Project 6mm-284 winchester

7-30 004



Project 6mm-284

From Vais to Arch to 6-284 some things never change.


“Whatever cartridge design that is necked up or down, blown out or shortened has already been experimented with”


This is a phrase I read years ago and it has stuck with me like copper jackets on bullets, as I recall in a recent VHA issue #71 an article on a 22-6.8, later to be compared to the 1940’s era Lindahl Chucker cartridge. Its funny how things are forgotten then rediscovered as with my latest cartridge notion which brought me thru a full circle process when wanting to wildcat my favorite 6.5×55 A.I. case. In a previous article I wrote for VHA issue # 68, a 6.5×55 A.I. chambering was chosen; while reloading the 6.5×55 A.I. brass I wondered what performance I could obtain from necking it down to a smaller caliber. After consulting friends about the wildcat chambering I came across “The Vais” rounds based on the 6.5×55 Swede cartridge.


George Vais improved the brass then necked them down to .224” and .243”. The Vais loads used a heaver bullet than I intend on using however the velocities looked very good with published data. Along with several short articles and ballistic data found on-line all my questions about necking down this case were answered. A 6mm (.243”) bore diameter was picked for this build to fill the gap between my 22 caliber and 6.5 caliber varmint rigs. I really liked the idea of the 6mm Vais cartridge it looked to be a very promising one with good velocities along with a vast choice of 6mm bullets. After researching custom reamers and reloading dies along with head space gauges the costs were reaching far more than I wanted to spend on this venture.


While re-reading the Vais articles I noticed a small reference in one section making the comment about a “ballistic twin”; this small statement opened the door to huge cost savings to my now revived project! The 6mm Vais ballistic twin is the 6mm-284! Again more research started and while pouring thru P.O. Ackleys handbook for shooters and reloaders  the 6mm Arch cartridge was found. Developed by Dr E.L. Arch the 6mm Arch is a 6.5×55 Improved case pushing 60 grain pills at velocities of 4200fps!!  Ok now I’m hooked and orders were placed for components to build a 1-12 twist 6mm-284 varmint rig. The action to be used if you haven’t already guessed by my other articles printed in this magazine (issue #60 & #68) will be yes once again a Mauser M98, now with consideration to chamber pressure the soft receiver core along with a case hardened surface, the Mauser action will hold up for many years of faithful service. P.O. Ackley’s volume II handbook lists several blown up actions along with pressure comments on several military conversions, the actions are nicely machineable and provide an excellent platform for accurate varmint builds. Bolt lock time can be improved by 40% (I’ll cover this later) and quite a few gunsmith/hobbyist/shooters have cut there teeth on customizing Mausers. Parts are abundant and many enjoyable hours can be spent machining parts for custom applications; bolt shrouds, bolt stops, receiver charger humps, rear tang, bottom metal…’s endless!


When built with correctly fit components the finished rig can easily shoot in the .2’s at 100 yard ranges, I know this because I have built and shot several sub-moa Mausers. First up the bolt needs a low handle so I shipped a Ruger M77 style handle and the Mauser bolt body to “the bolt man” James Robert from Paxton, MA, he will do a fantastic tig weld job at very reasonable prices along with bead blasting if requested. I decided to have the bolt handle polished bright while the bolt body would be bead blasted. During the time it took to have the bolt work completed I modified the bolt shroud to function with a side safety, I  will say building the fixture to machine the shroud was just as fun as milling the shroud itself!  The finish on the shroud and extractor were blued and the cocking piece was polished bright. Now focusing on lock time of the firing pin will need to be addressed and a Blizchreen 24lb firing pin spring from Brownells was ordered, I have noticed when using a Buehler wing type safety along with a 24lb firing pin spring the safety will be heavier to operate. The side safety will only need a moderate touch to function with the new spring installed and this will produce an improved lock time which is adequate for what is needed. With the bolt finished I completed typical action work; lap lugs, polish rails, chase receiver threads, square bolt face, and as usual contoured the metal to have a sporter look. A call to Boyds resulted in a nice pepper laminate varmint stock that was shipped right away, after pillars; action bedding then free floating the barrel this would serve the purpose of a load development platform. After all the heavy laminated Thumbhole bench rest stock would not arrive until quite some time later and I just had to see how this rig would perform!


I had earlier placed an order with E.R. Shaw barrels for a short chambered, 1.250” diameter straight no taper stainless steel 26”, 1-12 twist heavy varmint barrel.  I could now turn my focus on finish chambering this fine tube, headspace gauges and finish chamber reamer came from PTG and are excellent quality tooling. There is a special joy in finish chambering a custom built rifle and with only .009” (aprox. 3 sheets of standard paper) between the go gauge and the field gauge a light touch is all that would be needed to obtain a nice snug varmint/target chambering. I have always liked light pull weight triggers and thought I would try a Jard 8oz trigger; the fit was great along with smooth function, creep, over travel and sear engagement are adjustable. Looking thru the scopes I had on hand I decided on a Tasco World Class 24×44 target model, this will allow for some fine placement of the 1/8” target dot on the reticule.


I have spent countless hours on-line gathering data on 6mm-284 loads and then crunching the numbers with a Quick Load program ( VHA issue #70 has an excellent article on the use of this very effective program). The more I read gave fuel to the excitement of this cartridge! Keeping in mind as with any overbore chambering hot loads equal short barrel life. So even thou I plan to touch the outer fringes of that wonderful +4000fps I will slow things down to preserve the barrel some. RL22, RL17, IMR4350 and IMR4831 seemed to be the powders of choice for this 6mm along with 66grain custom H.P. jacketed bullets made by a fellow VHA member Dominick Gagliostro. Winchester cases already necked down to 6mm were purchased, full length resized and trimmed to 2.165” along with flash holes deburred.



The first trip out to the range was a nice mild 60 degree day with a slight breeze. I decided on RL17 & RL22 as starter powders and used mag primers from the start. With case length trimmed to 2.165”, necks turned to .014” thick an overall cartridge length measured at 2.800” to the tip of the 66grain match bullets. I was pleased to see three shot groups of ½” at a velocity of 3514fps while using 52grains of RL17, now for the surprise while grouping the RL22 loads of 53 and 54 grains both printed the first two shots in the same hole with the third opening the groups to just under ½” with a velocity of 3300fps. As I have read the secret to bringing this cartridge to life is with the use of slow burning powders, first round loads didn’t show any high pressure signs bolt lift was easy and 4000fps might be seen in the next load batch. (accuracy will trump velocity for me)

Very mild recoil and ease of load development is a wonderful thing to experience during beginning load development! The first twenty rounds gently seasoned the bore along with proper barrel cleaning and I am excited to load up the second batch of rounds to further check for accuracy and pressure. Time at the bench assembled another twenty test loads then off to the range. Temperature was at 57 degrees  with a slight breeze again, first up would be the RL22 batch with 55grain loads producing .243” groups @ 100yards with 3444fps. With the 24x tasco holes on the target could easily be seen and what a delight to look at one ragged hole! RL22 would not be the powder to produce velocities close to 4000fps as 58grains opened the group up to ¾” @ 3778fps.


RL17 turned out to be the velocity king with this barrel combination. As I slowly touched off the 8oz trigger mellow recoil allowed me to quickly re-sight the X-ring and after three rounds punched thru the paper I was glad to see that 54grains under the excellent 66grain match bullets printed a very nice .164” group @ 3844fps. Now seeking the 4000fps mark I went one grain hotter and found 55grains opened the group to .306” @3920fps, as the groups seemed to spread out with more RL17 an odd thing of slightly easier bolt lift was noted. When cleaning the barrel later that evening no copper fouling was found and the carbon quickly brushed out to leave a bright shinny bore that will be coated with (lock-ease) liquid graphite. Another test batch of RL17 & RL22 rounds were loaded up to check consistency, 54grains and 55graind respectively.  Bullet seating depth would be adjusted to find the sweet spot for both loads. As you can see by the load data chart both loads proved to be accurate and consistent, I will use RL22 for target shooting to save the throat while shooting RL17 for live varmint control. After load development was finished the Boyd’s stock was sold and the Richards micro-fit bench rest stock was shaped, bedded and pillared. Ordered as a blind bottom stock I made up new action screws and custom length pillars along with a cut down magazine box that I bedded in the stock to provide an extra locking point for the action when tightened down for accuracy.



I thought this would be a good time to check out a new optic line (new to me) so a Leatherwood/Hi-Lux 7-30×50 Uni-Dial scope was ordered. I have had a lot of conversations with Corbett Leatherwood regarding his optic line since there is a lack of reviews available on line, posted in the Varmint Hunter Magazine optic forum I started to test these scopes out and have posted results for members. As a little known company there quality recently has reached excellent levels for clarity, crisp image, durability and after talking with Mike Sexton at Iron Sight he ranks then as good as Leopold’s!

Features I like are the programmable elevation flags that will lock in any desired zero for 10 different ranges. The windage  turrent  has a zero set that will allow windage adjustments to be made without any chance of losing your original zero, then there is the unique feature of the objective focus adjustment knob that is located at a 45^ angle in front of the turrent housing! Unique to Leatherwood/Hi-Lux and very easy to operate. At the range I found tracking to be right on while shooting the “box” test and no point of impact shift was noticed as I ran thru the power settings while keeping a reference zero. This is a Second focal plane construction with a fast focus eye bell and a 50mm objective, another handy feature is the No-Math Mil dot reticle. With a quick frame of the target then look at the power ring (which will also indicate range) turn to elevation to the correct flag and dust that critter! A sunshade and flip up end caps are included along with a lifetime manufacture warranty this turns out to be a very nice optic.



Looking back at this build has shown me the potential of the 284 Winchester case. I am pleased with the accuracy and looks of the now completed rifle (as pictured with a 7-30×50 Leatherwood and Richards stock) in 6mm-284. I would like to think I have a complete collection of rifles chambered for my needs, however that all changed when my 22-284 Winchester barrel arrived a few days ago……I’m kinda liking these overbores!



winchester 284 cases, necked down to .243 and turned to .014″
flash hole debured,annealed necks/shoulder
CCI magnum primers
trim to 2.165″
C.O.L. 2.800″
bullets- custom 6mm, 66grain match j4 jacket
49grns 3346fps primers backed out slightly (to light load)
51grns chryno error clean necks, easy bolt lift (.50″ group)
52grns 3514fps clean necks, easy bolt lift (.50″ group)
52grns 3055fps dirty necks, easy bolt lift
53grns 3136fps dirty necks, easy bolt lift   (see note)
54grns 3300fps clean necks, easy bolt lift   (see note)
note: first two shots in same hole with third opening group to +3/8″
chrony placed 10′ in front of muzzle, 60 degree F, slight cross berrze, 100yards

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Groups during load development

Groups during load development



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2 responses to “Project 6mm-284 winchester

  1. I have 1910 FN Mexico Mauser with a 22″ barrel. A smith cast the chamber, declaring it to be a 6MM284. Using Lapua 6.5X284 brass and Lee dies, I resized the brass and loaded 85 grain Sierras to an overall length 2.755. Only one round would completely chamber. I could not close the bolt on the rest…any suggestios?

    • I have found that .014″ neck wall thickness works best in a no turn neck chamber. Also check the case overall length compared to the chamber casting (if cast with cerro safe remember that the cast will grow after about 24 hours). Mic the cast neck diameter to verify if it is a tight neck chamber or not.

      Hope this helps some


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