New G&P FPS Problem

[Shanker]

Hi, for Christmas I got a brand new G&P M4. I only shot it a few times and everything was going fine, I couldn't see any FPS problems because I don't have a chrono. On the 4th I went to No Limits, and when I chrono'd it, it was only shooting about 270 FPS. I thought the stock G&P's usually come out at around the 330ish FPS range. I separated the two receivers to install a new inner barrel, and I noticed the air nozzle doesn't move until you shoot, and I thought it was suppose to if you press it a little. Also, when you shoot it, it starts in a back position, then moves forward each cycle. If anyone could shed a little light on why this is happening, it would really help. Hey there might not be anything wrong, I just want to be sure.

Here's a picture if it helps:


It looks like the spring is compressed too (after a few semi-auto shots):

[Ike]

I don't think that the nozzle is your issue, everything sounds fine. Depending on where your gearbox stops in its cycle you may or may not be able to push it back. For it to be moving at the wrong time, your sector gear's tappet cam would have had to have been machined on the wrong side.

My G&P came shooting around 375fps out of the box. With a compression fix, I got it up to 405fps +/- 1fps, so it definitely sounds like you're having a compression problem. Take the barrel out, wash your bucking, check for rips or tears, and make sure that you re-install it correctly. It may not necessarily help your compression but it doesn't hurt to check and will definitely help your accuracy. The nozzle to bucking interface is often overlooked as a source of an air leak. If that doesn't help, you'll have to go into the gearbox and make sure that your cylinder and cylinder head are sealing properly, and that your piston head o-ring is lubed and intact.

Also, is it possible that the chrono was off or you were using heavy BBs? Was it getting noticeably shorter range than other guns, like a 270fps gun should be? I ask because I had an issue where I was chronoing my ARES with shitty BBs because they were the only .2s I had and was getting similar numbers, but when I dropped in some high-quality .25s my gun shot like a dream.

[Shanker]

I did clean everything in the barrel and replaced it all, but I never thought of the bb's. I was using the GI G4 .25s, do you think that's what it was?

[Ike]

So you were getting 270fps with .25s? That'd probably be 310-330 with .2s, which isn't too bad. I've heard some pretty bad things about the GI BBs and never anything good, so you may want to try another brand and see if your results are better.

[Shanker]

OK, thanks for all the help Ike. And just to be the first, I like the GI bb's, I have never see any chips, seams, or broken ones. But once I run out I'll get some Javelin's or something just to be sure.

[Biz]

You say you got it for Christmas, maybe you left the spring compressed last time you shot it, resulting in a lower fps.

[Shanker]

I always make sure to take a few semi shots just to be sure, but I can't remember that far back.

[Connors]

Leaving the spring compressed will not make the fps drop any more than maybe 5 or 6 fps, not 30-40. Using .25's to chrono, however, will give you that big of a difference. I do have to ask though, why would you chrono a gun at an event with .25's? That'll give a false reading and if you are shooting hot it could get someone hurt in the field. Tis why we chrono and base our fps and engagement limits around .20 bb's.

[Gimpalong]

I have a G&P M4A1 and it chronos between 310 and 330 depending on the chrono. I'd say that that range in velocity is normal.

My G&P M733 on the other hand chronos around 380...

[Crapshoot]

Feb 6, 2012 12:14:02 GMT -5 Ike said:

I've heard some pretty bad things about the GI BBs and never anything good, so you may want to try another brand and see if your results are better.

I've never had bad experiences with GI G4 bbs. I've put at least 13,000 rounds of GI G4 .20's through my Ares G36c with no problems whatsoever.

[Shanker]

Connors, It completely slipped my mind, I used to only use .20's until I recently switched to .25's, so I really didn't think twice about it. I'm about to buy a bag of .20's just for chronoing purposes only. I will definatly be more careful next time, I don't want anyone hurt.

[Biz]

Leaving a spring compressed since Christmas, would deffinitly drop his fps more then just "5-6", he could easily have seen a 30-40fps drop. If it's shooting consistent fps then it shouldn't be a compression loss, as it would be shooting +- 15ish give or take. And try a chrono with .2's, and even look up some YouTube videos of your same gun getting chronoed and compare.

[Ike]

We don't even know if his spring has been compressed, and I've never seen it adversely affect a gun more than a few FPS before, especially not in just 1-2 months time. Based on what Gimpalong said about his G&P guns having different velocities out of the box, Shanker's should be at about the correct power with .2s. And for the record, it's very easy to lower velocity and keep it consistent with a controlled air leak. Ported cylinders are an example of this, but lowering velocity on a given spring is very easy without getting crazy variation.