Mod Shop – Nerf Alpha Trooper – Spring replacement problem solving

Sorry all, another quick one this week. Still no internet at home so had to punch out a quick one without many pictures. Hopefully I’ll be back to normal by next week.

Went to a game on Saturday; brilliant fun, lots of people, great games. Throughout the day I had a couple of people ask me about spring replacements on their Alpha Troopers and specifically why they were so much more problematic than spring replacement on other reverse plunger based blasters. I went home that afternoon and had a play around with two different AT’s (both with different aftermarket springs) and sure enough, results were mixed. Both blasters were wildly variable in their ranges and sometime would fail to cock altogether. I then grabbed a brand new AT and took to it. Did the standard AR job and tried a couple of different springs and still no love. Played around for a while trying to figure out what was the problem and all of a sudden it dawned on me; if I pushed the back of the plunger forward after I fired, it worked every time. I pulled it all apart to find out was causing it and wow but was it obvious. The stock AT spring is longer than either the Recon or the Raider. This is because it’s slightly under load when the blaster is un-primed, which forces a locking mechanism forward. Have a look at the first two photos below and you’ll soon see what I mean.

Here is the blaster with a BTV1 spring, under no load. Pay careful attention to the small black spring above the trigger and the mechanism it’s attached to.Photobucket

Now compare that to the position here when I pull the plunger all the way forward. See the difference? The stock spring would keep it under load, even when the blaster wasn’t primed.Photobucket

Again, the BTV1 un-primed.Photobucket

Compared to the BTV1 with the plunger pulled forward. See our problem here? I stuffed around trying to make a spacer that was the right length to force the mechanism forward enough but the compressed length of the spring was then too much with the spacer in place.


Instead, really simple solution.


Cut the stock spring down and use a few coils from it in addition to the BT spring and we’re in business.


Unfortunately the priming bar and bolt sled aren’t connected to the plunger so no amount of pulling the priming handle forward will solve it, we have to push the plunger forward from behind.

I put about 70 darts through it with no problems. No idea on ranges as I was confined to a garage at the time, but seems about on par with any other sprung reverse plunger blaster I’ve done. It should get a game tested soon enough and I’ll report back on it’s workings then, but for the moment I think I’m on to a winner.

Cheers guys, hope to return to normal by next week. Current plan is to do a write up on one of the more advanced blaster modifications I’ve done recently.



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