6mmBR History

[glennburroughs]

How do I say this? I think the history of the 6mm BR as stated on this website is incorrect. In the "6BR Info Page" the comment is made that "Norma started with the 6mm Remington Benchrest case and made the neck longer and increased the base dimension slightly."

According to everything I can find on the topic Norma did not make the neck longer or the base larger. In fact, on Norma's website they specify the changes they made to the 6mmBR, "The throat on the 6 BR Rem was made for light bullets and did not work well with heavy bullets. Throat angle was changed to 1.5 degree instead of 3 degrees which made the cartridge much less sensitive. The small primer pocket and small flash hole improved performance. Of course twist was changed to stabilize the heavy bullets.".

Norma's changes were just in the chambering dimensions, not the case. Also, most die makers only offer 6mm BR Rem dies, and I understand this is because the cases are the same.

Am I wrong??

Glenn

 

[AlNyhus]

Glenn, here's a brief history of the 6BR.

-The original Remington 6BR was in fact .040 shorter than todays widely accepted version of the 6BR, which is the Lapua case stamped 6BR 'Norma'. Early chamber length was 1.520. Later Remington 6BR chambers had the neck lengthened .040 to 1.560.
-The original Remington 6BR brass was smaller at the back than the current Lapua case. This is because originally there was no factory brass for the 6BR chamber. You made cases for the BR chambers from the Remington URBR case...which was a full length 308 case with small primer pockets but with large flash holes. Very thin walls and some agressive annealing as they came from Remington made this radical case forming possible..if not always perfect in actual use. This URBR brass runs about .466 at the back end. The original Rem. 6BR chambers ran around .468 on the back end versus the current Lapua chambers that run in the area of .473 at the back. When the chamber spec. was changed to 1.560, Rem. released factory 6BR cases that were .040 longer than the original chambers but still keeping the original base dimension that was established when the URBR brass was the parent case. This way, the factory brass could be used in either chamber by just shortening the necks .040 for those guns with the original 1.520 chambers.

Unfortunately, the original 6BR developed a bad reputation for sticky cases, hard extraction and inconsistant neck tension. This was no fault of the case design itself, but rather a result of the extensive case forming that had to be done to make the 308 URBR case fit the 6BR chamber..remember, there was no factory brass at that point. Most BR shooters were only neck sizing at that point in time and the combination of difficult case forming, the poorly understood need to reanneal these cases after being formed from the URBR brass, minimal case resizing being done, dies that were improperly dimensioned, etc....all combined with shooters trying to push the new case design to very high pressure levels....gave the 6BR a bad reputation from the start. When the PPC cases came along, the 6BR was dead in the water from the avarage BR shooters point of view.

It's possible that if Remington had made factory 6BR cases available from the start, eliminating the need for shooters to make their own from the 308 URBR brass,the 6BR may well be the dominant 100-300 BR case today rather than the 6PPC.

So, basically here's how it shakes out:
-Early 6BR/22BR chambers: 1.520/.468 back dim.,from URBR brass)
-Later 6BR/22BR chambers: 1.560/.468 back dim.,Rem. brass)
-Lapua 6BR Norma chambers: 1.560/.473 back. dim.,Lapua brass)

Why Lapua chose to change the dimensions I'm not sure. But it resulted in a very heavy duty case with plenty of material around the primer pocket to stand up to very severe use.

Why die makers haven't discontinued the 'Rem 6BR' designation on their dies made for the Lapua case remains a mystery to me. I've worked with a few current 6BR dies from several mfgs. and they all have been dimensioned to work with the Lapua specs. I know that Wilson redid their dimensions quite a few years ago to work with the Lapua case, as did Redding.

How the 'Norma' designation came into play on the Lapua case is interesting...European guidelines call for their cartridge specs. to include the throat, thus the 'Norma' designation on the case...which has nothing to do with the actual case dimensions itself.

This isn't meant to be a complete treatise on the eveolution and history of the BR case..just a quick overview.

Bottom line: If you want to build a 6BR, use a reamer dimensioned for the Lapua brass and all will be well. Honestly, I can't imagine that there are many people out there chambering for the 'original' 1.520 or 1.560 Remington chambers.

Hope this helps. -Al

 

[glennburroughs]

Al,

Thanks very much for taking the time to compose that excellent response. Obviously you have some interest in the 6mm BR, along with considerable knowledge. I am a freelance writer and considering an article on the 6mm BR, and was wondering if you would be interested in continuing the discussion of this subject offline..... If so, please email me at:
gdburroughs@verizon.net.

Again, thanks for your response.

Best, Glenn Burroughs

 

[jawshunting]

Al, On the die issue. Does this go for Wilson dies also? I am about to order a neck sizing die and a bullet seater,Wilson)and the Sinclair site shows 6mm BR Rem. on both. My gun will be chambered for the Lapua case. Will the Wilson dies work? Thanks. jawshunting

 

[Dean]

Jaws,I use Lapua brass with my Wilson dies...all is good.

Dean

 

[Forum Boss]

Just one addition to what Al Nyhus said:

So, basically here's how it shakes out:
-Early 6BR/22BR chambers: 1.520/.468 back dim.,from URBR brass)
-Later 6BR/22BR chambers: 1.560/.468 back dim.,Rem. brass)
-Lapua 6BR Norma chambers: 1.560/.473 back. dim.,Lapua brass)

For a while Lapua brass, measured where the sidewall meets the top of the extractor groove, was running .471+, Hence the .473 or .474 dimension. Since 2003 or so, Lapua cases measure slightly under .470 at that spot,measured with my calipers). Accordingly, an "up to date" chamber may have a .472 or even .4715 dimension,to allow .0015 clearance). Dave Kiff "updated" his chamber reamers a while back to cut a .472" dimension, with a .470 dimension .200" up from the extractor groove.

I have one of the "tighter chambers" cut off the .472 reamer and my brass does NOT get tight in the back. Once-fired factory-loaded ammo measures .470". Very hot-loaded 3x cases measure about .471.

If your chamber is a .473/.474 at the extractor groove that may allow more expansion at the bottom of the case than is desireable. Keep in mind though that it is really the dimension upwards of that point,further up the case body towards the neck) that is key because the rim and groove area is unsupported.

FWIW, Wilson seems to have the current dimensions dead on. My Micrometer seater die is a perfect fit. After FL sizing with a Redding die, the fit is almost "air tight" but there is no binding.

 

[AlNyhus]

Paul, I'm aware of the changes in the Lapua base dimensions. The new Lapua stuff I have measures a dead on .4700. We continue to use the .473 chambers in our Lapua 6BR-based 30BR's and have had no issues with either case life or extraction. FWIW, most of the case/chamber fit problems I've seen with the BR case seems to originate at the case body/shoulder junction...reamers here are many times too small and dies sometimes don't size this area enough. I like the body/shoulder junction on my cases to end up at .458-.4585 after sizing. Dave's reamer spec. of .461,.4609, actually) is dead on for virgin Lapua 6BR cases.

I lean on my 30BR cases pretty hard and am not shy about aggressive sizing :thumb:. My current 30BR cases have been fired in excess of 50 times each, with only 3 trimmings of case length,about .005 per time) and periodic annealing to keep neck tension consistant.

Good shootin'. -Al

 

[Forum Boss]

Al,

I pretty much agree--when I have a tight case, the "rub" spot is at the shoulder. But I do know at least four or five guys who are having issues with bolt lift they claim is caused by the brass getting too big in the back.

For all I know their chambers might be quite a bit oversized, not just the thousandth or so that we're talking about.

Just wanted people to know that at least Kiff made a change to his reamers, based on the reduction of the brass diameter at the top of the extractor groove,i.e. web area).

 

[AlNyhus]

As always, good info from you, Paul.

Good shootin'. -Al

 

[glennburroughs]

The responses so far have provided a wealth of information on the 6mm BR and I am very appreciative, but I am still somewhat confused. To me the cartridge is not defined by the brass or dies, but the SAAMI or CPI specifications provided by the originator. And the brass specifications for both the 6mm BR Remington and 6mm BR Norma are pretty much the same; same base, same length, same neck, etc.

Are the die and reamer makers actually trying to adjust to Lapua's brass,which must be out-of-spec)? Does the 6mm BR Norma ammo produced by Norma meet their own specs?

The 6mm BR is one interesting cartridge.

Thanks again, Glenn

 

[AlNyhus]

To me the cartridge is not defined by the brass or dies, but the SAAMI or CPI specifications provided by the originator. And the brass specifications for both the 6mm BR Remington and 6mm BR Norma are pretty much the same; same base, same length, same neck, etc.

Glenn, in a perfect world this would be the case....the case spec. per SAMMI or CPI would be the standard..and dies and reamers would simply be dimensioned accordingly. But the reality is that this simply doesn't happen, for a lot of reasons. A perfect example of this is Winchester's 22-250 brass. While it was originally specd.,and supplied) at .469 ahead of the extractor groove, new Winchester brand cases barely get to .464. Now, if you're a reamer maker supplying 22-250 reamers with a .469 back dimension, you're going to have alot of unhappy gunsmiths since there is going to be a huge bulge at the back of the chamber on a fired case. And so it goes, on down the line.

Are the die and reamer makers actually trying to adjust to Lapua's brass,which must be out-of-spec)?

Yes, that's exactly what the die and reamer makers are forced to do...stay on top of what the brass being supplied actually measures...not what it should be. Paul's example of how Dave has changed his reamer specs. is a perfect example of a proactive mfg. staying on top of a situation. Wilson changing their die specs. is another.

Does the 6mm BR Norma ammo produced by Norma meet their own specs?

The Norma brand 6BR cases I have on hand measure .4675 just ahead of the extractor groove.

The 6mm BR is one interesting cartridge.

Glenn, it's actually one of the simplest you'll ever work with. Use a good accuracy smith with a known good reamer that works with Lapau brass and top it off by using high quality dies from a good supplier.

Hope this helps. -Al

 

[glennburroughs]

Al,and others that have responded),

Again, thanks for taking so much time to help me in my quest. I should tell you that I am a freelance writer in hopes of writing an article on the 6mmBR, and that is the reason for my post. The 6BR is not an easy topic to learn about, and your comments have added considerably to my knowledge. If I can actually get the facts together this should make an interesting story.

I am somewhat familiar with the 6BR; I have a Spencer-built rifle chambered in the original 6mm BR Match,one of Clay's favorite cartridges, with the short case), and a Holland-built, 8-twist rifle chambered for the Lapua 6mm BR Norma brass,no-turn neck). Clay recommended Remington 7mmBR brass as the base brass for the rifle that he built. If I could only have one rifle it would be chambered for the 6BR cartridge.

Rather than take up more space on this website I would enjoy conversing with you,and others) directly via email. If interested my address is: gdburroughs@verizon.net.

Many thanks, Glenn Burroughs