What allows the Springfield XD(m) 9mm versions to hold 19+1 rounds for their heights?


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bwh
January 21, 2014, 03:17 PM
The Springfield Armory XD(m) 9x19mm Parabellum versions (except for the compact versions) all hold 19+1 rounds, and the pistol heights are 5.75 inches (with the magazines inserted). The Glock 17's height, however, is 5.43 inches--and it holds only 17+1 rounds of 9x19mm Parabellum. This cartridge's widest part measures .392 inches, and so how can the Springfield hold 2 more rounds than the Glock?

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herkyguy
January 21, 2014, 03:35 PM
perhaps the width of the internal dimensions of the magazine itself is different than that of a Glock??

ATLDave
January 21, 2014, 03:49 PM
Maybe the follower is shorter. Some companies make aftermarket followers for some magazines that will add one or two rounds to capacity by themselves.

Maybe the baseplate is thinner.

Maybe the double column narrows later in the XD(m).

Maybe the magazine spring takes up less room when fully compressed.

Maybe the mag walls are thinner, allowing a slightly wider spread.

Maybe the mag is wider, allowing a wider spread.

And, as you note, they have slightly more room/height to work with.

Lots of possible explanations. Surely more than I have listed.

Edster12
January 21, 2014, 04:03 PM
Fat magazine!!! I would have to measure the two to see. Should have said something sooner. Was shooting with a friend this weekend I have the XDm and he has the Glock.

JTQ
January 21, 2014, 04:13 PM
How come the G17 holds 2 more rounds than the Beretta 92FS? How come the Beretta 92FS holds 2 more rounds than the Browning Hi-Power?

How come my 1911 Wilson 47D mag holds 8 while my Wilson 47 mag, that is the exact same external dimension, hold only 7?

Time marches on. The magazine makers try all kinds of tricks with followers, base pads, and springs, to squeeze in extra capacity. Sometimes they even make the mags longer. Sometimes the tricks work, sometimes they don't.

Mike J
January 21, 2014, 04:16 PM
I think they use shorter followers but I could be wrong. If you notice Mecgar offers aftermarket magazines that hold a couple more rounds than the stock magazines for a lot of pistol models. I believe they achieve this by making the follower shorter.

rcmodel
January 21, 2014, 04:19 PM
The Glock mag is plastic with a steel liner molded inside.
The side walls are kinda thick.

The XD mag is thin sheet steel.

So the mag walls are thinner then the Glock.

And it doesn't take much.
During the 10-round mag limit, Glock reduced the capacity 7 rounds just by bending a shallow kink in both sides the metal liner to take up slightly more internal space.

That prevented the rounds from staggering quite as far apart in the mag.

rc

Schwing
January 21, 2014, 04:44 PM
I think they use shorter followers but I could be wrong. If you notice Mecgar offers aftermarket magazines that hold a couple more rounds than the stock magazines for a lot of pistol models. I believe they achieve this by making the follower shorter.
The mecgar magazines also use a "More Compressable" spring which takes up less volume. This is according to a Mecgar rep that I met at the Rocky Mountain gun show.

gym
January 21, 2014, 06:50 PM
Measure the length and width of both mags and you should have an answer. If they are very close, it may be the magazine is actually longer on the XD, but sits higher in the frame. They have a very high slide which might absorb some mag length. "Just a guess". But I am looking at the XDM compact for myself in bitone, vs the PPQ.

RX-79G
January 21, 2014, 06:56 PM
Amateurish engineering and optimism? Shorter, less stable follower and a more highly compressed mag spring.

Wider mag bodies are not going to make the right and left columns of rounds sit any closer to each other. Each round will still take about 9mm of vertical space in the mag.

An easy way to get more capacity is to design the gun around a double feed magazine, like an UZI or rifle. That's how Steyr got 18 rounds into the GB.

HammsBeer
January 21, 2014, 08:35 PM
The difference in height between the two guns is .320, and one 9mm case is .392, so it's pretty close to the thickness of one cartridge (disregarding other things like internal pistol geometry).

So in a double column magazine you will have an extra round in the left coulumn, and an extra round in the right column, but you have only increased the needed height of the whole magazine by one round. Thus your two extra rounds, Tada!

Sam1911
January 21, 2014, 09:36 PM
rcmodel got the biggest part: The Glock mags have that plastic shell over the mag body and that takes up room. When you're talking about the difference between 17 rounds and 19 rounds, you really don't need to move any of the cartridges very far before you've added up enough room for another round, or two.

I've got an xDM 9 and the mags work very very well. Nice and predictable and very stable and strong. A well-built piece of kit. Obviously they took pretty great pains to optimize the arrangement of the column, the tube, spring, follower, etc. to make a very reliable, size-optimized setup.

Sam1911
January 21, 2014, 09:51 PM
Wider mag bodies are not going to make the right and left columns of rounds sit any closer to each other. Each round will still take about 9mm of vertical space in the mag.Actually, that's not so, or not stated very correctly. You could stack rounds single-stack style and each would take up the full vertical height of the case head (0.394"). Or you could lay two rounds exactly side-by-side and TWO rounds would take up 0.394" of vertical height. In between those two extremes, you could vary the mag width almost infinitely to allow the rounds to spread out more or less, and thus, together, take up somewhere between 1 x the number of rounds times 0.394" and 1/2 that height.

Here are a few drawings I did to illustrate the point.

Using the thickness of the walls and ribs of an xDM's magazine (0.066"), I get a total outside width of 0.526" and the width of the cartridge heads (0.394") inside. In this magazine, I get four rounds in 1.62" of vertical height.

http://www.thehighroad.org/attachment.php?attachmentid=193934&stc=1&d=1390354881

I could in theory make a magazine with the same wall/rib thickness that let the rounds sit fully side-by-side. That would require an outside dimension of 0.920" and an inside dimension of around 0.788" -- twice the diameter of one cartridge. I get EIGHT rounds in that same 1.62" of vertical height. (Though it probably won't feed very well.)

http://www.thehighroad.org/attachment.php?attachmentid=193935&stc=1&d=1390354881

If I play with things a bit, I can get other whole number integers of rounds into that same vertical height. Here's five. The mag has to be 0.790" in width, and 0.658" inside.

http://www.thehighroad.org/attachment.php?attachmentid=193936&stc=1&d=1390355078

And, of course, we need to see what an xDM mag really looks like. Here it is. It is 0.864" in overall width, and 0.732" inside. That gives an even stack of seven rounds in that same vertical height.

http://www.thehighroad.org/attachment.php?attachmentid=193937&stc=1&d=1390355296

That arrangement really reduces the amount of dead space inside the magazine (I think most double-stack mags are optimized this way to some degree) but it doesn't actually eliminate it. One round doesn't actually touch the next round on top of it, but bottoms out between the mag body rib and the lower quadrant of the round beside it. There's a smidge of room left between rounds on top of each other. It isn't much -- about 0.013" -- and it would take a lot of stacked rounds to "build" room for another in the mag just by removing that slop.

I can't squeeze another full round into 1.62" by letting the seven round stack gap open a bit wider, but I could make those seven rounds shorter, and when you're getting up into the double digits, you could quickly come up with enough room.

These little increments of gained volume are kind of funny in how they work. I have friends who play with open guns for USPSA who will buy big piles of parts to put together STI or PARA mags that hold crazy numbers of rounds -- over 30 for some. And the tiniest differences gain or lose them extra rounds. In fact, what works for one gun or mag body might not work for another. They're basically putting them together and seeing what they can get. Might be 27, 28, 29, plus. Depends on the spring, follower, mag body, base-plate, feed lips, and pixie dust, I think. ... And then they have to get these $150 monstrosities to RUN! :D

I'll stick with the much more sane xDM 19-rounders!

Kiln
January 22, 2014, 07:24 PM
The XDM was designed with optimization of mag capacity in mind. The Glock uses an older magazine design that did the same thing in it's day.

RX-79G
January 23, 2014, 02:00 PM
Sam1911,

No. Just absolutely wrong.

Double column mags do have the rounds touching top and bottom. They are arranged in hexagonal formation, like honeycombs are. It is the most space efficient way to pack circles together.

Anything with space above and below the round is called a semi-staggered magazine. Tanfoglio uses them for it's .45 guns, and the Glock 36 uses a very flattened out version of this. All double column, single feed magazines transition from double column to semi-staggered in the tapered portion at the top.

The non-staggered version you came up with would make a great April Fools joke - it only saves the space of one half of a cartridge, total. It also would not feed because neither right nor left cartridge has precedence, so they are just as likely to lock together as feed up. I don't know what you're going to do with a half of a round extra space in the magazine, but that isn't going to get a 17 round mag up to 19 rounds.

Sam1911
January 23, 2014, 02:06 PM
Good, glad we're in agreement there.

KTXdm9
January 25, 2014, 11:35 AM
Superior engineering.....

Fixed that for you. ;)

bwh
March 9, 2014, 05:39 PM
Could you please tell me what computer program you used to create those drawings?

bwh
March 9, 2014, 05:41 PM
Actually, that's not so, or not stated very correctly. You could stack rounds single-stack style and each would take up the full vertical height of the case head (0.394"). Or you could lay two rounds exactly side-by-side and TWO rounds would take up 0.394" of vertical height. In between those two extremes, you could vary the mag width almost infinitely to allow the rounds to spread out more or less, and thus, together, take up somewhere between 1 x the number of rounds times 0.394" and 1/2 that height.

Here are a few drawings I did to illustrate the point.

Using the thickness of the walls and ribs of an xDM's magazine (0.066"), I get a total outside width of 0.526" and the width of the cartridge heads (0.394") inside. In this magazine, I get four rounds in 1.62" of vertical height.

http://www.thehighroad.org/attachment.php?attachmentid=193934&stc=1&d=1390354881

I could in theory make a magazine with the same wall/rib thickness that let the rounds sit fully side-by-side. That would require an outside dimension of 0.920" and an inside dimension of around 0.788" -- twice the diameter of one cartridge. I get EIGHT rounds in that same 1.62" of vertical height. (Though it probably won't feed very well.)

http://www.thehighroad.org/attachment.php?attachmentid=193935&stc=1&d=1390354881

If I play with things a bit, I can get other whole number integers of rounds into that same vertical height. Here's five. The mag has to be 0.790" in width, and 0.658" inside.

http://www.thehighroad.org/attachment.php?attachmentid=193936&stc=1&d=1390355078

And, of course, we need to see what an xDM mag really looks like. Here it is. It is 0.864" in overall width, and 0.732" inside. That gives an even stack of seven rounds in that same vertical height.

http://www.thehighroad.org/attachment.php?attachmentid=193937&stc=1&d=1390355296

That arrangement really reduces the amount of dead space inside the magazine (I think most double-stack mags are optimized this way to some degree) but it doesn't actually eliminate it. One round doesn't actually touch the next round on top of it, but bottoms out between the mag body rib and the lower quadrant of the round beside it. There's a smidge of room left between rounds on top of each other. It isn't much -- about 0.013" -- and it would take a lot of stacked rounds to "build" room for another in the mag just by removing that slop.

I can't squeeze another full round into 1.62" by letting the seven round stack gap open a bit wider, but I could make those seven rounds shorter, and when you're getting up into the double digits, you could quickly come up with enough room.

These little increments of gained volume are kind of funny in how they work. I have friends who play with open guns for USPSA who will buy big piles of parts to put together STI or PARA mags that hold crazy numbers of rounds -- over 30 for some. And the tiniest differences gain or lose them extra rounds. In fact, what works for one gun or mag body might not work for another. They're basically putting them together and seeing what they can get. Might be 27, 28, 29, plus. Depends on the spring, follower, mag body, base-plate, feed lips, and pixie dust, I think. ... And then they have to get these $150 monstrosities to RUN! :D

I'll stick with the much more sane xDM 19-rounders!
Could you please tell me what computer program you used to create those drawings?

bwh
March 9, 2014, 05:51 PM
Maybe the follower is shorter. Some companies make aftermarket followers for some magazines that will add one or two rounds to capacity by themselves.

Maybe the baseplate is thinner.

Maybe the double column narrows later in the XD(m).

Maybe the magazine spring takes up less room when fully compressed.

Maybe the mag walls are thinner, allowing a slightly wider spread.

Maybe the mag is wider, allowing a wider spread.

And, as you note, they have slightly more room/height to work with.

Lots of possible explanations. Surely more than I have listed.
Your answer greatly helped me, but could you please either tell- or provide for me a reliable source hyperlink about additional factors allowing box magazines to hold more rounds?

Sam1911
March 9, 2014, 08:16 PM
That's just a simple line-drawing program. Any CADD program would do the same.

If you enjoyed reading about "What allows the Springfield XD(m) 9mm versions to hold 19+1 rounds for their heights?" here in TheHighRoad.org archive, you'll LOVE our community. Come join TheHighRoad.org today for the full version!