Minimag shootdown and two questions

[wolftune]

First, to secretweaponevan, thanks to your help, I can now get my velocity up above 280 fps.

However...I now have discovered that there's shootdown.

Basically, each shot (shooting about 2 bps or faster) drops about 10 bps. So I'll go something like 285, 272, 263, 251, 239, 230, etc. If I wait two or three seconds, I'm back to about the BPS where I started.

I tried two different, full HPA tanks, one I know that is preset to around 800 PSI (Guerilla myth). Changing tanks didn't make any difference. I also recently replaced all the o-rings and the bolt spring. Maybe I didn't oil everything well enough? Any suggestions?

Also, two separate questions that are probably unrelated:

First, in Tom's video, he shows that the bolt should not sit directly on the bumper but should instead have a bit of space (due, I think, to the power tube o-ring). After shooting, when I take my marker apart, my bolt is flush with the bumper, almost like it's sealed to it. Is this a newer design or is this wrong? If so, could this be my problem?

Second, the on/off assembly goes in okay, but it seems like it's not seating quite right. Maybe I'm just being anal. I have all the o-rings right as far as I can tell. My question is, should the "On/Off bottom" have a 'bounce' to it after it's seated? In other words, should it be able to move in further than it's resting place when pressure is applied? When I push it, it moves further into the chamber until it's almost flush and then bumps back out to where I can see 2 lips. Is this normal?

This is my first Automag/Minimag, sorry if they are noob questions. Any help is much appreciated, thanks in advance.

[secretweaponevan]

First, to secretweaponevan, thanks to your help, I can now get my velocity up above 280 fps.

However...I now have discovered that there's shootdown.

Basically, each shot (shooting about 2 bps or faster) drops about 10 bps. So I'll go something like 285, 272, 263, 251, 239, 230, etc. If I wait two or three seconds, I'm back to about the BPS where I started.

I tried two different, full HPA tanks, one I know that is preset to around 800 PSI (Guerilla myth). Changing tanks didn't make any difference. I also recently replaced all the o-rings and the bolt spring. Maybe I didn't oil everything well enough? Any suggestions?

Also, two separate questions that are probably unrelated:

First, in Tom's video, he shows that the bolt should not sit directly on the bumper but should instead have a bit of space (due, I think, to the power tube o-ring). After shooting, when I take my marker apart, my bolt is flush with the bumper, almost like it's sealed to it. Is this a newer design or is this wrong? If so, could this be my problem?

Second, the on/off assembly goes in okay, but it seems like it's not seating quite right. Maybe I'm just being anal. I have all the o-rings right as far as I can tell. My question is, should the "On/Off bottom" have a 'bounce' to it after it's seated? In other words, should it be able to move in further than it's resting place when pressure is applied? When I push it, it moves further into the chamber until it's almost flush and then bumps back out to where I can see 2 lips. Is this normal?

This is my first Automag/Minimag, sorry if they are noob questions. Any help is much appreciated, thanks in advance.

Glad to help!

Shootdown can be caused by a restricted airpath or a gummed up regulator.

Restricted airpath can be caused by:
Using microline instead of macroline or steel-braided hose.
An ASA that doesn't push your tank's pin down enough.
Some debris (think teflon tape) in your valve somewhere (usually in the on/off).

Check your spring pack/reg piston area to make sure it isn't all crapped up with old grease.

The two lips are normal, it is so you can extract the on/off assembly with your fingernails. I just checked my on/off and it has some "smoosh" to it too.

Your powertube and bumper should be fine.

[wolftune]

Glad to help!

Shootdown can be caused by a restricted airpath or a gummed up regulator.

Restricted airpath can be caused by:
Using microline instead of macroline or steel-braided hose.
An ASA that doesn't push your tank's pin down enough.
Some debris (think teflon tape) in your valve somewhere (usually in the on/off).

Check your spring pack/reg piston area to make sure it isn't all crapped up with old grease.

The two lips are normal, it is so you can extract the on/off assembly with your fingernails. I just checked my on/off and it has some "smoosh" to it too.

Your powertube and bumper should be fine.

Okay, thanks. I'll try a deep clean, oiling/lubing, and making sure the pin is getting depressed enough. i have macroline steel-braided hose, so that shouldn't be the problem. Hopefully, it's just the pin.

[wolftune]

Okay, thanks. I'll try a deep clean, oiling/lubing, and making sure the pin is getting depressed enough. i have macroline steel-braided hose, so that shouldn't be the problem. Hopefully, it's just the pin.

Well, I cleaned everything, checked out all the parts to see if there was any debris, rechecked all the o-ring placement, and put 2 drops of oil in the ASA and fired a bunch. I also checked the ASA pin with other ASA's that I know have a strong "pin pusher", and it's fine.

I then gassed up and shot a bunch of paint. Velocity still drops at least 10 BPS each shot if I'm going over 1 ball per second. I just don't get it. It's bumming me out because I'd like to play with this marker in the near future. Any other suggestions? Is it possible that my steel braided hose is bad? Or that it's bent too much (it does 180 degrees of turn over about 4 inches between the drop forward and the expansion chamber)? I intuitively feel like it's something in the valve, but everything looks good and clean.

Any help much appreciated, thanks.

[Drizit]

did you split the valve and pull out the reg pin and spring from the front half? little bits of teflon tape sometimes get stuck there. The reg seat should sit nicely in the back half of the valve without falling out if it does try flipping it over and putting it back. lastly... more oil... 2 or 3 drops is all you NEED for regular maintenance... if the marker has been neglected though I've found putting in lots (as in fill the bottom of the ASA with it.) will help wonders. Also don't just look at other ASAs compared to yours actually try one. On some tanks if the pin is pushed too far it will also block air flow. Lastly see if you can hunt down a new spring pack for the back of the valve... a dud spring pack can cause all kinds of things, even if you just borrow one for testing.

[wolftune]

did you split the valve and pull out the reg pin and spring from the front half? little bits of teflon tape sometimes get stuck there. The reg seat should sit nicely in the back half of the valve without falling out if it does try flipping it over and putting it back. lastly... more oil... 2 or 3 drops is all you NEED for regular maintenance... if the marker has been neglected though I've found putting in lots (as in fill the bottom of the ASA with it.) will help wonders. Also don't just look at other ASAs compared to yours actually try one. On some tanks if the pin is pushed too far it will also block air flow. Lastly see if you can hunt down a new spring pack for the back of the valve... a dud spring pack can cause all kinds of things, even if you just borrow one for testing.

Thank you, I'll try all the above.

[fishmishin]

I saw were you said you cleaned everything but did you actually pull the spring pack out and make sure it wasn't gummed up. That is the biggest cause of shoot down I have seen in guns that have been stored for any length of time. If not take the regulator nut out, pull the spring pack out and take another look at it. Sometimes it is fairly easy to miss some of the gunk built up on it. If it is gunked up run some hot water on it for a couple of minutes and use a toothpick or a small straight screwdriver to clean out between the coils on the spring pack. Once you have it cleaned really good give it a good coat of Gold Cup, and re-install. Then try checking the velocity, I am almost 100% certain you will be good to go.

[athomas]

Also check the ASA pin length. Too long or too short and it will starve the gun.

[wolftune]

Also check the ASA pin length. Too long or too short and it will starve the gun.

Thanks for all the suggestions.

I checked the reg pin and spring and it was clean.

I put a lot of oil in the ASA and shot it through the marker.

I tested 2 different ASA's and it made no difference.

Then, I took the spring pack out yesterday. When I looked closely, it did indeed have a fair amount gunk, so I washed it with a strong stream of water until it looked clean. Then, I re-lubed it with a silicone based grease made by Smart Parts I think (hope that's okay, it's made for paintball equipment) and put it back in the gun. I was going to test it when...my 3 month old started wailing. Dang. I'll have to test this soon and let you guys know.

[secretweaponevan]

Also check the ASA pin length. Too long or too short and it will starve the gun.

I learn something new from you every day. Didn't even occur to me that too long could restrict gas flow too.

Thanks, athomas.

[wolftune]

Okay, so I tested the mag again after cleaning the spring pack. Still shootdown. Then, I listened to the valve while shooting and could actually hear the air recharging. That clearly isn't right. Then, I realized that the source of the sound was from the ASA or the expansion chamber (couldn't tell which).

So I bypassed the gas-through grip/expansion chamber with by going straight from ASA into the braided hose going to the valve and there was absolutely no shoot down. So it must be the expansion chamber.

I then took it apart. There's really not much to it except two small holes at the top and bottom to allow air through and a "pit" that I assume is there to catch liquid co2.

Any suggestions on how to deal with this? I'd rather not buy a new gas-through. Can I just drill out the holes to increase the volume of air allowed through? This wouldn't affect my operation because I use HPA. Doesn't seem dangerous, but I've been wrong before.

Thanks again for all your great advice. By doing all this troubleshooting, I've really learned my mag. What a cool marker.

[frans42000]

Any suggestions on how to deal with this? I'd rather not buy a new gas-through. Can I just drill out the holes to increase the volume of air allowed through? This wouldn't affect my operation because I use HPA. Doesn't seem dangerous, but I've been wrong before.

You have already discovered that yourself.

An HPA powered mag has no need of an expansion chamber. All it is to you is a gas through grip. In Co2 set-ups an expansion chamber is a buffer between tank and gun that allows Co2 time to shift from liquid to gas as well as attempting to prevent liquid from entering the regulator.

HPA set-ups have no liquid to expand into gas.

Drill that sucker out. And triple check for leaks.

[wolftune]

You have already discovered that yourself.

An HPA powered mag has no need of an expansion chamber. All it is to you is a gas through grip. In Co2 set-ups an expansion chamber is a buffer between tank and gun that allows Co2 time to shift from liquid to gas as well as attempting to prevent liquid from entering the regulator.

HPA set-ups have no liquid to expand into gas.

Drill that sucker out. And triple check for leaks.


Excellent, thank you! I'm really excited to finally get this think field worthy!

[Drizit]

or depending on the build of your X chamber just pull the disks out all together... lighter and better flow... best of both worlds :D