cal30_sniper
WKR
I finally got a chance to start load development in my new 6mm-284 UM build, and figured my info/results may be of interest so some of the others that have been experimenting with various small-caliber recipes. This is an old cartridge, but one I feel deserves a second look with the rise of slow burning powders and heavy for caliber bullets that didn't exist when it was essentially written off as a barrel-burner in its previous life.
I agonized over interior ballistics and mag length dimensions for quite a while before arriving on this as a "goldilocks" solution. Initially I had hoped to do something based on a necked down 6.5x55 improved, but have become convinced over time that the reason a universal 6.5x55 improved hasn't really taken off is because a better thing already exists in the 6.5-284 case.
Things I've learned since going down this road:
The Rifle:
The Great:
Load details:
Range results:
I've got 35 rounds down the tube now. Firing was slow to keep the heat down, and I did commit the blasphemy of cleaning after the first session. All shots fired in slow 5 round strings with some breaks to walk and check targets, calculate groups, log data, etc. between. All groups were sub-MOA, with my final group being the best at just over 0.5 MOA (barrel seemed to tighten up during initial break-in). Velocities are higher than expected, with the strings I fired increasing from 2940fps to 3000fps over the 7 groups. I started running into pressure signs around 2960 or so, and looking back at the cases afterwards there are very slight ejector marks and a few instances of tiny primer craters even on the 2940fps loads.
Conclusion:
Velocity is about 300fps faster than factory Berger/Norma/Hornady loads with lighter 105-109gr bullets from my 18" 6mm Creedmoor. I'm probably overpressure with these loads, but not exceptionally so. If I am, the BAT action is handling it extremely well.
I'm going to back off the load slightly and try a few strings around 2900fps. Gordon's load data was pretty far off on this combo relative to other loads I've worked up in similar cartridges. This is the first time I've used Gordon's with Retumbo, so that's likely the culprit.
Shootability is phenomenal. I can't detect any difference in felt recoil from my 6CM that's also mounted in a Rokstok with a similar weight barrel profile and optics setup, but clearly this is a significantly superior ballistics package compared to the 6CM.
Overall, I'm very happy, and plan to spend a lot more time working with this after I finish up my Utah restricted rifle hunt this fall.
I agonized over interior ballistics and mag length dimensions for quite a while before arriving on this as a "goldilocks" solution. Initially I had hoped to do something based on a necked down 6.5x55 improved, but have become convinced over time that the reason a universal 6.5x55 improved hasn't really taken off is because a better thing already exists in the 6.5-284 case.
Things I've learned since going down this road:
- Building on a Tikka action would have alleviated the mag length restriction of a Rem 700 SA. Oh well. I like my Tikkas. But, back to back I feel the ergonomics are better on the Rem 700 short action, even though the Tikka has many other tangible benefits.
- Building a 6 PRC wildcat would have accomplished the same thing. Oh well. I had already collected 500 pieces of Lapua 6.5-284 brass which should last me a very long time, and I believe the shape of the 284 makes for a slightly smoother feeding setup. Not sure if an extra fits in the mag or not compared to a PRC case. Possibly? In the end, the -284 case tickles my fancy for something nostalgic and unique in a way that the PRC case wouldn't (back to the original quest of a x55 or x57 improved parent case)
The Rifle:
- BAT Vesper SA
- Ace 2b 18" 7TW Barrel, fluted
- 6mm-284 chambering
- UM Bottom Metal and Standard Mags
- Rokstok
- UM Low Rings
- Maven RS1.2
- TBAC brake and Ultra 7
The Great:
- The action is phenomenal. Compared to my other Defiance actions (I have a short AnTi, a short AnTi-X, a medium Ti-X, and a long AnTi), this thing is in a league of its own. I really like the bolt knob/handle, and the fluting pattern on the bolt seems to leave a lot smoother action than the somewhat sloppy feel induced by the deeper/fewer flutes on the Defiance bolts.
- The UM Standard Magazine feeds this cartridge very well. I had previously messed with 284 cases from binderless AICS mags and couldn't get them to feed well from either standard or magnum magazines. Not sure if UM tweaked the feed lips or not, but these feed great from the 3.15" mag box in the UM design.
- Speaking of mags, I like the UM bottom metal mag release a LOT better than the Hawkins DBM setup on some of my others. I thought the protruding magazine in their design might annoy me, but so far it hasn't at all. If I feel differently after time in the field, I'll be sure to update this.
- Build took forever. I think it was about 15-16 months from initial order to delivery. Oh well, I had other projects that kept me more than busy in the interim, and didn't nag them about it.
The throating is quite long. I sent in dummy rounds with a 115 DTAC at 3.100, and asked for it to be throated about .030" off the lands. My hornady checker has me at 3.360 or so off the lands, which is a pretty long jump. Not sure why they did that, but I wish we would have at least talked about the reasoning behind the change (if there was any). I figured I'd shoot it before I complained about this and see how it did. Seems to do fine even with the long jump.Edit: turns out I’m just a moron and the chamber neck was a little tighter than my OAL checker dummy cartridge. Measured the old fashioned way, I’m into the lands at 3.127”, which is exactly the .030” I asked for over the dummy rounds I sent in.
Load details:
- Lapua 6.5-284 brass necked down through 25-284 and 6-284 dies
- Remington Large Rifle Primers
- 115 Nosering DTACS at 3.100"
- Lots of Retumbo (I'm not posting quantity, as I'm 100% sure I'm over standardly accepted pressure limits)
Range results:
I've got 35 rounds down the tube now. Firing was slow to keep the heat down, and I did commit the blasphemy of cleaning after the first session. All shots fired in slow 5 round strings with some breaks to walk and check targets, calculate groups, log data, etc. between. All groups were sub-MOA, with my final group being the best at just over 0.5 MOA (barrel seemed to tighten up during initial break-in). Velocities are higher than expected, with the strings I fired increasing from 2940fps to 3000fps over the 7 groups. I started running into pressure signs around 2960 or so, and looking back at the cases afterwards there are very slight ejector marks and a few instances of tiny primer craters even on the 2940fps loads.
Conclusion:
Velocity is about 300fps faster than factory Berger/Norma/Hornady loads with lighter 105-109gr bullets from my 18" 6mm Creedmoor. I'm probably overpressure with these loads, but not exceptionally so. If I am, the BAT action is handling it extremely well.
I'm going to back off the load slightly and try a few strings around 2900fps. Gordon's load data was pretty far off on this combo relative to other loads I've worked up in similar cartridges. This is the first time I've used Gordon's with Retumbo, so that's likely the culprit.
Shootability is phenomenal. I can't detect any difference in felt recoil from my 6CM that's also mounted in a Rokstok with a similar weight barrel profile and optics setup, but clearly this is a significantly superior ballistics package compared to the 6CM.
Overall, I'm very happy, and plan to spend a lot more time working with this after I finish up my Utah restricted rifle hunt this fall.
