October 4th, 2012

TECH TIP: Diameters Vary Among Bullets of Same Caliber

Choosing the right-diameter bullet can have a big effect on accuracy in match rifles. “Wait a minute”, you might say, “doesn’t one simply choose a 6mm bullet for a 6mm barrel and a 7mm bullet for a 7mm barrel, what’s the big deal?” Well… it’s not that simple. Not all bullets of the same nominal caliber actually have the same true diameter. We’ve seen different-brand 6mm bullets vary by as much as a full thousandth (.001″) in diameter. We have seen undeniable evidence that a poor “fit” of bullet diameter to bore dimensions can result in a poor-shooting gun, even one with a high-grade barrel.

Conversely, if you find the bullet diameter you barrel likes, that may instantly improve your accuracy. The accuracy gain may be more significant than making changes to the bullet seating depth or even powder charge. The importance of bullet diameter is compounded by the fact that 6mm match barrels are available with both .236″ and .237″ land diameters. Some barrels prefer “fat” bullets while other barrels prefer “skinny” bullets.

Last year, Jason Baney measured 12 different sets of 6mm Match Bullets, including a couple different lots of the same bullet design. Interestingly, Jason did measure the “old” Berger 105 VLD, the new-generation Berger 105 VLD (first lot from the new die), and the “new, improved” Berger 105 VLD from the new die, after it was polished. Ten (10) Bullets were measured per type. Each bullet was measured three times (3X) around the largest circumference, normally where a pressure ring would be located (some bullets have a pronounced pressure ring, others do not). NOTE: We provide the numbers from Jason’s tests, but remember that bullets from different production runs may have slightly different dimensions. You should augment our findings with your own measurements from later-produced bullets.

6mm bullet diameters

Download this CHART as an MS Word Document.

The first two columns of the chart show the smallest and largest bullet diameters measured for each 10-bullet sample. The third column shows the extreme spread over each 10-bullet set. Note, these numbers are NOT averages, but represent the “low” and “high” diameters for each set. (FYI: Jason noted that while the Lapua Scenars were very consistent, an earlier 2005 “JEVDAK” lot had smaller meplats than 2007 and 2008 lots.) A Mitutoyo Micrometer was used, zero-checked for each bullet.

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October 4th, 2012

New SIG M11-A1 Mates P228 with P229-width Frame

SIG Sauer m11-a1SIG P22X series handguns are justifiably respected for their accuracy, reliability, and build quality.* SIG Sauer has combined the features of its P228 9mm and P229 40sw pistols in a new high-capacity 9mm originally designed for Navy Aviators. SIG’s new M11-A1 is essentially a stainless slide P228 mated to a P229 anodized alloy frame. The wider P229 frame bumps capacity to 15-rounds of 9mm parabellum. The SIG M11 is issued to U.S. Naval Aviation and key units in other branches of the Armed Services. The new M11-A1 variant for civilians has been upgraded with a stainless steel slide, short-reset trigger, and 15-round flush-fit magazines. The M11-A1 features the same phosphate-coated internals, night sights, and MIL-STD UID label of the standard-issue M11. The M11-A1 should be available in gun stores this month. MSRP is $1125.00 while “street price” should settle under $900.00.

SIG Sauer m11-a1

*This is not just hype. This Editor owns a German-made P226. It is very accurate and extraordinarily reliable. I’ve also owned some polymer-framed pistols over the years. They are gone now, and not missed. I will never part with my P226. I could tell you the round-count over the years without a single misfeed, FTE or stove-pipe, but you wouldn’t believe it. More reliable than a Glock? My personal P226 has proven to be just that….
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