6 BR + 8208 XBR + Sierra 107

[Steve Blair]

I have been working with the above components in a Stiller Viper SS Drop Port, 30" Bartlein HV 8" twist and Shehane ST1000. The first series used Wolf KVB-5.56M, ended at 30.5 grains and showed some fine accuracy but pressures were very mild and max velocity achieved was only 2858. 30.3 grains produced a .211" 5-shot group at 100 with ES/SD 24.5/9.3, more than I like to see. I assembled a second series that started just below the previous max at 30.2 but switched to CCI 450 primers. I had excellent results with the 450 and 8208 in .308 Palma cases and thought it might work in 6 BR. The series ranged from 30.2 to 32.0 in .2 steps. The CCI 450s showed no significant pressure at any load. The edges were still comfortably round and no bolt lift issues were observed.

The best load of 31.0 grains produced a .122" 5-shot group (see attached) at 2902 fps and 17.7/8.5 ES/SD. The highest velocity was at 32.0 grains, 3004.5. The ES/SD figures are not as low as I would like and seating depth is the next variable. I may also try a few loads beyond 32.0 as pressure still seems reasonable. The brass is "blue box" Lapua 6 BR, neck turned to fit my .269 chamber. These loads have not been validated and the attached group may be a fluke. Two of the other groups were just above and below .250", so it shows promise. The complete load spec is below.

Lapua "blue box" 6 BR, 38.9 grains H2O, neck turned, pockets uniformed
Sierra 107 MK Moly seated 2.380, .012 off the lands
CCI 450 primers
IMR 8208 XBR filled with 6" drop tube, weighed to ±.02 grains on VIC 123
Redding dies, Co-Ax press, FL sized with .266 bushing

 

[Rtheurer]

Steve.

looks like you might have a winner on your hands for sure. How small are the kernals of powder if you had to compare to another powder. Im kinda out of town you could say and am intrested in trying this powder with the 95gr SMK's when i get back. I have a bunch of 450's too. amazing what a primer test will do. Ive seen it myself.

Again thanks for the info.

RussT

 

[cmillard]

wow, that seems like a lot of powder. how much varget are you able to shoot out of that barrel before you see pressure signs?

 

[Steve Blair]

Russ: They appear the same size as H322, quite small. It is fairly easy to trickle to exact weight. The density is higher, though.

Cole: I have only tried Varget in this rifle with Berger 105 VLDs when fireforming. 30.0 grains produced 2840. IMR lists 8208 XBR as just faster than H4895 but it does not behave like that. In .308 with Berger 155.5 FULLBOREs, I was able to get 2990 from a 26" barrel at reasonable pressure and fine accuracy.

 

[6BRonwheels]

I love IMR 8208 in the .308 using 155 grain Sierra Palma bullets. I also have had great accuracy and velocity with this powder in the 6mm BR using the Berger 108 grain bullet. I will never go back to varget in these two loads.

 

[cmillard]

steve, do you know the approximate freebore on your rifle. i have thought about trying 8208, but i typically like using the slower powders--i have been thinking about trying 4007ssc also. have you used a strain gage with the loads of 8208 that you are trying? currently i am shooting 30.0 varget, wolf srm primers, and 107 sierra just off the lands (.115 fb). avg vel is apx. 2818 fps. have ran 30.3 grains of varget, but accuracy really opened up and the primers started to crater.

 

[Steve Blair]

Cole,
Stiller chambered two identical barrels for this rifle using my reamer. It is a .104 freebore. No strain gauge but I have seen no significant case head expansion with a micrometer. The 32.0 grain load may have expanded .00005. I had varying results with the digital mike. My Viper SS is a Drop Port, so no ejector or extractor cut and the firing pin diameter is .061.

 

[Rtheurer]

Steve

It almost sounds like 8208 acts like a little slower powder than Varget R15,4895 type burning powders? Or at least in this specific case anyway. I have a Harrell Benchrest powder thrower and have never really been happy throwing Varget or R15 in it. 2520 is an absalute dream in it though.
I wonder if anyone else has had this same experience with this powder and 6BR case?

Very intresting. Thanks Steve for reporting, I may have not even given this powder a second thought if you would have not posted this thread.

RussT

 

[spclark]

I bought a few pounds of 8208XBR earlier this year with the idea of trying it as a Palma load after reading early reports. A couple of months ago I tested five different propellants (N550, H4350, H4831sc, RL17, 8208XBR) in a 6XC-chambered 30" Bartlein 1:7.8 Quadlite Carl Bernosky built for me back in 2008.

I'd planned on shooting mainly the DTAC 115 at 1000 yards but in two seasons it never really came up to my expectations so I switched to Berger's 105 VLD. At the last-minute I loaded up 5 rounds each at three different weights a grain apart & went off to test everything at 600 yards. 75° on a VERY windy day out there so I discounted for horizontal spread.

8208 was by far the most accurate, grouping two loads (1 grain apart) at about 1/2 MOA, the lower charge @ ~ 1-1/4" vertical dispersion, velocities of 3140 (SD4) & 3215 fps (SD9). I'd loaded another set at a grain higher (this stuff is DENSE so each load left more unfilled space than with the other propellants) but the high load of the two tested showed some pressure (Norma cases, KVB-7 primers) signs. Besides, 3200+ is enough for me with hBN-coated 105VLD's!

The next weekend I shot the lowest load in four relays at 1000 yards. My scorer commented that I was keeping up with a talented shooter on the point to my right using a 6.5x284, who eventually won the weekend. I was content to take 2nd place....

8208 meters a lot like N550 & has a very fine grain size. Some folks I've spoken to believe it to be intended to replace N133 for benchrest & hence maybe a tad on the fast side for 6XC but it seems to work just fine as long as the density / case volume isn't ignored. It'd be VERY EASY to add too much to a given case if one assumes it to be like other commonly used propellants. Until there's more information available please use it with caution in cartridges not on the suggested list.

I'll be very interested to try it for Palma against Varget / N140 next spring, also for 6BR which I'm just getting started with for 600 yards.

 

[JohnMill]

Hey Everyone,
So if this powder works for 6BR and 6XC then it should be ok for 6BRX shouldn't it? Any suggestions for a starting load? My case capacity is 41.3 of H2O which I believe is not typical. I've been up and down the scale with Varget and RE15. Never any excessive pressure sign, mediocre accuracy I think but never anything but extremely windy so don't know.

John

 

[Frankr]

I been shooting 8208 in 6BR 14 twist. with 65-70 bullets and it seems to be in my useage a bit slower than N135 but just a bit faster than varget. i did pressure test in my rifle to find max load,max at 34.0grs with 65v max 3,650 FPS and 3,565 FPS with a 70gr SBK at 85-90deg F. starting to show pressure at 34.0 grs. so my max is at 33.8gr with the 70gr SBK at @3,550 FPS . havent done enough shooting to get a good read on ES/SD but it has not been good so far.but shooting the load in the field out to 650yds it been quite deadly on ground hogs. i will keep working with the powder but so far i feel its too slow for bughole accuracy at short range for my useage,but would think that heaver bullets would be good.