Notes on selector spring, pistol grip, detent, etc.

[Battle Arms Dev]

We have received couple of questions regarding our selector's seemingly ease to flick out of Fire/Safe. We hold very tight tolerance on our selectors, as anyone knows, this can't always be said of other parts on the AR, especially cast or plastic parts.

The following are our findings re: detent spring tension, pistol grip and their effect on the perceived stiffness on the engagement/disengagement of the selector.

Detent springs aren’t created equal, just the two I happened to have on hand are of slight different lengths. One of them is about 1 coils longer in length (though same number of coils).

Pistols grips (USGI, Magpul MIAD, Tango Down Battle Grip, etc.) aren’t created equal. The part we are interested in is the depth of the detent spring housing/hole. With the same spring inserted in these three (USGI, Magpul, TD Battle Grip) grips, the spring seats deeper in the USGI than Magpul MIAD and TD Battle Grip, by about 2 coils.

Can spring length make a significant difference? Depends on which spring and which grip are being used. A shorter spring inside a USGI grip will yield less spring pressure on the detent, than a longer spring inside a MIAD or TD Battle grip. I was able to test and verify this. A shorter spring inside a MIAD or TD Battle Grip doesn’t feel significantly different, but without precise instrument to measure the pressure, I’d say one can hardly feel the difference.

The difference of a shorter spring + grip that seats the spring deeper, and a longer spring + a grip that seats the spring just right, is noticeable when the selector is rotated out of Fire/Safe.

Short spring + USGI = sloppy feel, less positive click, easy to rotate out of position

Longer spring + MIAD or TD Battle Grip = more force is required to rotate out of position.

[Battle Arms Dev]

Cast selectors are not precision machined like ours, this can be a bad thing (mostly not so good, but easily overlooked) and good (just one).

When a cast selector is installed, you can most likely move it side to side inside the receiver. The reason for this is the detent holes are much bigger than the detent (ours are 0.005 larger in diameter than the detent itself), there's quite a bit of slack. The side to side movement doesn't hinder the operation of the weapon. It can serve to accommodate out of spec detent/detent spring housing if it's drilled not where it's supposed to be drilled, e.g. a little bit too forward toward the muzzle, a little bit more toward the rear, a little to the left or right. Because of the slack, the detent usually has no issue seating in its general area.

Our detent holes are far more precise (0.005 larger than the detent). In a receiver where the detent/detent spring hole on the receiver isn't drilled to spec, the detent may not seat squarely in the detent holes on the selector. When the detent isn't fully seated, it then can be more easily rotated out of Fire/Safe.

While spring tension (length of the detent spring, the depth of the detent spring hole inside the pistol grip) can play a part, chief among the reasons our selector can feel loose has to do with the receiver.

We're investigating making our selectors more compatible with this aspect of the tolerance issues on the receiver, we could make the detent holes less precise, and have more side to side movement as a result.

In PIP1, we made the selector flat area diameter smaller to accommodate triggers that are not of USGI specs. In PIP2, we increased the width of this flat area to accommodate slightly out of spec receivers when a DMR trigger is in use. It's about impossible to make it fit every receiver made, and receivers that haven't even been brought to market, the tolerance issues will be with us forever.

[Battle Arms Dev]

Cast selectors are not precision machined like ours, this can be a bad thing (mostly not so good, but easily overlooked) and good (just one).

When a cast selector is installed, you can most likely move it side to side inside the receiver. The reason for this is the detent holes are much bigger than the detent (ours are 0.005 larger in diameter than the detent itself), there's quite a bit of slack. The side to side movement doesn't hinder the operation of the weapon. It can serve to accommodate out of spec detent/detent spring housing if it's drilled not where it's supposed to be drilled, e.g. a little bit too forward toward the muzzle, a little bit more toward the rear, a little to the left or right. Because of the slack, the detent usually has no issue seating in its general area.

Our detent holes are far more precise (0.005 larger than the detent). In a receiver where the detent/detent spring hole on the receiver isn't drilled to spec, the detent may not seat squarely in the detent holes on the selector. When the detent isn't fully seated, it then can be more easily rotated out of Fire/Safe.

While spring tension (length of the detent spring, the depth of the detent spring hole inside the pistol grip) can play a part, chief among the reasons our selector can feel loose has to do with the receiver.

We're investigating making our selectors more compatible with this aspect of the tolerance issues on the receiver, we could make the detent holes less precise, and have more side to side movement as a result.

In PIP1, we made the selector flat area diameter smaller to accommodate triggers that are not of USGI specs. In PIP2, we increased the width of this flat area to accommodate slightly out of spec receivers when a DMR trigger is in use. It's about impossible to make it fit every receiver made, and receivers that haven't even been brought to market, the tolerance issues will be with us forever.

[Battle Arms Dev]

regarding the receiver.

The receiver will not allow the detent to go through the detent hole.  On my receiver, the detent protrudes about half way and is stopped.

If your receiver's detent hole isn't drilled properly, it will stop the detent from reaching up as far as it should be allowed to, the detent bottoms out and can only go so far, where no amount of spring tension would help the mushy/spongy feel.

On such receivers, a detent that's not protruding into the selector hole in enough length is enough to engage the factory selector that has a shallow detent groove. Our detent groove is deeper to prevent the selector from being backed out when rotated out of the detent holes, and this would cause the mushy feel issue.

[Battle Arms Dev]

We designed our selector groove with tall shoulders, so the selector cannot be backed out when it's rotated out of the detent holes.

If you do a search on "AR selector install", you will see that some folks advocate that you rotate the selector to 45 degrees, and from there you can push it out the side, all without removing the pistol grip, detent spring and detent.

We can hardly argue this is a good attribute.  In the picture below the tall shoulders to either side of the detent start to make sense:

There is no way to push the selector out, short of removing the pistol grip, detent and detent spring.

The deeper groove on our selector, among other things, was done to ensure minimal lateral movement.  We are bringing the depth of the detent groove up a little to ensure the detent spring retains more its spring pressure against the detent, at the same time we're also keeping the tall shoulders to prevent the detent from jumping over the groove.

These changes will make their debut on the current 45 degree, 90 degree semi auto selectors, and the CASS-3P, SA (semi auto) selectors in September.

To be sure, since the lack of spring tension can and does happen with other MIM selectors, and over all, fewer than 0.05% of the users of our selectors experience this, not all the mushy feel will be addressed by this, but we're eliminating this anyway :p