Barely touching just enough to lessen the wobble.
It's more important to be able to push the rear takedown pin out to its detent.
^ This - exactly.
Some degree of wobble between the upper and lower will not actually negatively impact your accuracy/precision, or the function of your rifle,
@bigdaddyz1776 . For an average shooter, using vetted-for-gun range-fodder ammo, it's really going to be the ammo and the shooter's skill that's going to be limiting factors. And in many cases, even if you've managed to make the upper wobble "less," dry, inserting a magazine can cause the wobble to come back (or like
@Recusant , a slightly wobbly upper/lower can tension-up to no wobble at all, when there's magazine tension
) - and even if you've got it perfect, over time, the wedge/tensioner material will compress or wear, and you'll see that wobble return yet again.
Both the late William Larson (
Iraqgunz on M4C.net, Semper Paratus Arms) as well as Chad Albrecht (SOTAR) absolutely despised the Accu-Wedge. The late and legendary Pat Rogers also had a picture of it in his "book-of-infamy," detailing an Ascu-Wedge induced failure that required separation of the upper/lower in order to make-function again.
I don't believe that Larsen really felt that strongly about tensioning screws - he only thought that they were extraneous and not needed.
Albrecht outright thinks they have no place on a serious gun, and recommends removing them.
IIRC, acceptable gap between upper and lower is 0.5 mm (20 thousandths of an inch), and a simple feeler gauge can be an asset, here. Gauging, you'll see just how huge of a wobble something that's just under the 20-thou mark can produce, it's literally cringy..... I'm pretty sure that on the SOTAR FB Group, there's video of a member's billet upper/lower combo from one company that was gauging 15- to 17-thou, and you'd swear it was listing-over like the Titanic......
Getting more technical, the by-Hoyle don't like them because the extra tension will -over time- eccentrically wear ("egg out") the rear takedown pin holes. This will actually then
worsen the wobble (rinse and repeat, yeah, not good, right?). And if tolerances are bad enough, carrier drag on the top of the lower extension (from the tensioning mechanism forcing the upper upwards) can also manifest as a concern.
More widely accepted fixes include shimming the front take-down pin, using oversized takedown pins (IIRC, JP and Griffin), or selecting an upper/lower pairing more carefully (hence a part of the reason why some folks pay for "matched" upper/lower sets - there's that video of a Hodge where a lights/laser/canned upper just sits there, without either front or rear pins in place
), or even looking for an upper with perhaps a bit thicker anodizing. Overall, unless the slop is *_really_* bad and the gap excessively wide, this is just something that bothers our OCD, and doesn't at all impact either accuracy/precision or function.
Many of you have seen this picture before. The upper/lower fit on this Frankengun (billet lightweight Battle Arms Development lower on a complete BCM upper -
https://www.thearmorylife.com/forum/threads/lets-see-your-ar-setups.258/page-2#post-3579 <---- I mistakenly wrote "forged" in that thread) is on the sloppy side - I've never gauged it, but it's definitely noticeable. The lower came with a tensioning screw, but I've never bothered with it....
I'm not the greatest shooter, and here, I'm using just 55 gr. range-fodder (I think it was either Wolf Gold or Indy, c.2014-'16). I can go all day on the torso at the 300 standing unsupported. Stabilized like this, the 6" plate is boring, too.
When I zero for class, at the 50, as long as I put in the work, a nice 5-leafed clover is not out of the ordinary, again with just trashy 55 gr. fodder.
Oh, and I've mortared this gun a few times, too, from induced stoppages in training classes. It has yet to snap in half, even though the fit is kinda sloppy.
