slide failure -- won't lock on last round

[carry2011]

I'm having a problem the slide failing to lock back on nearly every last round of a magazine. I'd like some help identifying the cause of the problem.

What is failing:

• Slide fails to lock back on the last round, occurring on all magazines.
• Had 3 stovepipe failures to eject, today (across 350 rounds).
• Had 1 failure to feed on the ramp, last session (across 250 rounds).

What appears to be okay:

• Slide stop looks in good shape (no burrs, worn areas).
• Slide is moving a bit "gritty", so could use some tuning.
• Recoil spring -- new Wolff 1lb over factory strength.
• Recoil guide rod -- stainless and in great shape, with snug fit of the spring.
• 8 15rd magazines each exhibit this problem.
• Magazine springs -- all are new Wolff springs.
• Gun is cleaned immediately following every range session, as are the magazines.
• Minor amounts of oil used in key wear places, on slide rails, recoil spring, magazine springs.

I have yet to send the gun out for a tuning, which will include throat/polish of the barrel mouth and feed ramp, tuning of the extractor and ejection, tuning of the magazine feeds.

Gun: Browning BDM 9mm semi-auto, 15+1 rds, in lightly-used condition (< 5K rounds). Using Wolff recoil spring @ 1lb over factory rating. Using fresh Wolff magazine springs in all mags. Magazines are factory Browning BDM.
Ammo: Remington UMC 115gr FMJ.
Usage: This is my second BDM. Years ago, I had my first one and shot over 35K rounds through it. Noticed that it had feeding problems up to the first 4-6K rounds, then smoothed out considerably (to 1 jam every 2-3K rounds after the first 4-6K "hump"). Darned near flawless, after it was broken in. But, not this one (yet).
Skill: Decent shooter, decently accurate, practice every few weeks and ~10K rounds per year, have a fairly firm Weaver-style grip.

Suggestions? Most-likely causes?

 

[wally]

I'm not familar with the BDM, but usually when I have double stack, single feed magazines that don't lock the slide back its because the followers don't come up quite high enough to push up the slide lock lever. I've had generally very good success by carefully filing a little off the top of the sides of the followers so they can ride up high enough in the tube when empty to activate the lever.

If you mess up, its pretty easy to order a replacement follower.

--wally.

 

[4v50 Gary]

Slide lock back is generally attributable to the follower not engaging the slide stop such that it forces the slide stop up. You might want to try a factory spring in that magazine.

Here's why. Springs are designed to work at certain speeds. When the aftermarket folks offer their ware, it changes the way the gun functions. If the action is too fast (hyper-function), then the slide moves too fast for the speed of the magazine spring to push the follower up to engage the slide stop. Thus failures happen. Same with follower springs. If too week, it can't push the slide stop up fast enough to intercept the slide's forward movement.

Try switching back to factory stuff and see what happens.

 

[KIMBER45TLE]

Simular Problem

Had a simular situation happening with one of my Wilson magazines. I took it apart and cleaned it. It was filthy inside as I had never cleaned it since getting it. Solved the problem, but I still took the drive up to Wilson Combat and picked up three more spring kits just to be on the safe side.

What 4V50 said is also true. You change out parts you change out the functionality of what is going on.

 

[carry2011]

Try switching back to factory stuff and see what happens.

On the previous BDM, I had kept the magazine springs and the recoil spring fresh with the Wolff units, but that gun didn't exhibit these issues (after break-in). And this gun didn't show the slide-lock issue last session, which used the same mags and Wolff springs.

The mags are clean, inside as well as out. The followers have no burrs and are all feeding smoothly ... except for one, which needs replacement.

Hm. I'll try putting the stock mag springs back. Perhaps the difference is just enought to matter.

Thanks.

 

[Majic]

Why did you change all the mag springs?

 

[BulletFan]

I'm reasonabley sure it's not

your magezine springs. If the problem resided solely in your magezine springs you could wouldn't be experiencing this problem with ALL of your magezines. I think the combination of a new firm recoil spring and the slide being "gritty" is causing the slide to recoil back just shy of the slide stop. First and foremost I'd get rid of anything that would cause you to refer to it as "gritty." Clean the slide rails and guide rod, oil the spring liberally and put just a dab of penetrating oil on the rails. Something just viscus enough to lubricate, but not enough to pick up a bunch of dirt. I think once the slide operates the way it should with a fresh spring, it will likely rack all the way back to the slide stop.

Also, two questions for you:
1.) If you have the empty magezine in the gun and you pull the slide back yourself will the follower push up the slide lock and lock the slide in place?
2.) Not that this is a solution, but have you tried some particularly hot rounds like +P or something similar? I wonder if a higher recoil round would uncover the problem.

Let me know how it works out!
Hope this helped.
Matt

 

[gezzer]

Mag springs installed proerly so the folower nose does not droop.

Try putting the original springs back in the gun and mags and see what happens.

 

[carry2011]

Why did you change all the mag springs?

Because this is a pistol manufactured early in the game, and the magazines are also early models. These magazines have been sitting a long time in those boxes (faded & worn). They seem functional, but I wanted to be sure, so I resorted to a well-known and previously-tested (on my prior BDM) spring. New Wolff springs fit the bill.

First and foremost I'd get rid of anything that would cause you to refer to it as "gritty."

Would love to smooth the slide, but I'm not a gunsmith. This is first on the list, when I send it to the shop in August.

Clean the slide rails and guide rod, oil the spring liberally and put just a dab of penetrating oil on the rails. Something just viscus enough to lubricate, but not enough to pick up a bunch of dirt.

Did this. Cycled the slide for a minute or so, then lightly re-oiled.

... with a fresh spring, it will likely rack all the way back to the slide stop.

I'll have a chance tomorrow to hit the range. I'll definitely test with the original springs.

1.) If you have the empty magezine in the gun and you pull the slide back yourself will the follower push up the slide lock and lock the slide in place?

No. But then, the BDM has never, ever done this, either this or the previous pistol. Uncertain why. I always thought this the strangest thing about the BDM's operation, with my first BDM some years ago. Doesn't make sense that it would fail to slide lock when manually cycled on an empty magazine, yet would never fail to slide lock when auto cycled. Of course, this one's experiencing this problem regularly, now.

2.) Not that this is a solution, but have you tried some particularly hot rounds like +P or something similar? I wonder if a higher recoil round would uncover the problem.

I've tried a moderate +P, yes. Didn't have issues, then, but that was only for 30 rounds. Not enough for a good test.

Next step: I will definitely give the spring swap a try, both the recoil spring and the magazine springs.

 

[Sheldon]

I would try the original weight spring and then possibly a lighter one to see if that helps. It could very well be the rounds you have aren't strong enough to cycle the slide back far enough for reliable lock back.

The other place to look is the foloower of the mags to see that they engage the slide stop positively.

 

[Cousin Mike]

I would try the original weight spring and then possibly a lighter one to see if that helps. It could very well be the rounds you have aren't strong enough to cycle the slide back far enough for reliable lock back.

My sentiments exactly. Heavier springs are usually used for race-guns that shoot a lot of super-hot +p ammunition with much higher pressures. If you're shooting regular FMJ for practice rounds, I would suggest a spring at the recommended original weight.

 

[carry2011]

I would try the original weight spring and then possibly a lighter one to see if that helps. It could very well be the rounds you have aren't strong enough to cycle the slide back far enough for reliable lock back.

Hm. If this were the case, wouldn't I see at least some failure to lock on other rounds than just the last round? With 1000 rounds that I've put through this (new-to-me) gun so far, the only failure to lock has strictly been after the last round, on the empty magazine. Strange, if the springs were the issue. But, yes, still worth eliminating the variables and trying the spring swaps. Will do that today.

 

[steve98664]

I've had the same problem on a semi I have, a CZ70. The only change I made was to put in +10% springs from Wolff. This tells me my slide spring is weak or the Wolff springs are really strong. It feeds better with the wolff springs and I don't need the slide to lock back. I'm gonna leave mine alone for now.

HOpe that helps.

 

[Walt Sherrill]

Try the original recoil spring. Wait until the gun is broken in more and the slide smooths up some.

In the future, TRY CHANGING ONE THING AT A TIME... Save yourself time and headache. In this case, the fix was worse than the original problem. <grin>.

Mag springs don't weaken with a lack of use, if they've been stored unloaded.

I'd but the original spring back in the mags, if you have them, and keep the new ones for late replacement. (That is, if the original springs function properly when the gun is running again.) You're arguably throwing out good springs.

 

[PoPo22]

lockback

I had similar issues with a .45 commander. It was consistently failing to lockback after the last round on most magazines. I initially thought it was the recoil spring (it was a used gun and I wasn't sure if the spring was the reccommended poundage), but I also noted a little wear on the "slide lock". As advised by others, if the recoil spring is not correct, it can affect the cycling rate and distance the slide is pushed.

I decided to try one thing at a time, trying a different "slide stop" first. The replacement of the slide stop cured the problem, it now functions perfectly with all magazines.
Good Luck

 

[MachIVshooter]

Gun: Browning BDM 9mm semi-auto, 15+1 rds, in lightly-used condition (< 5K rounds). Using Wolff recoil spring @ 1lb over factory rating

I have had issues with wolff springs being thicker and not allowing the slide to go back far enough to give ample time for the mag to push up the slide lock. In some guns, this even caused regular short-cycling.

 

[carry2011]

What is failing:

• Slide fails to lock back on the last round, occurring on all magazines.
• Had 3 stovepipe failures to eject, today (across 350 rounds).
• Had 1 failure to feed on the ramp, last session (across 250 rounds).

Problem solved, it looks like. Replaced the recoil spring with a fresh, factory-weight spring (Wolff 13-lb) one, and the earlier problems have all disappeared. At least, during 500 rds today, none occurred. So, while it is a bit early to be absolutely certain, I'm fairly confident the recoil spring swap did the trick.

One thing: When slipping the recoil spring over the guide rod, I did notice that one end of the spring was tighter than the other. One end definitely opened up "wider", whereas the other grabbed on the end of the guide rod. At the previous shooting session, I had the guide rod inserted into the wide/loose end of the spring, leaving the end of the guide rod during cycling to catch or stick on the "tight" end of the spring. When installing the recoil 13-lb recoil spring this time, I made sure to slide the guide rod into the tight/narrow end of the spring.

Anyway. No more FTF, stovepipes or jams. Yaaaay!

Thanks, all.

Now, for that BDM trigger job, smoothing of the rails, throating of the barrel, polishing the barrel and chamber ... A retentive's job is never done.