M700 6 Dasher

07/20/13

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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:

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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.

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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.

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Spindle spider

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:

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Finished bedding

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:

Statistics for 6 Dasher Case Fireforming        
         
Base to Shoulder Length, in. - Measured with Stoney Point 0.350" comparator insert
         
Length, in. 1.254 1.255 1.256 1.257 Neck Splits
Number @ Length 1 25 110 32 2
         
Total Cases in Sample 170        
Mean Length, in. 1.25603        
Variance Length, in.  3.62209E-07        
Standard Deviation length, in. 0.000601838        
Split Cases, % 1.18        

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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