My X300u-B started walking off my Glock 17 Gen 3 all of a sudden after months of it just being hand tightened.  I didn't even realize that it wasn't slotted into the single picatinny rail.  So now I need the "Universal Wedge" (as instructed by this forum.

But what I'm wondering is: is the B even meant for polymer guns, and would the A fit a gen 3.

"The X300U-B uses the T-Slot Mounting Rail System which is best suited for metal framed handguns as well as AR-15 or similar style rails. The T-Slot system is also used on the X400 series of weapon lights. The main issue that people had been experiencing with the T-Slot style mount on polymer guns is the overtightening of the light causing reliability issues with the gun or under tightening of the light causing the light to come off. The Rail-Lock system is definitely prefered for use on polymer framed handguns but for use on an AR, the T-Slot has some distinct advantages."

I had to change the rod out for my X300A to fit my Zev (was slightly looser on the picatinny rail that feels more LIKE a metal frame, but is not - now is not going ANYWHERE and i shard to pop off).

The X300U-A does come with the "U" (universal) rod, but I think its slightly loose.  Cant recall, and dont feel like swapping it all out if someone here knows first hand that "A" fits Gen 3.

A few comments, for what they’re worth:

The -A works great with Glocks, in my somewhat limited experience (only have one). I’m inclined to think it was designed specifically for the Glock rail, but not sure.

Most Glocks up through Gen 4, with the exception of the SF models (I think), did not have an actual Picatinny rail, which is why Surefire recommends the Universal clamp option. It wasn’t until Gen 5 that Glock standardized with a Picatinny slot on the rail.

I found that the -A model did not work well with SIG Picatinny rails. The light went on just fine on my P226, but the fit was so tight that I couldn’t depress the tabs enough to clear the rail slot. I eventually had to disassemble the clamp on the light to get it off the pistol. I bought a new X300U-A last year and ran into problems again. On my P320 polymer frame, the -A slid on fine, but the tolerances were so tight that the clamp didn’t have enough room to pivot and fit down into the Picatinny rail slot, so I couldn’t get it to lock in place. I ended up returning it and buying a -B instead, which works perfectly.

Despite what Surefire says about plastic vs metal frames, when using the -B on a polymer frame, I think you just need to be careful not to crank down the clamp to the point where it starts to deform the frame. SIG rails seem very beefy and robust, which is both why the -A doesn’t seem to fit and the -B seems to work just fine.

B would be my pick.

1000000000000000+

I like the A on Glocks and B on everything else.

I got an A for a great deal a while back and every time I fiddle with it I wish it was a B.

A is too complicated. Fits well on a P80 but I'd need to swap parts to get it to fit on my P320, or Timberwolf Frame, or VP9.

Streamlight TLR-1 fits great on all of them.

I like the A for quickly changing between guns and not having to worry about the screw backing out. I over torque and thread lock my TLR1's and TLR7a's because they eventually walk loose if I don't. I've also observed this on other people's setups, friends and strangers alike.

I prefer the A model.

I’ve got 7-8 all on Glocks and they fit nice.

If I need to snug them up cut a piece of bicycle inner tube about a 1/4 inch wide and an inch long

Put it between the light and front of trigger guard and push the light until it clicks in place.

I don’t want any wobble and this is a simple fix if you find one that does.

If seen more than one B model tightened so much it flexed a Glock frame.

I know better but still only put B models on steel guns.

Attached File

I'm in the same camp. I've owned both an A and a B; no longer own the B. I'll have to try that inner tube trick as the A model is loose on Sig X frames; fits the standard frame perfectly though. On Glocks the A is a no brainer as Glock rails are consistent and lock up perfectly.

I have a G21 SF and A model fits fine, so not an issue there. It is a gen 3, so not sure if you meant just gen4s.

No, sorry, “clamp” was a poor choice of a word. I meant the Universal insert / adapter in the -A model that fits in the slot in the Glock frame, vs. the Picatinny insert. It sounded like the -A model that he got only came with the Picatinny one, which doesn’t fit early Glocks well because their rail slot wasn’t made to Picatinny specs.

(A) all day everyday… but I am a Glock guy.

I’m running two A’s with P plates on two Gen 5 Glocks I have

I’m running a B with the P plate on a full size p320 comp build.

I’m running a B with U plate on my S&W metal.

And I have a few TLR-1 HL on other guns.

All are good to go and work well.

While I think surefire are better lights, the tlr-1 fit everything except Glock way better. Plus you can get 2 to 3 tlr-1 for the price of a surefire depending on sales.

I only own Glock handguns, so that may drive my decision making a bit, but “A” all the way.  I’ve owned exactly one “B” model and hated it.  Then the cheap mounting screw snapped in half.  Got a replacement screw and promptly sold it off.

I’ve owned probably 15+ “A” models at this point without issue.  Still have two X300Ts, two X300Us, and an X300V.  They’re stupid simple and just plain work.  My $0.02, worth what you paid.

For me it depends on the rail, but if an A will fit tightly then that's what I prefer because it's easier to get on and off to change batteries. I have an A Turbo on my 6920 and FNXs. Berettas have a skinny rail so they get a B, and CZ rails only contact the A towards the front of the mount so they get a B as well.

I use the A on pistols and B on 12 o’clock rails on carbines.

I prefer As

If its loose I'll layer tape on the back to wedge it in.

That's after making sure the spacer is installed. Most people don't actually know there's a spacer on the door. It's pinned in.

I'm wtih you on this one.