June 21st, 2007

6mm Bore Diameter and Bullet Selection

Long-time visitors to this site will recall that, in 2006, Jackie Schmidt did an extensive 6BR accuracy test with his rail gun. It was fitted with a straight, heavy contour .237″ land-diameter Krieger barrel. Many interesting discoveries came from that test, including the relationship of barrel length to velocity. Jackie cut that barrel down in 1″ increments from 33″ to 28″ and we only lost 8 fps per inch.

That test barrel also showed a very strong preference for Berger 105gr VLD bullets, which (at that time) measured about .2433″ at the pressure ring. To our surprise, however, the accuracy of Lapua 105 Scenars was good, but not what we anticipated based on results in other rifles. We noted that the Scenars were extremely uniform in weight and dimensions. However, the max bullet diameter was around .2428″. So these Scenar bullets were about half a thousandth skinnier than the 105gr Bergers.

Lapua 6mm 105gr Scenar

Can the Scenars shoot superbly in a Krieger? The answer is yes, if the Krieger is a .236″. Bore dimension (specifically land diameter) DOES make a difference, based on recent results from Jackie.

Jackie has recently learned that the Lapua 105 Scenars WILL shoot with blistering accuracy in a Krieger barrel–a Krieger .236″ bore barrel. Jackie told us: “Well, I have to admit it… you guys were right about those Lapua Scenars. I just built up a long-range 6BR rifle for a friend. We put a Krieger 4-groove .236″ barrel on it, and, man those Scenars shot like a house on fire. The accuracy is just amazing. After my experience with the rail gun project I never would have believed it. But yes, the Scenars are outstanding in a .236″. I personally shot a measured .270″ 5-shot group at 200 yards with the Lapua 105s in that gun. And the velocity–you wouldn’t believe it–we were seeing 3000 fps with a full case of Vihtavuori N150. In a long barrel, with a .236″ bore, the N150/Scenar combo is a winner–for accuracy and velocity. You just have to match the bullet to the barrel. Skinny bullet? Go .236″. It works.”

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