COMPARISONS OF SPECIES OF WOOD FOR GUNSTOCKS”
By BENSON H. PAUL, Silviculturist
Forest Products Laboratory, 1– Forest Service
U. S. Department of Agriculture
The use of large quantities of black walnut for gunstocks, with its
consequent inroads upon merchantable stands, prompted the Forest Products
Laboratory during the present war to investigate the possibility of gunstock
production from other species. Studies of alternative species showed black
cherry (Prunus serotina), red maple (Acer rubrum), yellow-poplar
(Liriodendron tulipifera), sugar map1;77Cer saccharophorupl, and yellow
birch (Betula lutea) to be suitable for such use.
A comprehensive study of black walnut by the Forest Products Laboratory provided a basis for its comparison with other species.? Data were
Obtained on the rate of growth of black walnut, its variation in specific
gravity for both open-grown and forest-grown trees, measurements of shrinkage
in the radial, tangential, and longitudinal directions with respect to the
orientation of samples in the trees, and tests of hardness for wood representing various types of growth.
Subsequent studies produced comparative data on these characteristics
for a number of other species recommended as of possible usefulness for gunstocks (tables 1 and 2 and figure 1). In addition to the Laboratory tests
of wood quality, gunstock blanks were experimentally machined by several
cooperating gunstock manufacturers, who subjected the recommended species to
the manufacturing procedure and proofing tests given black walnut stocks.
The species studied were also considered with respect to their availability. Several are more abundant than black walnut in certain areas and
doubtless can be brought to shipping and manufacturing points with greater
ease and lower hauling and transportation costs than can black walnut. Such
advantages may be enhanced by logging of more than one species in the same
forest. Differences in log prices ordinarily favor these so-called
“substitute” species .
Comparison of Species
Black cherry closely resembles black walnut in most of the characteristics investigated. Samples gave a somewhat smaller range in specific
-Maintained at Madison, Wis., in cooperation with the University of Wisconsin.
2″Black Walnut for Gunstocks,” by B. H. Paul. Southern Lumberman, April 15,
Rept. No.D1725 Agriculture-Madison
gravity, with an average of 0.49 as compared with 0.52 for black walnut. In
radial, tangential, and end hardness, black cherry wood averaged a little
lower than black walnut in the green condition. In the dry condition, however,
end hardness of black cherry averaged slightly more than that of black walnut.
Differences were greater toward the upper limits of the ranges than at the
lower limits; that is, while much black walnut was considerably harder than
black cherry, none of the black cherry was softer than the softest black
Average shrinkage in volume was 12.9 percent for black cherry and 13.2
percent for black walnut. Tangential shrinkage of black walnut averaged 9.0
percent, that of black cherry 8.7 percent. Radial shrinkage of black cherry
was decidedly less, averaging only 4 percent as compared with 5.9 percent for
black walnut. There was only a slight average difference between longitudinal
shrinkage of black cherry and black walnut, the averages being 0.27 and 0.25
Black cherry is reported to be rather plentiful in the northern
Appalachian region, particularly in Pennsylvania, West Virginia, and New York.
Many second-growth stands now of merchantable size contain a considerable
proportion of black cherry.
Red maple follows closely the specific gravity range of black cherry
with a low value of 0.40 and a high value of 0.60. The average is 0.51, very
close to the average for black walnut. In hardness, red maple and black
cherry were about the same in the green condition. This was also true for
side hardness of these species when dry, but average end hardness of dry red
maple exceeded that of dry black cherry by about 10 percent.
Shrinkage values for red maple in all directions are well within or
close to corresponding limits for black walnut and black cherry. Its radial
shrinkage is relatively small, ranging from 2.6 to 4.4 percent and averaging
4.0 percent, the same as black cherry. Longitudinal shrinkage keeps well
within the range for black walnut but averages slightly more.
Red maple grows from Canada to Florida and from the Atlantic Coast
westward to Texas and the Plains States. It is a common tree in moist
situations, becoming a swamp tree in the South. Red maple is fairly abundant
in many parts of its range, far exceeding either walnut or black cherry in
total volume and availability.
Second-growth yellow-poplar frequently produces wood of relatively
high density well within the specific gravity range of black walnut. Trees
selected for high density produced wood ranging in specific gravity from
0.34 to 0.60. More than 75 percent of the samples tested fell within the
specific gravity range of black walnut and coincided fairly well with the
ranges of black cherry and red maple. Yellow-poplar having a specific gravity
of less than 0.42, based on its weight when oven-dry and its volume when
green, is not recommended for gunstocks.
Shrinkage of yellow-poplar is relatively low. Radial shrinkage
averaged 4.2 percent, tangential shrinkage 7.7 percent, and longitudinal
shrinkage 0.27 percent.
Rept. No. D1725 –
Hardness of yellow-poplar in the green condition averaged lower than
that of the other species investigated, but most of the individual values for
samples with a specific gravity above 0.42 were within the hardness range of
black walnut. The same was true for material tested in the air-dry condition
(figure 1). While greater care must be taken to select yellow-poplar trees
that contain material of suitable weight and hardness, such trees give a
high yield in gunstocks because of their relative freedom from large knots,
cross grain, and other defects.
Yellow-poplar grows from central New York and southern Michigan to
northern Florida, west as far as Illinois and, in the South, as far as southeastern Missouri, eastern Arkansas, and northeastern Louisiana. The highdensity wood is found in thrifty second-growth trees on good sites. In order
to utilize this species successfully for gunstocks, a method of selection of
the trees in the woods is useful.-2
Specific gravity values of sugar maple are within the range of black
walnut but occur most frequently in the upper part of its range. The average
value for sugar maple is 0.58, as compared with 0.52 for black walnut. In
the United States sugar maple has ordinarily been considered somewhat too
heavy for gunstocks. It has, however, been used for British stocks produced
in Canada as well as in the United States to fill lend-lease orders, and
evidently has given satisfactory service.
Sugar maple averages a little higher than black walnut in tangential
shrinkage, yet the range 8.4 to 11.0 was no greater. Radial shrinkage
values for sugar maple fell within a narrower range and averaged lower than
black walnut. Along with higher specific gravity values, sugar maple has
greater hardness than the other species under consideration.
Birch has been used as a source of gunstocks in Europe, and our
native yellow birch has been used to supply machine gun butts and stocks
for nonmilitary guns. Its use for this purpose has, however, been restricted
by the freezing of this species for aircraft veneer. Nevertheless, there are
considerable quantities of yellow birch in logs below veneer grade that could
be used advantageously for gunstocks. This is a source of supply that could
be considered for lend-lease gunstocks or gunstock blanks.
The specific gravity range of yellow birch is closer to that of sugar
maple than to that of the other species investigated, the total range being
0.47 to 0.63 and the average value 0.55. Its radial shrinkage, 5.9 percent,
averages higher than that of any of the other species, while its average
tangential shrinkage is midway between that of black walnut and sugar maple.
The hardness of yellow birch is about the same as that of black cherry when
tested in a green condition and slightly higher than that of black cherry
when tested in an air-dry condition.
3″A Field Method of Determining Specific Gravity by Use of Increment Cores
or Auger Chips,” Forest Products Laboratory Report No. 1587.
Rept. No. D1723 –
Yellow birch grows in the Lake States, New England, New York, New
Jersey, Pennsylvania, and south along the mountains into Georgia. There are
still large stands of yellow birch saw timber in the Lake States, the
Northeast, and the northern Appalachian region.
Broaden Sources of Supply
The wide range found in the important characteristics of black walnut
indicates that, unless some special attention is given to the selection of
black walnut, the other species investigated can supply material having
equal physical and mechanical properties. Regardless of the species chosen,
the best results in manufacture will be obtained if an attempt is made to
segregate the material on a basis of uniform weight and exclude material
with extremely high or extremely low values.
The use of additional species having satisfactory characteristics from
the standpoint of wood quality will facilitate gunstock production in the
following ways: (1) create a larger source; (2) make it possible to log for
more than one species in a locality; (3) shorten log hauls, thus expediting
production and cutting logging costs; (4) reduce length of rail shipments of
gunstock blanks; (5) expedite kiln drying by using species that will dry in
a shorter time than black walnut; and (6) utilize species of lower commercial