Re: Insufficient Headspace on 300 RUM Reloads 3500 fps
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Crosshair22</div><div class="ubbcode-body">Besides the go, no-go, and field gauges, where can I find the SAAMI specs. for my caliber's max. headspace? I agree, the remaining rounds will be torn down but I suspect the muzzle blast probably was a factor in the wild velocity variations in the first twenty rounds fired. I had these results for first twenty rounds using 180 grain Barnes TTSX, RL22 @ 85.8 grains: 3107, 3210, 3217, 3254, 3226, 3191, 3287, 3145, 3243, and 3254. The next six rounds got really wild readings climbing in vel: 3257, 3279, 3284, 3343, 3491, and 3508. The last 10 rounds after moving the chrono. only demonstrated an extreme spread of less than 67 fps. with an average velocity of 3146 fps. So my question remains can insufficient headspace cause the extreme pressure spikes by pushing the case necks thus causing higher neck tension on bullets? </div></div>
Well, to answer your question about headspace, having too little headspace will not allow you to close your bolt, so there's the issue with the six rounds not chambering. You probalby didn't bump those shoulders back enough when you resized them.
Too much headspace, will cause your cases to stretch and possibly lead to case head separation, sooner rather than later.
You need to buy the set of Hornady/Stoney Point headspace gages and measure a fired case, from your chamber and then bump the shoulder back between .001" and .002". Drop in gages are cut to a random spec and are really only good for quick visual cues.
I don't think headspace is the issue with the whacky readings...more likely your chrono was glitching, or your barrel was heating up, expanding and allowing the bullet to pass through the bore with less friction, and hence at a faster velocity.
Chronos can be 'iffy' devices and much like reloading manuals, they're only a guide, not an absolute.
My Sierra V manual, shows their 175 SMK and 180gr class of bullets, including the 180gr SMK and Reloder 22, at 3200 fps and 89.4 grs (max), but Sierra is 'generally' a conservative manual. This is with a 26" Savage 116 LA rifle.
Throw into this mix, the fact that the Barnes are typically 100% copper bullets with 'driving bands' and all bets are off.
Chris