[RIFLE] Load development in a benchrest rifle
Toby Bradshaw
accuracy shooting in rifles, and I offered a method that has worked for me
in benchrest shooting. Since I just finished putting together a new light
varmint/sporter for the upcoming benchrest season, I thought I'd describe
how I "worked up a load" for competitive shooting. The main take-home
lesson remains that good equipment is very forgiving, and "load
development" in accuracy shooting is not the time-consuming factorial
experiment that some would have you believe.
The key to successful load development is to start with the best possible
components, to eliminate as many sources of error as possible. My new LV
rifle is based on a Stolle Panda with right bolt and left port for
shooting speed (as much as a single-shot bolt action can be considered
"fast" :). If you haven't seen one, the Stolle action is made by George
Kelbly's in Ohio, and is a work of art. The Panda weighs less than two
pounds yet has a flat bedding surface 1.5" wide and over 8" long, broken
only by the cutout for the trigger bracket (the trigger bracket allows
trigger R&R when the action is epoxied into the stock). The action wears
a Hart 1-14 twist 6mm barrel 21" long with a "max heavy" varmint class
taper, about 0.950 at the muzzle, chambered for 6PPC with a .262 neck.
Jim Borden of Tunkhannock, PA did the smithing and it is top shelf. I
used a Lee Six gripless stock, which is at least 10 oz. lighter (the Six
stock I got weighed 18.5 oz. before filling and painting) than the
McMillan, but which needs quite a bit of filling and sanding compared to
the McMillan. IMO, on a 10.5 pound rifle there's no point in giving up
barrel weight just to make the stock prep easier. I bedded the action
then epoxied it in place after painting the stock, and put a Jewell
trigger underneath and a 36X Leupold in Kelbly rings on top.
I turned the necks on 25 Lapua .220 Russian cases after expanding the
necks to 6mm and running them through a Redding 6PPC FL die to set the
neck/shoulder junction back (no expander ball used, *ever*). The Redding
die is impressive for its ability to size the brass to just maximum specs
for 6PPC. It moves the shoulder back 0.001 below the minimum headspace,
which is perfect for BR rifles where the headspaces are set to 0.001 or
less above minimum (generally a "go + 0.001" is used as a "no-go" gauge).
The FL die is 0.262 in the neck so it doesn't touch the case neck after
turning. I turned the necks to give 0.0004" clearance with the 68gr
Bruno BT 7S ogive bullets I prefer. This is a "fitted neck" and doesn't
require resizing after shooting. Jim Borden (like most BR smiths) ships a
"neck gauge" with each rifle, which is just a barrel stub with the
chambering reamer run in about halfway up the shoulder. Loaded rounds
must be a slip fit in the gauge to be safe, and the gauge is also very
handy for determining bullet seating depth at land contact (by dropping a
bullet in the gauge and measuring how deep it goes, then measuring the
length of a fireformed case resting against the shoulder of the gauge, it
is easy to set cartridge OAL to put the bullet right on the lands, then
record the stem setting on the Wilson die and you're set.; takes more time
to describe than to do :). The Lapua brass is the best brass of any kind
I've ever seen -- incredibly uniform in all dimensions and *none* running
out more than 0.001 at the head. They're a buck apiece but there are no
culls to speak of. They hold quite a bit more powder than the SAKO USA
PPC cases, and are very much like the original SAKO .220 Russian cases.
Naturally the primer pockets were cut to uniform depth (only touched the
corners on the Lapua brass -- even the primer pocket depths are *exactly*
on spec in this brass as delivered) and the flash holes de-burred (no burr
on *any* of the cases -- amazing stuff). I use Federal 205M primers, like
every other BR shooter in the world.
I use 70gr Nosler Ballistic Tips for fireforming, but any boattail bullet
will do. Flat base bullets won't go into the chamber with the neck cut
for boattails, because FB bullets have a pressure ring on the base. So,
off to the range with the powder measure, Wilson dies, arbor press, and
about 150 pounds of other crap like front and rear rests, wind flags, ...
After boresighting, I fireformed the brass with 26gr of Australian H322
with the Noslers seated 0.010 into lands to keep the case head against the
boltface. The expansion ring that is typically seen above the solid head
upon fireforming is generally absent in PPCs because the case
manufacturers make the cases close to maximum and the chambers are
minimum. I ran a couple of patches soaked with Shooter's Choice through
the barrel after the first couple of shots to see how much fouling was
accumulating. As usual for BR-quality barrels, fouling was minimal. I
don't follow any elaborate barrel break-in because I've found it
unnecessary. Just blast some fireforming loads downrange and clean with
Shooter's Choice every few shots, using a brush after perhaps 10 shots. I
use a Mike Lucas bore guide (the best bore guide I've ever seen) and a
Parker-Hale rod. I zeroed the scope with the first few shots then shot 20
Noslers at the same target, not really aiming carefully since I was just
fireforming. The 20 shots formed a round group 0.402" high and 0.380"
wide at 100 yards, so I figured there weren't any major problems. The
chronograph only showed about 2950fps for this load, which is way too slow
for the 6PPC. I usually shoot the 68gr Bruno bullets around 3250fps. So,
I cleaned the case necks inside and out, deprimed them, and primed them
again. I loaded 5 rounds each at 28, 28.25, and 28.5gr H322 with the 68gr
Brunos. I put in 6 clicks up elevation on the scope and went to the 200
yard target. It was windy and I was in a hurry, so I just sent them
downrage looking for a load without much vertical dispersion. The hottest
load looked best, with about 0.500" of vertical and 0.750" horizontal.
The usual pattern for load development is to put the bullet on the lands,
then increase the powder charge until vertical dispersion is minimal.
This must be done at longer ranges, like 200-300 yards, to be very useful
since even loads with lots of variation in muzzle velocity will group
decently at 100 yards for reasons that have been discussed in this
newsgroup many times. Beyond the point of "minimum vertical", the groups
will open up all over from the excess pressure and eventually a primer
will blow. In benchrest rifles in general, and in the Stolle action
particularly, there aren't a lot of pressure signs to look at until the
primer falls out of the case. The Stolle (unlike some other BR actions)
doesn't have an ejector, so there's no place for brass to flow under
pressure to give you a sticky bolt lift. Even the small flash hole on the
PPC case prevents extreme pressure signs from showing up early on the
primer. All loads I've used successfully in the 6PPC caused significant
primer cratering, but case life is still very good (>50 reloadings, and
still going strong). By this time I had to leave the range, but the next
week I returned on a rainy but intermittently calm day to find a load for
the 300 yard matches I shoot each month. I started with the 28.5gr H322
that looked OK at 200 yards and loaded additional rounds of 28.8 and
30.1gr. At 300 yards, the 28.5gr load had 4 shots with only 0.124 of
vertical, and 0.601 horizontal, but one of the 5 shots was up 0.713 from
the other 4. The 5 shots with 27.8gr H322 had 0.815 vertical, and at
30.1gr the group was blowing apart from too much pressure. I then loaded
10 each of 28.5 and 28.9gr. The flags were hanging straight down when I
started the next group at 28.5gr. The 5 shots were 0.752 high and only
0.259 wide. I immediately went to the adjacent target with the 28.9gr
load, and the 5 shots made a no-wind group of 0.365 high and 0.186 wide.
Four of these shots were in a 0.107 bughole. Not bad for a 10.5 pound
rifle at 300 yards! The wind picked up a bit and I went back to the two
loads for another pair of groups to verify that the 28.9gr load is
suitable for competition at 300 yards. The 28.5gr load again had 0.716
vertical, and the 28.9 was very flat at 0.290. Note that *any* of these
loads is shooting reasonably well considering the distance, and *proving*
that two loads are different requires a lot of shooting and measuring (a
lot more than I did this time, or than I ever do).
So, in a couple of range sessions with 70 or 80 rounds fired (including
fireforming) I'm set for a season of BR shooting out to 300 yards. The
load will have to be reduced in hot weather (usually about 0.1gr for every
10 degrees F), but by starting with a good rifle, excellent reloading
components and tools, and by paying attention to the only variable the
load can really help you with (vertical dispersion), my time at the range
is spent productively. Compare this with the "factorial experiment" of
varying powder types, charge weights, bullet makes/types/weights/lot
numbers, primers, seating depths, _ad nauseum_. In looking at the
equipment lists from major BR shoots note that only a few barrelmakers,
bulletmakers, powders, and cases are used. There's a reason for that!
Don't reinvent the wheel -- the same components and loads that work well
for others will work well for you in similar equipment. The same thing
can be said of factory rifles, except that accuracy levels are lower and
compromises have to be made in bullet selection. Good bullets and good
brass will still make a big difference though, assuming your bench
technique and wind doping are not the major contributors to group
enlargement.
Good equipment is very tolerant of mistakes, so I need the best equipment
possible to cover up my many and varied boo-boos. If you like accurate
rifles but you've never had the pleasure of shooting real benchrest
equipment, make a point of going to a BR match and try to find somebody
who'll let you pop a few caps in their rifle. You'll probably have to be
pried loose!
Toby Bradshaw -- Biochemistry SJ-70 -- to...@u.washington.edu
Banning guns to prevent murder is like banning soccer to prevent riots.
John H. LeBourgeois
Toby, could you break down the cost of the components you bought here so we
can have an idea of reasonable prices ( and I'll know how much I have to
sell to get one ;)
Toby Bradshaw
John H. LeBourgeois <jl...@well.sf.ca.us> wrote:
#
#Toby, could you break down the cost of the components you bought here so we
#can have an idea of reasonable prices ( and I'll know how much I have to
#sell to get one ;)
Action : $550-$750 (Stolle Panda $650 or a little more)
Barrel blank : $220
Fit and chamber : $150
Jewell trigger : $125
Six gripless stock : $175 (+ a lot of filling and sanding and painting)
Bedding and paint (if you pay somebody) : $200 up (WAY up for nice paint)
36X Leupold : $435 (last time I bought one -- may have gone up)
Bore guide, stock tape, etc. : $30
Lapua brass : $1 each
Bruno 68gr BT 7S : $130/K
-Toby Bradshaw
to...@u.washington.edu