Effects Down Range: bullets and ballistic coefficients.
Last time we studied the effects of muzzle velocity deviations and their importance to hit probability. In regards to sheer hit probability we saw that a single digit SD (like what is seen in good handloads) gained us an additional 100yds over an SD of 15fps (like good factory ammo). I also said that a low BC bullet will be more affected by velocity deviations than a higher BC bullet. Using the same AB Analytics WEZ we will compare bullets to determine what the payoff is.
We will make the same assumptions as before: shooter and rifle can shoot within 1MoA, has a Kestrel to record atmospherics, can read wind (or has no wind), and knows precisely the range to the target.
To keep this as apple to apples as possible we will use Parker bullets since Bob makes more styles of bullets in more weights than anyone else in his Ballistic Extreme (BE) and Match Hunter (MH) lines. Having shot quite a few of them over the years I know the BC’s are pretty optimistic but we will take them at face value for the purpose of this test. We will consider the 275gn BE, 275gn MH, 300gn BE, and 300gn MH. All velocities were pulled from pressure traces and we will model 7fps and 15fps SD’s for all.
The 275gn BE is a very popular bullet among guys who shoot muzzle-loaders. I think it is probably the most popular bullet out there for guys who are serious about muzzle-loaders because they tend to shoot well and kill well. They can be shot fast and the recoil is not bad. The problem is they are about as aerodynamic as a shoe-box. Until the 275MH came out several custom builders advocated them as the ultimate long range SML bullet capable of dispatching deer to 500yds.That is someone trying to sell you a product instead of success. The truth is it only retains enough velocity to be effective to 410yds under PERFECT conditions and past about 300yds gets blown really badly in the wind. The 300gn version is identical in form, just slightly longer and heavier and only gets to 382yds with 1800fps. Neither has ever been a long range proposition despite what anyone has claimed.
275gn BE, MV 2900fps, SD 7fps, 90% hit probability under ideal conditions 732yds
275gn BE, MV 2900fps, SD 15fps, 79% hit probability under ideal conditions at same range
300gn BE, MV 2800fps, SD 7fps, 90% hit probability under ideal conditions 732yds
300gn BE, MV 2800fps, SD 15fps, 78.4% hit probability under ideal conditions at same range
The MH line of bullets is significantly more aerodynamic than the BE and are a superior design for increasing desirable flight characteristics. According to AB Lab’s research for every caliber length increase in the nose of a bullet you reduce drag by some 19%. That is to say that just changing shape can make a huge difference in aerodynamic performance. The 275gn MH carries that 1800fps to 465yds (50yds increase) and 300gn MH to 492yds (110yds increase).
275gn MH, MV 2900fps, SD 7fps, 90% hit probability under ideal conditions 765yds
275gn MH, MV 2900fps, SD 15fps, 80.9% hit probability under ideal conditions at same range
300gn MH, MV 2800fps, SD 7fps, 90% hit probability under ideal conditions 765yds
300gn MH, MV 2800fps, SD 15fps, 79.8% hit probability under ideal conditions at same range
The shot simulations show that lower BC bullets have shorter ranges under ideal conditions and that when you have poor SD’s your hit probability drops more than with a higher BC bullet. In the case of big bore guns like an SML the differences are not as dramatic as with smaller bore guns since the same 25gn in a .45 is not nearly the increase that it is in a .264 bullet. In the case of the SML it would appear that 100fps in MV is worth nearly the same as a small increase in BC (think about the range increase of the 275 vs 300 MH) but choosing the pointer bullet in the same weight class always shows an increase in performance (think about the range increase from either BE to MH). That is an important choice to make when you are working around a fixed parameter like muzzle velocity. Next time we will introduce wind.