Gun Trouble

[Shadowrich]

In mine I'm using:

prom 509 tightbore
systema hop sleeve with o-ring bucking
area 1000 polycarb piston
area 1000 polycarb piston head
type 0 cylinder

in a classic army m15

this is driving me nuts... There is no way we all would chrono +/- 3 fps if we had air leaking or a messed up hop up. I'm not sure if I mentioned this already, but I've chronoed my gun two times on different chronoes. Once at Airsoft Knoxville and once at Chattanooga. At Airsoft Knoxville I actually chronoed at 296, and at Chattanooga I chronoed at 300. So the Chronograph was not broken.

[MARC]

O.k. Like most are saying if you are only shooting 300 w/.25s with that setup something is wrong.I have built a number of guns with 170% springs and never had that poor of a result.I Have two rifles shooting 540fps plus and when i buy hop packings it sometimes takes 7 or 8 to find one that actually works.I Have an ICS M4 that shoots 390's with a M120 and has a stock barrel.Also just because the compression feels fine by hand means nothing,I chased that problem with a rifle for two months until finally i changed the o ring on the piston head and gained 150 fps.Not to say that is your problem but something is not right.And back to the question on gears, I use a stock gear set in my fully automatic guns and the phoenix gears in my sniper rifles.What Brand spring are all of you using? Also did you ever chrono these rifles before upgrading them? A .05 Raise in bb weight does NOT equate to a constant percent of fps loss.The Higher the fps the less the spread.In my hunt for the elusive 550fps I have used a unbelievable amount of parts trying different combos, and as a result I have figured out that most of the parts available for these things suck.I would be willing to bet it is something related to either the piston head o ring or the hop packing.

[Shadowrich]

[Len013091]

[ParaTweeT]

[Streak]

Without pressure from another bb it probably won't fall into place. Which is why you will sometimes have a bb in the chamber after your mag runs dry. When the air nozzle comes forward it pushes the bb into the hop packing/bucking just before the piston lets go. If you're not having feeding problems then your problem lies somewhere else.

As far as the o-ring goes, it could be that the o-ring isn't expanding fast enough to make a seal before the piston has already started to travel. Which would cause a loss of overall volume. I've seen the o-ring switch work in a similar situation. You're about to find out that sometimes in upgrading airsoft guns, the solution to a problem doesn't always seem to make sense at first.

From what I can see, the common denominator between all of your guns is the piston assembly. Spend a couple of bucks at Lowes and buy a pack of o-rings and try it. If that doesn't work start looking at hop packings. The bottom line is this, whatever is going on in your guns is probably the same. Causing similar low chrono readings. Unfortunately it's going to take changing out parts to track it down. We've all been through it.

[Shadowrich]

Thanks for correcting me on the bucking name. I'm not sure if I will be able to make it down to the tech thing this Saturday. I just got my wisdom teeth pulled today, and am having to miss work on saturday for it. If I feel better and swelling has gone down I may be able to make it, but I kind of doubt it. I'm startin to see that I'm not going to be able to find this problem without switching some parts. I think I'll start with the air nozzle and work my way around the piston head o-ring, bucking, and other related things. Since I'm going to try a new nozzle does anyone have any suggestions, or are they all just about the same? Big
B said earlier that guarder makes one with an o-ring in it, so I'll probably try that one.

[dogsoldier]

[bigb]

[Streak]

Take the original o-ring and piston head to home depot or lowes and go to the plumbing dept. There are alot to choose from but only one really matches up. Watch the inner diameter and the thickness of the o-ring. Keep in mind that the replacement needs to have a little movement for expansion on the piston head.

[ParaTweeT]

[bigb]

I went to home depot and got some orings and my compression was dramatically increased. I'm going to airsoft knoxville today to check on the chrono.

O-ring specs

Brand: Danco
Size: # 14; 15/16" O.D. 3/4" I.D. X 3/32"

I found them in the Faucet repair section. They come in a 10 pack for around $2.00.

[bigb]

gained 30 fps; up to 330 now. Vince was saying it could be the prometheus barrel causing an fps drop; sounds crazy that a tightbore would do that but i guess the fitment in the hopup chamber is different.

[Skidude]

[Streak]