Clint Dahlstrom
The availability of target grade 90 grain 223 bullets (Sierra,
Berger and JLK) has raised the question of whether the
D.C.R.A. ought to amend its "80g bullets for the 223" rule. Jim
Thompson has asked our members to share their knowledge,
experience and opinions. Since Arizona winter weather allows
shooting, we have been asked to do some preliminary testing.
Unfortunately this has been more difficult and much slower than
one would expect. The 90g 223 bullet requires an unusually fast
twist barrel (1 in. 6 ½ or maybe 1 in. 7) which are both special
order items from our barrel makers. I was surprised and perturbed
when my normal supplier awarded me a three month wait.
Fortunately a friend provided a used barrel which I installed on a
Remington 700. Unfortunately there was another delay when an
automobile accident broke the stock off just behind the trigger
guard. However epoxy and haste seem to have worked. Our
normal range schedule allows one long range shoot per week so
we have managed some preliminary testing but not enough, fast
enough, to develop extensive recommendations for the February
Canadian Marksman deadline. You will have our current opinion
but I can't guarantee its lifespan.
Ordinarily, in writing for the Canadian Marksman, I have had
something to say which I thought was dependable and which
would stand on its own. This is different. This is a project which
is not going to be resolved by one simple data set - no matter how
impressed I may be by the result. I have started some initial grunt
work but the D.C.R.A. may require a lot of measured long range
groups to justify a decision. I know Canadian weather isn't
currently suitable for long range group shooting but if you decide
to start now you may have your barrel and chamber in time for
spring. Help?!?!?
308 VERSUS 223 Most Canadian shooters think that the
308 is superior to the 223, particularly (and some say only)
beyond 600 yards. The origin and the justification for this
opinion are complicated by our long standing rule of the past
which required those with Bisley aspirations to shoot 308.
Another current opinion maker is the ± $400 barrel changing
expense.One of the things we need to do, at the outset, is to settle
the argument on this critical element - "Is the 308 enough better
than the 223 to justify a rule change?" Then, if it is, the next
question is whether the 90g bullets will allow the 223 to equal the
308 performance. My personal opinion is simple - the 223 is not
quite as good as the 308 up to 600 yards and beyond that it is not
nearly as good. That is one person's opinion based on the rifles he
has owned and used. We now have to determine whether this
opinion is valid.
The ballistic tables in the Sierra 50th Anniversary Edition of their
reloading manual spell out some aspects of the question very
clearly. Ballistically up to 600 yards the 308 has little advantage
over the 80g 223 but at 1000 yards it is about 10% more effective
(Fig.1). However I have included some data for various velocities
with the modern 90g bullet (from the Sierra information office)
which suggest that it has the potential to be 308 equivalent if we
find a good hand load for the bullet.
So far I am quoting ballistic tables which are mathematical statements
of corporate aspiration and expectation. Unfortunately
these tables don't speak to group size which, for target shooters, is
the critical element. In the years since Messrs Chase and Bullock
taught me to use the Plotomatic I have kept track of the vertical
dispersion of sighters, of the whole vertical group and of the
group less one or two flyers (if present). The purpose was to
evaluate how well the combination of rifles and hand loads were
performing. Some of the shooting was coached team or rapid fire
or bad weather or some other excuse for not doing the book work,
but about 2/3 of the shots were measured and recorded. I have
retrieved the iron sight data on 4 single shot target rifles - 3 in 308
caliber and 1 in 223. The 308s fired a total of 9794 shots and the
223s fired 3300. The vertical dispersion of the scoring groups
(excluding sighters) was the critical element being retained. The
horizontal dispersion was only a measure of the wind behavior
and my judgment that day.Up to 600 yards the 308s had a vertical
dispersion of about 1 ¾ minutes which increased over the longer
ranges to about 2 ½ minutes at 1000 yards. The 223 starts at about
2 minutes of vertical dispersion at 300 yards, and gradually
increases to nearly 3 minutes at 1000 yards (Fig. 2). The numbers
being quoted are averages of ten to thirty groups at each range -
they may not be good enough to brag about but they are what
happened.
Clearly, in these examples, the 80g Sierra bullets did not shoot as
well as the 155g Sierras at long range. Therefore I consider it
worthwhile to investigate the 90g 223 bullets.
Preliminary 90g Bullet Testing
Under existent circumstances it would normally have been impossible
to provide the D.C.R.A. with significantly useful data on the
90g bullets in the 223 by Feb. 1. However this time the fates were
abnormally kind. The friend who provided me with a 6 ½ twist
223 barrel was German Salizar (pronounced Herman) who is an
outstanding competitive marksman and an enthusiastic devotee of
the art of making good target rifles shoot better. He is particularly
interested in 300 meter competition and has evaluated a number
of small bore rifles and cartridges in his quest for X's by the
bushel. In his ± 1300 shot 90g 223 test he concluded that 26.2
grains of N550 with the JLK bullet was an optimal load which
was effective at both I.S.S.F. and long ranges. Unfortunately
Salizar's study was not available for publication so we decided to
do an independent parallel study to provide data for the D.C.R.A.
to consider.
The Ben Avery range where we do our testing allows at least one
half day of long range shooting each week. The shooting may be
at 600, 1000 or the three Palma yardages and it may be practice or
competition. Consequently test groups may have 10, 15 or 20
rounds. I used a telescope (10x at 600 and 800 yards and 24x at
900 and 1000) shooting prone over a small metal bench rest. This
isn't very fancy but it's portable and better than my performance
with a sling. I fire a few sighters to get the elevation right and to
judge the wind. When I start for record I do not adjust the sights.
I keep the same elevation hold for each shot but I do hold off
The Canadian Marksman, Winter/Spring 2008 17
laterally to compensate for wind. I plot the impact of each shot
on a bull's eye diagram (which is not moved Plotomatic fashion).
The vertical dispersion on the plot is what I measure and record.
The horizontal dispersion is Mother Nature's sneering appraisal of
my wind judgment which I ignore.
Measurement of groups fired at 600, 800, 900 and 1000 yards is
provided in Figures 3, 4, 5 and 6. In evaluating these diagrams
one should bear in mind that most of the groups for the 80g 223
and for the 308 were 10 shot groups while most of the groups for
the 90g 223 were 15 or 20 shots. The generality presented in the
summary diagram (Fig. 7) is that the 90g 223 is better at long
range than the 80g 223 and about equal to the 155g 308.
The debatable point in that generality is the 90g 223 1000 yard
group average which is about the same as the 80g 223 average and
substantially more than the 155g 308 average. Ordinarily the rate
of group size increase between 900 and 1000 yards is similar to
that shown by the 80g 223 and the 155g 308. The rate shown by
the 90g 223 is abnormally steep. There is some sort of problem
here but currently I know neither what nor why.
Considerations in Load Development
The just described testing is encouraging but it will certainly be
helpful and maybe necessary to identify other encouraging
powder-bullet combinations before contemplating a rule change.
Persons considering the development and contribution of such
data to the D.C.R.A. may find some of the background of our
efforts helpful.
Perhaps the most critical aspect is to stabilize the variables -
investigating one variable at a time is just right. It is very
disconcerting to recognize a real improvement and then have to
speculate on which of the altered components is responsible.
One of the first decisions is primer choice. Ordinarily I use
Remington B.R. on account of past satisfaction but in preliminary
testing I had one punctured Winchester and one punctured R.W.S.
primer. This appeared to be a mechanical rather than an excess
pressure phenomenon so I chose K.V.B. Magnum, a Russian
primer that is reputed to be more durable in impact than its
competitors. There were no punctures in several hundred rounds
thereafter. It would be wise to exercise care in testing loads with
velocity above 2800 fps. (Fig. 8)
Since I was emulating German Salizar's load development, the
powder used was N550. Others doing 90g testing are apt to
consider other on-hand powders. On another project I did extensive
testing of powders with 80g 223 bullets. The results of these
tests (Fig. 9) in conjunction with the N550 data (Fig. 10) will
allow the calculation of starting loads with other powders. These
calculations will involve powder charges and velocities but there
will be no pressure data. It would be easy to calculate reductions
in powder charge and in velocity when the 90g bullet replaces the
80g bullet and fail to take into account that the pressure will go
up. How much we don't know so you have to start significantly
below your calculated powder charge and gradually work up.
When looking for a new accuracy load I sometimes find it useful
to prepare a sequence of loads with gradually increasing powder
charge to shoot over a chronograph at a 100 yard target. (Fig. 10)
What one hopes to see is a coincidence of low extreme spreads in
velocity with minimal horizontal and vertical dispersion.The
difference between one load and the next is only 1/10 grain of
powder so one also hopes for several adjacent charges with
similarly favorable results. In Fig. 10 the 26.5g loads with the
Berger and JLK bullets seem moderately attractive.
I must admit that operating in 1/10g steps in powder weighing
demands precise equipment and careful operation. One is really
pushing the equipment to its limit. However 1/10g of N550
powder is 14 fps with JLK and Berger bullets and that velocity
difference (if maintained to 1000 yards) is almost ½ minute
(actually 3/7).
The previous discussion has centered on a desire to make a small
case cartridge perform as accurately as one with a substantially
larger case. We would like a 223 case with 26 grains of powder
and a 90g bullet to perform as well as a 308 with 46 grains of
powder and a 155g bullet. To do that the 223 has to deliver about
110 fps to its bullet for each grain of powder while the 308 needs
to deliver about 60 fps for each grain. Powders and primers do
exist that can deliver these velocities but there is a problem in the
loading. Equipment is available that will deliver powder with ±
0.05 grain accuracy (well almost) but the accuracy is the same for
223 powder as it is for 308 powder. Therefore the effect of
powder weighing errors is about twice as much (in fps) for the 223
as it is for the 308.
Conclusion
When one is trying to rush a job one avoids problem areas if possible
and concentrates on the successful activities. The foregoing
discussion has omitted two problem areas. The first is that the
Sierra bullet often disintegrates within the first 100 yards when
loaded with 26 ½g of N550 (2850 fps). The group made by the
bullets that do reach the target is large. We have not investigated
this problem. Secondly we once had a problem when 2 out of 10
Berger bullets disintegrated a very few feet forward of the 1000
yard target (±2860 fps). 7 of the other 8 had ½ minute of vertical
dispersion. This happened only once perhaps because we loaded
mostly about 2830 fps thereafter.
The testing reported here, though brief, confirms German Salizar's
opinion that 90g bullets shoot quite well with loads of 26.2g of
N550. He used JLK's but Bergers were available at the time of
our test and JLK's were not. The 1000 yard stage of our test was
not as good as 600, 800 and 900 yards. We do not know why.
Overall the 90g 223 is about equal to the 155g 308 which is to say
that it is quite a bit better than the 80g 223.
The question is what to do next. It would certainly be nice to have
more data, to sort out the 1000 yard group problem etc. etc. One
could ask the D.C.R.A. membership to voluntarily undertake
additional long range testing. The problems here are the cost of
installing a new barrel and the difficulty of getting time and
opportunity to do enough testing. Past experience in such efforts
has been disappointing.
The second option is to arbitrarily change the bullet weight rule
now and oblige people to decide for themselves whether they will
use 80 or 90g bullets. Most will stay with the 80g but the chance
of gaining an advantage will tempt some into investing in and
trying out the 90g option. If they are successful others will follow.
We have tried a three year term for such trials and that didn't work.
People will not undertake the cost and effort of the 90g trial unless
they have a guaranteed opportunity to benefit if their exploratory
gamble is successful.
18 The Canadian Marksman, Winter/Spring 2008
Fig. 1 Comparison of the trajectories of the 80 and 90 grain 223
bullets with the 155g bullet in the 308 load. The 3000 fps load with the
80g bullet is near maximum but even so it has a minute more drift in a 10
mph wind at 1000 yards than in the 155g Sierra in the 308 load. Note the
similarity in the 308 and 223 trajectories and the 90g Sierra wind drift of
97 in. at 2700 fps muzzle velocity.
Fig. 2 Comparison of group sizes in 223 and 308.
The four rifles represented in this diagram performed very respectably in
several years of Canadian Full bore competition.
Fig. 3 600 yard group sizes with 90g 223 Berger bullets.
These were very impressive groups. Availability dictated the use of
Berger bullets. The Sierra and JLK bullets were not tested.
Fig. 4 800 yard group sizes with 90g Berger and JLK bullets.
These are very respectable groups. The increase in average group size
from 600 to 800 yards was 0.16 inches.
Fig. 5 900 yard group sizes with 90g Berger and JLK bullets.
The increase in average group size from 800 to 900 yards was 0.50 ins.
Fig. 6 1000 yard group sizes with 90g Berger and JLK bullets.
The increase in average group size from 900 to 1000 yards was 0.80.
Expansion of group size with increasing range is normal but the
increase rate after 800 (and particularly after 900) seems abnormally
high. I have no explanation as yet.
The Canadian Marksman, Winter/Spring 2008 19
Fig. 7 Comparison of the 90g 223 test groups with standard rifles.
The 90g 223 performed as well as the 308 3 gun average up to 900 yards
but there was a drastic increase in group size to the 80g 223 level at
1000 yards. When one compares Figs. 4, 5 and 6 it is evident that the
whole group dimension expanded much more rapidly than the core
dimension. Apparently the "fliers" are flying further particularly at 1000
yards. The reason is not yet apparent.
Fig. 8 Primer testing. At the outset of a new hand loading program
it is wise to do a brief test of the available primers. This test used a
load of 26.5g of N550 in 10 shot groups at 100 yards. Had I forged
ahead without this test and loaded my first test batch with R.W.S. or
Winchester primers (which have both worked well in the past and will
again when I recognize and cure the current problem) I would have
been perturbed. As it was this preliminary test was a time and
frustration saver.
Fig. 9 Powder data for 80g 223 loads. The foregoing illustrations
allow one to forecast the velocity effect of changing the weight of
N550 powder in 90g 223 loads. Since published data on loads with
other powders for 90g 223 is not available one must resort to "ratioing"
from 80g 223 loads. This figure derives from earlier 80g 223 testing.
The problem with such procedures is that one has no way to measure
pressure and when the bullet weight goes up the chamber pressure
goes up and the safe bullet velocity goes down. The only way for the
average hand loader to cope with this problem is to carefully estimate
the load for a modest velocity and then deliberately start with a lower
load (minus 1 grain or more). Then go up ¼ grain at a time to where
you wish to be. Overly cautious? I sure hope so - that's the object of
the exercise.
Fig. 10 Loads and velocities for 5 shot groups with 90g JLK and
Berger bullets. When this test was begun it seemed possible that the
Sierra bullet might not be compatible with the upper velocities in the
JLK-Berger testing so that testing was deferred. The average velocity
increase for 1/10g of N550 powder is 14 fps. However you will see
that the velocity difference is not exactly 14 fps which demonstrates
that my equipment and I cannot weigh precisely 1/10 grain. However
we get fairly close and the overall average is OK. The purpose of
these tests is to identify velocity segments that have low extreme
velocity spread, S.D. and group size. Loads of 26.4 to 26.6g for both
JLK and Berger seem worth investigating.
