Author Topic: 'Tensioning bolt' that tightens up lowers and uppers? (wedge replacement?)  (Read 7728 times)

Offline FDGI

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From what I understand, a few AR lowers are being made with some sort of tension screw/bolt that can be tightened to adjust for sloppy fit.  From what I've heard, adjustment is located very near the grip hole, underneath.

Does anyone have any idea what this design is called?

Does anyone know at least how it works in theory?

...I'm going to complete an 80% next week, and was thinking while I had access to tools, maybe I could add this feature, because I plan on having multiple uppers and who knows how they will all fit together once I'm done, so I thought this might be a smart idea(?)  Can't be THAT hard, right?

Offline Johnny_V

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Other than making you feel good, a tensioning bolt is really useless. Machined properly, the slop is negligible. Besides, every upper is machined differently and will fit the lower differently, making it a bigger pain in the ass when switching uppers (remove the pistol grip, tension the upper, put the pistol grip back on). Personally, I use a dedicated lower for each upper. My AR10 is what some consider to be a loose fit, but is tighter than a friend's AR10 SASS from Armalite and both shoot just fine.
Johnny_V
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Offline goober

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here's an example of one that supposedly does not require grip removal to adjust:


(this is an ad from a company called "CNCmfg" in San Diego, CA)
heatware username: goober

Offline FDGI

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Thanks, goober! Yeah, that fits the description, doesn't it?

The fact that they say you can adjust it with the grip on makes me think it doesn't work the way I thought it did:)

>the slop is negligible.
I like 'snug'.  I know it's not supposed to affect accuracy, but I dont like 'play' in anything. Hell, I'm not even a great shot - I just dont like wobble, if I could avoid it by drilling an extra hole.

Offline Johnny_V

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Hell, I'm not even a great shot - I just dont like wobble, if I could avoid it by drilling an extra hole.

Too funny. I know what you're saying. I am constantly criticized by my eldest brother because I make things toooo tight.

On a serious note though, most of the slop can be eliminated by careful machining, especially in the pivot recess area. Excessive width in this area tends to magnify slop. Just my 2.....
Johnny_V
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CCW OH & PA

Offline BuhByeHarry

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Re: 'Tensioning bolt' that tightens up lowers and uppers? (wedge replacement?)
« Reply #5 on: November 06, 2014, 10:19:08 PM »
The question about the bore in the receiver curvature probably refers to the 2013 Civilian Marksmanship Program Rules for tightening AR15 Receivers...

A screw may be inserted in the back radius of the pistol grip where it
joins the lower receiver. This screw may extend into the rear lock-down
lug of the upper receiver for the purpose of securing the upper and lower
receivers. The screw head may not protrude above the original surface
of the receiver. Both ends of the original takedown pin must remain in
place so that the original outside configuration is not changed.

IMO..."The only thing that should wiggle on a semiautomatic rifle is the sling."