Adding a tensioning screw to an AR lower

[clm2112]

Another quicky project. The latest 80% lower I got from Tactical Machining had a extra hole already under the rear cross-pin. This is to take the slop out of so-so fitting uppers by pushing up on the rear take-down pin lug.

While I've never considered this a problem (the rattle is just something you get used to) I figure I'd try making the same setup on another lower.

Not too hard to do. Used a 1/4" end mill to create a pocket in the receiver. Put it on the center-line (you can use the regular grip screw hole as a guide.) and position it on the rear take-down pin holes in the lower. Then drill it 7/32nd and tap 1/4-28 tpi. The "pin" that will tighten up the upper/lower fit is just a 1/4-28 x 1/2" long steel setscrew. Drop of blue loc-tite after paring the lower with the upper.

 

[Racer7696]

Works well. If you google ar15 trigger shims, there is a company that makes shims . One of there products is a small triangle piece that fits in reciever and puts pressure on the takedown pin. People that do the shims and triangle piece say it's amazing how there groups shrink .

 

[Racer7696]

Works well. If you google ar15 trigger shims, there is a company that makes shims . One of there products is a small triangle piece that fits in reciever and puts pressure on the takedown pin. People that do the shims and triangle piece say it's amazing how there groups shrink .

Triggershims.com is the conpany

 

[Mooner]

I think I first saw this from toolboxe's channel. Same concept just much cheaper.

Leapers UTG AR-15 Accurizing Wedge

The UTG AR-15 accurizing wedge will improve upper and lower fit, and improve accuracy. The wedge is placed in the lower receiver beneath the rear...

www.midwayusa.com

 

[NavyVet83]

I think I first saw this from toolboxe's channel. Same concept just much cheaper.

Leapers UTG AR-15 Accurizing Wedge

The UTG AR-15 accurizing wedge will improve upper and lower fit, and improve accuracy. The wedge is placed in the lower receiver beneath the rear...

www.midwayusa.com

All of my AR's have these. I consider them a standard part when I'm assembling

 

[bapegg]

I have use the cheap Leapers wedges in a couple of my AR's. But to be honest, they don't make a difference what so ever when it comes to accuracy. My precision setups in 22LR, 223 Wylde, and 6 ARC do not have wedges or tension screws. And I can shoot 3/4" groups at 100 yards with the 223 and 6 ARC all day long and 3/4' or smaller groups at 50 yards with the 22LR.

That being said, I can see using a tension screw or wedge if the upper receiver to lower receiver is a really sloppy fit.

 

[clm2112]

I have use the cheap Leapers wedges in a couple of my AR's. But to be honest, they don't make a difference what so ever when it comes to accuracy. My precision setups in 22LR, 223 Wylde, and 6 ARC do not have wedges or tension screws. And I can shoot 3/4" groups at 100 yards with the 223 and 6 ARC all day long and 3/4' or smaller groups at 50 yards with the 22LR.

That being said, I can see using a tension screw or wedge if the upper receiver to lower receiver is a really sloppy fit.

I'm glad you said it... I was reluctant to point it out so as not to offend, but you are right on the mark. The fit of the upper and lower have absolutely no effect on how accurately the rifle can shoot. All of the mechanical accuracy the rifle will ever have is encapsulated in the upper receiver. And the aiming system is also bolted onto the upper... the lower is just along for the ride.

It does however effect the confidence the shooter has in his or her rifle. The loose fit can be distracting, and the person doesn't shoot their best because they are worrying over the rattle. So yeah, it is worth doing in that respect.

 

[Bongo Lewi]

Another quicky project. The latest 80% lower I got from Tactical Machining had a extra hole already under the rear cross-pin. This is to take the slop out of so-so fitting uppers by pushing up on the rear take-down pin lug.

While I've never considered this a problem (the rattle is just something you get used to) I figure I'd try making the same setup on another lower.

Not too hard to do. Used a 1/4" end mill to create a pocket in the receiver. Put it on the center-line (you can use the regular grip screw hole as a guide.) and position it on the rear take-down pin holes in the lower. Then drill it 7/32nd and tap 1/4-28 tpi. The "pin" that will tighten up the upper/lower fit is just a 1/4-28 x 1/2" long steel setscrew. Drop of blue loc-tite after paring the lower with the upper.

Best AR tip ever.

 

[bapegg]

I'm glad you said it... I was reluctant to point it out so as not to offend, but you are right on the mark. The fit of the upper and lower have absolutely no effect on how accurately the rifle can shoot. All of the mechanical accuracy the rifle will ever have is encapsulated in the upper receiver. And the aiming system is also bolted onto the upper... the lower is just along for the ride.

It does however effect the confidence the shooter has in his or her rifle. The loose fit can be distracting, and the person doesn't shoot their best because they are worrying over the rattle. So yeah, it is worth doing in that respect.

Using a wedge or tension screw is a placebo at best. And I have seen them actually cause damage when the upper and lower are extremely loose.

A wedge or tension screw can push the upper receiver up enough that the bolt can start rubbing/ binding on the buffer tube. Granted the loose fit between the upper and lower would have to be on the extreme side for this to happen.

But if someone wants to use a wedge or tension screw (if receiver is already drilled and tapped) then go ahead and do so. Both are cheap enough that a person won't be out but a few dollars if neither works to their expectations.

 

[Bongo Lewi]

I haven't found accuracy to be a factor, but the rattle always bugged me. Some are worse than others as noted.

I built two AR carbines and one pistol from 80% lowers and called it a day. Interesting and fun, but not worth it to me. I never really bothered to accurize those ARs, other than using upgrade triggers and good quality barrels. The hobby-grade mill I have did an awesome job. Two of the three guns, I bought the upper and 80% lower together. For the first, everything a-la-carte. Not surprisingly, that gun rattles more.

Even solidly reliable, non-premium factory-made guns like Rock River claim sub-MOA accuracy out of the box. Using premium ammo... good 'nuff for me in the AR realm. My long-range precision interests pivot around bolt guns. I generally stick with 308 and 6.5 Creedmoor. I can reliably ring steel at 600-800 yards with those guns and decent midrange-priced optics. Some higher-end ARs of the right caliber could probably do that, but for civilian use, a semi-auto makes no sense to me for anything beyond 300 yards.

When I was more active competing in 3 gun, I owned but later traded a Lone Star Armory AR. Not cheap. I'd describe it as semi-custom. At 100 yards, it could deliver half-inch groups out of the box in .223/5.56. Surprisingly light too. No rattle! Wish I had kept it.

 

[Racer88]

I have only one AR-15, which a friend built for me several years ago. It is an "accurized" AR.

I have since changed the grip and the trigger (now Geissele National Match).

It has the AR-15 "wobble" between the upper and lower. Not bad, but it's there. I tried to install one of those "accu-wedges" but it would not fit. I forget why... maybe something to do with the Magpul stock. In any event... I couldn't use it.

Nevertheless...

600 yards:​

100 yards:​

(Federal Gold Medal Match factory ammo)​

^^^Damn that "flyer!"^^^

My daughter (at age 15) did this at 200 yards with the AR:​

(Also FGMM factory ammo)​

 

[Dbliz]

I'm glad you said it... I was reluctant to point it out so as not to offend, but you are right on the mark. The fit of the upper and lower have absolutely no effect on how accurately the rifle can shoot. All of the mechanical accuracy the rifle will ever have is encapsulated in the upper receiver. And the aiming system is also bolted onto the upper... the lower is just along for the ride.

It does however effect the confidence the shooter has in his or her rifle. The loose fit can be distracting, and the person doesn't shoot their best because they are worrying over the rattle. So yeah, it is worth doing in that respect.

Hmmmm...If this is true, did I waste my time pillar bedding my non-AR stocks?

 

[Racer88]

Hmmmm...If this is true, did I waste my time pillar bedding my non-AR stocks?

Naaaa... working on guns is never a waste of time!

Thanks for joining the forum and participating by posting! When you get a chance, please write up a quick “introduction” (or RE-introduction if you were a former MGB forum member) of yourself over in the Introduce Yourself! section. Tell us about yourself, your building experience, and how you found the forum.

Jump into other threads, too! Come on in... the water's fine!

 

[Bongo Lewi]

I'd suggest no effort to accurize is worthless. The question is how much did it help. Once you add a good barrel, trigger and optics, further tweaks help but their effect is small.

It's kind of like handloads vs. high quality match grade ammo. Today, the difference isnt what it used to be. I placed and won matches with match quality factory ammo and bolt gun that was pretty much bone stock except for the trigger and optic. Once you get to a certain level of quality/precision I'm convinced it's more about the Indian than the the arrow.

 

[CECannonJr]

Another good tip I picked up on for an AR-15. I thought I would share it with you guys.

If you change components like I sometimes do, you'll discover that the takedown pin spring behind the back plate can be a PITA when changing a buffer tube. The back plate compresses the spring and holds it in place. For changing out buffer tubes without having to deal with this spring, you can trim about 3 or 4 coils off the spring and tap the 1/16 hole it fits in with a 4-40 tap just deep enough to put a 1/16 set screw in the hole with a little blue Loctite.

After that, you can change out the buffer tube with no trouble from that spring. Some may find this helpful.

 

[Dbliz]

Another quicky project. The latest 80% lower I got from Tactical Machining had a extra hole already under the rear cross-pin. This is to take the slop out of so-so fitting uppers by pushing up on the rear take-down pin lug.

While I've never considered this a problem (the rattle is just something you get used to) I figure I'd try making the same setup on another lower.

Not too hard to do. Used a 1/4" end mill to create a pocket in the receiver. Put it on the center-line (you can use the regular grip screw hole as a guide.) and position it on the rear take-down pin holes in the lower. Then drill it 7/32nd and tap 1/4-28 tpi. The "pin" that will tighten up the upper/lower fit is just a 1/4-28 x 1/2" long steel setscrew. Drop of blue loc-tite after paring the lower with the upper.

View attachment 12938
View attachment 12939
View attachment 12940
View attachment 12941
View attachment 12942

Since I don't have a mill what are your thoughts on drilling from the top with a drill Press?

Another quicky project. The latest 80% lower I got from Tactical Machining had a extra hole already under the rear cross-pin. This is to take the slop out of so-so fitting uppers by pushing up on the rear take-down pin lug.

While I've never considered this a problem (the rattle is just something you get used to) I figure I'd try making the same setup on another lower.

Not too hard to do. Used a 1/4" end mill to create a pocket in the receiver. Put it on the center-line (you can use the regular grip screw hole as a guide.) and position it on the rear take-down pin holes in the lower. Then drill it 7/32nd and tap 1/4-28 tpi. The "pin" that will tighten up the upper/lower fit is just a 1/4-28 x 1/2" long steel setscrew. Drop of blue loc-tite after paring the lower with the upper.

View attachment 12938
View attachment 12939
View attachment 12940
View attachment 12941
View attachment 12942

Since I don't have a mill what are your thoughts on drilling from the top with a drill press? Hopefully to keep the hole from drifting?

 

[Bobster]

Since I don't have a mill what are your thoughts on drilling from the top with a drill press? Hopefully to keep the hole from drifting?

These are my general recommendations--all scenarios will have their specifics.
I think measuring and setup BEFORE you even drill is very important. A good jig and vise to clamp the piece in place and square (perpendicular) to the drill bit.
Center punch precisely with a sharp punch--I have different punches I use for alum or steel. The alum punch is more pointy, steel more blunt.
Start with a pilot (small) drill bit and work your up--if the pilot is centered, the following holes should also be centered. Use sharp, quality drill bits which are less likely to "walk". The bit in the chuck should spin without wobbling--cheap bits will have visible wobble.
Do not drill deeper than you have to--it is better to drill shallow and have to drill a little deeper--once the metal is gone, it is hard to put back.

 

[One Ping Only]

Hmmmm...If this is true, did I waste my time pillar bedding my non-AR stocks?

I'd agree with BL's reply...and one of the most important concerns regarding a stock for a bolt-action is to make sure the barrel is free-floating from the end of barrel to the rcvr.

 

[Bongo Lewi]

I got a lot of disapproving looks from old school benchrest shooters with my factory gun. Understandable. Some of those guys spent 20 grand on custom stocks, gyro treated barrels, triggers, and so on. When a guy with a $2000 rifle shoots as well as someone who spent ten times that, some tend to declare you a heretic. It's pretty common for people who have been doing something a certain way for a long time to get stuck in the mud and refuse to accept things have changed or the technology has gotten better.

It's important for me to mention that some of the traditional long distance shooters were generous in sharing tips and tricks. How to use a spotting scope effectively, reading the wind, and understanding the mirage effect on your sighting, scopes, and other things. People are funny. Some encourage you to be the best you can and others are afraid you might be better than them with your cheap gun and factory ammo. All competitive sports have those personas.

 

[Racer88]

I got a lot of disapproving looks from old school benchrest shooters with my factory gun. Understandable. Some of those guys spent 20 grand on custom stocks, gyro treated barrels, triggers, and so on. When a guy with a $2000 rifle shoots as well as someone who spent ten times that, some tend to declare you a heretic.

^^ For sure! ^^

They spent more on their front bipod than I did my whole rig! No kidding.

And they are all measuring their home brew cartridges and adjusting the "COAL" (cartridge overall length) right there on the shooting line. I'm just shooting factory "match" ammo.

It's important for me to mention that some of the traditional long distance shooters were generous in sharing tips and tricks.

I did not find that to be the case. They were assholes for the most part. At my first match, I asked the old fart they "squaded" me with a simple newbie question. He said, and I quote, "That's for you to figure out. You're on your own."

I went back a few times, and it was no better... worse, in some cases. Once with my daughter... that was the worst experience of all. So, I'm done with that shit.

And THAT'S why I won't get involved in competitive shooting of ANY kind. Fuck them all. Insecure assholes. I don't need to play gun games. I'll just do my own thing at the open range.