Hey Tom or an AGD tech--Emag chrono question ?

[CFD323]

Here's an excerpt from the RT Chrono procedures page at http://www.airgun.com/rtchrono.html

"...It is important to understand that when the air chamber is filled with hot air under pressure, it cools off rapidly over several seconds. This cooling will reduce both the chamber pressure and the velocity.

If you fire the RT while the air chamber is hot (high pressure) your velocity will be higher. If you wait, the air chamber will cool and velocity will drop noticeably. The faster you fire your RT the more consistent your velocity will be."


That being said, here's my question. After reading the post (from Eric_AGD) that said that using the superbolt can cause your chrono velocity to actually be 30fps higher than with the stock bolt, I took my Emag out today to chrono it. I gassed it up and chrono'd 4 shots in a row at 252. Then it bounced a little between 250-260 but stayed fairly consistent at this low speed. This seemed weird as I was expecting the chrono speed to be up over 300. (Last time I chrono'd my stock bolt the speed was right around 275-280.) (When I chrono'd, those were the first shots I fired when I gassed up the gun.) I then took off the chrono and rattled off 2 strings of about 10-15 balls each at a very quick pace. I then chrono'd again and now the speed was up around 295-310. It was consistently that high too. Now, I figured this was due to the valve heating up due to the aforementioned rapid firing but if that were the case, wouldn't the valve cool down fairly quickly (as the RT Chrono instructions state it would) and I would see my chrono speeds start to drop ? And if not, why does my gun originally chrono in the 250's and then after a little while, chrono's in the 290's/low 300's ?

Give me a clue here. Maybe I'm just a moron...

:confused:

[Restola]

dont feel bad, i dont understand either :)

[BlackVCG]

Well for one thing, before you chrono the gun, set in the piston by firing a few shots before you chrono. This will give you a true reading of where the velocity is. Any time you make a change to the velocity, it will fluctuate the first few shots until the piston sets in. Usually it will go from a high reading to a low reading once the piston is set in.

If you follow the chrono procedure for the RT by putting your E-Mag in Manual mode and firing, holding the trigger back, releasing and then immediately firing a shot after that. You will get the highest velocity reading your valve will produce in rapid fire. If you rechrono slowly firing one shot after another, you should notice the velocity to be less than the reading you got when performing the RT chrono procedure.

What's the input to your gun?

[CFD323]

I'm using a preset 68ci 4500psi Centerflag tank. I believe the pressure is set at 750.

After I gassed up the gun, I immediately chrono'd the gun. I didn't take any "warmup" shots first, just chrono'd it. That was the low chrono's in the 250's. That's when I fired off a couple quick strings of 15 balls or so. Then I rechrono'd and it was up around 300. I never changed the velocity, just chrono'd. Next time I'll fire off a few shots and then chrono and see how consistent I am then. I was wondering if I needed to fire off some "warmup" shots first before I chrono'd to get the most accurate reading. I'll try it today and see what happens.

Thanks for the help.

[[M@g_D@ddy]]

everytime i go to do that in manual mode, i chop a ball. is my input too high making my valve too reactive? it's a preset crossfire at 800-850

[CFD323]

Today I played and had some more problems at the chrono. I will be calling AGD Tech Dept tomorrow if I don't get any replies on this tonight.

I didn't chrono my gun for the first game we played but I noticed that before we started I was shooting all over the place. I would hold my gun as steady as I could and fire at a 2x6 board that was about 40' away. 3 balls would hit perfectly and then the next 2 or 3 would curve all over. Kind of like shooting when you have paint in the barrel-it curves and goes all over the place. I figured it was 1 of 2 things : either my velocity was up too high or maybe because I was shooting medium bore Diablo Blaze in my Boomstick (small bore barrel).

So after the first game, I shot off a quick string of about 15 balls. I then chrono'd the gun. It started at 284 and then everytime I shot the speed would be lower (284,277,271,262,251,244). I figured maybe this was because the valve was hot and the lower speed each time was due to the valve cooling down a little, although that didn't seem right considering how much of a drop there was. It seemed to stay kind of consistent around 240ish. (and when I say kind of consistent I mean 3 balls in the 240's then the next would be 260, then one at 230). So I figure whoa, I'm shooting way too slow so out comes the allen wrench and I turn it up about 1/4 turn. I would have thought this would have cranked up my speed but I was only in the 260's.
I chrono'd again and it started around 300 and then like the first time dropped with each shot til it settled in the 250-260's. I ended up turning it up even more so that it would stay somewhere between like 270-290. I also noticed that the velocity was still not very consistent. I would get one shot of 270, then one of 290, then 275, then 260. I only broke 2 balls out of 670 so I know the speed wasn't too high. And I've shot Diablo Blaze with my Boomy before and it's been fine.

What I would like to know is: Why is the stupid thing so inconsistent over the chrono ? I want to start tournaments but I can't with the speed bouncing all over !! I'm gonna tear apart the whole valve this week and regrease everything. I'll also make sure I check all the o-rings/valve seats etc too. I regularly oil my gun too. If anybody's got any ideas at all, I'd love to hear 'em !!

Normally I play on private property so I never chrono'd my gun before a week or 2 ago. Maybe this has been going on the whole time and I never knew it.

Here's all the specifics :
Emag
Centerflag preset 68 4500 tank (pressure at 3500 when I started)
Diablo Blaze paint
Boomstick barrel (small bore I believe)
Temp was around 40 degrees F
using a superbolt w/foamie attached (which works great !!)

[BlackVCG]

Take out the valve. Unscrew the black reg. body from the front valve body. Inside you'll see in the front half a brass reg. seat holder, there will either be a small o-ring inside of it, or the o-ring will be in the pocket on the black reg. body. Make sure to keep track of that o-ring. If it's dirty, replace it.

The next o-ring that directly affects velocity is the o-ring under the brass piece. Lift up on that and you'll see the o-ring. Pull it out and replace/clean it. Next, unscrew the velocity adjuster all the way keeping track of how many turns it takes to take it off. Drop out the two coil springs and then from the front end, push out the brass piston with a toothpick. Make sure it's clean by wiping it down and reoiling it. If the o-ring looks bad, replace it. Take a q-tip and clean off the smooth surface the piston rides on inside the reg. valve body.

Reoil everything by hand and put it back together. Screwing the velocity adjuster in as many times as it took to get it off should get the gun back up to speed. If it doesn't gas up, you didn't screw it in far enough. Feed some oil like KC Trouble Free through the ASA and dry fire 50 or so shots with the barrel removed. Make sure your barrel is squeggeed and dry before you start shooting paint. If the paint to barrel fit is tight and you properly serviced the valve, you should see groupings of about +/- 5fps

[CFD323]

Hey Black , thanks for the response. I'll get on it tomorrow to see if it fixes the problem or not. Next question : you say to oil everything by hand as I'm putting it back together. Do you mean just use the Autolube that came with the gun, or do I use some grease on it ? And if I use grease on it, what type do I use ? Will vasoline work ? Automotive grease ?

Should this also fix the problem of the velocity slowly dropping when I chrono it ? Or is that how the RT valve works ? Starts off high and then after 5 chrono shots, it settles in at velocity ?

[BlackVCG]

Just use the autolube that came with the gun. Don't use grease. Just put a drop of oil on your finger and rub the o-rings around in the oil to get them completely oiled one at a time and then reinstall them.

This should fix all of your velocity problems, if it is a problem with the valve in the first place.