Problem with Sten stock sliding down

[Bret]

I purchased a Sten MkII. Oddly enough it didn't come with the stock because the owner lost it. Not a problem since it was a good deal and they're pretty available. I purchased stock like this from Numrich.

The Sten runs fine in full auto, but every once in a while the stock slides down while I'm shooting it. Any idea what the cause is and how I can fix it?

 

[Starvingboy]

Are you missing the inner spring cap? it has a big 'ol button which fits in the rear stock hole and keeps everything from moving around...

 

[Bret]

Assuming that you're talking about this part, it's there.
https://www.gunpartscorp.com/products/469910

Is it possible that the recoil is causing the cap to move forward somehow, like perhaps when the bolt is all the way forward? If so, might it just be a weak recoil spring?

 

[Villafuego]

Is the spring/cap retainer turned/locked fully in place?

It should be flush with the rear of the tube, and the end of the cap should protrude about 1/3-1/2" thru it

 

[Bret]

I'll check and let y'all know.

 

[rentprop1]

sometimes you've gotta put a little curve in the plate to hold pressure against the cap, just put the tip in a vice and bend away slightly

 

[Battering ram NIB]

I think every sten is different. My loop stock fits in perfect, but I own a t stock and a mk5 stock - neither will fit. Too tight

I’d buy another stock and test it if I were you

I also don’t think your stock can come off with that nipple sticking out the back of the gun. Make a video or show some pics ?

 

[rentprop1]

I also don’t think your stock can come off with that nipple sticking out the back of the gun. Make a video or show some pics ?

if that recoil spring is about shot the reverse recoil, the forward momentum of recoil ( if you would ) there wouldn't be enough pressure to hold the cap and nipple rearward. I'm betting the stock is sliding down just before that force return forward, also pushing out on the cap

 

[Bret]

Here's a video of what's happening.
https://youtu.be/MzX9B62Igxc

 

[Battering ram NIB]

The plug in the back shouldn’t move

Turn it more or inspect why it’s not locking in? Might be worn out?

I checked mine. The plug is very solid. I sometimes have to take a needle nose pliers to get mine to twist so it will lock in

 

[Mackjack]

Makes sense why it didn't have a stock when you got it. Musta fell off in the woods somewhere while original owner was in a gunfight with rebel soupcans or squirrels.

 

[Bret]

Here's a picture from the rear. I don't see anything to lock it or keep it from moving forward.

Battering ram NIB, is your setup the same or different?

 

[Battering ram NIB]

It goes in and twists into a groove

If the groove is worn it could do what yours is doing
I see wear marks that say it’s possibly happening

Is it loose going into the groove? Mine is very tight to where sometimes I have to use a pliers or screwdriver to twist it in and out of the groove

 

[Bret]

It's not tight at all. You just line the cap with the cut in the receiver, push it in a bit, twist clockwise a bit and then let go. When you push on the cap or button, they each push in easily. BTW, the groove doesn't look worn at all. I'm wondering if perhaps the cap is not correct for the receiver. Do you have a MkII? If so, does the cap appear identical?

 

[boomer535]

First I would replace the recoil spring, you may just have a weak spring. I have had my Interport Sten for over 25 years and never had that problem. My Sten came with the loop stock like you have. I also have used a T stock on it although I had to do a little fitting with a file to get it to fit.

 

[boomer535]

The recoil spring is what puts pressure on the cap to hold the stock on. The only thing that twist ring does is keep the recoil spring from shooting out when you remove the stock. Get a new recoil spring. It fact, buy yourself a Sten MKII parts kit too, just to have for parts. Another tip, if you have your gun jamming on the last few rounds in a magazine the problem is almost always a weak spring in the magazine.

 

[Bret]

I purchased a new recoil spring (and a box type magazine loader). I should be able to provide results in a week or so.

 

[Battering ram NIB]

yes I have a Mk2. I had more time today and took it apart to inspect mine better. I was wrong. it does move, but not easily. it should move 3/4" or so.

my spring is 10" long. measure yours. ill bet its much shorter. mine was replaced maybe 600 rounds ago.

the spring has so much tension that I don't see how it could pull that plug backwards, but mine is a shorty sten. the tube is about 1" shorter, so there is more tension on my spring. that's why last night I couldn't even get the plug to move forward. my gun is pretty tight everywhere though


as for the loader? the best one by far is the Austen one. they are around $100-150 when they show up, but I picked one up for $40 with a BIN on GB a while back. sometimes people don't know what they have. they are very desirable, so typically there are multiple bidders

 

[Cat Bath]

Sorry I'm late to the party.
Mine did the same thing until I replaced the rubber buffer inside the "stock retaining button" (pictured above)

Best I can figure is that the spring bound up inside the button and pulled it forward every time it decompressed.
My particular problem was that the rubber buffer pad degraded and covered the spring with sticky goo and therefore wouldn't slide inside the button.

I assume a missing buffer pad might do the same thing.
Try stuffing a wadded up paper towel or part of a rag in the cap and doing a mag dump.

Hope this helps.

 

[boomer535]

I never had a buffer in my endcap. My bolt never went back far enough to bottom out on the endcap. I always thought a buffer was nor required on the Sten.