New to me Sten is runaway

[FAL]

Hoping someone can point me in the right direction. I'm new to Stens, having just acquired a full auto Sten. Took it to the range for the first time this weekend and sometimes it would continue to run when I let off the trigger. What should I check?

 

[APEXgunparts]

Hoping someone can point me in the right direction. I'm new to Stens, having just acquired a full auto Sten. Took it to the range for the first time this weekend and sometimes it would continue to run when I let off the trigger. What should I check?

Check the SEAR and the SEAR engagement on the bottom of the bolt.
They can wear and get out of shape due to repeated use.

Richard

 

[chuckp]

What ammo were you using? Weak ammo can cause an open bolt gun to sometime runaway due to not enough energy in the bolt to go back far enough to catch the sear.

chuck

 

[Traveler]

What ammo were you using? Weak ammo can cause an open bolt gun to sometime runaway due to not enough energy in the bolt to go back far enough to catch the sear.

That’s good advice. Weak ammo like Remington UMC can do that (about 1100 fps). It was for this reason the British dropped MK 1z (1200 fps) in WW2 and went with MK 2z (1300 fps) for their SMGs (Sten and Lanchester). The Mk4 Sterling (L2A3) was designed to use MK 2z.

A weak trigger spring can also cause the Sten to run away. Along with pulling the trigger forward it also provided the force to raise the sear and tripping lever through the pawl.
Ace hardware has a spring that’s very close to the original trigger spring and isn’t expensive.

If it’s not the ammo, take the trigger mechanism out, clean it, check it, oil it and try again.

 

[FAL]

Great info guys. I plan to take it apart this weekend and check it out. Very much appreciated!

 

[FAL]

What ammo were you using? Weak ammo can cause an open bolt gun to sometime runaway due to not enough energy in the bolt to go back far enough to catch the sear.

chuck

Just to circle back and close out the thread. I checked the sear and the bolt and all looked good manually, couldn't get it to not catch, oiled it up and cleaned it, and then I tried some different ammo (S&B 124 grain I think) and it ran fine, no issues. I think it was the ammo...easy fix!

 

[gman552]

Thanks for the follow-up.

What was the original ammo that caused the runaways?

European ammo like S&B, GECO and Prvi Partizan seem to run hotter than weak sauce like Remington UMC and Aguila.

 

[FAL]

I think it was two different kinds of ammo. Winchester white box 115gr and Remington UMC I believe is what we originally tried..clearly underpowered for my Sten.