Post #1
This thread is an update describing some of my recent trials with the Barnes 160-grain bullet. (As usual, the verbiage-to-shot ratio is pretty high.)
Standard Warning: For the work described below I used a bolt rifle with a 0.451-inch barrel, which is rather different than the AR-based rifles usually used with this cartridge. If you try to duplicate my results with a different rifle, different components, or different techniques, really bad things may happen to your firearm, or to yourself, or to persons standing near you, or to your dog, or to a passing tweety-bird. Be careful. This information is coming to you via the internet, where untruthful persons post untruths and truthful persons make typing errors.
The last results in my work with lighter bullets was posted on this thread: The Need for Speed, Part A - Preliminary Trials. The objective of the work is to explore what velocities can be safely obtained with the cartridge. Using lighter bullets usually allows increased velocities, but conventional wisdom and techniques do not always work with straight-sided cases.
The lightest .451-452 bullets that are readily available are the Barnes 160-grain all-copper bullets. Last fall, using this bullet with a case full of 2400, I recorded a velocity of 3100 fps on my chronograph at 10 feet from the muzzle. This was obtained using my Springfield 1903 bolt gun with a 20-inch barrel.
Barnes designed these 160-grain bullets for the GAP cartridge. The bullets have been supplied with two different Barnes product numbers: #45165 in boxes of 20, and #45106 in boxes of 40. The first, an XPB type, may be no longer manufactured. The second, the TAC-XP, is the current form. Barnes says their various XPB and TAC-XP bullets are "similar". For the .451" 160-grain bullets, I could find no measureable differences whatsoever.
This bullet creates problems in handloading for the 450B for two reasons. Problem #1: The bullet's maximum diameter is only 0.4500, so that the case doesn't really squeeze the bullet after normal FL resizing, as it would a 0.451 or 0.452 bullet.
Problem #2: The bullet has tapering sides. The taper is intentional. Barnes writes in some of their reloading information: "The Barnes #45165 160-grain XPB bullet has a slight taper on the base to prevent bulging of the case wall once the bullet is seated. Only a slight amount of case mouth belling is needed prior to seating the bullet in the case." From the viewpoint of 450B reloading, there is too much "slight taper".
The bullet tapers from its too-small 0.4500 diameter midway in its straight size to only 0.4450 at the base. When loading, if you taper crimp this bullet after it's seated, the case might grab the bullet tightly at the mouth of the case, but not so tightly down the length of the bullet. This is a problem in this cartridge, because sufficient case mouth tension is critical to getting the powder to burn properly.
The image below may make the point clearer. (The black front end of the bullet is a shadow, not bullet coloring or coating.)
Forum member rohk has noted in another thread that the similar General Bullet 160-grain hollowpoint bullet is consistently 0.451" in diameter. That should make that bullet much easier to work with.
(Continued below in Post #2)