Figure 4-8. Method of Sealing With Neck of Cartridge Case (With "Buried" Projectile Ammunition).
is entirely sealed off from the seam. Tn spite of the fact that the cartridge case material is quite thin at the neck, there is no tendency for the ease to be blown out at the seam, providing of course that the gap is not excessively large. The permissible width of the gap depends entirely on the thickness of the material at the neck of the case. For the thickness found in typical 20-mm cartridge cases, experience has shown that a gap nf over V32 inch can be tolerated without failures. In a well-constructed weapon there should be no trouble experienced in keeping the final width of the gap well below this figure and consequently there will be little danger of case blowouts.
The objections to this method of sealing are sim ilar in some wavs to those citcd for the method previously described because its use requires the cylinder to be cammed forward to effect the seal. Hence it has the same mechanical difficulties and the same tendency to slow down the rate of fire. The form of the ammunition also presents problems, particularly in the larger calibers where it is necessary for the projectiles to be provided with rotating bands. With ordinary ammunition, the cartridge case is crimped to the projectile behind the rotating band but with the "buried" projectile type of cartridge. the case must cover the entire projectilc. Such a round is not only difficult to assemble properly, but the projectilc is also required to move through the neck of the case for a considerable dis-
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