FPS Drop CA M15A4

NovaKaynE · April 25th, 2009, 21:37

I have a Classic Army M15A4 Carbine. One of the newer ones. Everything is metal inside of it. I bought it off mopic last season.

I recently installed a crane stock on my gun and opened the mechbox to run the wires to the rear. Last season, I was shooting 300-320 FPS with .20 g's and today I went to chrony it at a game and it was shooting around 260 or so.

When I opened the mechbox, I just bent the wires backwards, I didn't solder the wires. I just turned them around and ran them through the gear box. It is completely stock. There were no upgrades done to the gun at the time. Just the rear wiring modification.

Can a low charged battery cause a drop in FPS? Can the motor height effect the FPS?

I played with the gun today and it worked fine. It was just shooting really low. I want to get it back up to what it was.

TriChrome · April 25th, 2009, 21:48

What weight BB's did you chrono with, and was the hop-up turned all the way off when you chronoed?

Having a low battery won't cause the FPS to drop at all.

NovaKaynE · April 25th, 2009, 22:02

It was chronied with .20's. And I am maybe 50% sure the hop up was fully turned off when it was chronied today. I took the upper receiver off when I got home to try and have a look at the hop up and the rubber was not visible when looking down the barrel. Do you think that would have effected it?

lemegacool · April 25th, 2009, 22:16

battery and motor heigh will not in any case influence fps... maybe the spring was left partially compressed in the mechbox causing it to loose it's elasticity... try with another spring

NovaKaynE · April 25th, 2009, 23:11

That could be it. I left it sitting for the winter.

gunscythe · April 25th, 2009, 23:18

I had a similar thing happen to mine. I put some moly grease (just a bit) on my mechbox air output (part of the tappet?), to seal any air leaks and it went up to 330fps again. I would say air leak rather than spring going bad over one winter.

lemegacool · April 26th, 2009, 02:37

Quote:

Originally Posted by gunscythe

I had a similar thing happen to mine. I put some moly grease (just a bit) on my mechbox air output (part of the tappet?), to seal any air leaks and it went up to 330fps again. I would say air leak rather than spring going bad over one winter.

maybe both!

but one winter is enough to mess up a compressed spring!

gunscythe · April 26th, 2009, 03:20

Quote:

Originally Posted by lemegacool

maybe both!

but one winter is enough to mess up a compressed spring!

How do you decompress a CA spring? On my ICS M16 I press the button and it releases. On the CA it always seems to load.

lemegacool · April 26th, 2009, 03:26

usually you just fire a semi auto shot to decompess it but if i was to leave a gun for a long time stored i would use small pliers to pull the anti reversal latch to fully decompress it.

Styrak · April 26th, 2009, 05:34

Quote:

Originally Posted by lemegacool

usually you just fire a semi auto shot to decompess it but if i was to leave a gun for a long time stored i would use small pliers to pull the anti reversal latch to fully decompress it.

The only way to really fully decompress the spring is to take it out of the mechbox

Scopedog · April 26th, 2009, 10:04

Like others have stated it's probably a spring that has remained compressed for too long. Having a better air seal around you hop-up feeder tube could help as well.

I have the same CA M15 as you. I recently replaced the spring with a Modify S100 (rated at around 360-370fps), Modify cylinder/cylinder head/piston/piston head/nozzle, and a KA hop-up (with O-rings). I think the better nozzle and KA hop-up contributed a lot to my increased velocity. It chrono'd at yesterday's FTF game at 390fps.

The O-rings on the KA unit help to make a better seal at both the mechbox/nozzle and the BB feeder portion. Before installing these parts I fed a single BB into the stock hop-up, covered the feeder portion with my finger and fired. That seal I created with my finger resulted in a 10-15fps increase when run through my chrony. That's why I focused on better air seal when I performed my upgrade. Your mileage may vary of course depending on the mags you're using and how well they sit on the hop-up.

If you want to swap the spring and happen to go with Modify springs, keep in mind that the number/meter ratings they use are conservative. As an example, a Modify S100 is comparable to a 110 for other brands.

NovaKaynE · April 26th, 2009, 10:18

Thanks for the replies everyone. I'll get to work on it soon and let everyone know how it goes.

NovaKaynE · May 2nd, 2009, 18:07

It was a compression problem. I had the exact same thing happen on my other gun after Illusion installed some new gears for me last season. Seems that whenever you take it apart (judging from what happened with both my guns, same problem on both) the air nozzle loses its seal. I simply added a new air nozzle and put a 110 in the gun. Shes shooting at 380 now thanks to Tyson.

So if this ever happens to you. Try putting a new air nozzle in it.

m102404 · May 3rd, 2009, 14:04

J, your air nozzle wasn't sealing with the cylinder head nozzle, causing the air compression loss. You're CA spring was pretty soft/short...but I never put it back in to chrony afterwards.

I tried a BNIB o-ring air nozzle and it wasn't a great fit either. I then tried another and another until I got a good seal (I have about half a dozen spares at any given time).

So...while the "fix" was a new air nozzle...just dropping in a new part doesn't always solve the problem.

Glad to hear it's shooting well...when we're up against each other at the next game, it's good form to give your gun doc a warning shot before you lace him up. LOL!

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April 25th, 2009, 21:37	#1
NovaKaynE Trader rating Join Date: Mar 2008 Location: Durham Region	FPS Drop CA M15A4 I have a Classic Army M15A4 Carbine. One of the newer ones. Everything is metal inside of it. I bought it off mopic last season. I recently installed a crane stock on my gun and opened the mechbox to run the wires to the rear. Last season, I was shooting 300-320 FPS with .20 g's and today I went to chrony it at a game and it was shooting around 260 or so. When I opened the mechbox, I just bent the wires backwards, I didn't solder the wires. I just turned them around and ran them through the gear box. It is completely stock. There were no upgrades done to the gun at the time. Just the rear wiring modification. Can a low charged battery cause a drop in FPS? Can the motor height effect the FPS? I played with the gun today and it worked fine. It was just shooting really low. I want to get it back up to what it was. __________________ *The Distance Between Courage & Stupidity Is Exactly Nine Millimeters*

April 25th, 2009, 21:48	#2
TriChrome Trader rating Join Date: Aug 2008 Location: New Jersey, USA	What weight BB's did you chrono with, and was the hop-up turned all the way off when you chronoed? Having a low battery won't cause the FPS to drop at all. __________________

April 25th, 2009, 22:02	#3
NovaKaynE Trader rating Join Date: Mar 2008 Location: Durham Region	It was chronied with .20's. And I am maybe 50% sure the hop up was fully turned off when it was chronied today. I took the upper receiver off when I got home to try and have a look at the hop up and the rubber was not visible when looking down the barrel. Do you think that would have effected it? __________________ *The Distance Between Courage & Stupidity Is Exactly Nine Millimeters*

April 25th, 2009, 22:16	#4
lemegacool Trader rating Join Date: Aug 2008 Location: notre dame des prairies /quebec	battery and motor heigh will not in any case influence fps... maybe the spring was left partially compressed in the mechbox causing it to loose it's elasticity... try with another spring __________________ member of fire team NOM. my other regular forum: www.toyotanation.com / gen3,gen4 camry

April 25th, 2009, 23:11	#5
NovaKaynE Trader rating Join Date: Mar 2008 Location: Durham Region	That could be it. I left it sitting for the winter. __________________ *The Distance Between Courage & Stupidity Is Exactly Nine Millimeters*

April 25th, 2009, 23:18	#6
gunscythe Trader rating Join Date: Sep 2006 Location: North	I had a similar thing happen to mine. I put some moly grease (just a bit) on my mechbox air output (part of the tappet?), to seal any air leaks and it went up to 330fps again. I would say air leak rather than spring going bad over one winter.

April 26th, 2009, 03:26	#9
lemegacool Trader rating Join Date: Aug 2008 Location: notre dame des prairies /quebec	usually you just fire a semi auto shot to decompess it but if i was to leave a gun for a long time stored i would use small pliers to pull the anti reversal latch to fully decompress it. __________________ member of fire team NOM. my other regular forum: www.toyotanation.com / gen3,gen4 camry

April 26th, 2009, 10:04	#11
Scopedog Trader rating Join Date: Feb 2007 Location: Toronto, ON	Like others have stated it's probably a spring that has remained compressed for too long. Having a better air seal around you hop-up feeder tube could help as well. I have the same CA M15 as you. I recently replaced the spring with a Modify S100 (rated at around 360-370fps), Modify cylinder/cylinder head/piston/piston head/nozzle, and a KA hop-up (with O-rings). I think the better nozzle and KA hop-up contributed a lot to my increased velocity. It chrono'd at yesterday's FTF game at 390fps. The O-rings on the KA unit help to make a better seal at both the mechbox/nozzle and the BB feeder portion. Before installing these parts I fed a single BB into the stock hop-up, covered the feeder portion with my finger and fired. That seal I created with my finger resulted in a 10-15fps increase when run through my chrony. That's why I focused on better air seal when I performed my upgrade. Your mileage may vary of course depending on the mags you're using and how well they sit on the hop-up. If you want to swap the spring and happen to go with Modify springs, keep in mind that the number/meter ratings they use are conservative. As an example, a Modify S100 is comparable to a 110 for other brands. __________________

April 26th, 2009, 10:18	#12
NovaKaynE Trader rating Join Date: Mar 2008 Location: Durham Region	Thanks for the replies everyone. I'll get to work on it soon and let everyone know how it goes. __________________ *The Distance Between Courage & Stupidity Is Exactly Nine Millimeters*

May 2nd, 2009, 18:07	#13
NovaKaynE Trader rating Join Date: Mar 2008 Location: Durham Region	It was a compression problem. I had the exact same thing happen on my other gun after Illusion installed some new gears for me last season. Seems that whenever you take it apart (judging from what happened with both my guns, same problem on both) the air nozzle loses its seal. I simply added a new air nozzle and put a 110 in the gun. Shes shooting at 380 now thanks to Tyson. So if this ever happens to you. Try putting a new air nozzle in it. __________________ *The Distance Between Courage & Stupidity Is Exactly Nine Millimeters*

May 3rd, 2009, 14:04	#14
m102404 Tys Trader rating Join Date: Apr 2006 Location: Toronto	J, your air nozzle wasn't sealing with the cylinder head nozzle, causing the air compression loss. You're CA spring was pretty soft/short...but I never put it back in to chrony afterwards. I tried a BNIB o-ring air nozzle and it wasn't a great fit either. I then tried another and another until I got a good seal (I have about half a dozen spares at any given time). So...while the "fix" was a new air nozzle...just dropping in a new part doesn't always solve the problem. Glad to hear it's shooting well...when we're up against each other at the next game, it's good form to give your gun doc a warning shot before you lace him up. LOL!

FPS Drop CA M15A4

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