Posted: 5/27/2011 2:54:46 PM EDT
[Last Edit: Duffy][Edited]
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This is a subject that comes up now and then, so we'll stick this here to serve as general information, as it applies not only to our own selectors, but all selectors.
There is a gap between the underside of the selector lever and receiver wall. The extent of the gap is a matter of receiver thickness. We took measurements from couple of dozen receivers before deciding the length of the selector center. What it comes down to is the thickness of the receiver. The milspec thickness is .880 +.015 -.002, or .878 to .895. We based our selector axis off one of my Colt SP1s, which is 0.898 and on the thick side. Even within the same company, there are variations. This is a factory selector on an AR10 
This is the prototype selected for production, after we've reworked the length of the selector center. The difference in amount of gap between the left and right is 0.01, the reference receiver is a Colt SP1. 
Colt, Bushmaster Armalite, DPMS, LMT and KAC are all pretty well within specs. POF and another billet lowers are notably thicker, at 0.905 and 0.911, while Olympic Arms are notably thinner than specs. There's NO way to make a safety selector and have it fit flush with all brands of receivers, as mentioned, even within the same manufacturer there's slight changes. The same ambi selector that fits flush on a Bushmaster, LMT, and KAC will almost be too tight for a POF. With a standard, non-ambi selector, this isn't an issue. If you haven't noticed, the axis usually sticks out a little on the right side, while some don't. This can be a problem for ambi selectors, too much protrusion on either side, it won't be as low profile as can be, and the lever will pinch your finger when you rotate the lever from Safe to Fire while its extended in the "finger outside the trigger guard" position (this is actually somewhat unavoidable, we just try to minimize the pinching). There is no problem with the lever sticking out and not sitting flush (it will never be flush, the original Stoner design calls for a gap between the lever and the receiver, and for good reasons). In terms of rounds fired, eight M16 with our selectors had 100K rounds through them in less than four months without any failure. Semi auto selectors have far more rounds fired, as there are more semi auto selectors in the hands of users 
CASS-3P, M16 (picture taken before our patent paperwork was filed to mask the patent pending dovetail interface) 
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With the CASS-3P family selectors, M16 and the upcoming semi auto, the selector center will protrude a tiny more than the current semi auto 45 and 90 degree selectors. The reason is the female dovetail interface is on the tip of the selector center, and there must be enough clearance to ensure the male dovetail interface, which is on the bottom of the CASS-3P lever, does not come in contact with the receiver, or bind when there's debris between the lever and the receiver.
The selector center must be sufficiently long to accommodate various receiver thicknesses from different manufacturers. If Colt made all the receivers, we'd be able to make ours more form fitting, alas the thicknesses are all over the place, making compatibility a serious issue we must address. 
That the levers do not sit flush with the receiver isn't necessarily a drawback. Levers that protrude further out have the effect of extending their usable purchase. On the flip side, the trigger finger side lever can pinch your hand while it's being rotated from Safe to Fire, but in our experience, even when the gap is very small, pinching can still take place. It is then quite unavoidable, and the gap isn't the culprit, the 90 degree legacy throw is responsible for that. One might argue that such gap doesn't exist for SIG, HK, FN, etc., this may be true, but remember these manufacturers do not have dozens of other companies making receivers for them, all with slightly different dimensions 
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On the left, the original 90 degree selector, on the right, the CASS-3P, SA (semi auto)
Note that though the CASS-3P appears to stick out more, it's only the selector center that's longer than the regular selector. The CASS-3P's center houses the male interface of the dovetail, and must be sufficiently long to accommodate a variety of receiver thicknesses. In this picture, you can see the CASS-3P family of selector centers are longer than the original 45 and 90 degree, semi auto selector centers (left two) 
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I have a 3p on a Noveske M16.
I have also installed the 3P on other lowers set up for M16s. I will say that YOUR specs are off and there is no excuse for poor engineering. Your selectors stick out far too much. They need to be much more flush. You over compensated for variations between lowers! I dont buy the excuse you are pushing The 3p is a fine selector! It has only one flaw and that is that it needs to be more flush. |
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This is the first time I've heard the words poor engineering associated with our products. On some receivers they will stick out more, there's no getting around that.
If we make them flush with one brand of receivers, we risk incompatibility issues with others, then these customers may make the same unflattering comments
When things work, we don't always hear about it. When we do, we rarely publicize it, we prefer to let the merits of our products do their own talking. One such report from a customer was that he had a POF billet receiver, other ambi selectors couldn't work because his POF receiver was thicker than spec, the only one that would work was ours. If you're unhappy with the selectors, please contact us for a full refund 
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Our selectors, M16 and semi auto, are designed according to receiver thickness specified by TDP. We've seen old M16 receivers that measure as thin as 0.61! 
On these receivers, the sear pin sticks out on both sides of the receiver, with these receivers, unless it's a special ambidextrous selector, the levers WILL stick out. Photos courtesy of Cory F. 
We will put a note on our site so buyers are aware of these huge variations on receiver thickness. When users contact us about the gap on receivers, they don't always tell us how old these receivers are, only that they're Colt or Bushmaster, nor do they tell us the thickness. It's assumed that all of the M16 receivers are done to TDP specs, this isn't true. From 0.880 (current TDP specs) to 0.61 (probably a Vietnam era receiver), the difference is quite large. We will entertain the idea of making a shorter center, but we can't not make centers for 0.61, 0.75, and 0.81. While a center made for TDP spec will work on all of these, the reverse is not true. I hardly think this is "poor engineering" on our part, rather it's a misunderstanding of specs, and how the manufacturing date and year may factor into whether a receiver is CURRENT spec or not. |
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I like the gap on the BAD 45 degree ambi selector that I just bought. I think it is less likely to bind with the clearance. I had one of the other manufacturers of ambi selectors and it dragged on the right side of my Noveske Gen 2 lower.
I think that the biggest source of problems will be the location of the detent. I could see the drill of the detent hole easily running in or out .010 inch. That would be enough to make an ambi selector drag on one side if minimun length on the selector was chosen. |
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The location of the detent hole can have an effect on the amount of gap on either side of the receiver. On most receivers, the gap is pretty even. On some receivers, the gap is wider on one side, and narrow on the other. We usually get blamed for this, folks can't believe that we're not to blame for it
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Here's how it looks on a thicker receiver that has very little gap between the levers and the receiver wall. Had the receiver been thinner, the gap would be more pronounced.
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Whereas in the first few years when our selectors were purchased and used mainly by folks well versed in the AR, the availability and popularity of the selectors in recent months have reached customers that may be new to the AR system. The oft-asked question during installation regarding the selector is the seemingly out of spec length of the selector center (drum, axis). Folks familiar with the AR, but new to the ambidextrous selector ask this question as well, so we'll share the info below for everyone.
When a selector is installed before the detent, spring, and pistol grip are put back on the lower receiver, the selector will be free spinning and OFFSET to one side or the other, usually the left lever is almost flush with the receiver, and the selector center protrudes a great deal out the right side of the receiver. This is because the detent has not engaged the detent hole or detent groove on the selector center yet, so the selector is simply sitting on one side of the receiver. Selector lever flush with the receiver prior to re installation of detent, spring, and pistol grip: Left side: 
Right side: 
Once the detent, detent spring, and grip are installed back on the receiver, and the detent is seated / engaging the detent hole or groove, the selector will be centered in the receiver, and the gap between the lever and receiver should be about even on both sides. Left side: 
Right side before the lever is installed 
After the lever is installed 
If you see a lot of selector center protrusion on one side of the receiver prior to putting everything back on the lower receiver, it is normal
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Please measure your receiver width. Forged receivers widths are going go vary, they're largely dependent on the raw forgings. If yours is 0.87 or so, the gap will be rather pronounced.
Just within Colt we've seen widths ranging from 0.74 to 0.895, and I'm sure we haven't seen everything. We can't produce different lengths of centers to accommodate various widths, as we'd be making a dozen versions based on 0.02 increments
When a receiver is as thin as 0.87 or less, any ambidextrous selector will produce a gap between the levers and the receiver, but the gap is only a cosmetic issue. The 0.02 worth of lateral protrusion can't make the difference between a snag hazard and non-snag hazard. Let's take a look at the gap produced by the selector on an FN SCAR. The gap between the factory receiver and selector selector levers is very noticeable, both the selector and receiver are made by FN. We suspect this is done for the same reasons there's always a gap designed into the levers of selector levers, they could have kept the gap small, but they went the other way. 
Unlike the FN SCAR, the AR has far greater number of manufacturers, some make receivers, some make selectors, and not everyone has followed the specs. The only way for us to make a selector that will fit a wide range of selector widths is to make the selector center just long enough for the average width, which happens to be the similar to the Colt SP1 width which we used as a reference. Folks that have thicker receivers can't use ambidextrous selectors made only to fit milspec receivers, we routinely hear from customers who switched to ours when others failed to install (for lack of clerance). |
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Thank you NSZ85 for posting this video!
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