SBR Lever / Bolt Lock Back Problem Solved

Majorlk · Sep 24, 2012

The solution to the bolt failing to lock back with NDZ's SBR lever installed is very simple: clip two turns from the Bolt Latch spring! It should be noted that this is exactly the same fix for bolt lock back failure that has been recommended almost from the introduction of the 15-22.

For the past three weeks I have been testing (with NDZ's knowledge) both the original SBR lever and the new, lighter lever. Here are the results:

Unmodified Spring:

25-round magazines - occasional failure without any lever attached.
10-round short magazines - no failures.

With original lever - 95 percent failure with long magazines.
With original lever - no failures with short magazines.

With new lever - 50 percent failure with long magazines
With new lever - no failures with short magazines.

Two turns clipped off Bolt Latch spring:

Original lever - no failures with long magazines.
Original lever - no failures with short magazines.

New lever - no failures with long magazines.
New lever - no failures with short magazines.

(it should be noted that the springs in the short magazines are considerably stronger than the ones in the long magazines)

Test Conditions:

Five (5) 10-round short magazines, 8 months old. Five (5) rounds per magazine, each one reloaded five (5) times for each test.

Four (4) 25-round magazines, 8 months old and four (4) two weeks old. Each magazine loaded with five (5) rounds and reloaded a minimum of ten (10) times for each test.

These tests and the results have been shared with the folks at NDZ, both via eMail and in person (they are only about 20 minutes from me).

If you are having trouble with either the original or new lever, simply clip two turns from the Bolt Latch spring.

w0ady · Sep 24, 2012

sometime this week ill test my version 2 lever with the uncut spring then go from there.

Majorlk · Sep 24, 2012

w0ady said:
sometime this week ill test my version 2 lever with the uncut spring then go from there.

I'm anxious to know how you fare with the test. The guys at NDZ will want to know, too. They really are a nice bunch.

hkyplr · Sep 24, 2012

I wonder if clipping one coil would still work. I have to wonder if clipping coils is going to have any unintended negative side effects.

Majorlk · Sep 24, 2012

hkyplr said:
I wonder if clipping one coil would still work. I have to wonder if clipping coils is going to have any unintended negative side effects.

1 - don't know. All previous recommendations say two.

2 - Well, after well over 800 rounds on Friday and today, I haven't found any. I can't envision what else would affected except the locking back of the bolt. That's the only thing the bolt latch does. If one doesn't care about locking back the bolt, the whole latch and spring could be removed and everything else would function just fine.

tacticool22 · Sep 24, 2012

All of my testing showed that one coil is not enough and 2 is just right. If you take off three or more the bolt release can rattle around and possibly get in the way of the bolt because it won't have tension to keep it in the "out of the way" state.
The lighter spring tension of the long mags sometimes does not have enough power to overcome the bolt release spring. So we reduce the bolt release spring pressure by shortening it.

Majorlk · Sep 24, 2012

tacticool22 said:
The lighter spring tension of the long mags sometimes does not have enough power to overcome the bolt release spring. So we reduce the bolt release spring pressure by shortening it.

I find it interesting that the springs in the short magazines are so noticeably stronger than the ones in the long magazines. I think the whole problem rests with the weaker springs.

Even without modifying the spring, the short magazines were 100 percent lock back with both the original and lighter levers.

Noahsdad · Sep 25, 2012

I think major hit the nail on the head. Seems as if 90% of all malfunctions encountered on the rifle for me at least are directly attributed to the weak mag spring on 25rd mags. Zero malfunctions with shorty mags. Even with old dirty ammo.

Majorlk · Sep 25, 2012

Noahsdad said:
I think major hit the nail on the head. Seems as if 90% of all malfunctions encountered on the rifle for me at least are directly attributed to the weak mag spring on 25rd mags. Zero malfunctions with shorty mags. Even with old dirty ammo.

It'a also interesting to note that the short magazines are less than half the length of the long ones and yet the springs are only 1/4th shorter.

BTW, stretching the springs doesn't do anything. As soon as you load 25 rounds into the magazine, the springs revert to their original length.

I'm of the opinion that S&W needs to rethink both the long mag spring and the bolt release spring.

tacticool22 · Sep 25, 2012

Smith wouldn't even need to change the springs. They can put a slightly longer core pin in the mold to deepen the hole. That would have the same effect as shortening the spring.

Majorlk · Sep 25, 2012

tacticool22 said:
Smith wouldn't even need to change the springs. They can put a slightly longer core pin in the mold to deepen the hole. That would have the same effect as shortening the spring.

I hadn't thought of that.

Now someone is going to try to drill the hole "just a tad deeper".

Majorlk · Sep 25, 2012

I just did my grandson's rifle and realized I put the little detent on the wrong end of the spring - to the inside.

w0ady · Sep 26, 2012

3/4 mags didnt lock back with an uncut spring.

stimr2 · Sep 26, 2012

I'm glad it's a easy fix. I only had to take off one coil. I wonder how many people have had to cut the spring.

Sent from my Galaxy Nexus using Tapatalk 2

Gunzilla · Sep 26, 2012

Since installing my NDZ extended bolt release I've been having issues with the bolt not lock back after the last round fired....i'm going to try this fix, I need a remedy...it's annoying to have to reach up to recharge the rifle.

THANK YOU for taking time to do this test and for sharing the results with us!!

Majorlk · Sep 26, 2012

Followup ...

My grandson and I spent the morning at the range (the kid LOVES to burn up grandpa's ammo!) and we put a little over 800 rounds through 11 25-round magazines. Not a single failure of the bolt to lock back after the last round.

As far as I am concerned, the fix is in!!!

Majorlk · Sep 26, 2012

stimr2 said:
I'm glad it's a easy fix. I only had to take off one coil. I wonder how many people have had to cut the spring.

Sent from my Galaxy Nexus using Tapatalk 2

Every one that wants the SBR to work.

agp · Sep 26, 2012

This is awesome news. I had the original sbr and returned it. Looks like I will be ordering a gen 2 sbr today.

Majorlk · Sep 26, 2012

The guys at NDZ put in a lot of time and effort (money) into trying to solve a problem that really wasn't their problem in the first place. As TactiCool and others found out, S&W made the spring too strong in the first place. The failure to lock back existed long before the SBR came on the scene. I simply don't believe the people who put MagPul's BAD on their 15-22s have not had exactly the same problem us SBR folks have had.

Personally, I like the original better, but I would be more than happy with the gen 2 version.

mn_doggie · Sep 26, 2012

Majorlk said:
Followup ...

My grandson and I spent the morning at the range (the kid LOVES to burn up grandpa's ammo!) and we put a little over 800 rounds through 11 25-round magazines. Not a single failure of the bolt to lock back after the last round.

As far as I am concerned, the fix is in!!!

800 rounds.... But didya hit anything?

SBR Lever / Bolt Lock Back Problem Solved

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