300 RUM +220gr Modded 220gr MK's - 03/01/24
I had a tack driver Sendero 300 RUM 220 Sierra Match King load (4-shot <0.5 MOA 100yds), but could not find a good 220 gr boat tail hunting bullet. Hornady ELD's are too long & don't stabilize with its 1:10 twist. I'd seen some claims of guys drilling the Match Kings, and as I'm a machinist, I thought I'd try.
I indicated a #3 center clamped in a v-block with a Bridgeport within 0.0002" then used a 5 /16 (0.3125) volley to clamp the bullet. Prior to machining, I sorted and filed the metplats to within 0.001" all the same length so I could touch off once chucked up. I touched off & drilled 0.250" deep, feeding the knee up. The pilot of the center drill is 0.125" . After drilling, I left the bullet chucked, dropped the mill in backbeat and used a mill file to deburr the tip while still chucked.
This yielded a 216gr hollow point, and among 10 bullets I weighed 0.2gr different, as good or better than unmolested 220's. With a load of 92.5gr of 24N41 2890fps, I fired into some very tough high density foam a buddy had who works at a mild shop. It traveled 18" deep & we recovered the projectiles. Perfect uniform mushroom expansion 0 .765" dia.
We've tested Sierra 6.5 140 Game Changers in 6.5-300 Wby, 130 ELD Match in 6.5 PRC, and 120gr Barnes TTSX in 264 WM, and the RUM 220 Sierras by far are the best. The Barnes immediately ripped the petals off and went straight through like an FMJ.
I indicated a #3 center clamped in a v-block with a Bridgeport within 0.0002" then used a 5 /16 (0.3125) volley to clamp the bullet. Prior to machining, I sorted and filed the metplats to within 0.001" all the same length so I could touch off once chucked up. I touched off & drilled 0.250" deep, feeding the knee up. The pilot of the center drill is 0.125" . After drilling, I left the bullet chucked, dropped the mill in backbeat and used a mill file to deburr the tip while still chucked.
This yielded a 216gr hollow point, and among 10 bullets I weighed 0.2gr different, as good or better than unmolested 220's. With a load of 92.5gr of 24N41 2890fps, I fired into some very tough high density foam a buddy had who works at a mild shop. It traveled 18" deep & we recovered the projectiles. Perfect uniform mushroom expansion 0 .765" dia.
We've tested Sierra 6.5 140 Game Changers in 6.5-300 Wby, 130 ELD Match in 6.5 PRC, and 120gr Barnes TTSX in 264 WM, and the RUM 220 Sierras by far are the best. The Barnes immediately ripped the petals off and went straight through like an FMJ.