|
Express 28g No 7.5s plastic wad and fibre wad compared
I have heard it said that the plastic
wad and cup was the biggest advance in shotgun ballistics since the choke was invented.
However, some ranges insist on the use of fibre wads (it is
worth noting that although some plastic wads are photodegradable, this is
not the same as biodegradable). Shooters often see fibre wads as a
disadvantage. The reasons cited are shot deformation when it passes through
the forcing cone and choke, galling of the lead as it speeds down the bore
and the wad running into the back of the shot once it has left the barrel.
The common belief is that plastic wads are much superior.
To test for the differences in
patterning Express ProComp 28g 7.5 plastic wads are compared with Express
ProFibre 28g 7.5 fibre wads. From the Express website both have a claimed
muzzle velocity of 1400fps and shot with 3% antimony. Both are mid-priced
shells. The pellet count from unfired shells was 368 for the fibre and 377
for the plastic wad which is close enough to allow direct comparisons of
the pellet coverage.
The gun used for the test was a
30" Browning B25 with Teague screw-in chokes. 1/2 choke was used for
the tests being a common choice for sporting shooters and (with luck) enough
constriction to start to show any ill-effects of the unprotected fibre wad
shot being misshaped by the choke.
Individual patterns and
average pattern width.
Fibre wad patterns and
spread summary.
Patterns and overall summary of Express ProFibre
28g No7.5 fired from 25yds.
Average Spread
|
Average shot to shot variation
|
|
19.5" |
+/- 1.17" (6%) |
Plastic wad
patterns and spread summary.
Patterns and overall summary of Express ProComp plastic
wad 28g No7.5 fired from 25yds.
Average Spread
|
Average shot to shot variation
|
|
17.69" |
+/- 1.25" (7.1%) |
It can be seen that the average
spread of the plastic wad shells at 17.69" is about 10% tighter than
that of the fibre wads at 19.5" (the spread figure is the diameter
that accounts for 75% of the pellets).
Although not shown here, the fibre
wad spread is near to the average spread of many other plastic wads that
have been tested. It is this particular Express plastic wad shell that is
throwing a tighter than normal pattern.
In practical terms it makes little
difference. Unless one needs the extra couple of yards offered by the
tighter pattern, the extra spread of the fibre wad will help with a wider
pattern.
Analysis
of shot to shot repeatability.
The repeatability of spreads of +/- 6%
and +/- 7.1% for the fibre and plastic wad respectively are both very good.
However, it should be borne in mind that this is an average spread, the
extreme variation is obviously much larger. This is why it is always
necessary to average several patterns. Shown below is a plot of the shot
to shot spreads where the average, extreme variation and typical variation
can be seen.
The conclusion of these tests is that
both shells are very repeatable. The range of shot to shot repeatability
for other shells tested ranges from a low of +/- 5.5% to the highest at
+/- 14%, again these are average shot to shot variations. The extreme
spread can be much higher.
Because both shells have a similar
pellet count and very similar variations in shot to shot spread, with a
sleight of hand it is possible to directly compare the relative coverage
of the two sets of patterns. The trick is to re-scale one set of patterns
to the give the same average spread as the other. Next, passing a
simulated edge-on clay across the pattern and finding the
probability of a pellet striking it can reveal any gaps
in the pattern (possibly caused by the wad ramming into the shot soon
after leaving the muzzle).
The fibre wad patterns were rescaled
to 35yds to simulate a more open pattern - probably about the limit for
this shell and choke combination and the plastic wad loads were rescaled
to 38.61yds so that they have the same average spread.
Shown below is an example of how such
a more open pattern looks.
Express ProComp 28g No7.5 (plastic
wad) fired at 25yds, rescaled to simulate 38.61yds.
Looking at the pattern data below, it
can be seen that the patterns over the 9-shell average are almost
identical. The distribution of pellets in the 10", 10-20" and
20-30" areas are almost identical. Similarly the probability if
hitting the small area of an edge on clay is almost identical. What this
means is that there is no evidence of the fibre wad shells having inferior
patterns. This includes any effects of the wad affecting the centre of the
pattern or shot deformation leading to more fliers.
Summary of pellet distribution and pattern
performance of Express ProFibre shot at 25yds, scaled to 35yds.
|
|
|
Summary of pellet
distribution and pattern performance of Express ProComp (plastic
wad) shot at 25yds, scaled to 38.61yds.
|
|
|
In terms of quality of pattern, there
is nothing to separate these two shells. There is the possibility that
there may be differences at extended range using tight chokes. This is a
future test.
To date only two types of fibre
wad have been tested, this Express ProFibre and also a Hull Cartridge
ProFibre 28g No.9 (see separate report). In both cases the fibre wads give
excellent repeatability of spread. Plastic wads by comparison offer the
best and worst in performance.
A theory of how plastic wads affect pattern width and
repeatability.
A deduction from this is that the
main detriment to repeatability of spread is not pellet deformation during
powder ignition, or passing through the forcing cone, or through the bore
and choke, but the launch conditions of the pellets. In the case of a
fibre wad, the muzzle determines the launch conditions. It is made of
steel and very repeatable! With plastic wads, however, there is the added
variable of how the wad behaves just as it traverses the muzzle and then
how it opens in flight. I have seen many shot wads lying on the ground
that have only partially opened which suggests the process can be very
variable.
I'm also wondering if the reason some
plastic wad shells group tighter is not because they are deforming the
shot less that leads to better aerodynamic properties of the pellets, but
rather because they are delaying the point at which the shot
becomes free flying and hence moving the whole pattern a yard or two
further up-range.
These ideas are also tentatively
supported by the results from the skeet gun comparing No.9 shot where the
plastic wad shell gave widely varying spreads but also gave a tighter
spread on average, i.e. sometimes the shot cup opened early, and sometimes
it didn't.
Both the graph above showing the shot
to repeatability and the similar graph for the skeet gun show the plastic
wad grouping tighter on average than the fibre wad. However, in both cases
the widest patterns from the plastic wad are very near the average of the
fibre wads. This also tentatively suggests that the maximum spread from
the plastic wad is when the wad opens straight away, and when this happens
the spread is close to that of the unconstrained fibre wad. However, if
the wad delays opening, the pattern at a given range appears a little
tighter. A few plastic wad shells achieve the feat of moving the pattern
up-range without ruining the repeatability. Unfortunately, some don't!
Implications of wad performance on the wisdom of
backboring.
If fibre wads do have an advantage
it calls into question the merits of backboring. Even the
proponents of backboring say that it is not compatible with fibre wads
because they risk not making a good gas seal (unlike the skirt on a
plastic wad that can expand). Given this I would not be wanting backboring
on my gun - especially if a particular range or event mandates that fibre wads must be
used. The same argument applies regarding extended forcing cones. Both
backboring and extended forcing cones seem (to me) to claim small gains
that are seldom proved but acknowledge risks that can be profoundly bad
for the shell performance.
More fibre wad loads need to be
tested. At a personal level, if on average they behave in a more
repeatable way then I will move over to them.
The performance of plastic
wads is questioned in colder weather and also the manufacturers can change wad
supplier and the shooter would be none the wiser. If plastic wad
performance can make the difference between excellent or terrible
repeatability, personally, I'd rather remove this gross uncertainty and
settle for the 'safe pair of hands' of a fibre wad. They might not offer
the ultimate in range, but repeatable pattern width is more use to
me.
This is particularly so if the clay
is close. Incomers at skeet can be 5-7yds away. If a plastic wad fails to
open there will be almost no spread whereas the fibre wad could be giving
up to 10" diameter spread. That's quite a difference.
|
