Chinchaga Bullets

Some ballistic coefficients for 257 caliber bullets and muzzle velocities at which data was recorded
257/180 2600fps G7 0.358
257/163 2666fps G7 0.328
257/150 2761fps G7 0.337
257/141 2745fps G7 0.332
257/135 2909fps G7 0.300

Stability twist requirements:
257/180 (1:7” twist)
257/150, 163 (1:7 twist)
257/135 (1:8” twist)

Test rifle 1:6 twist Jury barrel Red Deer, Alberta. Chambered 257 SAUM. Bob Galloway, Rocky Mtn House (Custom GunWorx) chambered it and threaded to a Pierce Precision Receiver.

Please post any questions to my email:
[email protected]

Not tested yet:
257 cal 150 GR. Length 1.563”,
1:7.5” will stabilize, 1:7.0” will be better.

Working on 257’s again. Reamer was designed for 257/135-145’s. It should work okay with 257/185’s. Shown alongside 308W cartridge. Have 1:6.0” twist barrel waiting for receiver. 1:7.5” twist shows borderline stability. 257/185PP is 1.695” long. 257/180OT measures 1.700”. Cartridge is 300 WSM, ran fully into 300 SAUM, then necked down in 257 WSSM.

375/430ST bullet. Heaviest 375 I can make. Needs at least 1:10 twist. Length is 2.153”, Boat tail is 0.348”, nose is 0.887”, bearing surface is 0.918” G7 BC 0.564

375/300ST bullets. 1.727” long, bearing surface 0.487”,
nose 0.887”. Needs 1:12” twist or faster. G7 BC 0.384

Terrible day, have to send these 308/210ST bullets to a customer, when I should be sending them downrange. I’m going Monday!

Equipment to measure and verify BC numbers has finally arrived. Will be testing all bullets in the next few weeks.

308/215 Grain. Length 1.485”,
Boat tail 0.190”, Bearing surface 0.642”, nose length 0.653”. Open tip.

New bullet. 308/264ST. 1.846”long, 0.918” bearing surface, boat tail 0.190”, nose length 0.728”. Minimum twist 1:9”, 1:8” would work best

308/242GR with steel ballistic tip. Length 1.734”, bearing surface 0.810” long, boat tail 0.190”, nose length 0.728”.
9.5” twist will stabilize, 9.0” or 8.5” twist will be better. Similar bullet, same profile 236GR G1 0.694. G7 0.385.