Springs and Slide timing issues

[Eric Larsen]

In s/autos recoil springs play a major part in slide timing..and proper function of the gun. I have Wolff (heavier than OEM) recoil springs in my s/autos as I usually shoot hotter loads thru my guns. I also use +5 and +10% recoil springs in my mags for a little extra added push getting rounds chambered when using the heavier recoil springs.

Theoretically, with the heavier recoil springs, after firing a round and the slide is traveling back to extract/eject the spent casing, the slide is going to slow and stop faster. It will return to battery with more force with the added spring force. This quickens the cycling time of the gun/slide...giving less time for the round in the mag to "chamber" than a gun with a stock recoil spring.
Thus the extra power mag springs...putting a little more spring/push on the round waiting to be chambered in the mag.

I realize in normal/slow fire this really isnt an issue because the mag spring has more time to "stage" the next round and will be ready to be stripped from the mag by the returning slide. But, in the case that quick shots are needed like double taps etc, the extra spring strength will be of benefit..getting the next round staged quicker when the slide cycles very quickly.

With all of this explanation out of the way...my question is this.
Can mag springs be too much for even a heavier than OEM recoil spring to overcome. Kahr 40's come with a 20# OEM recoil spring.
They recommend changing it every 2000 rnds due to the guns design/caliber being hard on springs..they die a quick death.
I have used Wolff 22# recoil springs for a while and like them alot, but after about 500-700 rounds of "hotter" 40 ammo the recoil spring seems to weaken alot. I notice that the mag springs are putting enough force on the rnd that is contacting the slide, that it starts to alter the action of the slide. I will just replace my recoil spring with a new unit and all is well.

But I gotta wonder, SHOULD mag springs be too much for a recoil spring to overcome? If so, what is the proper fix? Changing the recoil spring more often (500-700 rnds is NOT ALOT) or going to a lesser strength mag spring? I realize, its probably a matter of balancing the two springs rates out for a dependable gun but thought Id ask the question.
Alot of people have WAY more experience with this sort of thing and I thought Id pick your brains....

Shoot well and thanks

 

[Walt Sherrill]

Theoretically, with the heavier recoil springs, after firing a round and the slide is traveling back to extract/eject the spent casing, the slide is going to slow and stop faster. It will return to battery with more force with the added spring force. This quickens the cycling time of the gun/slide...giving less time for the round in the mag to "chamber" than a gun with a stock recoil spring.

We've discussed this before.

I still don't understand why its a TIMING issue, since the SLIDE is the device that is stripping the round from the magazine.

If the magazine were feeding the round independently of the slide, then timing might be an issue. But since the slide DETERMINES when the round is fed, timing seems to be irrelevant.

It seems to me that as long as the slide moves the proper distance back (to properly catch the next round), it can't help but get the next round -- regardless of the spring weight. Now if the spring keeps it from going all the way back, that's different.

 

[Eric Larsen]

Walt,
You have a point...it may not be a matter of timing as much as general physics. One force (recoil spring) being strong enough to overcome another (mag spring force being put on the slide).
The two mechanical functions are independent of each other in one way and work togethor in another.
They do work togethor in general as the mag spring has to put enough force on the round to get it "staged" fast enough to keep up with the recoil spring/slide travel time. If you have a quick cycle time and a bad mag spring that cant "keep up", this is where you get problems with FTF's. Correct?
Now take that problem and reverse it...you have a weaker recoil spring and strong mag springs..it wont cause FTF's but actually interrupts the action/travel of the slide. Where do you fix the problem? Thats my question.
Thanks for the reply and shoot well.

 

[Blackhawk]

Excellent analysis, but I'm going to avoid your question, or at least deflect it.

If the mag lips don't conform to the shape of the casing or are not smooth, the mag spring can be more critical. Brass riding on smooth steel is a natural antifriction arrangement, which works great with a lubricant (not gonna happen here) and pretty good without provided that the contact force is low enough. Roughness of the mag lips may cause the contact pressure to be too high for smooth functioning. This would be most apparent with fully loaded mags.

A secondary problem develops when the mag and recoil springs are strong enough to handle the top rounds but not the bottom rounds of a mag. That may be due to the mag spring being compressed beyond its optimum range resulting it being overloaded when new, which is necessary for its desired function.

Stick with me. A compression spring has a design operating range that rarely includes being fully compressed to where the coils are touching. Typical mag springs don't have enough room to operate within their design range from the first to the last round. They're compressed too much, and they're required to expand too far. Best performance is when the same pressure can be maintained against each casing, but that's never going to happen.

The goal should be to minimize the pressure differences between rounds pushed against the magazine lips, and the easiest way to do that is to make sure the lips are smooth and conform to the casing. If both the first and last rounds feed properly, then that's about as good as you're going to get.

Mags also get dirty from firing. Powder residue is an anti lubricant, which requires a stronger spring to overcome.

Yadda, yadda, yadda....

 

[ggruber]

one other thing you can try is to replace your mainspring (hammer spring). this will affect timing also.

i live at the other end of the spectrum. i am disabled and shoot very, very light loads. i use an #11 Wolff spring -- with heavy duty mag springs. But I have also reduced the Kimber stock main spring #20 (don't quote me on that) with a #17 or #18 spring.
Hammer reset is part of timing. maybe this will work for you too.

by the way, i surprised the hell out of myself yesterday at the range by consistently knocking down those nice 8 inch steel plates at 32-34 yds with my powder puff loads. This was at an outdoor range. At the indoor range i used to limit myself to 15-18 yards because i didn't feel that the load was accurate enough beyond that.

 

[Walt Sherrill]

You have a point...it may not be a matter of timing as much as general physics. One force (recoil spring) being strong enough to overcome another (mag spring force being put on the slide).
The two mechanical functions are independent of each other in one way and work togethor in another.
They do work togethor in general as the mag spring has to put enough force on the round to get it "staged" fast enough to keep up with the recoil spring/slide travel time. If you have a quick cycle time and a bad mag spring that cant "keep up", this is where you get problems with FTF's. Correct?

I'm still unconvinced. I'm not sure its even a matter of general physics.

The force with which the magazine moves the cartridge up has to be limited, or it will put too much upward pressure on the underside of the slide, causing the slide to slow. But its funny that most mags springs are far more interchangeable than you'd think. (I've swapped a lot of different springs out, experimenting, over the last couple of years, with no problems. As long as the magazine is generally the same size, the mags seem to work, regardless of where the spring comes from.)

A weak mag spring will cause problems, regardless of whether the slide is moving quickly or slowly. The rounds just won't get pushed up properly...

Now take that problem and reverse it...you have a weaker recoil spring and strong mag springs..it wont cause FTF's but actually interrupts the action/travel of the slide. Where do you fix the problem? Thats my question.

It'll only cause a problem if the upward pressure is so great as to slow the slide. Most factory mag springs shouldn't be that strong. Have you EVER encountered that problem? I haven't...

A weak recoil spring generally won't cause the kind of problem you're describing, 'cause the slides going to come back so forcefully, its going to REBOUND and move back more easily. The problems it'll cause is battering of the frame. The gun will generally still function, but ejected shells may end up in the next county.

I just don't buy your theory of "timing." And calling it "general physics" doesn't improve it, either.

You may be onto something, but its going to take more information and some additional theoretical steps before it'll make the kind of sense I need to accept it.

In response to ggruber's comments about hammer springs affecting timing...

I would argue that a reduced hammer spring shouldn't affect "timing," either -- as I'm still not convinced there's much "timing" to affect. It can affect the ease with which the trigger can be pulled, and the force with which the hammer strikes the firing pin, all of which will affect accuracy, ignition, and function. But if the cartridge goes bang, it should shoot and cycle, regardless. If it fires, the hammer is going to reset, regardless of the weight of the hammer spring, as long as it doesn't take a bumper jack to set it, and the the mechanical parts are functioning properly -- and you're not doing something with the trigger finger that keeps the hammer from resetting.

Maybe a knowledgeable gunsmith can speak up and tell us all where we've gone astray.

 

[Eric Larsen]

I do know that the mag spring can effect the recoil spring/slide operation. Its the case with my K40 as I type this. I can pull the slide back...say 1/4" inch and let it go. With the mags out it will return to battery every time. With the mag in place the slide will stop about 1/16-1/8" before battery. If I "bump" the rear of the slide it will go into battery...and If I drop the mag it will go into battery with no help. To me this is the mag overpowering the recoil spring.
It hasnt affected the gun during actual firing yet as I change the springs when this happens.

Slide timing is important and is more critical on some smaller/high powered s/autos and how they function.

A fullsized gun with a long/heavy slide and a longer travel length will be less effected by timing problems.

As the mag spring is pushing up on the rnds, they are not in the feeding lips yet and are kept down by the rail on the bottom of the slide. Once the round is fired and the spent case is ejected by the rearward movement of the slide, the slide goes back far enough that the rail goes behind the round in the mag. This is when the rnds are allowed to hip the feeding lips and top out in the mag. The slide changes direction and the front side of the rail
hits the "topped out rnd" in the mag, stripping it from the mag and is then fed into the chamber. If your mag springs are not up to the task, in time given, you will have FTF's and the faster this has to happen the stronger your mag springs need to be.

The time between the rnds being pushed down by the rail, the slide continuing rearward just enough to allow the rounds to top out and then be stripped from the mag is dependant on travel length and speed. Shorter slide travel = higher spring weights.

In a short slide travel gun like a Kahr K40 the recoil spring weight is more important to keeping the gun working properly than say a fullsize 75B 9mm. Also you have to take other variable into consideration like the caliber and its inherent recoil...more power is going to send the slide back faster/more forcefully than a weaker round. Slide weight has to come into play...a heavier slide will be harder to push than a lighter one but will also carry its weight farther, making it harder to stop..than a lighter slide will start off faster and stop easier.
With all of this taken into account...the K40 is more dependant on timing being controlled with proper spring weights than other guns that have different designs.
The time window that the top rnd in the mag has to get from under the rail and up into the feeding lips, ready to be pushed out by the transversing slide is substantially less than other guns.

Kahrs and Wolff tech guys have stated this also...but I have yet to ask the question to them.

So, which is the way to go? Replacing the recoil spring more often or go to the weaker but still strong OEM mag springs?

This is more of an issue for me with this gun as its a CCW...for a target/plinker I would be less of an issue...

Sorry for the "gun/slide 101" but some may not understand how this actually takes place...at least what I was taught.

Thanks for the rant and shoot well

 

[Blackhawk]

Again, your analysis is right on the money, Eric.

But if the next round is adding significant drag to the slide rail because of an overly strong mag spring, you should see evidence of that on the slide. Since that same rail rides on the hammer, it should have some lubrication on it.

As the slide rail travels back past the end of the next round, the round snapping into place in front of the rail is nearly instantaneous. If the recoil spring is too strong, the slide may not travel far enough, and if it's too weak, the gun won't go into battery. It's unlikely that the mag spring would be too weak, especially for the top rounds, which brings me back to dirty mags causing a problem.

In any event, the mag/slide interaction is mechanically timed by the positions of the parts with the mag spring merely ensuring that rounds are in the right place. I don't see where delays would enter in. If the springs are within the ballpark of having the right tensions for their independent functions, the gun should function properly.

All in all, I think we're just yapping about semantics....

 

[Eric Larsen]

Blackhawk, maybe so I was just curious which direction I should go...1
Its just the dead recoil spring after 500-700 rnds seems like a very short life span for a 22# Wolff spring... For this reason I questioned whether or not my mag springs may be overly sprung....but again they are standard x/p Wolff. Ill give Kahr and Wolff a call on Tues and see what they recommend.
Shoot well
And BTW there is no hammer...striker fired DAO..just like a Glock.
I lube the rail slightly anyway....shoot well

 

[Walt Sherrill]

A fullsized gun with a long/heavy slide and a longer travel length will be less effected by timing problems.

The slide on a full-sized gun doesn't necessarily travel a bit farther than the slide on the compact gun. In most cases, the distance moved is the same.

The breechface, which is in contact with the back of the round as it sets in the barrel, moves back just enough to help eject the used round and pick up the new round. That distance is basically the same regardless of barrel or slide size, given the same caliber round in the same basic type of gun.

And as Blackhawk says (as did I before hand), its all mechanical.
The term "Timing" implies independent parts that aren't connected, but which must be made to work together. In the case of a semi-auto pistol, there is no "Timing" issue, at least not in the way the term is normally used -- they're mechanically connected, and push WILL come to shove, etc.

In a revolver, timing CAN be an issue, since worn parts on the cyclinder itself, or a worn hand, can cause the cylinder not to advance the proper distance, so that the cylinder doesn't line up properly with the barrel. "Timing" here refers to the fact that the gun can be fired BEFORE the cylinder is properly aligned (i.e. too soon). That is a problem.

With a semi-auto, as long as the parts are properly proportioned and properly connected, the gun will go bang -- if the springs allow it to cycle properly. Proper function (the springs let the slide move as far as it should), not timing (speed of travel, etc.) is the issue.

Maybe the problem isn't a DEAD recoil spring, but one that is too strong, not allowing the gun to cycle properly? Maybe you should move DOWN a pound or two and see if the problem is solved.

 

[Blackhawk]

An aside:

I was curious, so I put a round in a double stack magazine and marked the top of the case with a magic marker. Then I repeatedly opened the slide about 1/2" and let it close again. Upon removing the magazine, it looked like the cartridge had rotated a bit. Remarked it copiously and repeated. Sure enough, the round rotates ever so slightly as the slide rail goes back and forth over it.

Means nothing to me, but it seems interesting....

 

[Walt Sherrill]

What you're describing is what I'd call the underside of the slide (the bottom of the area that houses the firing pin.) It contacts the round as the slide moves back and again after it has picked up a round and moved forward.

Marking the base would make the movement even easier to see.

You had me confused for a minute: the term "slide rail" usually refers to the parts of the slide in contact with the frame -- and the rails on the frame are sometimes called slide railes.

 

[Blackhawk]

You're exactly right Walt. I got so excited about something I forgot Nomenclature 101, and now I don't remember what I was excited about.

I didn't let the slide go back far enough to let the slide engage the base of the round for stripping. I was just testing the pressure of the mag spring against slide.

 

[Kat]

Static vs. Sliding Friction

I do know that the mag spring can effect the recoil spring/slide operation. Its the case with my K40 as I type this. I can pull the slide back...say 1/4" inch and let it go. With the mags out it will return to battery every time. With the mag in place the slide will stop about 1/16-1/8" before battery.

This is not a valid analysis. You're confusing static friction with sliding friction. Two totally different animals. The friction between two objects at rest (pulling slide 1/4", STOP, then let it go) is much higher than when the two objects are moving relative to each other (when the slide is moving at 20 ft/sec (guesstimate) when the round comes in contact with slide). Guessing the normal force applied by the typical mag spring to be about 5 lbs(f), I would venture to guess that the relevance of which to the proper operation of the slide and feeding of next round would be rather negligible.

One thing that hasn't been mentioned, that I would be more concerned with, is the mag spring's role in controlling the acceleration of the round that's being fed as it gets stripped from the mag. The static frictional force between the mag lip/follwer and the round has a way of reducing the acceleration profile to lower level thus allowing for controlled transfer of the round into the chamber. With a weak mag spring, the round will move uncontrollably fast, resulting in greater chance of bouncing off of the feed ramp and missing the chamber openning. This point is easy to see in feeding of long skiny rounds like .22LR in a blowback breech design. Anyway, this was my conclusion as to why my Remington 597 .22LR semi-auto rifle is so ammo sensitive. Someone correct me if I'm totally off.

I guess to get back to the original question, I would say there's not much to worry here, but if you feel you need to keep things balanced, replace both springs at the same time, not just one or the other.

Anyway, I do enjoy these more technical discussions on the forum, so keep 'em comming....