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6 Dasher Rifle Project
Project Started July 11, 2006
The goal for this
project is to build a long range target and live varmint rifle
around a variant of the many 6mmBR Improved designs. I chose the
6 Dasher primarily because I have had correspondence with
multiple shooters using this cartridge, and it has a well
established track record of extreme accuracy. I went with the
improved variant over the standard 6mmBR since I am primarily
interested in shooting at 1000+ yards, and wanted to be able to
launch the 105/107 grain VLD match bullets at about 3000 FPS.
The Dasher is capable of this using only 33 grains of powder,
with reasonable pressures and barrel life. The standard 6mmBR,
while you can load it to this level, will not yield good brass
or barrel life.
Another factor for
choosing the 6 Dasher over other variants was the availability
of dies from Redding, on a semi-custom basis.
I am hoping that this
rifle will duplicate the ballistics of my 6mm-22/250 AI, with
much less powder. This will (hopefully) lead to better barrel
life, less recoil and muzzle blast, and slightly lower reloading
costs. However, the primary benefit that I expect to enjoy is
the spectacular accuracy of this cartridge. While the 6.5-284
can launch bullets with higher BCs at the same or higher
velocities, yielding (on paper) less wind drift, the 6 Dasher's
inherent accuracy advantage should prove to be more effective in
the field than the higher BC bullets with less angular accuracy.
At least, that is my desire.
I am using the
Remington M700 stainless short action from my now retired 220
Swift Ackley Improved, along with the Jewell HVR trigger as the
foundation for this rifle. Everything else is new.
The specifications
for the rifle are as follows:
|
Caliber |
6 Dasher
(6mmBR Improved) |
|
Barrel |
Broughton
5C, 1:8 twist, stainless, 30" finished length, contour
1.250" straight cylinder |
|
Reamer |
Dave Kiff of
Pacific Tool and Gauge
– 6 Dasher, 0.272 neck, 0.110 freebore |
|
Receiver |
Remington M700 right hand stainless short action. Receiver
is
blueprinted; single point chasing of the receiver
threads, locking lugs, and receiver face. Bolt was
re-machined by truing the front and rear face of the
lugs, bolt nose and outside diameter, and bolt face. The
bolt has four small beads TIG welded where the receiver
raceway contacts the bolt body, which were subsequently
machined to provide 0.001” clearance when in battery.
The receiver ring is drilled to accept a locating pin
for the Holland's recoil lug, allowing switch barrel use
in the field. Oversize (shop made) stainless bolt knob
installed. |
|
Firing Pin |
Speedlock Systems low mass firing pin and CS spring |
|
Recoil Lug |
Holland's,
pinned, stainless |
|
Trigger |
Jewel HVR, bottom
bolt release, top safety |
|
Sight
Rail |
Custom Picatinny
rail with 20 MOA offset, from Brett Evans at Northwest
Armeswerks. Pinned to the receiver with 0.125" dowel
pins. |
| Stock |
Richard's
Custom Rifles Lowrider in Green Mountain Camo
Rutland laminate, with polished BAT triggerguard. Stock
has a Limbsaver pad, with about 3 pounds of lead shot in
epoxy added to the butt and handgrip area to balance the
heavy barrel. Pillars are Richard's custom stainless
models, with polished escutcheon on the bottom. The
barrel action is bedded with Devcon 10110 epoxy.
Action screws are Richard's custom as well. |
|
Scope |
Nightforce
NXS 12-42X56 with NP1-RR reticule |
|
Rings |
Leupold QRW high, 30MM |
| Weight |
9.5360
kg, or 21 lb 0.4 oz |
Progress Log
7/22/06
The action is tuned
and ready.
The bolt has been TIG
welded, and the beads machined to make for a perfect fit. The
action lugs have been finished lapped with 800 grit lapping
compound. A few light passes of the bolt locking ears along the
bolt raceway with the 800 grip compound made the action very
smooth.
The Speedlock Systems
firing pin assembly is installed. The firing pin camming surface
on the bolt body has been polished to reduce bolt lift forces.
The receiver ring
face has been drilled to accept the 3/32" dowel pin used with
the Holland's recoil lug. The drilling was done in the mill,
using Holland's drilling fixture. This is a very well made
fixture, and holds the action and the lug in alignment allowing
you to get the drill located in the precise spot for the pin
hole. A good investment if you are going to do more than one.
I was unable to
locate any of the Weldsmith single shot followers that Brownells
used to carry, so I had to make my own. A custom follower was
fabricated from 6061 Aluminum, and fitted to the bottom of the
action. It will be epoxied into the action prior to bedding
using J-B Weld or Devcon 10110 epoxy.
Here is a photo
gallery of the action work so far:
Remington M700 stainless short action Bolt with TIG welded beads Action in Holland's drilling fixture Action in Holland's drilling fixture Action drilling fixture exploded view Action drilling fixture with lug installed Action bottom with shop-made single shot follower A closeup of the finished follower Speedlock firing pin assembly
Action ready for barrel fitting. TIG welded beads machined down to provide 0.001" clearance when in battery, but allows free bolt movement when cycling action. The end result of drilling the receiver with a 3/32" drill to accept the dowel pin that holds the recoil lug in alignment when tightening a barrel. This allows simple switch barrel use in the field, requiring only an action wrench and a vise. This recoil lug pin hole drilling fixture from Holland's Shooters Supply is very well thought out and manufactured. It allows very close alignment of the drilled hole in the receiver to the hole in the Holland's lug, by mounting vertically in the mill. Here the fixture with action in place is shown in the vertical orientation, as it is in the mill vise for the drilling operation. This view shows the action, fixture, lug, lug pin, and the fixture lug centering mandrel. Here you can see the centering mandrel holding the lug tightly against the receiver, with the pin in place. A view of the action underside, and the single shot follower. The center channel of the follower was machined in the mill, using the DRO arc cutting feature and a 0.5" ball end mill. The radius of the channel arc is 0.750", 0.050" larger than the bolt diameter. The arc center is concentric with the bolt centerline. Here you can see the follower set in place in the action magazine cutout. The outside radius was roughed in by eye in the mill with the 0.5" ball end mill cutter, and finished by hand on the belt sander. It will be permanently held in place using J-B Weld or Devcon epoxy before the barreled action is bedded into the stock. This view shows the very light Speedlock Systems firing pin assembly installed in the cocking piece and bolt shroud. Lock time is significantly reduced with this pin and high quality CS spring, and less shock is transmitted to the rifle.
Remington M700 stainless short action
Action ready for barrel fitting.
8/19/06
The 20 MOA sight rail
was pinned to the receiver with 0.125" dowel pins. The rail was
also bedded to the receiver with Devcon 10110 Steel epoxy paste
for a perfect fit.
I also bit the bullet
and installed a shop made oversize bolt handle. The bolt was
held in the mill vise with Vee blocks, and the handle knob was
turned down using a boring head. This is the part that made me
very nervous, as I was afraid of ripping off the brazed on bolt
handle if the boring head cutter hooked up badly. I took only
0.005" per pass, and made this a slow but careful job. I'd do it
again in a heartbeat, it was not at all bad. The remaining stub
was threaded 5/16-24. The knob was turned from 1" 303 stainless
stock, and threaded to fit the bolt stub. It was threaded on and
locked in place with J-B Weld epoxy. A bit of bead blasting
finished the job. See the final photo gallery for a view of this
modification.
8/27/06
The Richard's Custom
Rifles Lowrider stock has been prepared for final assembly and
bedding. It is finished with Waterlox. Each coat was wiped on
after a light rub with a white Norton synthetic pad (0000
equivalent grit). After curing, the finish was hand rubbed with
rottenstone on a water soaked felt pad. Next, it was polished
using 3M Machine glaze (automobile finish compound) and a
Porter-Cable random orbital buffer. A coat of 1 Grand carnauba
wax finished the job.
Finished stock - Waterlox original finish, about 8 very thin coats Lowrider stock showing recessed foreend Laminations - Rutland plywood
Finished stock - Waterlox original finish, about 8 very thin coats
The next steps will be fitting the barrel
to the action, and pillar bedding the barreled action to the
stock.
9/4/06
The barrel was
received, and the process to fit and chamber the barrel was
commenced. After the fitting, the barreled action was pillar
bedded to the finished stock. The photo gallery below documents
some of these steps. Please note that since these photos were
taken, I have upgraded the chambering setup with a 100 PSI high
pressure gear pump to provide for extremely efficient chip
clearing during reaming. See the Tooling
page for more details on this pump system.
Finished chamber (6 Dasher) Final inletting in the mill
Shop made, it is used, in combination with a 4-jaw chuck, to center barrel in spindle such that the bore at the chamber (or crown) end is perfectly concentric to the axis of rotation. Tenon length is set to maintain proper clearances between bolt and barrel. Threads are 16 TPI (Remington). After threading, the action is tested for proper fit. It should be close, but not tight. This counterbore establishes the proper clearances for the bolt nose. This attachment is used to provide coolant under pressure to the bore of the barrel while reaming the chamber. The lathe coolant pump is used to feed a high pressure (100 PSI) gear pump, along with an outboard micron sized filter to keep chips out of the flow. Here the reaming is about to commence. Note the flow of coolant through the reamer pilot bushing slots. Also, note the dial indicator on the magnetic base, measuring the tailstock position via a shop made indicator arm. With this setup, I can read absolute reamer depth even after retracting the tailstock to clean the reamer or check headspace. The total indicated runout of this chamber was 0.0002" after cutting. Not bad. The view through the borescope was excellent. The barrel was crowned with an 11 degree type target crown. Note the very slight ring around the bore produced by lapping the bore edge with a 0.5" brass ball and 800 grit lapping compound. Action with barrel installed, ready to bed. This setup was used to do some final inletting prior to bedding. About 0.100" clearance around the action was needed to provide room for the bedding epoxy. Here you can see the final inletting. Note the 2" long recess in front of the recoil lug. This is to provide for the bedding compound to support the first 3" or so of the barrel. This 1.25" diameter, 31" barrel really needs this added support. The barreled action touches the stock only at the back of the tang, and on the electrical tape wrapped around the barrel to set the forend spacing. Here the stock has been bedded, and all excess epoxy has been cleaned. The tape holds the stock firmly to the action. Devcon 10110 steel filled epoxy was used.
Shop made, it is used, in combination with a 4-jaw chuck, to center barrel in spindle such that the bore at the chamber (or crown) end is perfectly concentric to the axis of rotation.
9/6/06
The action was
removed from the epoxy, and the excess removed in the mill. The
action was assembled (trigger, bolt release, sight rail) and
installed into the completed stock. It is now ready for breakin
and brass fireforming. Here are some photos of the last steps
and the final results:
Fully assembled action ready to install into the stock
The excess epoxy was trimmed away in the milling machine using a 0.250" end mill. Slight relief cuts for the trigger pins were made just in case. Mandy Sue - My helper and all-round shop dog - She is one of 6 in the house... Note the bedded and pinned 20 MOA sight rail, and shop made oversized stainless bolt handle. Nightforce 12-42X56 NP-1RR NXS scope installed, Leupold quick release rings.
The excess epoxy was trimmed away in the milling machine using a 0.250" end mill. Slight relief cuts for the trigger pins were made just in case.
9/10/06
The barrel was broken
in, and initial fireforming load development was performed. I am
simply stunned by the performance. Even when fireforming the new
BR cases, it made better than 0.5" 100 yard 5 shot groups over a
range of 30.5 to 32.5 grains H4895, with a corresponding range
of velocities from 2841 to 3001 FPS. CCI 450 small rifle magnum
primers were used. There was a bit of (3 - 8
mph) wind cross range.
Here are the pictures of the 100 yard groups over that charge
range. The circles on the target spots are spaced 0.250":
I tried it at 200 yards, but was losing the light, and the wind
picked up a bit more. There was a vertical sight adjustment
between the two 200 yard groups, hence the POI shift upward:
Breakin was complete after the 5th shot - no copper, nothing but
a bit of powder fouling that two patches of Butch's took care
of. This Broughton barrel is the best from a fouling perspective
that I have ever owned to date.
I have done no seating depth tuning, or anything else. Without a
doubt, this is the most tolerant cartridge I have ever loaded.
The OCW looks to be at about 32.0 grains, but it is hard to tell
with these targets - the impacts are so close. More testing is
planned tomorrow at 200 yards.
The following
pictures show the technique of forming a false shoulder on the
6BR case prior to fireforming. This is essential, as it prevents
the firing pin strike from driving the case too far into the
chamber, possibly stretching the case web to failure, or at
least weakening it. The shoulder is formed easily by first
expanding the case with a 25 caliber expander mandrel, using a
bit of Imperial Sizing Die Wax to lubricate the neck interior.
Next, the case neck is re-sized to 6mm using a Redding Type S
bushing neck die with a 0.267" bushing. The bushing is allowed
to float about 0.010" so that the shoulder will cause a very
nice, tight "crush" fit when chambering the case.
From left to right,
an unformed Lapua 6mmBR case, a case with the false shoulder
formed, and a fully fireformed Dasher case. The loaded round is
shown with a Sierra 107 grain MatchKing seated 0.010" off the
lands for this rifle:
9/11/06
More fireforming
testing today, all at 200 yards. IMR4895 was used instead of the
H4895, based on a QuickLoad analysis. It showed higher
velocities for less pressure.
Here are some
results. There were light variable winds, all around the
compass, at about 5 to 9 MPH. Very unstable conditions.
5 Shot group, 0.010"
back from hard into the lands:
These are 10 shot
groups, seated at 0.005" back from hard into the lands:
I need to work on my
technique! This rifle tracks so well in the bags, it is easy to
get complacent about cheek weld and other details. I am sure
that these groups could be a bit better if given a bit more
attention to technique.
The 107SMKs liked to
be nearly jammed into the lands. It will be fun to see what can
be done on a calm day.
The expand-then-resize
method seems to work well. There were 2 neck splits out of 170
rounds fired, and the case length after fireforming was very
consistent:
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Statistics for 6 Dasher Case Fireforming |
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|
|
Base to Shoulder Length, in. - Measured with Stoney
Point 0.350" comparator insert |
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|
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|
|
|
Length, in. |
1.254 |
1.255 |
1.256 |
1.257 |
Neck Splits |
|
Number @ Length |
1 |
25 |
110 |
32 |
2 |
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Total Cases in Sample |
170 |
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Mean Length, in. |
1.25603 |
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Variance Length, in. |
3.62209E-07 |
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Standard Deviation length, in. |
0.000601838 |
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Split Cases, % |
1.18 |
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Accuracy seemed to
degrade a bit after about 85 rounds fired. A quick cleaning
showed no copper fouling, and only a bit of powder reside.
Accuracy returned after this cleaning.
Next steps: Load
development using fireformed cases and RL-15!
10/8/06
Entered a prone 60
shot 600 yard F-Class match at Wenatchee, WA, and shot a 589-16X using the
fireforming rounds. This was on the slightly more difficult M63
target, not the new 600 yard NRA F-Class target.
10/14/06
Shot this 10 shot
group at the Cascade 600 yard range today, using the fireforming
loads:
Can't ask for any
better performance. That string finished fireforming the last of
the 500 Lapua 6mmBR cases.
The Dasher loads look
to be optimum at about 32.75 to 33.0 grains RL-15 behind the 107
SMK, CCI450 primer, OAL 1.782 to ogive (0.010" back from hard
in). Consistent 0.5" 5 shot groups at 200 yards.
10/21/06
I spent the better
part of today working up Dasher loads with the fireformed cases.
I was using RL-15, and tried three different primers, and three
different bullets. Actually, two different bullets, but one was
tried bare and moly'd.
Short summary:
With bare bullets, the OBT/OCW is right at the predicted 33.2
grains RL-15, giving 3075FPS with the 107SMKs, and 3095FPS with
the 105AMax. This is out of the 31" 5C 8.3" twist Broughton
barrel.
The AMax is a clear winner, by a long shot. It groups right at
0.5" for five shots at 200 yards, consistently, no flyers. The
SMKs were no where near as consistent, with flyers out to about
0.8". This was with the bullets seated 0.010" back from hard in.
I played with this seating depth by +-0.010", and the 0.010"
backoff was the clear winner, with the lowest SD/ES and best
overall group size, for all bullets.
The primer that won was the CCI450, again hands down. The CCI
BR-4 was a close second, and the Federal GM205 was a distant
third. The SD/ES with the 450's was on the order of 6 and 18
respectively for five shots, consistently.
The moly'd AMax needed 0.5 grains more powder (33.7 grains) to
get the velocity back up to the 3095 levels, but I only tested
this bullet with the BR-4 primers, as I had used up all the
CCI450 primed cases by that point. It might be good with the
CCI450s. However, this barrel does not foul at all, so I may
just skip this extra step.
So, my best load looks like 33.2 grains RL-15, 105Amax seated
back 0.010", with CCI 450 primers. I am going to proof these at
600 yards, perhaps as early as next weekend, weather permitting.
With the SD/ES that low, and 0.5" groups at 200 yards, it should
be very good at 600.
I am going to record all the group sizes and velocity
statistics, and do some data analysis as time permits. The
results will be posted here.
10/22/06
Performed some
analysis on the data taken yesterday. Here is a picture of the
performance of the winning load combination:
6 Dasher
Lapua brass, fireformed, neck sized with a 0.268" bushing
RL-15, 33.26 grains
Hornady AMax, seated 0.010" back from hard into the lands (1.758
to ogive)
CCI 450 primer
Here are some
statistics from the tests:
107SMK and CCI450
Primer:
105AMax and CCI450
Primer:
105AMax and Federal
GM205 Primer:
These data support
the choice of the AMax and the CCI450.
QuickLoad shows that
the exit time of the 33.26 grain AMax and SMK load is right at
the OBT for a 31.5" barrel - 1.335 mS. I am using 31.5" to
calculate the OBTs from the equations, as the original model
assumed a chamber length of 2.25", and the 6 Dasher is about an
inch shorter. his makes the barrel effectively about 0.5"
longer, as the return reflection actually occurs in the middle
of the chamber. I plan to update my OBT tool with this
correction factor, based on actual case length.
10/28/06
Tested the
performance of the 107 SMK and 105 AMax RL-15 Dasher load at 600
yards. The results were not conclusive, as the winds were highly
variable, and they picked up during the test of the AMax load.
The come-up (from a
200 yard zero, 3070FPS) for the 107AMK was 9.00 MOA, and for the
105AMax (from a 200 yard zero, 3090 FPS) it was also 9.00 MOA.
QuickTarget predicted 9.59 MOA for the SMK, and 9.58 MOA for the
AMax. If you correct the BC's in QuickTarget for these two
bullets to yield these measured drops, you get a BC of 0.624
(published BC is 0.518) for the SMK, and 0.590 for the AMax
(published BC is 0.500). Clearly, they are not that high, but
the Nightforce scope only needed 9.00 MOA to adjust to the new
zero.
Here are some 10 shot
targets:
The 107SMK load
(33.25 grain RL-15, COL to datum 1.782"). The flyer was the
shooter, not the rifle:
The 105AMax load
(33.25 grain RL-15, COL to datum 1.758"). You can see the
effects of the wind change during the group:
Additional testing
will be required in order to accurately determine the superior
bullet for this load. At this point, both appear to shoot
equally well. The SMK seems to be more prone to flyers, but that
is also based on very little actual data, just a perception.
11/19/06
Entered another prone 60
shot 600 yard F-Class Open match at Wenatchee, WA, and shot a 593-22X using the
33.26 RL-15 and 107SMK Dasher loads. Here is a shot of me and
the Dasher plinking at the tiny MR-63 target 600 soggy yards
away. The fog was moving in and out, sometimes obscuring the
targets completely.
It was raining, 45
degrees, and very light to no wind. I won the class, and a nice
turkey to boot! This was a charity match, where the proceeds
went to needy families. Winners got a turkey, and a big smile.
Definitely need to work HARD on the wind reading skills, as the
wind can turn a 0 MOA rifle into a 3 MOA rifle, in a heartbeat.
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