Recoil vs bullet weight
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: memilanuk</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: dbooksta</div><div class="ubbcode-body">Since (apparently) momentum is the dominant factor in "recoil," <span style="font-weight: bold">the heavier bullets will have <span style="font-style: italic">less</span> recoil than lighter bullets with equal muzzle energy!</span> </div></div>
Dunno about equal muzzle energy, as nobody I know loads to a specified ME, but most people do load workup looking for a target MV. </div></div>
In order to have a useful discussion on the trade-offs of different bullet weights I assumed that one loader for a particular rifle would tend to load to the same pressure levels. E.g., loaders who like to shoot "hot" will (hopefully) stop around the max pressure regardless of which bullet they're working up. So I pulled up Hodgdon's loads for .308 and for each bullet weight took the highest muzzle velocity published for the "do not exceed" load. I don't think there is any better way to eliminate external variables than to use Hodgdon's test data for a particular pressure peak. Obviously if you load different bullets to different pressures you don't have a sound basis for comparison.
Anyway, the useful observation from those data is that muzzle energy is pretty much constant for bullets between 140-200gr loaded to the same pressure levels.
Of course loaders tend to measure and talk in terms of muzzle velocity, but the useful "invariant" for this question is energy = MV^2 * bullet weight.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: memilanuk</div><div class="ubbcode-body">
Plugging some real-world numbers thru JBM yields the following:
Berger 155.5BT @ 3000fps, 48gn powder, 17.5lb gun (actual numbers from my F/TR rifle last year):
Recoil Velocity: 5.6 ft/s Recoil Energy: <span style="color: #FF0000">8.7</span> ft•lbs
Recoil Impulse: 3.1 lb•s
Berger 230 Hybrid @ 2550fps, 45 gn powder, 17.5lb gun (load values from someone I know running the bigguns in his F/TR rifle):
Recoil Velocity: 6.5 ft/s Recoil Energy: <span style="color: #FF0000">11.5</span> ft•lbs
Recoil Impulse: 3.5 lb•s
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The load you quote for the heavier bullet has 7% more muzzle energy and 25% more muzzle momentum, so of course it will have more recoil by either measure.
My observation is that, all else equal, heavier bullets (within a reasonable range for the caliber) loaded to the same peak pressure (which is the benchmark safe reloaders follow) produce the same muzzle energy.
There seems to be some disagreement as to whether "felt recoil" is proportional to energy or to momentum. If the former, than heavier bullets produce only slightly less recoil than comparable lighter bullets due to reduced rocket-effect recoil. If the latter than heavier bullets produce significantly less recoil.
