6mmBR Norma Chamber

lejarretnoir

lejarretnoir

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What type of chamber are the 6BR Norma gurus using to get those .001" groups?
I've seen the original Norma specs and I made up one slightly tightened in the neck and body for unturned necks.
Are you turning necks for tight neck chambers?

6mmbrnorma.png
 
I have a factory Savage, and no threat of a 0.001" group! But, it will shoot quite a few 3 shot groups in the 0.1XX" range. Based on fired brass neck measurements it is about 0.271" mid neck, but has nearly a 0.002" taper. If anything the neck is too tight at the mouth end. I do not neck turn, and use the older cardboard box Lapua brass, which is thicker in the neck.

While some still turn, most are going no turn. This has been complicated by Lapua admitting some of their older brass (cardboard box) was too large and some of it was exceeding CIP maximum neck dimensions when loaded. The newer "blue box" brass is about 1-1.5 thou smaller in neck OD loaded. As a result PTG have a no turn reamer spec based on the old brass (0.2720-0.2708 taper), as well as a new blue box no turn reamer (0.2704 no taper). If you are interested in a copy of the PDF drawing PM me with an external e-mail and I can send it to you.
 
I've have also been fiddling with a 6br build and chamber blueprint for a while.

Ron,
Would you consider buying a crap load of brass and work backwards to a custom reamer specification, or would you just run the standard no turn reamer??

I am leaning toward tun ing the reamer to suite the brass, but (straight up) I am out of my depth here.

Thanks!
 
X-fan said:
I've have also been fiddling with a 6br build and chamber blueprint for a while.

Ron,
Would you consider buying a crap load of brass and work backwards to a custom reamer specification, or would you just run the standard no turn reamer??

I am leaning toward tun ing the reamer to suite the brass, but (straight up) I am out of my depth here.
Click to expand...

The "blue box" reamer from PTG is essentially a Lapua brass reamer already. Lapua is by far the most popular brass choice. Norma makes it but it is more expensive, and potentially not as good. The neck is the only sensitive dimension in any case.

Lapua brass in a tight chamber will likely last 40 reloads or more, so a huge amount of brass is not needed.

What is more controversial is whether or not the cases should be neck sized and the shoulder bumped, or full length sized each time. Quite a few full length size, but not with a standard FL die. They either have a custom FL die made to match their reamer, or make their reamer to match a specific die -- most likely Forster. Forster will hone out the neck in their standard die so you do not need to use an expander ball. And if the reamer matches the Forster body, you can full length size each time with minimal working of the brass.

I use a Forster Bushing/Bump die and size the neck to give 0.001" grip on the bullet, and at the same time bump the shoulder back 0.001".

I would avoid neck turning. It is no where near as simple as it first looks.
 
Mick, my gunsmith, does my chambers with his reamer. It is a JGS 6BR Norma reamer and he specs them with "no-turn" .272" neck. I have all "original" Lapua brass though.

NOW.... Lapua changed the dimensions of their brass. The factory brass used to have a neck wall thickness of 0.0140". The now have less than 0.013" so the definition of "no turn" has changed.


If you want a true no-turn neck with minimal clearance, you will want a .269-.270" neck. I will be completely honest though.... I have seen and shot some particularly impressive loads using SAAMI .005" neck clearance. I think chamber/neck dimensions are not as important as leade/free-bore. Ensure you have a frreebore for the bullets you use. Sierra and Lapua 107/105 bullets have different optimal freebore . I think the reason for this is that Bergers have ALWAYS worked for me stuck intot the lands, and sierras like to touch, so it doesn't matter how large the neck is, the bullets are self-centering with their position relative to the lands.

I would spec a .185" freebore as a good "work with all" freebore measurement.
 
If your intent is to shoot short range then you will want a 12 or even slower twist and a shorter free bore. It will be harder to find a reamer for that purpose as most use the 6BR for longer ranges with the 8 twist and 100 plus grain bullets, which need a longer throat.

I believe most short range 6PPC's use 60-70 grain flat base bullets in about a 14 twist. No reason that you can't do the same in a 6BR, but that is not the common use of them.
 
If your intent is to shoot short range, nothing can touch the 6 PPC... not even the 6BR. Different brass, different bolt face and a dfferent bore diameter..... 2370" vs. .236"
 
This is for F-Class, so yes a 1-8" twist is a go and 105-107grs bullets.
Interesting how Lapua has changed neck thickness. I'll need to buy new brass, cause I only have a few pieces left of the old Norma stock when they first came out.
 
The original 6BR Remington used a .266 diameter neck and the necks were, of course, turned to fit. Common practice at the time was to turn necks to provide .001 clearance if one intended to size the necks. Within a year or so, Fred Sinclair decided necks should be .262", probably because this was becoming the accepted size for the PPC. Now, the PPC necks were made .262 (as opposed to the original standard for the PPC of .264) because the Sako brass wouldn't clean up at the .0103" thickness necessary to run fitted necks in a .264 necked chamber (fitted necks were turned so that there was ony a couple tenths clearance and neck sizing was unnecessary. This was popular for a time in short range BR but few run a true fitted neck anymore). This wasn't a problem with the 6 BR. Since the brass was formed from what was essentially slightly thinned 308 brass, the necks were plenty thick enough to clean up at whatever. My "fitted" necks for the 6BR measured .2656 with a Sierra bullet seated.
Many years later, sometime after the 7mm BR became available, Remington changed the specs on the 6BR making it .050 longer and increasing neck diameter to .272". The differences between the Norma and Remington chambers are now miniscule.
I agree completely that neck diameter, within reason, is unimportant. the only real effect a larger neck can have is to shorten case life. As the brass work hardens, it can also cause the cases to size eccentrically if hardness varies at differnt points around the neck.
One reason many people believe there is a big difference between 6BR Remington chambers and those for the 6BR Norma is that many gunsmiths had a penchant for having reamers ground to provide minimal clearance at the head of the case. Since Remington brass usually ran about .466 at the head (as opposed to the .471 chamber spec), these gunsmiths were having reamers ground to .468 or so. When the Lapua brass came along and measured .470, the undersized custom chambers would not accept the brass.
Enough top BR shooters claim the PPC cannot be matched with the BR that it is hard to argue with this contention. However, I have shot both in identical rifles since 1979 and I can't shoot well enough to tell the difference. My best PPC shot well enough that I could usually shoot a group of .150 or less any time the wind quit blowing. My best BR was about the same.
Around 1980, Nobby Uno was competing with a 6BR and I was using a PPC. When I won it was because I was lucky enough to have the wind blow my shot into the group while Nobby was unlucky enough that it blew his out. By the way, it just as often happened the other way around! The point is, at that time, there was little to choose between the two cartridges. If formed factory brass had been available for the BR early on, the PPC might not enjoy the near monopoly on the short range venue that it does today. Regards, Bill
 
Leeper said:
Enough top BR shooters claim the PPC cannot be matched with the BR that it is hard to argue with this contention. However, I have shot both in identical rifles since 1979 and I can't shoot well enough to tell the difference. My best PPC shot well enough that I could usually shoot a group of .150 or less any time the wind quit blowing. My best BR was about the same.
Click to expand...

I think your experience validates the physical reality. I looked at the two cartridges and concluded the big difference between the 6PPC and the 6BR was the number of high end guns chambered in 6PPC compared to 6BR. The more horses in the race, the more likely you are to win.

I do think there are a couple of minor differences between them, with one going each way as being better. In the 6PPC's favour, the bolt face is smaller. As a result the bolt thrust is about 13% less than the 6BR. This gives the gun less force to deal with during the time the bullet is still in the barrel.

But, on the other hand, the 6BR has a bit more boiler room capacity. The best velocity node I have found in mine is about 3420 fps. I can fairly easily get that velocity in a 68 grain with a 26" barrel, but do go over normal max powder loads to do it. In a 6PPC I suspect especially with a shorter barrel you either may not be able to reach that velocity node, or would have to really push the pressure. This may more than offset the advantage of the reduced bolt thrust at the same pressure.

But, as I think you were saying the differences are so small, that the big factor is just the number of them in use and the money spent on them.
 
I have to admit, I've never shot any BenchRest comps, don't know much about it except what I've read in books, magazines nor owned a pure BR gun.
Interesting that the 6BR setup for short range could also compete dead even with the PPC. I did not know this.
Also interesting about all the different BR brass dimensions. Thanks for the reamers specs from Ron AKA.
 
Thanks for clearing that up Bill.

There is a lot of confusion with regard to the correct 6BR chamber.

Now I see why!
 
I think a reamer made for the old Lapua brass will work just fine with the ever so slightly thinner neck of the latest brass. A little neck clearance does not hinder accuracy what ever and in this instance I doubt there is enough clearance for the neck to expand beyond it's elastic abilities. Sizing should always be done anyway for consistent 'grip'. I went though the tight neck process with a couple of guns... it is a pain and if you can avoid it with quality Lapua brass I would suggest you do that.
 
The bottom line in regards to 6BR versus 6PPC if the 6BR were BETTER it would be used in short range BR. The fact that it is not tells you something. It is not a matter of if there is more of them versus the 6BR it is bound to win. IT OUTRIGHT is the KING of shortrange. PERIOD.

CBY
 
Even if it was just as good, which is debatable, the 6PPC is so well established that it is unlikely any other cartridge will make any serious inroads. There is, after all, nothing wrong with the PPC.
Go back in time though, if you will, to the time when 220 Russian brass was suddenly unavailable. There were a lot of guys searching for an alternative and had ready-made brass for the BR been available, the BR may well have been ascendant.
It is important to keep in mind as well that short range shooters are just like most others. They are conservative almost to the point of superstition. It takes a lot to make them change.
When the PPC was developed, it was developed as a replacement for the then popular 6x47 ( in no way related to the current 6x47 Lapua wildcat). The 6x47, popular though it was, needed a replacement. The 222 Mag brass was a bit small for a 6mm. In addition, it seemed like, about the time you were approaching the accuracy level you needed, the primers would loosen. My best 6x47, which was very good indeed, gave me brass life of about four firings. The PPC case was bigger and the brass was noticeably stronger. Whether or not it was this ability of PPC brass to operate at higher pressures that made the difference, I can't really say. The first PPC I made for myself shot slightly better than my 6x47 and brass life verged on immortality! In addition, my PPC shot so well with various combinations, it was difficult to decide on a load. Not so with the 6x47; it was touchy.
The BR was much like the PPC but with a major difference; brass availability and forming.
The forming of brass for the PPC was a snap. You just had to neck up some 220 Russian, turn the necks, and shoot it. With the BR, you paid through the nose for some basic brass, paid through the nose for a set of forming dies, then got to work. You formed, annealed, turned, fired it three or four times to form the thick brass, reamed out the donut, and there you were. No wonder the PPC came out on top! Back then, I only reluctantly built anything but a 6PPC because all that forming work for the BR was not only labour intensive, it resulted in inferior brass with a real potential for problems.
Today, with good, ready-made, brass available, I think the BR is a much more viable option than it was originally. Especially if a guy wants to do something other than meekly follow the crowd! The PPC is still the first choice but a BR is now an option which is easy to use. Regards, Bill.
 
Another little tidbit in the history of the 6BR is that it pretty much started as a Remington BR project for short range. When Norma standardized the cartridge they made changes to optimize it for heavier bullets and long range. They increased the length of the neck, throat, and changed the lead in from 3 deg. to 1.5 deg.
 
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