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6mm for Encore

The 6mm bore size in general gets quite a bit of interest and serves such a broad spectrum of applications from varmint on up with some folks feeling quite comfortable using it on elk even.

Accuracy is usually quite natural with it, recoil is modest, and there is such a broad, broad selection of bullet weights and styles available now, something that was rather lacking not too many years back when finding a good reliable game bullet was sometimes a problem. Not so today.

I tend to speak what is on my mind, and with just doing a 6mm/06 Improved, 6mm is on my mind.

.243 Win. is a very popular, well proven round, but tends to elicit a yawn as being about as mundane as .30/06 & .270 Win. All three have been around as staple items so long.

Starting at the top of the scale with 6mm-06 Imp. being the most extreme of the larger capacity 6mms a word or two is in order about fireforming cases for this one. In short, if you are not adept at being creative necking down cases for proper support at the shoulder when fireforming, this one can be a problem. Even when necking down .30/06 cases, it is best to not go all the way down the neck, but rather back off some with the larger neck diameter dies you use, then do the final nudging of the shoulder area with the 40 degree 6mm Imp. size die.

Test firing this one, I even played with .280 Rem. brass, which is longer in the body and gives a little more shoulder area to support the case against the impact of the firing pin, and it works reasonably well.

Giving essentially the same ballistics, the .240 Weatherby is a bit better balanced for case capacity, but its main asset is the belt to headspace on.

More and more I am realizing just how important it is to have a good, solid support of the case, such as with a case rim or belt. Given that we can regulate & fine tune headspace with whatever cases we use, rimmed and belted cases are making more and more sense.

I get accused of beating dead horses, but sometimes it just has to be done….. this time in regard to just how much case shoulders DO collapse when the firing pin drives the case forward in the chamber.

It is STRONGLY recommended that you keep this in mind and for your own information, remove the extractor and simply fire the primer only in an empty case that is otherwise ready to load. Popping the primer without the extractor in place will show you just how much the case shoulder is collapsing.

With the 40 degree case shoulders, the first hurdle is getting the case fireformed without stretching it, but once that is accomplished, the 40 degree shoulder is far and away the best for rimless cases. The 40 degree shoulder shows virtually no collapse from the impact of the firing pin.

Once you make your own observations, you will have a better handle on what is going on, then take steps to minimize stretching if possible. The key is to keep headspace to a minimum to start with and have as ample a point of contact at the neck/shoulder junction as you can.

The .240 Weatherby and the .224 Weatherby are the only two current Weatherby rounds I will chamber in the Encore.

The long freebore is a factor when it comes to accuracy, but so long as the freebore diameter is kept closely matched to bullet diameter and aligned well with the bore, they will shoot well.

In my collection of reamers is one you may never have heard of since it appears to be all but forgotten. I can’t tell you when I chambered the last 6mmx.350 Rem. Mag…. or you could call it the 6mmx6.5 Rem Mag.

Its case capacity is very, very similar to the .284 Win. case necked down to 6mm, the 6mmx.284 Win., which of course also works quite well in the Encore, even with its rebated rim. The number of them I have done is relatively small.

It is sort of a tossup between these two, 6mmx.284 and 6mmx.350 Rem. Mag….. choose your options. One has a pretty substantial shoulder to headspace on, the other has the more rigid belt as well. Both fall into the “short fat” case concept with its better distribution of the primer flash for more consistent ignition.

Similar in case capacity, but in a longer powder column is the 6mm Rem. Ackley Improved, which is best done on the .444 Marlin case, again, sidestepping the weaker case shoulder and shoulder collapse issues by using the rim of the .444 case to stop the forward movement of the case.

Fortunately, using .308 Win., 7mm-08, and .260 Remington size dies as “form dies”, the .444 case works down to 6mm very easily, and you don’t have to spend a fortune on specialized, high dollar form dies to do it.

Of all the above, I tend to lean toward the 6mm Rem. Imp., though the .240 Weatherby data has more wow factor. Maybe some of you can vouch for whether the published data for it is legit & readily doable or not. Except for the freebore factor, 6mm Rem. Imp. and .240 Weatherby should otherwise be essentially twins when fired over the chronograph.

All of the above EXCEPT the .240 Weatherby (its body is smaller in diameter) can be rechambered from any .243 Win. factory chamber AND with the advantage of cutting out at least some of the factory throat while getting at least a short section of new, minimum diameter throat aligned with the bore for best accuracy.

The only down side to starting from a factory chamber is not having the option of cutting a chamber that produces less bulge at the case head. Whatever diameter is there to start with is at least what you will end up with, plus a tad from any chamber misalignment and the polishing process.

What follows has to start from a barrel either unchambered or per chance a custom barrel with a chamber smaller and/or shorter than .243 Win. Given no factory throat in a new barrel, all of the resulting throat is to my spec.

.243 Win. Imp. has to start from a somewhat shorter chamber than the standard .243 Win. This is for the express purpose of fireforming without excessive case stretching. Thus you canNOT rechamber a standard .243 Win. to the “improved” as “improved” is defined. You CAN rechamber to that configuration ok and take steps to give adequate support for fireforming starting from, say, the .308 Win. case, but NOT using a standard .243 Win. case. However, such a progeny has to be christened with a different name that does not include “improved.”

Backing off the form dies and the final 40 degree die so as to move the case shoulder and chamber shoulder contact area forward for a snug fit will let you fireform correctly just as is the case with the similar process you go through for the 6mm/06 Imp. Ie, highly doable, but best done at the hands of a reloader who has his brain wrapped around what is going on inside the chamber as evidenced by what he sees and measures from the outside, then is careful to watch for indications of case stretching before charging head long through a batch of cases only to find they are all ruined from stretching.

The 6mm Remington is still one of the best of the 6mm’s and one we will be particularly diligent about filling the many requests we have had for it. It, too, like the 6mm Rem. Improved can be made rimmed using .444 Marlin brass quite readily.

Quick note on the 6mmx.30/30 Ackley Improved. Fun little round, it is one I get requests for now and then, but usually just in Contender barrels. Down side for the Encore is it does not do anything the standard, easier to work with .243 Win. does not do better. On the plus side, there is the case rim. Another down side is the thin brass, but it is cheap, easy to form once you get past the pain of custom form dies, and throwing cases away after a few reloadings does not dent the budget too hard.

6mm BR…… amazing little round and done right has proven itself a real winner in the accuracy department.

It and the smaller 6mmx.223 may not set the world on fire with dazzling ballistics, but both deliver a lot of good accuracy at a small cost and with very moderate recoil and muzzle blast.

Toss into this latter category the old 6mmx47, the short lived 6mm TCU, and 6×47 Improved.

Choose the power level that suits your interests and needs the best. All the above are just some quick examples that come to mind, but of course one can always get creative and come up with all sorts of variants if custom dies are not a stumbling block.

The ever popular 6mm bore size has LOTS of possibilities and a tremendous range of bullet weights & types available. With a good supply of .243 Win. barrels on hand to rechamber and with unchambered barrels due in after the first of the year now that BPI/Bergara is closed for the holidays, you have a lot of choices available if you admire the 6mms anything like I do.

For any of the above, just respond to this email address, and Kurt will get you lined up with a barrel.

All the best!

Mike Bellm

Filed under: Shooting