Slide/magazine Interaction

[bountyhunter]

This may be the dumb question for the day, but I am still not sure I completely understand why single stack mags have this "personality trait":

As you load the first few rounds in, the nose of the rond has good upward "lift" on it and will feed very well.

As you get near mag capacity, the nose lift goes away and you can get feed ramp nose-slam dead stop jams because the slide coming forward catches the top of the round and rotates it's nose down....and drives it into the flat bottom of the feed ramp.

I thought I knew why it does it in a single stack 9mm magazine.... they are not "straight wall" cases so they curve as you stack them up.

But in a .40?

This is a ten round CMC power mag and it feeds well for round counts up to about 8, above that it will nosedive jam the first round. It has the 'spring load" follower with the piece of metal angled upward at about 30 degrees from the horizontal base piece.

Why do the "straight wall" cases lose their "nose lift" as the round count increases? With ten in, that top round just wants to lay it's nose down and not hold it up.... hence the jam.

[ima45dv8]

How old are the mags? I've had serious death-jams with .45 mags due to the top round getting a nose-down attitude when slammed in with the gun at slide lock. It has always turned out to be weak springs. Replacing them cures the problem.

HTH...

[bountyhunter]

How old are the mags? I've had serious death-jams with .45 mags due to the top round getting a nose-down attitude when slammed in with the gun at slide lock. It has always turned out to be weak springs. Replacing them cures the problem.

HTH...

They are new, hardly ever been used to date.

[Eager]

That happened to me to some extent because I "overenthusiastically" cleaned my Wilson and CMC 10rd mags by shoving a mag brush through the lips. The mags lips expanded and sometimes rounds would be allowed to sit up too high in the lips causing feed problems. In the worst cases round would just jam in the mag inside the gun. Sometimes the mags would not drop free because of this, although some would. Some of the mags I did this to I was able to beat back into shape.

[bountyhunter]

I'm still not sure why it is that with only a couple of rounds in the mag (and the spring lightly compressed) the top round is held very firmly up at the nose.... and as more rounds are added, the nose gets progressively less well supported allowing it to roll down easily.

I suspect it is because the "spring load" effect of the angled follower is felt more with fewer rounds above it....

Still wondering if there is a way to make this better?

[IronEqualizer]

Hmmm......I just recently purchased 6 CMC 10rnd mags and shot my first match in limited 10. I have been shooting SS. I also just had my 1st malfunction in at least 10 matches. Had to be the new 10rnd mags. Had one rnd jammed at a weird angle upward into the barrel and one dbl feed all on the same stage. Have not had any problems with CMC 8 rnders. I am gonna start slicking my rnds up with a silicon rag before loading the mags to see if that will help. On another note the mags have been flawless in practice. Go figure. Maybe just Murphy working on me.

[superdude]

Ah yes, the famous, or infamous, top rounds nose dive feed failures.

The phenomena you described is well known. The more rounds you load, the greater the change of angle in the top round. A noticeable change in angle occurs after there are about 4 rounds in the mag. I’ve spent many hours loading and measuring mags of various sorts, and all the mags I’ve measured thus far suffer from the same problem, but the effect is rather pronounced in 1911 single stack mags. I hope to write an article on this matter, with the hope it will be published in a gun mag or at least on the web. I’m working on a website for the 38 Super and that information will end up there in some form at some point (www.38super.net - sorry, but its free advertising!)

You’re right that the effect is more pronounced with tapered cases like the 9mm. but the problem still exists with straight walled cases like the 38 super.

The cause of the changed angle is a little tough to figure out. The angle of the follower changes, but its not obvious why. Some folks have speculated about the magazine spring and laws of physics and all that – which I didn’t understand but I’m not all that bright when it comes to anything involving math.

I suspect that the rather unique configuration of the Chip McCormick follower is an attempt to correct this change of angle to some degree. It might help a little, but in the final analysis the top round still nose dives.

This problem plagues 45 single stack mags to no end. This might explain why some manufacturers market 45 mags that hold only 7 rounds and other manufacturers sell ones that hold 8. The feeding reliability with 8 rounds is a genuine concern. (Putting in that 8th round dramatically changes the angle of the top round, and it nose dives terribly. It’s the same thing with 10 round mags for the 45 single stack.)

For example, I have an aluminum frame single stack cut for a ramped barrel that I put a 45 top end on. When I load a mag with 8 rounds and the top round is a hollow point, it can nose dive so far that the edge of the hollow point bullet actually hits the aluminum frame below the barrel’s feed ramp – it has the scars to prove it – and of course the cartridge stops dead. With only 7 rounds in the mag it behaves better and only rarely jams. With 6 rounds in the mag it runs fine. You can get around that with loading hardball rounds as the top rounds, but that’s not quite what I want to put in this gun because its for self defense. Oh, and even the proprietary Pow’RBall round nose will jam there – I tested that hypothesis. And by the way, all mags act that way, Colt, Springfield, CMC, Wilson Combat. It’s a chronic problem, and the folks at EGW pointed that out to me.

I converted the gun to 38 Super and the problem went away. It still nose dives with a full 10 round mag, but it doesn’t dip as far because the center of the bullet is much higher than a 45 and the bullet always hits the feed ramp (so far!).

So, how is the problem fixed? It does not look like there is a magic bullet (sorry about that terrible pun) to fix the nose dive angle problem. From what I’ve read it has been tried. (but feel free to invent a better mouse trap! You will be adored by millions!) The only advise I can give is to polish the inside of the magazine lips where it contacts the case and its rim. This will allow the round to move forward a little easier (less friction) and will reduce the tendency to nose dive. And round nose bullets will make the contact point on the feed ramp a little higher, but from what I understand its hard to find 40 caliber round nose bullets.

Also remember that as you put more rounds in the magazine the spring pushes back all the harder and causes more friction between the top round and the inner feed lips. This only makes the problem worse.

Rest assured that you do not suffer alone. Lots of shooters are pulling their hair out because the top rounds nose dive and stops dead. Well smoothed feed lips – read well used feed lips – and well used brass – they gets smoother with tumbling and polishing – the problem is less frequent.

Hope this helps.

Edited December 12, 2006 by superdude

[bountyhunter]

Very interesting. If this article gets written, please post a link to it.

Here are additonal thoughts:

With only one cartridge in the tube, the round can angle itself and basically follow the angle of the follower.

As more rounds stack up, the edges of the tube tend to "flatten" the angle of the collective pile with respect to the mag tube..

In other words, it gets progressively harder for the round to be at an angle steeper than what the tube walls dictate..... so the follower is less able to force the noses upward.

Another major factor: that spring which is trying to push the nose up has only so much strength, and pushing up fewer rounds is easier than trying to hold up a stack of eight.

It's an interesting problem..... but, a minor in mechanical engineering clearly has not armed me well enough to solve it.

Edited December 12, 2006 by bountyhunter

[superdude]

Okay, lets see if I understand what you’re suggesting. I’ve been reading this over so that I can try to address your idea. Are you saying that the front and back of the magazine (not the sides) influence cartridge angle? That would only be true if a cartridge was in contact with both of them. It is not. Or at least is shouldn’t be. If rounds do contact both the front and back of the mag, there can get stuck. So there is plenty of room there. There is enough room for a cartridge to lie in the magazine at any angle relative to the flat back side. As long as cartridges are loaded to normal specs, a wee shorter if they are hollow point or flat nose bullets, the nose can pivot up and down and still not touch the front of the mag.

Is that what you meant or am I really off base here? Please feel free to straighten me out.

By the way, I loaded some mags and measured the front-to-back distance. This did not change no matter how many rounds I put in. I didn’t expect it to based on the strength of the material, but I could have guessed wrong so I measured it in 2 mags, a 45 ACP and a 38 Super.

[bountyhunter]

Addendum:

On the CMC 10-rd mags, I have noticed that eight will feed NO PROBLEM.... but #9 and #10 will only feed if I position them just so.

I "tap back" the first eight against the back wall and then the #9 and #10 are "stair cased" slightly forward, with #10 as far forward as possible so the nose will go up the magwell without hitting anything.

The rims of the #9 and #10 rounds tend to "drag" a touch on the groove of the round below them, making it more likely for the nose to rotate downward as the slide pushes against the top of the (rear) of the rim.

Okay, lets see if I understand what you’re suggesting. I’ve been reading this over so that I can try to address your idea. Are you saying that the front and back of the magazine (not the sides) influence cartridge angle? That would only be true if a cartridge was in contact with both of them. It is not. Or at least is shouldn’t be. If rounds do contact both the front and back of the mag, there can get stuck. So there is plenty of room there. There is enough room for a cartridge to lie in the magazine at any angle relative to the flat back side. As long as cartridges are loaded to normal specs, a wee shorter if they are hollow point or flat nose bullets, the nose can pivot up and down and still not touch the front of the mag.

Is that what you meant or am I really off base here? Please feel free to straighten me out.

Feel free to straighten us all out. I don't think anybody knows exactly why the top two rounds are cranky to feed.

It seems to me there is a "baseline angle" of the cartridge as set by the follower. With only a few rounds stacked, it is steeply up at the nose and has good up lift at the nose.

As you stack on more rounds, the "angle of declination" gets flatter and the amount of "upward push" on the nose decreases. Past eight rounds it gets flat enough and weak enough that the slide coming forward can roate the nose down enough to slam-jam it into the bottom of the feed ramp.

Edited December 18, 2006 by bountyhunter

[benny hill]

Mostly , it is due to the fact that factory mag's have to tight of lip's. The 45's come at .375 but need to be opened up to .415 or so to run great. The 40's need to open up to .380. With a good ramp this will take care of the nose dives or at least on all the ones I work on.

[cking]

I find the fixed timed mags, the ones where the round retention area ends abruptly are very sensititive to overall round length, and bullet ogive. Now if your loading your own vary the overall length will help clear things up.

However I like the old orginal tapered release mags they get the nose up and let rear of round up sooner and are much easier to tune.

So I guess I say I'am early release guy

[superdude]

dear early release guy. we won't think less of you because of it.

frankly i don't have a good reason for why the angle change of the rounds in the mags. my brain is too small to solve that one.

[LPatterson]

Okay, lets see if I understand what you’re suggesting. I’ve been reading this over so that I can try to address your idea. Are you saying that the front and back of the magazine (not the sides) influence cartridge angle? That would only be true if a cartridge was in contact with both of them. It is not. Or at least is shouldn’t be. If rounds do contact both the front and back of the mag, there can get stuck. So there is plenty of room there. There is enough room for a cartridge to lie in the magazine at any angle relative to the flat back side. As long as cartridges are loaded to normal specs, a wee shorter if they are hollow point or flat nose bullets, the nose can pivot up and down and still not touch the front of the mag.

Is that what you meant or am I really off base here? Please feel free to straighten me out.

By the way, I loaded some mags and measured the front-to-back distance. This did not change no matter how many rounds I put in. I didn’t expect it to based on the strength of the material, but I could have guessed wrong so I measured it in 2 mags, a 45 ACP and a 38 Super.

I think you need to look at the follower as part of the cause. In a 7 round mag the follower tail is usually longer which is what limits the mag to 7 rounds. Since the tail is shorter it allows the follower to tilt which will cause the follower to be touching the front & back of the mag body. Wilson uses a follower with a front plastic lip that the spring is forced against to stop the follower from changing angles. For my CMC 10 rd mags I bend the tabs underneath the follower, then insert the spring & bend the tab back capturing the spring. This seems to help keep the nose of the follower a little higher as the spring is compressed. On some I have clamped the follower tail in a vice & bent down the lower leg of the follower that the spring rides against. I checked some mags & I think Benny Hill probably has the best corrective action.

[scorch]

I have this problem with my 10 rnd 45 cal Wilson Mags, but none in the wilson 8 rnd mags. In the ten rnd mag the 8th, 9th, and 10th rnd has space between it at the front. I loaded the Round nose Laser cast bullets out to 1.272 and fixed the problem. But check the Throat on your gun before going this long. Thanks Benny Will check the deminsions on my mags.

[IronEqualizer]

Mostly , it is due to the fact that factory mag's have to tight of lip's. The 45's come at .375 but need to be opened up to .415 or so to run great. The 40's need to open up to .380. With a good ramp this will take care of the nose dives or at least on all the ones I work on.

What is your process for doing this? Bending or filing?

[bountyhunter]

I think you need to look at the follower as part of the cause. In a 7 round mag the follower tail is usually longer which is what limits the mag to 7 rounds. Since the tail is shorter it allows the follower to tilt which will cause the follower to be touching the front & back of the mag body. Wilson uses a follower with a front plastic lip that the spring is forced against to stop the follower from changing angles. For my CMC 10 rd mags I bend the tabs underneath the follower, then insert the spring & bend the tab back capturing the spring. This seems to help keep the nose of the follower a little higher as the spring is compressed. On some I have clamped the follower tail in a vice & bent down the lower leg of the follower that the spring rides against. I checked some mags & I think Benny Hill probably has the best corrective action.

Interesting, I hadn't thought of that.

Edited December 19, 2006 by bountyhunter