Home Forums Hunting & Shooting Ask The Gunwriters Bullet Mass vs Exp vs pressure

Ken I hope the title not to techinical. The question I have is..
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<br>I have noticed that many a time a high SD bullet for caliber seems to be very efficent in reaching the 2000 to 2400 fps range. This seems easly done with pressures in the 35 to 45,000 CUP range and barrels of 20 inches or so. To get any more velocity out of these type bullets the pressures go up in a hurry for little gain and long barrels seem to add little. I have noticed this seems to be aroung the .280 and more SD for many diameters., ie. the 175 in 7x57mm, 160 in 6.5x55mm, 200 in 8x57mm, 250 in 338-06 and such.
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<br>I am no expert in this area, but it seems you end up with a high momentum bullet with moderate working pressures and proven on game preformance. One of the reasons I bring this up is the 220 Howell with high SD bullets such as the 75g spitzers and the milatry 5.56 with 69g bullets. Am I imanaging something here or is there really a 'ballistic' area here of the most for the least? Sorry if the question is not framed exactly right, but that is why I was hoping to get some education from your experience in this area.

Don't feel bad. You're not alone. I know only too well what it's like to wonder about something yet not be able to wrestle the wonder into the form of a clear question. I can sense your question only in a general way, so I'm not sure how best to try to answer it. So let me come at this from my own angle, and you look to see whether this answers your wondering.
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<br>First, let's recognize and shed the false, vain idea (which sales and magazine hype has set like granite in our understanding) that muzzle velocity indicates performance and provides a valid index for measuring and comparing performance.
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<br>Then we can agree that down-range performance (trajectory and impact velocity, which means impact energy) is the only legitimate criterion for evaluating the exterior ballistics of a cartridge and load.
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<br>Once we see this and look into it, we find that giving-up a lot of muzzle velocity with a light bullet -- to gain the superior weight and shape of a heavier bullet -- pays-off big-time down-range. A heavier bullet with a higher ballistic coefficient has to leave the muzzle at a lower velocity, but such a bullet usually retains enough more of its launch velocity to be traveling significantly faster out yonder where the bullet meets the prairie dog -- where it counts.
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<br>In one comparison I ran last year or the year before -- the .220 Swift factory load versus a moderate-pressure load in my larger .220 Howell -- a 50-grain bullet at about 3,800 ft/sec and a 75-grain at about 3,500 or 3,600 ft/sec -- I was a little surprised to find that the lighter bullet, which was significantly faster at the muzzle, slowed to the same velocity as the heavier bullet at some little distance short of 200 yards. And from that range beyond, the heavier bullet was increasingly faster than the lighter bullet.
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<br>Besides, the lighter bullet's sizzling muzzle velocity from the smaller cartridge required barrel-burning high chamber pressures. The heavier bullet, fired from a 25% to 30% larger cartridge, owed its launch velocity to a much more moderate and more barrel-coddling chamber pressure. If I loaded the heavier bullet, in the larger cartridge, to the same high pressure as the factory loaded the lighter bullet in the smaller cartridge, the faster bullet would slow to the same velocity as the "slower" bullet much nearer the muzzle. I wouldn't be surprised to find that the "faster" light bullet was faster only to about a hundred yards or even less.
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<br>I still don't know precisely what you're wondering about, so I can only hope that I HAVE answered some part of it and have NOT increased your puzzlement. Please don't hesitate to ask further.

Ken,
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<br>You answer some of it. Let me give it another stab.
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<br>I have noticed that heavy bullets (ie SD 280 or more) launched for cartidges of moderate chamber pressures (ie 35 to 45,000 cup) seem to have the following characteristics....
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<br>1. they are not as sensitive to barrel lentgh after 20 inches (vel loss per inch)
<br>2. even though pressures are moderate, they have high momentum (ie mass * velocity)
<br>3. They seem to get more out of the moderate pressure then say lighter bullets (ie SD of 250 of less) using moderate pressure loadings.
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<br>Given these it seems there is a 'sweet spot'(or range) for most cartidges of moderate pressures with high SD bullets. They give good preformance in the areas of firearm life, extrenal ballistics, and on game performance.
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<br>I am reminded of how reliable the 7x57mm with 170 to 175g bullets has been. Or to get even older yet the 45-70 with a 500g loading, the drop was alot but that was very perdictable, but the bullet had low wind drift and it was easy on the guns and devestating on game. Also there is the 6.5x55mm with 140 and 160g loads that performs well beyond what the 'paper' stats say it should, even in long range target shooting. Even the more modern 7mm Rem Mag seems at it best with the 175g or more. I will end with the 30-40 Karg with 220g loading, moderate pressures, but very good on game performance and repeatable external ballistics.
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<br>I just seems that moderate pressures and a high SD bullet go together well. To get lower SD bullets to preform well you use higher pressures and sacfice more perdictable down range perfomance. Drop is very consistent, can not say that for wind effects. I guess this the long way of asking is my perception correct here, or am I missing something? BTW Exp in the subject was for expansion ratio.

A very enlightening,we have all read the tables,now the why.