Getting a gun to shoot <300 FPS?
 

We have an upcoming Zombie game and we're wondering if there's any springs designed for sub-300 FPS. I can't really seem to find any, so would cutting some down and swapping them work?

Some of the guns include CA and G&P M4s, some shittier brand M4s, and an ARES G36C.

Any help or other ideas would be awesome.

Thanks.

new spring. M90 or lower.

This may help its a Spring Comparison Chart
http://www.airsoftcanada.com/showthread.php?t=4911

Any stock TM spring...

I got dozens... want some?

They all shoot 280 right on the spot.

That'd be perfect, I'll take this to PMs

According to that chart (and some of the sites) M90 springs bring the FPS to about 330, which is still a bit much. Thanks guys.

If worst comes to worst use a Guarder SP85: http://www.airsoftgi.com/product_inf...oducts_id=3391

However other than that I would stick with the stock TM springs. Although I was always under the impression that the stock springs were "1J springs" and shot between 300-328 FPS.

My TM m733 shot 290 on the button stock.

The Spring comparison table also has them shooting sub-300.

I was hoping to avoid AirsoftGI because their shipping rates are attrocious.

Stock TM springs for the win for sub-300fps, but you'll have to either use a stock TM piston with it, of just cut off the hook that attaches to the piston itself.

In the batch I have, 2-3 hooks are cut... the rest are new... When you cut the hook and use it with a bearing spring guide and a long (M16/500mm) inner, you get about 300-310 from a fresh spring.

Older springs run between 275 and 290 (again, depends on barrel lenght and cylinder porting).

Yup, just reinforcing the idea for him........ ;)

Be careful on full auto, if you're set up for fairly high RPM on a 380ish spring, shooting 300fps might over-speed your mechbox on full auto. I recommend sticking to semi as much as possible

comparison charts dont mean much really, I have a fresh 140 in my g36 tbb 415mmib and I shoot a average 420 on the nose. the charts will say I should shoot 440ish , if I remember the charts correctly

It'll be semi-only, and the ammo will be very limited, so I don't forsee any problems. We just want these so we can get away from springer pistols and shotguns.

Look at the amount of upgraded parts in the chart's test platform, most deal with the "best configuration" possible as far as air sealing, efficiency, etc.

Case in point, the PDI 150% spring is listed at ~395fps w/0.20g, and when I first bought one for my stock TM MP5A5, I sat at a very pretty 350fps within about +/- 2fps. Within two months of casual shooting in my basement over the winter, it blew out the front end of my mechbox.

Over the years of doing gun work, quite a few bought and asked me to install PDI 150% springs, a couple ran around 350fps, quite a few ran upwards of 425fps, all with relatively stock guns, some had bearing spring guides installed (+ ~15fps), tightbores (+ ~10fps), etc. Easy enough to calculate within 10fps or so, but after seeing the 75fps range those springs can shoot at regardless of upgrades (had some bare stock guns shoot that high easily), I sorted out some were up to 3/4" longer than others (my 350fps spring was 6 3/8" long, got a couple 150% that were up to and just past 7" long), and also made of thicker steel spring wire, making compression and install damned close to impossible, and also massive fuse blowing during testing.

Illusion did a great job putting that comparison chart together, but for those that want to get a certain fps with their gun and NOT looking to add in all the bells and whistles he did, the chart is pointless. For some springs, look at the m/s rating and judge for your own set up, for others like PDI, stay away from them, they turned to crap after 2004, at least as far as AEG springs go.

+1, that chart is as accurate as can be!
If you compare with ehobby's own spring ratings, they're 50-100fps UNDER what the spring is capable of at it's best.

I just tend to hope for the math route, hoping the rating is actually meters per second, add on the rough increases of a tightbore, bearing spring guide, and ballpark it. Of course, seems different manufacturers have different concepts on how long a meter is, in which case, the above spring chart gives an idea of what one might expect when comparing an untried spring compared to a known one.

A M90 or 100% spring should work. Try to avoid cutting down springs as it's very much less than exact.

Since a tightbore, bearing spring guide, bearing piston head and how nicely the internals are setup will all tend to boost your FPS a bit you can hedge your bets a bit and if your m90 spring is a non linear spring (i.e. a Modify sp90 has closer packed coils on one end) you can reverse the spring and put the tighter pack at the front closer to the piston head. That will kill off some FPS as I've regularly seen a sp90 spring hit 340fps in a nicely tuned setup.

As always...a chrony is the only way to know for sure. And the peace of mind of doing that many guns....and then then powering them back up afterwards...will pay for a cost of a chrony right there.

My lil m4* shoots a solid 350 with a modify 90 spring in it. With a 100 it gets to shy of 400. I've seen m85 springs. That might do it?

* (g&g m4 cqd w/cqbr 6.04 barrel stock internals except for piston head & viton rubber o-ring)