Robinett announced something new this week — a 108gr, 6mm boat-tail projectile. Yep, that’s right … a BIB boat-tail. The new bullet features a conventional, tangent ogive shape, but the boat-tail is only .082″. That’s quite short compared to other 6mm bullets in the same weight range. Why the shorter boat-tail? Randy believes that a short boat-tail delivers the desired drag-reduction in a long-range bullet, while offering a larger base for the expanding gas to push. In addition, Robinett strongly believes that short boat-tails can be made with much less run-out (on the tail section). With longer boat-tails, Randy says, there is much greater risk of the tail section being swaged off-center.

Looking at the new bullet, we were concerned with the long bearing surface. Would that increase in-barrel friction and thereby reduce velocity compared to other 6mm bullets of similar weight? Apparently not. Our Asst. Editor Jason Baney has tested some BIB 108 prototypes. Jason’s Oehler chronograph revealed the BIB 108s will run within 10-15 fps of other similar-weight 6mm bullets, with the same powder charge. Jason pushed the BIB 108 up to 3200 fps without problems. (Test rifle was a 6-6.5×47 with 1:7.8″ twist barrel). Jason has not done extensive group testing, but he says these bullets definitely show promise accuracy-wise. He notes, however: “with the BIB 108s you’ll want a bare minimum 0.090″ freebore, and a longer freebore would be better.”

BC and Bullet Specifications
What about BC? Calculated (G1) BC for the new 108s is 0.543, but Robinett says “real world testing suggests an actual BC of about .52, as opposed to the calculated 0.543″. The new bullet is designed to perform well in the popular 8-twist 6mm barrels. According to Randy, the “ideal twist rate is 1 turn in 8.3 inches. This produces a 1.5 Stability Factor (Sg) 1.5 at sea-level, standard conditions. The Sg with 1:8.5″ twist is still a very good 1.4 Sg.”

Photos by J. Baney © 2009 AccurateShooter.com. Camera: Canon G10.

The BIB 6mm, 108gr BT features an 11-caliber tangent ogive, 0.052″ meplat diameter, and a 12 degree x 0.082″ long (abbreviated) BT. The BIB 108s are fairly “fat”, measuring 0.2435+ at the pressure ring and 0.2433 in the middle of the bearing surface. Given the bullet shape and dimensions, Randy believes “this bullet will prove easy to tune.” For more information visit BIBullets.com.

Robinett is now accepting orders for the new 108gr 6mm BIB. The 108s will cost $320.00 per 1,000, plus shipping. Minimum order quantity is 250 bullets. To order, please call (515) 438-4010, or e-mail bibrob [at] netins.net.