6mm Bullet Diameters — Update

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. There is solid evidence, for example, that skinny bullets like the 105gr Scenar may shoot best in a .236 barrel.

German Salazar recently measured a selection of 6mm bullets, recording bullet diameter, overall length (OAL), and bearing surface length. His results are interesting.

Salazar Measurements

Some months ago, Jason Baney measured 12 different sets of 6mm Match Bullets, including a couple different lots of the same bullet design. Notice, some bullets measure a bit different, compared to German’s numbers — this may reflect lot variances and/or measuring methods. 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).

Baney Measurements

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. A Mitutoyo Micrometer was used, zero-checked for each bullet.

Two Tips for Better Ultrasonic Cleaning

There has been much interest in Ultrasonic case cleaning. Here are two tips to achieve the best results:

De-gas the Solvent Before Adding Brass
One of our readers, Eddy M. in Glasgow, Scotland writes: “I have read a couple of articles recently about ultrasonic cleaning of cases and not one has mentioned de-gassing the cleaning liquid before starting to clean items. As an engineer who travelled around for ten years servicing ultrasonic tanks I would like to point out that the cleaning liquid when first put into the tank has invisible disolved air bubbles in it which will absorb ultrasonic energy until the liquid de-gasses. (10 minutes in a powerful industrial tank–longer in a small hobby tank). You must let the tank run on its own for 20 minutes on the first use of the liquid to allow this to happen. Only after the new liquid or re-introduced liquid has been de-gassed will the tank give good results.”

Apply Dry-Lube Inside Case Necks
Jason Baney has found that Ultrasonic cleaning leaves the inside of the case-necks so “squeaky clean” that there is excess friction when seating bullets. On a fired case that has been cleaned conventionally (no ultra-sound), a thin layer of carbon remains to lubricate the bullet entry and exit. To restore that lubricity in cases cleaned with ultrasound, Jason applies a dry lube to the inside of his case necks. Jason prefers the $10.95 moly dry lube kit from Neconos.com. With this kit, small carbon steel balls transfer moly to the neck when you place your brass nose-down in the container.