6BR questions...

J

Jackson~in~GA

Guest
As some of you know from my other thread I have decided to build a 6BR repeater on a 700 action. I don;t have any prior experience with the 6BR , and was curious as to what I would be best with as far as a barrel twist and length goes. I was thinking maybe a LV contour barrel 24" long. What length does it take to make the cartridge perform? Is it worth the effort to turn necks or chamber with a reamer that won't require it. Also is there a twist that can stabilize the 95gr bullets and still work for lighter bullets down to 55gr? Thanks in advance. ~Jackson
 
Jackson, much of what you want to know is here:

http://www.6mmbr.com/6mmbr.html

For 95gr VLDs you'll probably want a 1-9 twist, for 95gr BIB FB bullets you can get by with 1-10. I've got a 1-9 so I can shoot the VLDs.

More commonly folks are shooting 105-108gr boat-tailed bullets with a 1-8 twist, but it would be hard to throat the chamber to touch the lands with both the 105-108gr bullets and the 95gr VLD -- the 95 VLD has a very short bearing surface.

Any of these twists will stabilize the lighter bullets, too.

Toby Bradshaw
baywingdb@comcast.net
 
I suggest you go with a .272nk, .030 freebore and an 8" twist. This will allow you to shoot darn near every combination you can dream up....... well.

Ohhh, and why limit yourself to a 24" bbl? I say let it finish out as long as possible and then you can set it back if need be. Maybe get some more life out of it....and freshening the crown can be beneficial.

Don't worry about "overstabilization," there is no such thing. "Over rotation" is real, but it has only to do with blowing up bullets and with the slight decrease in 100yd accuracy due to bullet eccentricity. And by "slight" accuracy degradation I do mean slight! Your 100-200yd accuracy will still be stellar with light Match bullets.... Your bullet will still nose over to follow the flight path, it can't help it. Even high rotation bullets don't fly "nose high" as some will contend. You will be able to crank bullets like the 55gr and 70gr Ballistic Tips right up to the top of the velocity ladder with no detrimental effects.

You're in for a treat! :)

al
 
gotta dissagree....with Al....

I reccomend a .040" FB....:D !!!...because that is the reamer that I have .hahaha......Al is rite ....you dont want a lot of FB so that U can use the lil' bullets as well as the 105-107 class ....and of course a no turn neck ...it is a great combo....(((when I get a new reamer it will be .030")...Roger
 
Freebore

One thing you want to avoid is the shank of the longer bullets (Berger 105's, Sierra 107), going past the neck shoulder junction.

Anything shorter than a .060 free bore, and they will.

The 6BR is really two distinct chamberings. One, you use a 1-12 or 1-14 twist and lighter weight match bullets with a powder in the burn rate of N135, deadly at 100-300 yards. A .060 or shorter throat works great here.

The second concept, is a 1-8 twist, 28 inches of barrel, .060 or longer throat, and long VLD style bullets in front of Reloader 15 or Varget that make the 6BR a deadly contender at 600 yards,

There really isn't much in between, that is, not for optimum performance.........jackie
 
Jackie,

I've used the .030 freebore with 105's and let the shank hang down into the case. It's harder to get the velocity but for an all around chambering it works fine. Even with the .030 freebore it's easy to run in the 2750-2800 velocity range, 2900 is a push, hard on brass. Since the no-turn 6BR doesn't have a donut the only result of the short throat is a reduced case capacity.

Incidentally I recently loaded a bunch of 300WSM's with the new Barnes 168gr TTSX's and these things not only HANG DOWN into the case, there's a machined groove on the shank hanging down into the powder chamber! It scared me at first until I looked at the factory loads, they're hanging in even further.......

All I'm saying is, just hanging the bullets down past the junction isn't a real problem UNLESS you're interfering with a donut. And it lessens the usable case capacity.

al
 
Since I have a .060 freebore on my 6PPC, and friends have that on their 6 BR varmint rifles, I think that I can speak to this detail of chamber design. While you can get very acceptable varmint accuracy shooting light bullets in a fast twist barrel (Lots of 9 twist .223s do.) I don't think that anyone that was serious about competition at the shorter ranges would pick a fast twist to do it with. At the other extreme, for longer ranges, 600 to 1,000 yards, there have been credible reports that lead me to believe that loading to high pressures may be a requirement to reach the desired velocities, even with barrels that exceed field handy length, and throat lengths that are more "normal" for long bullets. Additionally, with my .060 freebore , there are only a couple of short range (light) match bullets that I cannot use, and I think that it would be fair to say that any any small advantage that they might have over all of the rest would be lost in the noise if they were used with a non optimal twist. The only application that where I would look at a shorter throat for a 6BR is a rifle that was going to be almost entirely used with 55 gr. plastic tipped varmint bullets. For that application, a friend has a barrel that was chambered with a zero freebore reamer that has a throat angle greater than 1 1/2 degrees, so that the rifling can be reached with some shank left in the neck. Of course this chamber would be totally unsuited for a 105. In my opinion, when the best results are desired, I think that it is better to design for a particular class of bullets. Switching barrels is so easy; that is the way that I would go.
 
6BR and half a thread hijac

Yes.... On thread #5 & #7

Jackie and Boyd....... I too use a .060fb in my 6ppc reamers...
I believe that between .050 and .060fb is perfect for 100/200/300 Benchrest ..
Would be perfectly suited for the question in this thread.. 8 twist 6BR.

I shoot the little 6mm 55gr B-Tips a bit and as short as the bearing surface is (the boat tail is not helping here either...:rolleyes:), I have no problems seating these little guys out to a fair amount of jam and still have "enough" bullet in the neck (I check concentrics and they is straight!)... This with a 1.5deg 30 throat.

So, yes I'd say go no shorter than .060fb 1.5deg 30 and shoot ALL the 6mm pills to your delight...!

Side note.... Speaking of the little 6mm 55gr Balistic Tips..... Wow...!
Got a box from Midway few months ago and was monkey'n around and saw what was VERY impressive.... ALL, EVERY ONE was within .0015 at the ogive....... This a MASS produced bullet, heck 80% were >>>THE SAME<<< "dead nuts" at the ogive... Has to be coming off the same dies...

Now....... Get this.........!

Was at a Bass ProShops two weeks ago getting some 20guage dove/quail shells... I waltzed over to the buwets section and saw two boxes of 6mm 55gr B-tip 250rds............. Turned them over and the sticker showed the same numbers/letter in what is what I'd guess is lott #..... Bought'em both.
Yes ... Holy cow, they meaured + -.0015 and from what I could tell 80% of 'em were DEAD ON............. Simply amazing...! This IS custom bullet consistency...!

Now is where this get UNGODLY...........................!

The bullet box I discovered this from showed totally different numbers/letters... Totally diff lott.....

There was a whopping .003 thous diff from the ones I had just bought.....!
Bet if I were to measure ALL 750, the total run out at the ogive would be well within .003...... Gotta be the same Dies/set-up...!
MY bullets arn't much better than this from production J4 bucket to J4 bucket....!

Ohhhhhh, they shoot REAL WELLLL......... I will give them an honest whirl at the Denton club shoots from time to time...!

Anyone else seen this...?.. By far..... OK, BY FAR! The most consistent >> Mass produced<< bullet I have measured for ogive.... The weights were damn consistent as well... .18 - .20 cents a bullet and this >good< is a heck of a deal!

Check'em out, I'd have to say the 70gr Btips prob do the same....?

Blog off..........:D:)

cale
 
6br

Jackson: A Shilen and Hart, both 1-14 twists have .265" necks, requiring neck turning the Lapua brass-- no big deal, now that I've learned the process. A third chambering is a 1-9.25 twist, with a .272" no-turn neck. Loaded Lapua neck dia. is .269", and use the .267" bushing. When the Shilen & Harts are "done", they will be replaced with chambers cut with the same reamer (Pacific) that was used for the .272" neck. I'm sure others will dis-agree, but in my case, I'm very happy with the .272" no-turn chamber neck dia. In my mind ( maybe wrong?), it seems like a waste to see all the curley-cues of Lapua brass laying on the benchtop, when they may be better served to be on the case neck. Nice to be able to use the Lapua, as it comes out of the box, with little preperation. If I feel the need to turn necks, there is always the 6ppc and a 22BR. Whatever though, the 6BR is a great ctg., probably my favorite 6mm.
 
I'm finding this discussion really helpful as I am just trying to decide how best to chamber a 6BR for a medium range prairie dog silhouette match I want to shoot monthly.

This match has two classes, light and heavy, determined not by the weight of the rifle but by the weight and caliber of the bullet used. Caliber in light class is maximum 6mm. Ranges are in light from 200yds to 385 meters and in heavy from 200 meters to 500 meters.

I'm mostly a long range shooter. My 1K light gun which is chambered in 6BR, 1-8 twist, 272 nk, .104 freebore and that shoots 105 VLD's or 108 Berger BT's very well will work fine for the heavy class.

But, in the light class I want to shoot 6BR also but can't use bullets weighing more than 70 gr. I doubt that the twist and freebore on my LG will work well with the shorter bullets.

I suspect I'm going to end up putting together another rifle for the light class. My question is....what would be the optimum 6BR twist, chamber, bullet and powder combination for ranges from 200 yd to 385 meters using bullets weighing 70gr or less? Target sizes range from 4"X2"" to 9"X5", not so tough, but wind drift is really an issue here in the desert.

I'd appreciate your thoughts. Thanks in advance.

Chuck
 
what would be the optimum 6BR twist, chamber, bullet and powder combination for ranges from 200 yd to 385 meters using bullets weighing 70gr or less?

1-14" is sufficient.... But just go with a 13 to 13.5 and you'll be set.

Benchrest handmade bullets... Now you can win...

cale
 
Another way to look at this conundrum.........

In retrospect I may just switch my vote for "all around freebore" to .060...... Here's my (revised) view. Given that the 6BR in an 8" twist WILL NOT actually be "competitive" in 100-200yd Bench Rest, no matter how you throat it......And given that even with a .060 throat it ABSOLUTELY WILL still be varmint-deadly accurate..... (I mean how can you actually MISS a varmint at 100-200yds??!!!)

And given that the .060 freebore truly IS a better choice for 600-1000yd shooting......... and within 100-200 WHO CARES! Except for pure-dee competitive BR you simply can't miss.


I'm convinced, I've got to agree with the others due to better logic.

Even if you do have to jump a few of the small bullets, it ain't gonna' really hurt you.




OK, it's official, I RETRACT my choice! I'll vote for .060 for the OP's setup. ;)

LOL



al
 
All of the input is greatly appreciated! I am not going to be shooting this rifle competitively, but I do want it as accurate as I can get it. However I do have a 600yd and 1000yd range and I would like to be able to shoot the heavier bullets on it. The lighter bullets would only be used on varmints so if I give up some accuracy jumping them to the lands I can live with it as long as it is still "minute of varmint"
 
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