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AR15.COM
4/10/2026 11:02:04 AM EDT
[Last Edit: Vaquero][Edited]
As the titles states, I’ve been seeing lots of new 211’s that have been locking back with one round left in the magazine.

I’ve been involved in helping field several 211’s.  The first range days had a total of about 20 pistols.


This has happened to new guns (and new mags) within the first 200 - 400 rounds.  It has happened with 21 and 23 round mags. All the mags are factory Sig.   It didn’t always happen with the first few rounds, but if it happens, it seems to happen after 50 rounds or so.  In some cases, it seemed to go away after 400+ rounds.

I thought it was possibly hand position pushing up on the slide release during recoil (or slide lock, whichever you prefer), but it seems to happen only on the last round.  Doesn’t matter if it’s a fully loaded mag or partially loaded mag. It also doesn’t matter if it’s a string of two rounds or five rounds. It also doesn’t happen every time with every magazine.

I also saw one set of mags that seemed to develop the problem and then lose it after a couple hundred more rounds.

Is this a break in issue? Is anyone else seeing this? Should I expect the issue to go away? Or should I count on only being able to fire 20 or 22 rounds?  Do I need to call Sig? Should I recommend switching to something else?

I’m leaning towards a mag break in issue, although I don’t understand it.  I had a couple of factory 21’s that I used in a 320. They had the same issue - locked back with one round early on. I dedicated them to be range mags, and eventually the problem went away.  They cycle just fine now. I haven’t tried those in a 211 yet, but that is my next step.

4/11/2026 11:32:35 PM EDT
[#1]
I've got 750 rds through my GTO with 115gr Fiocchi. Using the 21 or 23rd included mags + 3 23rd units I bought from Sig. No issues with it locking back with 1 left in the mag.
4/12/2026 12:28:12 PM EDT
[#2]
Definitely odd. What weight recoil spring are you using?
4/12/2026 9:56:58 PM EDT
[#3]
Quote History
Originally Posted By sunnybean:
Definitely odd. What weight recoil spring are you using?
View Quote


10#
All the pistols had the 10# installed, but not all of them had the problem.
4/12/2026 10:52:37 PM EDT
[#4]
Might ask in the 1911 section. It's not unheard of with 1911 and 2011. Pretty sure that's one of the main reasons the competiton 2011 guys all modded their mags to not lock back.
BikerNut:
Normal people like motorcycles. Real people like motorcycles.

People who don't like motorcycles are just... weird.
4/15/2026 2:00:46 PM EDT
[#5]
not gto, but i have a staccato P which i use diffferent mags from brands.  staccato, checkmate, dura mag.  

i have 1 dura mag that always locks open with one round left.   i just marked it and set it aside as range only
Sun's up, Guns up!

"The only place where success comes before work is in the dictionary"
-Vince Lombardi
4/17/2026 10:56:09 AM EDT
[Last Edit: Buffman_LT1][Edited] [#6]
Quote History
Originally Posted By Vaquero:


10#
All the pistols had the 10# installed, but not all of them had the problem.
View Quote
I was using the #8 spring that came installed
7/27/2026 8:41:35 AM EDT
[#7]
Just a follow up to this issue.

It’s gone away.  Nobody did anything to correct it other than shoot more. Not sure if it was a gun or mag issue, but it’s gone.

As a side note, I’ve used some of the Magpul 21 round mags with no issue.
7/28/2026 6:52:39 AM EDT
[#8]
Quote History
Originally Posted By Vaquero:
Just a follow up to this issue.

It’s gone away.  Nobody did anything to correct it other than shoot more. Not sure if it was a gun or mag issue, but it’s gone.

As a side note, I’ve used some of the Magpul 21 round mags with no issue.
View Quote


Definitely sounds like fresh Sig magazines are causing the problems.

Initially I didn't want to comment because I only use 10rd mags, but I haven't had this issue with my P211 GTO.
9/15/2026 7:43:09 PM EDT
[#9]
The easy test is to take a magazine with 1 round loaded. Take the slide off. Insert the magazine. The follower must just barely touch the stop lever's pawl. If it lifts the pawl even a little, that is your problem.

The P320 magazines are unfortunately very touchy in this regard. One would think that the travel distance of the follower between the empty and 1 round positions would be 9 mm, but it's far smaller in reality. I know about this because of the experience with P320 magazine adapters for Ruger PC, where die stamping alone often makes out-of-spec LRBHO transfer bars. If only they were made with MIM, but alas that is cost-prohibitive.

This does not remove the responsibility for SIG, but I suspect you're only 0.5-1.0 mm adjustment away from perfect function.

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