M40A1 XB Upgrade

[Dawg Bait]

I just placed a order for a PDI 340% spring. I am wounder what fps i should expect out of it, i just hope its under the fps limit, if any one knows please let me know, Thanks


Ross
Dawg Bait

[Bigmack]

340%?

meh.

should be like 550-560ish.

'cause a 300% is 520 with .2s..


with .2s, you'd probly be about 3-3.2 Joules...


'course, this is going off of an AEG scale... not sure if PDI has different ratings for their M40 springs...

(i doubt they do. i think you'll be in the 550 area.)

[Dawg Bait]

Thank you Bigmack. that helped. Now when i get it i gotta find someone in the holland Area that has a crono so i can see. I hope its not over 550... I f it is oh well.. i could use it for team prac's I have nothing else to say


Ross
Dawg Bait

[Bigmack]

heh. or snip off a twist or so...

[Dawg Bait]

You can do that?


Ross
Dawg Bait

[Bigmack]

can you? yes.

would i do it? no.

[Dawg Bait]

i see.. what are the risks of cutting it like you said.


Ross
Dawg Bait

[Munin]

Typically, a spring is coiled such that the turns at boths ends are "flat." That means that the coil will sit nicely on a flat surface (like the back of your piston or the rear part of your spring guide). If you trim the spring, you lose this "flatness," which can lead to the psring binding , or putting torque on either your piston or your spring guide. If you have a spring guide with a bearing, this really isn't too much of a problem, though.

The other problem is that if you screw up and trim too much off, you can't add it back on. It permanently alters the compression capabilities of the spring.

[Dawg Bait]

I see... Thanks guys



Ross
Dawg Bait

[frostee]

Can you trim it... yes. Would I... yes.

I obviously don't share the opinion of my teammates.
There should be absolutely no problems with trimming a spring down to decrease the force it applies, but there are a few thing you'll want to do to make sure you've done the job right.

Items needed:
-(1) Safety glasses
-(1) New spring
-(1) Dremel tool or die grinder with a thin cut-off wheel
-(1) Water to quench the spring after you've cut it
-(1) Scale or measuring tape
-(2-3) Nylon washers (O.D. small enough to fit in the cylinder, I.D. large enough to fit over the spring guide

First, I'm going to let you in on one of my airsoft smithing secrets, which is based on my experience with spring action rifles. If you look closely at the spring you'll notice that it is progressively wound. Meaning that the coil is tighter at one end than the other. Removing material from the tight coil side is, I believe, the best way to make consistent reductions in fps. I've cut more than one spring and I've found that a certain reduction in tight coil length results in a predictable (within reason) drop in fps. However, your experience may vary, depending on spring manufacture, coil wind, material, etc... You may feel that reducing the loose coil that goes into the piston is the direction you'd like to pursue and that's fine. You shouldn't have any problems cutting that end either.

Do not cut the spring with snips or any other bladed device. Instead, use a Dremel tool or die grinder with a cut-off wheel to cut the spring. The cut should be parallel to the end (flat to the end), similar to the way the spring looked when you first purchased it.

You'll find that the length of the cut you'll need to make to see an appreciable difference in fps is more than you would expect. I would consider starting with at least a half inch reduction in length to begin with. Using a cut-off wheel should give you a nice smooth cut that allows the spring wire to taper down and provide a flat end to rest against the spring guide or piston. However the end of the spring will be extremely sharp, take care. You''ll want to either be very careful, or use the grinder to remove the sharpness at the end.

Now that you've made the cut you'll want to try it out to find out how much you've reduced the fps. This is where the nylon washers become important. Another of my secrets to performing this work, is to use nylon washers to shim the end and protect the spring guide or piston, depending which end you've cut. The nylon washer should be small enough in outside diameter (O.D.) to fit into the cylinder, but have a large enough inside diameter (I.D.) to fit over the spring guide. The nylon washer will act as a bearing, to allow the spring to twist/turn without the cut, sharp edge binding against metal.

And the final secret I'll reveal today... you can also safely use nylon washers in-between spring sections. I'll let you ponder the implication of that statement.

*Edit- Addendum. This information for spring modification is only intended for bolt-action spring rifles, not for AEG's.

[Dawg Bait]

Thank you Frostee


Ross
Dawg Bait

[Munin]

I never said I wouldn't trim a spring. I just said you had to be careful. I trimmed the stock spring in my TM SR-16 - not to reduce the power but to remove the hook that connects into the rear part of the piston head. This way, I can easily switch between my stock and 140% springs based on whether I'm doing outdoor or CQB work.

[Dawg Bait]

Ok, i just got my PDI 340% spring, Now the hard part. Looking for someone in the Holland area that has a chrono that i could shot through a couple times to see the FPS of it.. Right now that i can tell. I have no plans for hop up anymore. Shoots Stright as heck. Accurate now.. Its is sweet. I just hope its not over 550..


Ross
Dawg Bait