A Rifle for the Long Shots – The 6mm DasherThe next task was to determine the best method for making the brass. The typical reshaping of a case using forming dies was not an option for the Dasher since the shoulder is longer than its 6mm BR parent case… not shorter like many wildcats. Investigation showed that Dasher cases were being devised in several ways. What appeared to be the most popular was to open the neck of a 6mm BR case with a .257 caliber or 6.5mm expander, then size the case neck about half-way down, leaving a ‘donut’ on the outside of the neck to headspace the cartridge. The cartridge is then chambered and fire-formed.
View of the Dasher with 300-yard targets in the distance.
Another often used method is to take a standard 6mm BR case and, using a bushing-type sizing die, size it such that the neck will have heavy tension on a seated bullet. The bullet is then seated into the lands and fired with a near full-power load. This method is certainly the easiest and has the advantage of not working the neck of the brass. In any case, a lot of barrel-burning is required with either of these methods to get the final product.
It was on a trip to the IBS 1000 Yard Nationals where I learned about a new type of forming die… at least it was new to me. Visiting the Hornady Manufacturing booth I mentioned my interest in the 6mm Dasher, and asked which fire-forming method they would recommend for making cases. One of the techs smiled and said, “Neither. Why don’t you use one of our hydraulic dies?” Then he described how it worked and showed me some brass he was using in the match… it was a wildcat cartridge he and Dave Kiff of Pacific Tool and Die had designed. He compared it with a case that had just been through a hydraulic die, and one would have to look closely to see the difference. With that demonstration I was sold on the concept.
Hornady hydraulic die. Case on left is standard 6mm BR and case on right is after re-sizing in the hydraulic die.
After returning home Ben Syring, Hornady’s custom die designer, was contacted. He advised that the various specifications for the Dasher are so similar between reamers that Hornady carries a standard set of regular dies and a standard hydraulic die. After a most enlightening discussion the hydraulic forming die was placed on order, along with a set of Hornady Match reloading dies.
During my Dasher research the use of Lapua 6mm BR brass to make the Dasher case was mentioned almost exclusively so I gathered up two hundred rounds. The cases were prepared by first seating spent primers in the unfired Lapua 6mm BR cases. Although obvious, it is imperative to insure the primers have been fired and the firing pin dent has not punctured any of the primers (as this would allow water to leak out of the case).
Each case was then filled to the very top with water and placed in one of Sinclair’s poly loading blocks. Next, the special Hornady shell-holder was slipped into the ram of the press. This shell-holder is similar to a standard version except it does not have a hole for primer service, otherwise the hydraulic pressure would drive the primer out of the case and through the hole in the shell-holder. Once the shell-holder was in place the hydraulic die, complete with die rod, was mounted in the press and adjusted so the base just touched the shell-holder.
To create a Dasher case a water-filled 6mm BR case would be retrieved from the block and the outside dried with a paper towel. Before inserting the case into the press each case was checked to insure it was full of water with no leaky primer. Once the case was in the press the handle was pulled down to move the case up into the die.
With the press handle held steady with one hand, the hydraulic piston (or ram) on the die was given several raps with a dead-blow hammer, making sure the hammer hit the piston directly on the top center. Finally, the case was removed, emptied of water and set aside. Once all cases were formed the spent primers were removed and both the cases and the hydraulic die were dried. That’s all there was to it… and no bullets, powder, primers or barrel wear was required. The results are cases that look very nearly like they have been fire-formed. A little over an hour at the press provided a hundred cases.
Left to right, 6mm BR Norma case, after hydraulic die forming, and a fire-formed 6mm Dasher.
The Savage rifle, along with the Krieger barrel and PTG reamer, was delivered to Eddie Webster, a top-flight gunsmith from Boones Mill, Virginia who put together a nice 22 PPC varmint rifle for me a few years ago (This very accurate rifle was the topic of an article in the Summer, 2013 issue of Varmint Hunter Magazine). A month or so after the rifle was dropped off at his shop Eddie called to let me know the Dasher was ready, so I headed for Boones Mill.
Eddie met me as I drove up and we went in his shop to examine my ‘new’ rifle. As he handed me the rifle he commented, “Whoever did the work on the action did an excellent job, I gave the action a thorough check and no accuracy work was required.” When asked what he had done Eddie replied, “I did my typical barrel installation for a bench rifle; the contour on the Krieger barrel was machined, then chambered and threaded, then the barrel crowned. After I was satisfied things were as good as they could be I test fired it at the range. Only had a few rounds so I could not start developing a good load.” The craftsmanship was typical of Eddie’s work; beautifully done. After our chat, and with a smile on my face, I took the Dasher and headed back home.
For a reasonable chance at a successful thousand yard shot I estimated the rifle should be able to shoot one inch groups at three hundred yards. Of course the shooter would have to do his part, and not being an expert at adjusting for wind or mirage, I would be the weak link in the chain. The initial load development would be using a bullet well known for its accuracy, the Hornady 105 grain A-Max.
These projectiles are reasonably priced, have proven to be very accurate and hold several long range records. In fact, several years ago Kyle Brown set a new 1000 yard world record for ten shots with a 4.2-inch group, and he was using Hornady’s 105 grain A-Max. At that rate Kyle might have gotten eight or nine prairie dogs with those ten shots. The general consensus is that Varget, Reloader-15 and H-4895 are three of the most popular powders for the 6mm Dasher. At the time only Reloader-15 could be located, but that was no problem as this powder was used to set a thousand yard world record with the Dasher.
On the first trip to the range, several fouling shots were executed followed by the first A-Max group at a hundred yards. It measured .275-inch, what I thought was a good omen. Over the period of several months load development continued, trying different powder charges and seating depths. The A-Maxes were averaging .409-inch at a hundred yards and 1.554-inch at 300 yards, good performance but I thought the rifle should do better. Don Lahr of Precision Ballistics was contacted and we discussed the goal of one inch groups at 300 yards. As expected Don was very interested in the challenge and said he would send me some 105 grain VLD bullets that “should do the job”.
When the bullets arrived there was a note enclosed: “I used the thick wall J4s, and the seating went exceptionally well by using just the perfectly sized seating punch, so the center of gravity should be very consistent for them all. The bearing lengths are all plus or minus 0.015-inches and the weights are all plus or minus 0.1 grain. I burnished the tip of every bullet with a finger nail buffer/shiner to remove any rough edges from the tooling and polish them. They should be very aerodynamic, concentric, balanced and uniform. In my humble opinion, these bullets are capable of groups two inches tighter at 1000 yards than out-of-the-box factory competition bullets. You should be able to shoot 2½-inch or smaller groups at 1000 yards. My rifles agree, as do reports from hundreds of my customers, that they prefer a seating depth jammed between 0.005 and 0.010-inch, with most doing best at 0.007-inch. Of course your gun may differ, but that should be a very close starting point. I’m confident that my bullets will not be the weak link in the chain for your trial.”
Testing was begun with the 105 grain Precision Ballistics bullets and continued over a period of several weeks. All manner of bullet seating depth was tried but accuracy was just slightly better than the A-Max bullets. Then one evening while scanning the internet I read about someone having problems setting an accurate bullet seating depth for ‘jamming’ because the case neck tension was too loose… this allowed the bullet to slide back into the case when chambered. That immediately rang a bell with me. A quick test of the bushing in the Dasher sizing die showed it would not hold a bullet snug enough to jam a bullet into the lands. There was no way of knowing how deep the bullets had been seated on my loads, so the last several weeks of testing had been for naught.
My morale was rather low at this point so I called Eddie Webster to discuss my woes. After listening to my tale, and with his normal enthusiasm, he commented, “I think the reamer we used has too much free bore for 105 grain bullets. Let’s return the reamer to Pacific Tool and Gauge and have them regrind it based on Dave Kiff’s recommendation. I’ll re-chamber the barrel with the new reamer… I think we can get it shooting the way you want it.”
Again my morale was elated, how could I turn down an offer like that? We set up a time to meet at Hardee’s restaurant, halfway between his place and mine. We had a cup of coffee, a biscuit and spent some time discussing the project. After the enjoyable session Eddie left with the rifle and I headed home with an optimistic outlook.
While the rifle was at Eddie’s the brass and reloading equipment were checked thoroughly. Although the case length variation within the Lapua cases was only 0.002-inch, they were all trimmed to 1.534-inches, then chamfered and de-burred. The flash holes were checked… each had been cleanly punched out. Just to be sure, they were touched up lightly with an RCBS flash hole de-burring tool. Each case was then weighed, with the result showing a weight variation of less than two grains… no sorting was needed.
The dies were checked and cleaned. The Hornady sizing die bushing was 0.263-inch; this would size the neck such that the inside diameter of a case neck would be 0.02-inch less than the bullet diameter, insuring the bullet would be pushed into the lands during the seating operation. The Forster Micrometer seating die was also checked and the results verified with a Hornady Lock-N-Load gauge… the bullets would be seated exactly 0.007-inch into the lands. Some test ammo was then loaded and set aside, awaiting the return of the rifle.