6mm Match Bullet Diameters
There’s been some controversy surrounding the “ideal” 6mm bullet diameter. This is compounded by the fact that 6mm match barrels are available with both .236″ and .237″ land diameters. It has become quite clear to us that bullet diameter is an important variable to consider when choosing the best projectile for your particular barrel. Some barrels prefer “fat” bullets while other barrels prefer “skinny” bullets.
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” 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).
Download this CHART as an MS Word Document.
Columns one and two 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 measured very consistently the earlier 2005 “JEVDAK” lot had noticeably smaller meplats than 2007 and 2008 lots.) A Mitutoyo Micrometer was used, zero-checked for each bullet.
Interesting numbers…. Explains why the 107 SMK gave pressure signs in my 6HAGAR upper with loads that didn’t using Berger or Lapua 6’s.
Anyone wanting this chart as a PDF document, drop me an e-mail @ hipowershooter(at)comcast(dot)net
This article is gibberish. The ES column is statistical nonsense. There is no indication of how accurately the micrometer measures. For this analysis to be worthwhile, significantly more accurate measurements need to be taken and compiled in a statistically valid approach.
EDITOR: “Gibberish”? I don’t think so. 10 bullets of each type were measured with a high-grade tool with known accuracy (and a 50 millionths readout). If you think this study is meaningless, perhaps you would like to go out and purchase 12 different types/lots of bullets yourself, and then take the time to measure them all and tabulate and publish your results. If you don’t think 10 bullets per type is a statistically meaningful sample, be our guest and go measure 50 each for us. That’s only 600 bullets, and at 2 minutes per bullet you should have the job done in 20 hours of continuous measuring with no breaks.
As Jason explained the third column is not an average, but is the difference in diameter between the smallest diameter bullet in the given set, and the largest diameter bullet. This gives the shooter an idea of the total variance in diameters he might experience. It will also give you a general idea of which bullets tend to be more consistent. You may believe this is all meaningless, but tests by this editor, by Jason, by Jackie Schmidt, and many other shooters have indicated that bullet diameter DOES make a difference. We had one .237 Krieger barrel that only achieved “average” accuracy with the Lapua Scenars. The same bullets shot like lasers in a .236 Krieger barrel.
As with anything–yes the testing could have been more complete. We could have taken an entire week, measured 500 bullets of each type, and done the measuring in a $5000/day test lab with a scanning microscope, and then repeated it with optical comparators. But to what end? The tool Jason used was sufficiently precise to reveal some important variances in bullet diameters. This is important information that was not available to shooters before Jason took the time to collect and measure the various bullets. I think most shooters will thank Jason for the effort and recognize that the data can be helpful.
John Campbell-Smith,
Thank you for your comment
The micrometer was a 50 millionths Mit. Yes, I know the 5th decimal place isn’t “real”…but it was there, so I showed it. Each measurement that showed the 0.00005 blinker was also repeated (and came up the same each time). I also took measurements at 3 points on the circumference of each bullet. So really each single bullet had 3-6 measurements. So each brand/lot had 30-60 measurements.
These were all done at the same time/temp/etc. The tool was also repeatedly checked on a “standard bullet” and never varied.
This table was not meant to be the comprehensive reference on bullet diameter variability, nor a table in a scientific journal article, but was as good as I could do without tools that cost more than my truck.
Even ignoring the 5th decimal place the numbers reveal some interesting info.
If you have the tools, by all means give us a more statistically valid table.
There is only one guaranteed way to resolve this dispute of accuracy – use a Laserlab to measure these bullets. It is completely unbiased, no human subjectivity, calibrated to NIST standard on every pass, measures .001mm increments over the length and has a resolution of less than .001mm on diameters.
We would be happy to lend one of these machines to you for any measurements you would like to make on cartridges, cases or bullets!