Looking for pic of CMP service rifle rule 6.2.3 example

DarthNul · March 28, 2015, 12:35 PM

I'm looking for pictures of an M-16/AR-15 service rifle showing the modification described below:

Quote:

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 pr
otrude above the original surface
of the receiver. Both ends of the orig
inal takedown pin must remain in
place so that the original outside
configuration is not changed.

I've found a lot of pics of a "tension screw" that pushes up on the take-down pin lug but I don't think that's the same thing.

JeepHammer · March 28, 2015, 07:32 PM

The idea is to make top and bottom solid and not rattle/move.

This is the idea behind the 'Accu-Wedge', the little rubber block dropped into the back of the receiver and the top end lug hits it to make the rifle more stable.

Now,
If you have an EARLY upper, the top end lug is usually longer.
The lug is EASY to drill out a little,
Press in a brass bushing, and cut/drill the bushing EXACTLY where it needs to be to make the break down pin an 'Interference Fit' which will make things a little more solid.

This takes SOME of the slop out,
But if the take down pin is sloppy in the lower receiver holes, you will still have that slop.
I've tried bushing the lower receiver the same way, and it's VERY hard to keep a bushing in the thin walls of the lower without a lip to hold it in place,
And as soon as they see the lip, you get disqualified.

-----

The problem I find with the screw from the bottom up to the lug is...
It pushes UP on the upper, creating a gap between top and bottom,
And it creates a 'Wobble' point, side to side.

The 'Best' situation is to find an upper and lower that take FORCE to get the pin in the hole.
Eventually, the hole in the upper will loosen up,
Just insert a bushing and it's tight again.

There is NOTHING in the rules that says the pin has to slide out with just finger pressure,
Carry a punch for tight fitting upper/lower that puts that pin in a bind,

KEEP THE PIN LUBRICATED, and chamfer the edge so it doesn't remove aluminum for the hole in the upper lug when it's tapped into place.

When the aluminum does scrape/hammer out in the upper lug hole, use a bushing in the hole and start again.

Remember, bushings in the aluminum upper lugs, both front and rear, are LEGAL.

For many years the M16s and AR15s had bushings in those holes, usually steel bushings.

That was dropped on the A3 versions, but there are PLENTY of SP1, AR15, M16, M16A1 and M16A2s out there with bushings in the front, rear, or both.

DarthNul · March 28, 2015, 11:46 PM

Thanks for the reply JeepHammer.

I've already got the rifle so handpicking uppers and lowers that are tighter is no longer an option.

I don't think the setup described in the rule is the same as the tension screw. I could be mistaken (which is why I'm looking for pics of this) but I think the rule describes a method for actually screwing the lower onto the upper at the rear.

The rule I quoted mentions that the screw head can't protrude so I'm assuming the screw head would be visible which would require this exception to the rule about modifications not altering the stock appearance of the rifle. The tension screw modification is covered up by the pistol grip so no special rule is needed.

JeepHammer · March 31, 2015, 07:46 AM

Screw from Lower to Upper,
Directly below upper lug,
would require you to drill through take down pin hole.

Same for upper to lower.

This would have to be an an angle, or directly from rear, from where the stock mounts.

I've not shot service rifle in a LONG time,
When I did, they eyeballed my 'Long Lugs',
Tig welding aluminum on the end of the upper lug,
Then working it down to match the lower PRECISELY, with a little interference fit.

Other than having to use a punch to drive the take down pin out, that didn't interfere with the 'Original' function.

----

By chucking up a bushing in a lathe, you can oversize the lug hole a hair,
Then turn bar stock down to press fit in the take down pin hole.

Drill the center of your bushing a little offset to centerline.

Install the 'Thick' side of your bushing DOWN.
This will give the take down pin something to bite on.

By making the lug a little longer, so it makes solid contact with the trigger group well in the lower,
Your upper and lower are solid,
Then work your bushing so the take down pin fits with interference.

This will SOLIDLY mate the upper and lower.
The only side effect is the pin has to be driven, it's no longer a loose, rattling 'Slip Fit'.

Another tip was to drill/thread a small hole in the bottom of the lug,
CAREFULLY pour a small amount of lead into that hole, just until the lead domes up over your hole a little.

With some 'Tapping' on the lead with a hammer,
Then when you get close, tap on the upper,
The lead will make for a PRECISE fit from upper to lower.

When it's painted black, no one notices.
It's a separate-able 'Bedding' between upper lug and lower.

Again, there is no obvious changes in parts or function.

-----

As for screwing top and bottom together,
I wasn't aware of it in my day...
Offset pins, bushings, painting over bedding, all kinds of stuff went on, but not attaching top and bottom receivers.

Everyone *Thought* they had some 'Secret' way to make the rifle more accurate/consistent, some of it worked,
Some of it didn't...

I see if one of the knuckle heads I know still shooting know about this screw you are talking about, if they haven't all retired...

jcj54 · March 31, 2015, 02:27 PM

http://aeroprecisionusa.com/userdocs/product/APAR501101-ar15-stripped-lower-gen2-anodized-4.jpg

March 28, 2015, 11:46 PM	#3
DarthNul Senior Member Join Date: December 21, 2010 Location: Minnesota Posts: 288	Thanks for the reply JeepHammer. I've already got the rifle so handpicking uppers and lowers that are tighter is no longer an option. I don't think the setup described in the rule is the same as the tension screw. I could be mistaken (which is why I'm looking for pics of this) but I think the rule describes a method for actually screwing the lower onto the upper at the rear. The rule I quoted mentions that the screw head can't protrude so I'm assuming the screw head would be visible which would require this exception to the rule about modifications not altering the stock appearance of the rifle. The tension screw modification is covered up by the pistol grip so no special rule is needed. __________________ The most feared gun control law proposal: Require buyers to register all gun purchases with their wives

March 31, 2015, 02:27 PM	#5
jcj54 Senior Member Join Date: February 28, 2011 Posts: 218	This: http://aeroprecisionusa.com/userdocs/product/APAR501101-ar15-stripped-lower-gen2-anodized-4.jpg

March 28, 2015, 07:32 PM	#2
JeepHammer Junior member Join Date: February 27, 2015 Posts: 1,768	The idea is to make top and bottom solid and not rattle/move. This is the idea behind the 'Accu-Wedge', the little rubber block dropped into the back of the receiver and the top end lug hits it to make the rifle more stable. Now, If you have an EARLY upper, the top end lug is usually longer. The lug is EASY to drill out a little, Press in a brass bushing, and cut/drill the bushing EXACTLY where it needs to be to make the break down pin an 'Interference Fit' which will make things a little more solid. This takes SOME of the slop out, But if the take down pin is sloppy in the lower receiver holes, you will still have that slop. I've tried bushing the lower receiver the same way, and it's VERY hard to keep a bushing in the thin walls of the lower without a lip to hold it in place, And as soon as they see the lip, you get disqualified. ----- The problem I find with the screw from the bottom up to the lug is... It pushes UP on the upper, creating a gap between top and bottom, And it creates a 'Wobble' point, side to side. The 'Best' situation is to find an upper and lower that take FORCE to get the pin in the hole. Eventually, the hole in the upper will loosen up, Just insert a bushing and it's tight again. There is NOTHING in the rules that says the pin has to slide out with just finger pressure, Carry a punch for tight fitting upper/lower that puts that pin in a bind, KEEP THE PIN LUBRICATED, and chamfer the edge so it doesn't remove aluminum for the hole in the upper lug when it's tapped into place. When the aluminum does scrape/hammer out in the upper lug hole, use a bushing in the hole and start again. Remember, bushings in the aluminum upper lugs, both front and rear, are LEGAL. For many years the M16s and AR15s had bushings in those holes, usually steel bushings. That was dropped on the A3 versions, but there are PLENTY of SP1, AR15, M16, M16A1 and M16A2s out there with bushings in the front, rear, or both.

March 31, 2015, 07:46 AM	#4
JeepHammer Junior member Join Date: February 27, 2015 Posts: 1,768	Screw from Lower to Upper, Directly below upper lug, would require you to drill through take down pin hole. Same for upper to lower. This would have to be an an angle, or directly from rear, from where the stock mounts. I've not shot service rifle in a LONG time, When I did, they eyeballed my 'Long Lugs', Tig welding aluminum on the end of the upper lug, Then working it down to match the lower PRECISELY, with a little interference fit. Other than having to use a punch to drive the take down pin out, that didn't interfere with the 'Original' function. ---- By chucking up a bushing in a lathe, you can oversize the lug hole a hair, Then turn bar stock down to press fit in the take down pin hole. Drill the center of your bushing a little offset to centerline. Install the 'Thick' side of your bushing DOWN. This will give the take down pin something to bite on. By making the lug a little longer, so it makes solid contact with the trigger group well in the lower, Your upper and lower are solid, Then work your bushing so the take down pin fits with interference. This will SOLIDLY mate the upper and lower. The only side effect is the pin has to be driven, it's no longer a loose, rattling 'Slip Fit'. Another tip was to drill/thread a small hole in the bottom of the lug, CAREFULLY pour a small amount of lead into that hole, just until the lead domes up over your hole a little. With some 'Tapping' on the lead with a hammer, Then when you get close, tap on the upper, The lead will make for a PRECISE fit from upper to lower. When it's painted black, no one notices. It's a separate-able 'Bedding' between upper lug and lower. Again, there is no obvious changes in parts or function. ----- As for screwing top and bottom together, I wasn't aware of it in my day... Offset pins, bushings, painting over bedding, all kinds of stuff went on, but not attaching top and bottom receivers. Everyone Thought they had some 'Secret' way to make the rifle more accurate/consistent, some of it worked, Some of it didn't... I see if one of the knuckle heads I know still shooting know about this screw you are talking about, if they haven't all retired...