cramer@uunet.UU.NET (Clayton Cramer) (01/25/91)
From: optilink!cramer@uunet.UU.NET (Clayton Cramer)
A little background, first. The original .223 ammunition for the AR-15 and
similar battle rifles was 55 gr. FMJ, designed for 1:12 twist barrels. To
improve accuracy and penetration, a new round called the SS109 was developed,
which uses a 63 gr. bullet, and designed for 1:7 twist barrels. This is the
barrel and round for the M16A2.
How much better is the SS109 at accuracy? They are enough more expensive
than the commercial 55 gr. ammo that I need some evidence to justify spending
the extra money. Unfortunately, a 4x scope wasn't enough to provide clear
evidence of the relative merits of the two weights of bullet.
Now I have some data to share with the rest of you. The test gun was an
Eagle Arms EA-15 HBAR; the scope was a 4x-12x Bushnell. The ammunition
used was PMC 55 gr. FMJ and SS109 ammunition made in Canada. Target
distance was 100 yards.
Wind was highly variable, between 5 and about 35 mph at the time of
testing, which created a series problem of reproducibility, for which
I have developed an ingenious, but perhaps not completely valid
control. In the following test results, I have shown both the
vertical spread and horizontal spread for each target.
The vertical spreads are remarkably consistent, and the horizontal
spreads vary in ways that would be consistent with
the variable wind conditions. Therefore, I think you can sort of
approximate still wind conditions with the vertical spread numbers;
in addition, these numbers are not far from those achieved by other
tests of Eagle Arms EA-15 HBAR rifles, so I can have some confidence
in these numbers.
Called flyers were discarded from measurements, as well as all of
target #6, because I was attempting to compensate for the wind so as
to put all the holes in the black part of the target, with predictable
non-reproducibility. Target #2 is interesting because in addition
to the vertical group being very tight, the horizontal group was
very tight also -- center-to-center distance for the three shot
group was .45". This was my first group with the SS109, and I may have
been fortunate to have hit these shots during a constant wind period.
For the PMC ammo:
target vertical horiz.
nbr group group
1 0.85 2.25
3 0.92 2.05
5 0.45 2.05
7 0.90 3.90
avg 0.78 2.56
For the SS109 ammo:
target vertical horiz.
nbr group group
2 0.40 0.25
4 0.50 3.00
8a 0.55 1.65
8b 0.60 3.10
avg 0.51 2.00
As you can see, the average for the SS109 ammo was significantly
better than the PMC 55 gr. ammo. Further, it would appear that
the SS109 is better able to resist wind problems. On the down
side, I had one jam with the SS109, and have had jams with it
before -- unlike the PMC ammo. (The SS109 is rumored to be
surplus because of overpressure and out of spec problems).
--
Clayton E. Cramer {pyramid,pixar,tekbspa}!optilink!cramer
Motto for San Francisco's "peace" activists: Think globally, fight locally.
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You must be kidding! No company would hold opinions like mine!