Discussion in 'Big Stuff--7mm, 30 Cal, .338+' started by APGE, Oct 6, 2019.
Why try the 250gr and not the 230gr?
Yesterday the 250’s registered 1,540 FPS at 1,000. The SD’s at the target were in the 8’s in each of 4 test relays, 2 with Palma brass and 2 with standard. The standard brass accuracy lagged about 10 points behind the Palma. My lower score with standard was confirmed by PJ who shot the 4th relay. Standard was loaded only .1 grains lower but for some reason seated entirely looser relative to Palma at 47.1.
Palma loads required incremental case twist seating similar to lug nut tightening to ensure straightness and bullet nose condition perfection. Standard loads received that too but there was simply no resistance for some reason and they crossed the target some 45 FPS slower. The striking accuracy and velocity differential was notable. The .1 grain difference was to account for a much larger BR2 primer. The Palma case is apparently smaller internally, - thicker walled - and tighter necked.
All the brass was new, and none of it displayed high pressure signs.
Once sorted out with the set up, the second Palma brass relay showed me very good accuracy with F-Open type holds. But 50 rounds to follow with myself and PJ shooting Standard Lapua brass weren’t accurate. I wish PJ could have shot the better load.
I want to see a 250 loaded into a 300blk case for reasons. would the 300blk be able to get 1k fps out of those? Not trying to thread Jack.
Just ordered a .308 1-8 twist Bartlein barrel 31" for a 300 RUM project...but I have a .308 Win reamer, could waste some time chambering to a long action Rem 700 at 3.410" C.O.A.L. with a throat reamer in .308 Win with 250 grain A-Tip, which would leave a lot of room for powder, and feed from the magazine...just for fun and to see the reality of it. I ran the 250 A- Tip at 2986 fps with the 300 RUM and a 26" barrel, but they are not stable, with a 1-10 twist..
Update: So I actually chambered the long action and 30" finish length barrel to .308 Win. After some testing with the new .715 BC 200 grain bullet, I feel I may stop here...ran the usual powders with expected velocities.. But one combination was giving me 2860 fps with good accuracy with a .715 BC 200 gr. Sierra MK...super ballistics for a .308 in case anyone is interested.
2860 for a 200 is blisteringly fast. What's the powder charge?
250 A Tip will run a little over 1300 fps in a 16" barrel. Use a 300 blk specific mag, milled (cut )out so you can feed 2.350" cartridges. My accuracy was not that great, But I had other projects to do...need to try other powders. Sierra Bullets Will have data on the new 230 gr and old 240 gr MK on line for starting loads.
I use Lapua Palma brass, Br4 primer, 50.8 grains of power pro 2000mr loaded to 3.175".COAL.. With a 30 " Barrel in a long trued 700 action. And I have a piloted throating reamer to keep extending the throat to get the COAL I want. I Was gonna throat 3.410" for the 250 A Tip, but this is a good load and a longer throat will ruin it for the 200's. You must have the long throat (cartridge OAL) in order to even try this... as it would be very dangerous (explosive) with a normal length 308 load.
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