Premature Slide Lock with the XD-40: Causes & Possible Cure
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CAUTION- The following article describes modification of a factory part, and is offered for reader interest and hopefully product improvement purposes. Doing so will probably void your warranty, and I will assume no liability for damages or injuries if you choose to repeat this procedure on your guns. Having suffered this malfunction once myself, I wondered what could cause this otherwise superbly-reliable gun to have this problem. When gremlins of this kind rear their ugly heads, there are basically ten steps to take toward killing them: 1. Establish that a problem exists. I wanted to make sure that this wasn’t just a fluke, so the first order of business was to poll a good cross-section of XD owners. No better place to do that than right here’ see it at www.xdtalk.com. When over 100 XD shooters responded to this poll, I was convinced that a problem exists, particularly in .40 caliber guns and magazines. NEXD (xdtalk member) has posted another .40 caliber specific poll at www.xdtalk.com 2. Identify the problem. In normal operation, the slide stop lever has a spring which exerts light downward pressure on it until the follower of the empty magazine engages it, overcomes the spring pressure and raises it into the notch in the slide. For the slide to lock open with rounds still in the magazine, something has to exert an upward force on the slide stop lever. 3. Evaluate the potential hazards that the problem creates. If, as the poll indicates, 10% of the XD's fail to fire in defensive shootings because the slide locked back- that's way too high. The potential hazard is that the operator could be KILLED. I refuse to recommend the .40+ Glocks because a far fewer percentage of them have experienced "explosive disassembly" on the range. I will make no exception for Springfield's product, until the problem is corrected. 4. Isolate the conditions in which the problem exists. It appears that in virtually all reported cases, either the gun or magazine involved has been of .40 caliber. The problem occurs when firing with .40 caliber XD’s, or firing 9mm XD’s with .40 caliber XD magazines. 9mm XD’s are evidently not afflicted with this problem, at least in any meaningful numbers- so long as you stick with 9mm magazines. In my case at least, I believe there is another contributing factor. The XD that locked open while firing had always functioned great when shooting from the bench, or in any relaxed shooting position where either or both hands are on the gun. It wasn’t until I started doing “yank & blast” two-handed drills that the problem manifested itself. I have been doing combat shooting with hard-kicking handguns for years; everything from 3” 1911’s to a 4” S&W .44 Magnum- with full magnum loads. In order to control these unruly beasts in “yank & blast” drills, I long ago adopted a two-handed hold that involves crushing the heel of the off-hand into the butt of the gun. In my case, this is the left hand. The photo below illustrates the result:  base-plate ( XD, etc.) this type of grip presses hard on the base of the magazine from the left, and if there is some play in the mag well the top of the magazine is going to move a few thousandths of an inch. If you are what my Dad used to call a “hard-handed individual” (weightlifter, bricklayer, mechanic, martial artist, etc.) this effect is probably magnified by that fact. 5. Eliminate potential causes which have no relevance. Often, one or both of the shooter’s thumbs bump the slide lock under recoil. As an old 1911 shooter I had to get over the "high-thumb" grip a long time ago, and these problems disappeared when I did. I trained a lot of cops over the years and have seen this problem resurface occasionally, with various auto-pistols. The established training solution is to turn the shooting-hand thumb down, and place the off-hand thumb on top of it. If the problem persists after that point, you either have a gun or magazine problem. The slide lock/release on the XD is unobtrusive, and protected to some degree by a shelf molded into the frame. I did not see it as being particularly susceptible to this problem, so long as the shooter makes a reasonable effort to avoid it. Unfortunately, this does not seem to cure the problem with 40-XD’s. A shelf on the magazine follower is what activates the slide lock- and when the magazine has rounds in it, the follower simply can't contact the slide lock. The problem has to lie somewhere else, unless the rounds themselves are hitting the inward extension of the slide lock. This was considered as a possibility worthy of further investigation. If the spring that acts upon the slide lock fails, the slide could certainly lock open when the lever jumped up under recoil. The slide lock would also probably flop around like a loose tooth, which was obviously not the case here. 6. Positively identify the actual source of the problem. I began by field stripping both our XD-40’s and checking the cartridge presentation characteristics with several different factory loads, and the reload I was shooting when my “slide lock incident” occurred. With double column magazines like the XD uses, live rounds rise in columns on either side. It was immediately apparent that those presenting from the left side of the magazine were very close to touching the inward extension of the slide lock, when the round above them was presented for feeding from the magazine. This essentially translates into the eighth, sixth and fourth round loaded into 10-round, .40 caliber magazines. I recalled that my slide lock malfunction had occurred on the third round fired, from a fully-loaded gun- the eighth round loaded in the magazine. With the slide off the gun and a magazine loaded with nine rounds, this became readily apparent. The round directly below the top round rode dangerously close to the inward extension of the slide release. By duplicating the two-handed grip described in #5 above, I noted that I could feel the slide stop rubbing the #8 cartridge when I moved it with my thumb. As I suspected, the condition was aggravated by the heel of the support hand pushing inward on the left side of the magazine baseplate. There was enough play in the magazine well to allow the top of the magazine to shift to the left a few thousandths fo an inch, under the pressure. Seeing for it myself wasn’t enough, however, and I needed to be able to illustrate it for those who have pulled their hair out trying to figure out what was causing this problem. Springfield Armory also has a right to be presented with the results of the experiment, to provide them with the opportunity to make the appropriate changes to effect a cure. So I took a Magic Marker and blackened the bullets on the four factory loads and one reload, as illustrated and listed below, left to right:  WW 165 FMJ, UMC 180 FMJ, Wolf 180 FMJ, UMC 180 JHP, 175 SWC reload rubbed on all but the SWC reload, as can be seen in the photo below. The aforementioned contact point shows up as a little brass “comma” on the nose of the cartridge. They appear in the same order as above:  “bump it up” a tenth of a grain before the next batch gets run off, and I’m sure that will be enough to insure positive function. Between the comparison of the cartridge presentation characteristics 9mm and .40 XD’s, I was pretty sure we had a winner here- but the bold type says “positively” identify the source of the problem- so I wanted to be sure. Since the poll indicated that this is a “.40 caliber problem”, I decided to compare the slide lock/cartridge clearance between the 9mm and .40 caliber guns. If a picture is really worth a thousand words, this one is worth the entire effort I put into this experiment. I used a resized case as the #9 (top) “round” in the .40XD photo, so a bullet wouldn’t block the view:  difference in clearance between the 9mm and .40 caliber guns. Unlike the .40 magazines, the 9mm magazines tend to arrange the top two rounds almost vertically. This creates plenty of clearance to allow good function, even under adverse conditions. In a final effort to insure that I just didn’t “get a pair XD-40’s with XD-9 slide locks mistakenly installed in them”, I decided to call Springfield and inquire if the 9mm, .40 and .357 XD’s use different slide locks, for each caliber. I was told what I suspected all along- the same slide lock is used on all three guns. 7. Correct the actual source of the problem. This problem can only be corrected by shortening the inward extension of the slide lock. This must be accomplished without over- shortening it, and negating the purpose of having a slide lock in the first place. The current-issue part was well (if not perfectly) engineered for the 9mm cartridge. Equally apparent is the fact that is does not allow sufficient clearance for the .40’s, particularly when dirt, sand and Mr. Murphy start playing a tune on the inside of your gun. Rounds which present up the left side of the XD-40 magazine are eventually going to contact the internal extension of the issue slide lock- and it evidently don’t take much contact to raise it enough to lock the slide. A slightly-stronger spring extension acting on the slide lock might also help prevent this malfunction, so long as it still allows it to function as originally designed. I disassembled both our .40’s, took measurements on the internal extension of the factory slide lock, and determined that both measured almost .174” exactly. I also noted that mine had some brass-colored transfer on it, where it had been rubbing the copper bullet jackets. I proceeded slowly, removing about .005” and reassembling each time, to insure that they would still raise the lock into position on an empty magazine. I stopped after removing .025”, which produced significant clearance for rounds in the magazine. The modified part is shown in the two photos below, next to an unmodified part. Hopefully this will give some indication, by comparison, of how much metal was removed. 
 with the modification. The difference is easily noticed, and leaves plenty of clearance for crud and fouling. I also repeated the “marked cartridge” exercise described in #6 above. It was now impossible to touch or mark any cartridge with the inward extension of the slide lock, regardless of the grip used or the effort made.  come up with a modified slide lock that will work in the .40 caliber guns. 8. Test to insure that the “correction” does not create problems of its own. The only foreseeable “problem” the modification could produce is a possible failure to lock the slide open after the last round is fired. I tested both guns by ripping the slide back on an empty magazine, and letting it slam forward as if it were being fired. The modified slide lock functioned as designed, each and every time. Even if it hadn’t, I would much rather have a gun that will positively function until it is empty. The AK is my SHTF carbine, and I know the drill. I can reload it and get it running again in short order. 9. Test correction under varying and severe conditions. See #10 Below. 10. Consider the problem solved. The jury is still out on these two- but after seeing the rub marks on test cartridges, I am pretty confident that .40 caliber bullet-noses impinging on the inward extension of the slide lock were the primary contributing factor in this malfunction. Too many of you reported that you had taken precautions to avoid shooter-induced malfunctions, and still the problem kept occurring. It was time to look inside the gun. Even if I were wrong on this, the situation creates an unnecessarily-fertile environment for a malfunction to occur. The difference in the round/slide lock clearance between the .40 & 9mm guns is striking. By my personal reliability standards, this situation needs to be corrected by Springfield before the XD-40’s can merit serious consideration as carry guns. Mine did get corrected, and the only reservation I had regarding the XD-40 is now gone. An old training axiom goes something like this; “This is simply A way to solve a problem. It may not be the ONLY way. Learn what works in your circumstances, and keep an open mind about new methods as they are discovered.” It certainly applies here. By xdtalk member: Invsst August, 06 2004 |
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