the sensore had been hit by a bb which caused strange results

then again i've also seen an aeg jump over a 10 shot string between 150 and 300 fps due to gearbox/hopup problems

also had people use 25 when the chrono was set for 20

also had people who shot a fun angles thought the chrono with bbs bunching off walls with strange readings

NakedDex

Lighting is a huge factor too. It can't be too bright and it must be even on both the entrance and exit ports. I've seen differences of up to 200fps due, simply, to poorly balanced light. Even chronoing outside is inadvisable.

Masada

turned out to be the hopup rubber not holding back the bbs in the end. shes firing 310 fps now.

evilrobotshane

I still don't understand how that happened over two hop rubbers and two hop units, but there's no arguing with results. Thanks a million for that, can't wait to plug me some multicam from outside of 10 feet.

Hivemind187

bullets wrote: »

I dont trust Chronos at the moment.

Recently got very contrasting results between
between two different chronos on the same AEG.
One reading on a borrowed Chrono had the AEG under the limit, arrived to a skirmish site an hour later and it was showing slightly over the limit.

~B

Chances are the fact you chrono'd in two different locations screwed up your test results.

Higher temperature = lower air resistance = higher velocity of the BB.

Too much light filtering into the back of the chrono = peculiar variances in readings.

Hell, even the brand of BB's can effect the results due to the quality control on the dimensions and weight.

I have seen some pretty wacky readings from chronoes with people who were under the limit by 4-5m/s being over the following day, without alteration (or at least thats what they claimed) being over the limit by 4-5m/s. I've even seen guns go from being 1.2j, be dropped on the mag well damaging the hop and have them come back at 0.5j. Infact, my M4-CQBR was firing at 310 in Dublin and 345-350 in Galway due to a combination of factors at the first Gathering.

evilrobotshane

Over time, this problem has slowly started reasserting itself. From the heady days of 310fps, it's declined to around 255 in the meantime.

Remembering what Masada had said in the shop about the hop-up rubber not being seated right, I stripped the hop-up unit yesterday to see if I could get it all purty. I stuck some PTFE tape around the end of it just in case, but the hop unit's so tight I doubt there's a significant leakage concern going on there.

There's only two potential oddities I can notice. One is that the edge of the hop rubber is visible through the BB in hole in the hop-up unit, which I'd have expected to want to be clear, but maybe that's not the case. The other is that the end of the opening for the arm that presses on the nub is catching the rear of the rubber, pushing it forward and causing the lips (as it were) to deform slightly so rather than being a perfect circle it tapers a little bit on the top half.

I pulled the hop unit back a little to undo some of that deformity, but I don't know if that'll hold. Upon reassembly, it's clocking 265fps, not a huge improvement but a little.

Any suggestions? Where should the hop unit be - pushed all the way as far as it'll go, or hanging back a bit so it can still access the hole in the top of the barrel but without the rubber showing in the BB access port? Is it just the unit sliding forward over time that's caused this to slowly regress?