monkey with a nf

What size spring do you use for homemades? I am currently using McMaster part 9637K26(same as KBarker's NF rifle mod) for my SNAP 1.5. It has a wire thickness of .08, with the coils spaced about 1/4" apart, and fits perfectly over 1/2" CPVC. The spring is 9" long, and the SNAP has a draw of 5".

However, I'm a bit worried that it's too strong. In addition to requiring quite a bit of force to draw, it has so far shot off the reducing bushing (before I screwed it down), the coupler/bushing assembly (before gluing it), and then the coupler/bushing again, as well as breaking the back endcap on the plunger head (which had, in retrospect, been sanded down too much). Note that there is no forward endcap on the plunger, as I don't have the right washers for the seal. Am I doing something wrong? Please help, as I don't want to have this thing blow up in my face...

I am attempting to build a magazine-fed pneumatic homemade, similar to(it actually started as) Flaming Hilt's version of the SOBR-P. As such, I am basing the tank off of an AT3K tank. I found that for every 1 cubic inch of airtank volume, something pressurized the same as an AT3K with four pumps has about 3.32 cubic inches of air. I have no idea how this translates to PSI, though I assume that it is below the limit of schedule 40 PVC.

When I run through the calculations, I find that the ideal length of 3/4" PVC for the optimum air volume for 12" 17/36" brass is about 5", but at the pressure I plan to use it should be about 1.5". Therefore, this is my planned tank volume (I'm using 3/4" because this is what I'm using as a valve). Does this all seem right? I'm trying to both have this get the approximate range and accuracy of a singled AT3K, and not have it blow up in my hands.

I have finally finished my latest mod: the At3kLS!

The whole thing:


Internals:

The pump hooks up where the bolt would usually slide- you pump the bolt handle to fill the tank.

Trigger bridge detail:

The trigger is bridged with a small LEGO peice- it's the right size and shape for what I needed. It's gooped to the LS trigger and the pin on the air tank fits through a hole in it, and is epoxied in place.

The barrel I'm using is 1' of 17/32" brass, nested inside 1/2" PVC and stuck in a coupler. I don't know ranges (it's too dark outside), but they should be the same as a singled At3k. This is a lot more comfterable to use than an At3K, and takes fewer pumps and has a lower chance of misfires than my LBB.

I've been attempting to integrate an AT3K into a LS shell (the LS is broken beyond repair). However, I can't get the trigger to work.


The white thing is a peice of coat hanger epoxied to the trigger plate and pin. However, it broke off the pin. Before I use stronger/more adhesive, will this work? I noticed the coat hanger bending, and I'm afraid it isn't strong enough. Should I use something stronger? (I would have just used a straight peice of metal, but it would interfere with the bolt- it's where I attached the pump.)

I recently modded my LBB with 12" of 1/2" ID PETG and a pressure valve plug. The tank will pump fine, but when I fire it with even 12 pumps, my darts fishtail and go shorter than they do with 8 pumps. The barrel seal also seems fine. I think the fishtailing is caused by too much power, but I don't get the poor ranges. Help?