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What's the truth on 6 BR velocities?

All,

I have just recently gotten three 6mm BRX rifles up and running. They are NRA Prone guns to be used at 600 and 1000yd competitions.

The load development has been with 105-107 gr bullets along with Lapua brass,Varget,VV140,and RL 15. Bbl lengths are all 29-31 inches.

Two different Oehler 35P chronographs have been used in the development process. All barrels are SS,.236 bores, 8 twist, and custom made. Two are button and two are cut rifled.

Now here is what has made me very curious. On this site, shooters are claiming to get velocities of 2900+ fps out of standard 6mm BR cases. Shooting a standard case at 2950-3000fps seems like an awful lot of velocity to me. The BRX rifles that I have tested will start to experience stiff bolt lifts at 3050 fps or there abouts with the 105-107 gr bullets.

I am beginning to question just why I would want to fool around with a Dasher or BRX if it is only worth 100 fps over a standard case? My experience is that one is no more accurate than the other, the little case if incredibly accurate in any of it's forms.

To my thinking, either the std. BR shooters are loading to very high pressures at the expense of case life, or their chronos need to be calibrated. Are the 5R or 5C barrels worth that much extra velocity over standard rifling? Can button or cut rifling make that much difference? How about .236 vs .237 bores?

What is the real velocities that a std 6 BR can achieve without risking life and limb.

Bob
 
Truth is, you won't know what your max velocity is until you fit the barrel. And your velocity will also depend on the chamber,freebore), and to a lesser extent, on some of the properties of the action.

BAD NEWS
Some barrels really are 80-100 fps slower than other barrels. We have taken rounds from the same box of 105gr Lapua factory-loaded 6BR ammo and it has run 2770, 2810, and 2840 in three different rifles.

Same ammo, same barrel lengths,within 1" OAL), three different speeds. The Lapua factory ammo is loaded near the nominal 58740 psi CIP max pressure for the 6mmBR Norma, so that range of factory ammo measured speed -- 2770 to 2840 fps, give you an idea of where you'll top out at 58,700 psi or so.,Will Lapua brass withstand higher pressure? Consider that the newer 6.5x47 brass is rated at 63,091 psi).
 
Thanks for the reply.

My testing has been done with Pac-Nor, Krieger, and now Bartline.

Just an opinion, going thru all the work that a wildcat entail, isn't worth 100 fps.

I would tell you that the BRX in three different rifles and bbls looks like 3050 is a stretch with Varget. You can probably get there easier with RL 15.

Perhaps the 5C or 5R rifling will make for some "Faster" velocities, that is the next bbl that will be chambered.

Bob
 
Just my experience but in my 6BR 2850fps was about it with 108gr Bergers, Norma Brass, RL-15 out of a Krieger 26" barrel. I ended up cutting it back to 2800fps due to brass loss.

Mike
 
Factory Lapua and Norma ammunition in my pressure test rifle with a 30" Krieger .237" bore barrel gives MV right at 2800. Most of my better loads are in the 2750 to 2830 range and they are at max pressure,MV depends on the powder, bullet, etc.). I don't doubt that there are many peoplepushing them harder, but I doubt they are within safe pressure levels. I'll definitely say that looking at a primer is no way to gauge pressure and if you have sticky bolt lift with proper case sizing, you're way past safe alreay.

The 6BR works very, very well at all distances to 600 yards in that 2750 to 2830 range, for more, there's always the 6XC. No sense taking big risks for miniscule "gains".
 
Glad to see some truth and common sense float to the top.

Velocity is nice to brag on, but accuracy on the target still trumps all.

My match loads for my Dashers run just under 3000. When I found the best load I took one case and loaded it 15 times in a row. All I had to do is neck size, never had to full length, and the primer pockets stayed nice and snug. I quit because there was no point in going further. There's no way a BR will do that running 2900 plus.

Al
 
I have 7 firings on standard case ALL over 2900 and they are fine. Don't assume unless you have tried other barrels. I switched to Broughton and haven't looked back. I'm not getting in a barrel maker debate but I have seen higher speeds with these barrels and RL15. I wasn't looking for the speed it just showed up when I found the pressure the barrel liked. Maybe my chrono is out to lunch but I know of others with similar results.
 
My 6BR 272 neck chambered in a 31.5" medium Palma, Broughton 8 twist, 5C gives me an easy 3000 with a warm, but not hot, load of RL-15, under 106 CR, meplats closed.

I have never blown a primer,CCI 450) and never lost a case, and my brass has been loaded at least 15 times -- no stretch becuase my chamber was cut correctly and I fire form with a crush fit of the brass.

I have set one NRA 600 prone record with this gun,lasted only about a month), and this is the same gun and load that John Whidden used to shoot 26 straight Xs from the prone at 1000 yards on his home range -- having never shot the gun before and without changing my stock adjustments. That amazing string,which you could cover with a closed fist) triggered a few things that I believe changed the long range game forever -- but that is another story.

Additionally, this was the same load of RL-15 and meplat closed 106 CR that Jason Baney used to win the World Open Heavy Gun class a couple of years ago with his little 6BR -- the giant killer. I believe,memory fades at my age) that Jason also used an 8T, 5C Broughton, but less than 30" and was running about 2970. Again, Jason's testing with this 6BR and closed meplats got the attention of some experts who posted on Jason's results. The closed meplats printed 18" higher than the unaltered tips and the closed meplats grouped,in round robin) 2.xxx verses 5.xxx of the unaltered tips -- better vertical and wind deflection and more accurate.

The bottom line is that RL-15 just gives you more fps at the top node -- with accuracy. My gun has shot many groups in the .1s and .2s at 100 with some "wallet" groups in the Os as if it were a fine BR gun. One reason for the accuracy is that I load to BR standards -- not the dump and seat so often seen in the prone game -- and the 6BR is simply easy to hammer.

Having said all this, barrels are just different. I have two Broughton 9T, 5C Broughtons chambered in the 284 Shehane and there is a lot of difference in the fps out of each barrel.

As has been said, you can run faster with a custom action like a Gilkes Ross or a Barnard -- especially with no ejector. And, especially with a bushed or small fireing pin that pop hard cup primers.

Also, you can get more fps if your chamber is throated to give you a bearing surface at or above the sized portion of your case. If the bearing surface is below the bushing sized line, you are just giving away loading volume and fps. With a properly throated chamber, you have more "boiler room" for fps and accuracy. The long neck on the 6BR gives you this option -- not as many options with the short necks on the Dasher or BRX and they have to get it done by moving the shoulder forward, and in the case of the dasher, expanding to 40 degrees.

Truth be known, a 40 degree shoulder,without moving it forward like a dasher or a BRX) with less body taper would leave you with more capacity AND a long neck. Combine that with the proper throat, and you have the best of all worlds, IMHO. This has been done with great success but I don't remember the name of the chambering,it is on this site).

Just kinda thinking out loud,and I hope this helps a little.
Jim Hardy
 
If any of you have done pressure testing on those loads, I'd be interested in the results. The Oehler 43 system is about $1500,maybe a bit more now) and is about the best investment you can make in your safety. I know my pressures.
 
German:

Jason Baney and I were shooting the same load. I "think" his barrel was 28" and mine is 31.5". I believe that Jackie Smidt's testing of the 6BR indicated that each inch of barrel with the 6BR was worth about 8 fps. If you take Jason's 2970 with the 28" barrel and add 8 fps for each inch to my 31.5" you get in the neighborhood of 2970 + 28 = 2998, which is right at my 3000 in my Gilkes Ross.

I don't know the pressure beyond the performance and reading pressure signs on the case, i.e., measuring case heads, inspecting primers and pockets, stretch in OAL, feeling of primers when seated, etc. Never a problem with RL-15, although for 600 yd matches I would often shoot .3 grains less than I did at 1000. There was no difference in the accuracy. I have used the same 200 cases over the 2500 rounds down the barrel, which comes to an average of 12.5 reloads per case. I have the 200 cases in two differenct 100 round boxes, and one box has been shot more than the other -- by several reloads.

BTW, I could not get these results with Varget. Accuracy yes. Accuracy and fps, no. Also, at the top node, RL-15 burns very clean with next to nothing on the necks. I understand from many that RL-15 is temp. sensitive, but I never experienced any problems at all. This is the ONLY 6BR I have ever owned and maybe it is the barrel -- but Jason is right there shooting the same barrel configuration.

It would be informative to run the figures on a 43. I do know that I had no problems on a 103 degree day at Ft. Benning a couple of years ago,before I started shooting a 284 Shehane at 1000) when the heat was so bad that I had to DQ myself because my condition was so diminished that I could not see the number boards half way through my last 1000 yard string. My match performance that day was horrible, and it was dangerous to even shoot that match, but no gun or brass or primer problems.

Jim
 

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