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Specna Arms magazine compatibility / feeding issue amelioration


Rogerborg
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Specnas are getting notorious for being fussy about mags, and my SA-E02 is no different.  With the stock hop unit (a decent rotary) It feeds fine off of its own mid caps, and is OK with hi-caps, but didn't want anything to do with other mid caps.

 

Reddit sez "lol just change the magazine catch lol", but nobody seems able to explain why, or for what, or how this helps.  So I decided to science it out by measuring mags, and testing the feed tube interface.

 

Specna mid cap vs M16VN short mag, total length front to rear, and from the front of the mag to inside the feed.

 

image.png.f1d212f977e7093408405810e75bcd18.pngimage.png.dbef1fc5daa21e705c8d55035430ce29.png

 

The overall length can be measured precisely, but it's harder to get an exact measurement on the front of mag to inside the magwell tube, so I've been a bit approximate there.  It might not be a full 1mm difference, but when the fronts are aligned, it's apparent that the Specna feed is further back.  With the rears of the mags aligned, they're a closer match.

 

The Specna mags also have a conical section at the top of the feed.  With the hop unit removed from the gun and tested with both mags (to isolate just that issue), this provides a noticeable smoother insert: it's a smart bit of design.

 

I'd seen speculation that the Specna hop tube was "pencil dicking" mags and not big enough to key in solidly without free play. I didn't find this.  If anything, the hop tube was slightly sticky when going into the VN mags, and there was no free movement at all once it was in.

 

The last significant point was the the BB stopper on the VN mags has a flat section that protrudes slightly into the tube, whereas the Specna doesn't.  This lip provides a significant obstacle to the hop feed tube, and it needs a harder push-and-wiggle to move the stopper back and get the feed tube right in.  Either because of this, or a stronger stopper spring, or something else in the magazine geometry, it also needs more effort to keep the hop unit pressed all the way into the VN magazines.

 

Some slight exaggeration for effect:

 

image.png.07c837fc64a420de7fe2f22d0423bcfa.png

 

So: what did I do?

 

1. Carefully filed and sanded a slight conical shape on the bottom edge of the feed tube to assist keying it into the mag.  There's a fair amount of material there to play with.  Just give it some help to find the magazine, and to let it get and stay all the way in.

 

2. Do some more aggressive filing on the back of the feed tube, to produce a flat ramp where it meets the BB stopper.

 

This looks aggressive, but bear in mind that most of the height of the tube is left intact, so there's still no free play.  The BBs are going up the middle, and as long as there's any material at the rear, the BB stopper will be pushed far enough back.

 

With this done, the feed tube isn't fighting as hard against staying all the way in the magazine.

 

image.png.39c00192039146a49350169089aea476.png

 

3. Magazine fettling.  Since I want to keep the Specna mags usable, rather than modifying the magwell I've added half a mm of tape at the front of the VN mags to give them the same size as the Specna mags, and to move the feed backwards to more closely match the Specna.  I've put some silicone grease on top to help it slide in without tearing, and might replace it with velcro depending how it stands up.

 

If I wanted to only use these mags, and not have the Specna mags fit any more, I'd put a velcro strip inside the front of the magwell instead.

 

Result: a smoother insertion and perfect feeding of the VN mags.  In fact, I got reliable feeding from one even before adding the tape at the front, so it seems like just a small mod to the end of the feed tube does help.

 

The mags need a good hard push to get the magwell catch locked in place, which is perhaps where the Reddit wisdom is coming from, but once in place they're solid. That's not the problem, at least on my example, with my magazines.

 

Best of luck.

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48 minutes ago, Adolf Hamster said:

ahh the joys of airsoft "compatibility" :P

 

Once you start measuring this stuff up, the really surprising part is that any of it ever works at all.

 

Half a mm doesn't sound like much, but side-by-side it's very obvious.

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1 hour ago, RostokMcSpoons said:

"Saw this, thought of you ..."

 

I was adding a comment there linking back here while you were adding a comment here linking over there. :D 

 

[EDIT] Well, I had added a comment, it vanished. I wonder if WuTube takes a dim view of external links now.

 

[EDIT 2] Yup, 2nd comment has gone as well. :( 

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2 hours ago, Pseudotectonic said:

Wouldn't chamfering the mag itself achieve the same effect / help even more?

 

Maaaaaybe.  However, the receiver, magwell, gearbox and hop are fixed points of truth, and the magazine has to sack up and fit them.

 

It really comes down to whether you want to make X mags fit 1 feed tube, or 1 feed tube fit X magazines.

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