by Avenger10 » Mon Aug 22, 2016 3:38 pm
A number of people have been asking about this...
BartZ Manufacturing believes the Armalite Rifle (AR) platform is slowly evolving into the Modern Sporting Rifle (MSR) and will be the rifle of choice for hunters and target shooters of the future. The only thing holding it back is the availability of suitable cartridges. To this end, we do more than just build rifles, we engineer hunting and long range target MSR’s. This includes rifle, cartridge and necessary accessories. BartZ already has one of its new cartridges (the 257 BartZ) available and others at various stages of development.
The 257 BartZ is more than just a cartridge to put our name on. The 257 BartZ is carefully thought out and designed with both hunting and target shooting in mind. For the hunter we needed a flat shooting round with sufficient energy and sectional density to make terminal hits on large game animals out to 300+ yds (BartZ is whole heartedly against the small movement of unethical hunters promoting extreme range shooting.). For the Target shooter we needed a precision round that was inherently accurate, reasonably fast with high B.C. bullets that could be easily loaded and would consistently shoot single digit standard deviations. When loaded with 110-120 bullets the BartZ 257 arrives on target at 300 yds with nearly 1100 ft/lbs of energy sporting B.C.’s and S.D.’s of ~.500 and ~.250 respectively. Our pet loads show extreme velocity spreads of less than 20fps with standard deviations well below 10.
At this time commercial ammunition is not available, however, we are presently negotiating with major manufacturers to solve this problem. In the meantime, 257 BartZ ammo is easily made by a single pass of 6.5 Grendel brass through our premium die set made by the boyz over at Redding. Then just load as normal. No fire-forming required. The 257 BartZ uses the same shoulder to base length and angle as the Grendel. The neck is where it’s all different. Grendel chambers are notoriously sloppy in the neck area. We have corrected that with a redesign.
Here’s where you ask the question “Why reinvent the wheel, the Grendel shoots just fine?”. Yes, it does but it has an extremely limited bullet selection and quarter bore bullets have higher B.C.’s. Part of our project was to take advantage of the variety of bullets weights commonly used in the AR platform by other cartridges. The 6mm AR, 25 Sharps, 6.5 Grendel and the 6.8 SPC are all fine rounds but owners of these rifles know bullet selection is extremely limited due to the magazine length constraint of 2.250. The 257 BartZ cartridge can be loaded with bullets ranging from 60gr Hornadys all the way up to 120gr Nosler partitions which is about the limit for hunting cartridges given our case volume and magazine length constraint. Bullet for bullet, the BartZ 257 also runs a little faster than these others as the operating pressure is slightly higher.
To date our favorite 257 BartZ load is Lapua brass, CCI 450 primers, XBR-8208 powder and the Nosler 110gr Accubond all at 2700 ft/sec. Tested pressures are ~54k psi. and we are getting 5-6 loadings on the brass before the primer pocket gives out. Energy on target at 300yds is ~1070 ft/lbs and wind drift at 600yds is < 5min. For the 1000yd shooters we are still supersonic at 1k yds. It is not uncommon to see groups of 1.5” at 200 yds with our production barrels.
It must be said, with all the trouble regarding Grendel bolts breaking do to their odd bolt face geometry we have opted to stay with the traditional bolt face depth on our BartZ bolts and thus have had zero issues throughout testing.
We would also like to point out that the quarter bore has a long standing tradition with the American rifleman.
Hope this all helps,
-Barttman
BRENTON USA | LONG-LOAD
www.brentonusa.com
517.281.2571