AR15.Com Archives
 Sten Mag Feeding Problems - How To Fix?
duncan  [Member]
10/6/2002 1:11:57 PM
I've got about 18 Sten mags - all used.

Shooting them in an Oly Arms PCR-9 using the SOCOM mag block. Some of the Stens are from Tapco and some locally.

Most work flawlessly - no misfeeds. I notice they have little if any wiggle play when fully inserted into the magwell.

I've checked the SOCOM block and the ammo and the PCR-9 is in good shape so I figure its the mags. Dremel polished the feed ramp and the cone shaped chamber area to enhance feeding.

But I did notice that the offending mags have some magwell play. You can wiggle them.

I've got several Sten mags that feed the 9mm ammo into my Oly Arm PCR-9 in such as a way that the bolt assembly forcing cone catches the case in the middle and heavily dents the case ruining it. And then I have a jam and a clearing drill!

Have to pry them out with a screwdriver.

Tried round nose, sharp HP, and open HP bullet profiles and the result is the same. Those few Stens cause them to jam into the top of the upper chamber lodging on the forcing cone part of the bolt action.

How do I fix those mags?

Take a hammer and vice grips to the range and tweak them?

Replace the springs with some Wolff glock 18 32-round extra power mag springs? They may work or I can mod them?

Was thinking that the mag lips need to be tapped down a tad more to get the bullet heading more forward and less pointing up to the handle above.

Ideas?
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Boom_Stick  [Team Member]
10/6/2002 7:03:33 PM
Try a few things to diagnose it.

1)Test the power of your recoil spring. Hold the rifle straight up and down. Pull the charging handle back, then ease the bolt forward until it engages the ejector. Slowly let go and see how fast or slow the bolt over comes the ejector. If it doesn't go forward tilt the muzzle down and it should go into battery on its own. If the bolt did stop on the ejector (as you were holding the rifle straight up and down), your recoil spring is weak. Before you go buy an extra power spring, stretch your existing one until it can over come the ejector, then test fire.

2) Ease a round into the chamber and watch what it does.

3) Inspect a jammed round to see if the lead has a print from stopping on the throat rim. My ammo use to stop on the upper throat rim and the bolt would crush it in half.


I use to have the same problem you did. I drimmeled the throat to a more aggressive angle and polished it. It still didn't fix the problem until I put a faux telstock on it(the faux stock had an extra-power spring). I put the A2 stock back on and the problem came back. I stretched the A2 spring and the problem went away.

Hope this helps.
duncan  [Member]
10/7/2002 1:19:06 PM
Thanks, I'll try that!
Gun_Collector  [Member]
10/8/2002 3:24:02 AM
I would try 9mm that a tad bit hot.

Wolf 9mm works great.

Sten mags were made by dozens of mom and dad shops in WW2 and so the tolerance will vary from mag to mag.

But I bets its all ammo related.

GeneStoner  [Team Member]
10/8/2002 2:00:02 PM
Another possibility is caked on cosmoline INSIDE the mag.

I know that when I initially got my Tapco mags they were well coated in cosmoline. And I thought that I had dissolved all the junk by keeping them submerged in a solvent tank over night.

However, upon recent disassembly of some of those mags, I found enough sticky cosmoline inside to think that it may have caused a malfunction(s) at some point.

Heck, if these ideas fail to work for ya, the mags were cheap enough to chalk up as losses; And thank goodness they weren't the overpriced Colt mags...

ps-- It probably wouldn't hurt to stretch out the mag springs while you have the mags apart.
Kaliburz  [Team Member]
10/8/2002 3:49:53 PM
It could be dirty inside the mags.... but you have to remember, most, if not all Sten mags are at least 60 years old... If it's the original springs in them.


Well, if you happen to "give up" on some of the Sten mags, IM or email me. Might be willing to take the offending mags off your hand. Love a tinker challenge......
duncan  [Member]
10/8/2002 4:52:06 PM
Thanks for all of the tips.

I cleaned the Stens in very warm water and degreasered them thoroughly to remove the cosmoline. Wiped them off and lightly lubed inside rails with Tetra gun grease.

I've also been shooting some NATO velocity and +P+ 124 grain JHPs and some law enforcement only NATO FMJ's and the problem continues somewhat.

I'll try strecthing the stock blowback spring and if not effective, stretch the mag springs to diagnose.

Hitting the range tonight so I'll let you all know.

Really appreciate your input. Make's a guy feel welcome.
duncan  [Member]
10/9/2002 6:50:15 PM
Boom_Stick, my Oly passed the recoil spring.

But I discovered that some of my magazine springs were a bit undersprung.

A gentle pull got all of my ammo feeding reliabily.

Thanks.

But I did notice that some of the Sten mags had thicker closer held lips while some had little metal holding the round in the mag. Avoid those!
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