Like the title says... and if there is another test, please help guide me to it.

Seriously... I figured the often quoted test, when discussing upper to lower slop, would have considerably tighter test parameters and or results.... Honestly, I am kind of let down.

The test concerns Combat AR's ... not precision AR builds. Not surprising considering the Vietnam War going on and the limited use of AR15's in civilian hands.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwjl2MyEgbHkAhUxCjQIHWVrDjsQFjAAegQIABAC&url=https%3A%2F%2Fapps.dtic.mil%2Fdtic%2Ftr%2Ffulltext%2Fu2%2F772939.pdf&usg=AOvVaw1mmuiZMZ9wqPkdWK-6JKNd

Because if it is the correct test... 2.2"s is a lot of room for improvement in a precision minded AR... heck in my opinion, the whole scope of that portion of the test parameters is seriously out-dated. ( 1973 Combat AR's ) ... and has , respectfully, little meaningful input for modern precision minded AR's.

It is hardly a "beat all" test showing a loose fitting of an upper to lower has no effect on accuracy... unless you are Ok with 2.2"s test parameter's.

" "Looseness between the upper and lower receivers should be considered to have a significant effect on accuracy if such looseness causes a change in extreme spread of more than 2.2 inches at 100 yards."

"The 2.2 inches criteria was chosen because new rifle acceptance criteria is 4.8 inches extreme spread at 100 yards and the user rejection criteria is 7.0 inches extreme spread at 100 yards. It is felt that any single parameter which could degrade the weapon from new-weapon-status to unfit-for-use is significant."

So their parameters were concerned with "Combat Accuracy", IMHO.... and pretty loose at that.

I wish the handguards had not been included , or tested separately.

We all know how much traditional handguards can affect AR precision, that is why we "free float" the barrel with modern tubes.


Text from the test..


2.2 EFFECT OF LOOSENESS BETWEEN UPPER AND LOWER RECEIVERS ON ACCURACY

2.2.1 Objective
The objective was to determine the effect of looseness between upper and lower receivers on the accuracy of M16A1 Rifles.

2.2.2 Criteria
Looseness between the upper and lower receivers should be considered to have a significant effect on accuracy if such looseness causes a change in extreme spread of more than 2.2 inches at 100 yards. The reasoning applied in Section 2.1.2 was also applied here.

2.2.3 Method
Ten M16A1 Rifles returned from combat in Viet Nam were measured for looseness between the upper and lower receivers. The three weapons exhibiting the most looseness were rebarreled and fired in this subtest.
First, each of the three test rifles was fired two ten-shot
targets by each of two shooters under each of the following conditions:

CONDITION DESCRIPTION
A The original looseness was left in the handguards and between the receivers. Firing was done from a benchrest. The handguards and upper receiver were rotated to opposite extreme positions for alternate shots.

B Same as "A" except that the handguards and upper receiver were allowed to seek their own positions.

C Same as "A" except that firing was done from the prone position.

D Same as "A" except that the handguards and upper receiver were allowed to seek their own positions, and firing was done from the prone position.

E The original looseness was left in the handguards. The looseness was removed from the receivers by inserting shims between them. Firing was done from a benchrest. The handguards were allowed to seek their own positions.

F Same as "E" except that firing was done from the prone position.

Page 6

Then, each of the three test weapons fired was fired two ten-shot targets by one shooter under each of the following conditions:

CONDITION ...............DESCRIPTION

CONDITION DESCRIPTION
A The original looseness was left in the handguards and between the receivers. Firing was done from a benchrest. The handguards and upper receiver were rotated to opposite extreme positions for alternate shots.

B Same as "A" except that the handguards and upper receiver were allowed to seek their own positions.

C Same as "A" except that firing was done from the prone position.

D Same as "A" except that the handguards and upper receiver were allowed to seek their own positions, and firing was done from the prone position.

E The original looseness was left in the handguards. The looseness was removed from the receivers by inserting shims between them. Firing was done from a benchrest. The handguards were allowed to seek their own positions.

F Same as "E" except that firing was done from the prone position.

Page 6

G All looseness was removed from both the handguards and the upper receiver. Firing was done from a benchrest.

H All looseness was removed from the handguards. The original looseness was left between the upper and lower receivers. The upper receiver was rotated to opposite extreme positions for alternate shots. Firing was done from a benchrest.

2.2.4 Results
The average extreme spread for all weapons and shooters is recorded by condition in Table 2.2-1. In addition, Table 2.2-1 also notes the difference in extreme spread between condition "A" and each of the other conditions. Since condition "A" exhibits maximum looseness and succeeding conditions have leqs looseness, any trend toward increased accuracy as the looseness is removed, should be reflected in consistently negative numbers in the AES column.
Only one condition differed significantly in extreme spread from condition "A". Condition "H" averaged 2.5 inches larger than condition "A". No cause for this unexpected increase in extreme spread could be found during the test. However, it was noted that the increase was due almost entirely to vertical stringing of the shots. It is hypothesized that perhaps the manner in which the handguards were epoxied to the barrel nuts was responsible.

2.2.5 Analysis
No detrimental effects on accuracy due to loose upper receivers and/or loose handguards were discernible in this test.

Page 7

TABLE 2. 2-1

EFFECT OF LOOSE HANDGUARDS & LOOSENESS BETWEEN UPPER & LOWER RECEIVERS ON ACCURACY

AVERAGE FOR ALL WEAPONS AND SHOOTERS.........

CONDITIONS..........A.....B......C.......D......E. ......F........G.......H....
.
Extreme Spread.....4.5...3.9....4.7....4.5....3.7....3.9.. ..5.8 ?...7.0

Chanage in
Extreme Spread.....0...-0.6 ?..+0.2...0.....-0.3....0.?...+?.3....+2.5



1, All extreme spreads are for ten-shot targets fired at a range of ?00 yards

"End quote."



Sorry about the ? marks... the text was illegible.

As long as they’re connected...

Completely agree with you about Consistent hold on a AR to repeatable groups... I just prefer to do that via good snug fit on my precision builds.

The more SD oriented AR's I don't worry about.

And the limited amount of AR's used in the test ( and the loose criteria ) is what bothered me about this very often quoted USGI test, is  that it shows "no effect" from the loose fitment... well heck yeah it shows no effect... if your parameters are so large.

And Just to clarify here is the conflicting comments... 3 of the 99 choosen fielded AR's were used for the loose sight test ... 6 of the 99 were used in the snug fit portion. I would "assume" the rifles choosen were worse case firearms.

I can't tell for sure how many of the 99 choosen AR's were used...

SECTION 1: SUMMARY1.1 BACKGROUND

In September 1970, USAWECOM sent LTC Eugene West and Mr. Lawrence Moore to Viet Nam to assess the accuracy and physical condition of Ml6Al Rifles being used in Southeast Asia. Upon their return, they reported several conditions which might be deleterious to accuracy.Their observations guided the direction and depth of this study.

1.2 TEST OBJECTIVES...The objective of this test program was to define which, if any,of several factors that might limit the M16A]'s accuracy potential,actually do significantly affect accuracy. More specifically, the following six parameters were evaluated to determine their effects on M16AI Rifle accuracy:

A. Loose sights

B. Looseness between upper and lower receivers

C. Loose handguards

D. Lubricant, corrosion, and heat in the bore

E. Mixing of ball and tracer rounds

F. Type of rest1.3

"DESCRIPTION OF MATERIEL"

Ninety-nine used Ml6Al Rifles were obtained from Viet Nam. Of these, ten were picked which best exemplified looseness in the hand-guards, receiver, and/or sights. These ten were inspected to quantitatively determine the looseness present. Nine of  the ten were then used in the test; three were used for an analytical determination of the effect of loose sights while the other six were rebarreled and fired in the studies of loose handguards and looseness between upper and lower receivers. In addition, seven new Ml6AI's and two MI6Al's which had previously been been fired in 6,000 round contractor endurance tests were fired during the test.

I would love to see a modern version test. And I believe the results would show upper to lower fit matters... especially if the Mil "definition" of "acceptable" accuracy was updated.

Lol... hardly anyone would consider the Mil. definition acceptable now a days in a civilian owned AR. I understand it was "acceptable" during that era, and with widely issue common weapons... but technology march's on.

I have had great results with snug fitting uppers and lowers. I prefer a solid fit...for me, It makes it easier to wield the AR for more consistent precision testing.