Cast Bullets
Recently my brother Robert and I revisited shooting lead bullets in the old smokeless powder battle rifles in preparation for the 100-, 200-, and 300-yard military rifle silhouette matches we would be holding. So it was a pleasure reading Mike Venturino's article in May's issue. (I have been shooting lead bullets in many smokeless powder rifles for more than 48 years, but had switched to mostly black powder cartridge rifles for a while.) We did this to examine the performance of Reloder 7 and XMP 5744 and to provide basic information to the other guys here who have not done this type of shooting before.
Reloder 7 and XMP 5744 perform equally well and extensive data for RL7 is contained in the current Lyman Cast Bullet Handbook. One issue not mentioned in Mike's article is bullet bearing surface length and case neck length. For gas-checked lead bullets to properly perform in any of the "high-power" smokeless rifle cartridges, the gas check should not extend below the bottom of case neck. If any bare lead is within the case, it will be melted by combusting powder heat unless the force of the primer detonating moves the gas check into the neck. The result of lead melting within the case is extreme accuracy degradation due to bore leading and bullet deformation. The second factor related to this issue is the amount of "free bore" in the barrel. If there is sufficient free bore to allow the bullet to move due to primer detonation force, there is generally no problem experienced when the gas check is below the case neck. Since most of the guys were using some type of .30-06 rifle, we noticed wide variations in the amount of free bore in the various barrels. Both my brother and I have 1903 Springfields rebarreled in 1944 and have a generous free bore. One late production Remington 1903 with its original barrel had almost no free bore. A late Remington 1903A3 examined was the same as our rifles. The same variation exists in the Model 1917 Enfields examined. All Swiss K31 rifles examined have minimal free bore.
The bottom line is before you select a bullet, check your case neck length and barrel free bore. If you do not properly accomplish this and allow the bullet gas check to extend below the interior neck bottom you will become very disgusted and drop the whole project.