The Need for Speed: The effect of cartridge velocity on target shooting

The Need for Speed: The effect of cartridge velocity on target shooting
Author:  Luther Cutts, Head Instructor (NSCA Level 3), Competitor 

One does not have to spend a lot of time on the shotgun range or in the clubhouse to hear someone’s theories on the velocity of their shotgun cartridges.  Not everyone puts a lot of thought into it, but some do, and some apparently put a whole lot of thought into this topic.

Rather than go through some of the more common theories, I thought I would approach this from more of a scientific perspective and include a sprinkling of personal experiences that appear to be relevant.  I hope to shed some light on some of the more commonly held beliefs and hopefully provide people involved in this great sport with some additional information, and thereby enable them to make informed decisions regarding their ammunition purchases.  I will caution you now, if you are not into numbers and little bits of physics, this article is likely not for you. 

The main principles that I hope to address in this piece are:

  • If I shoot a faster round, will it reduce my lead required to break a target, especially on targets at longer range?
  • Is muzzle velocity the most important determinant when considering long-range performance of a shotgun shell?
  • Are the composition and dimensions of the shot in the shell important?

There are almost certainly more questions, but these are the ones that I am most familiar with.  What does the science tell us?

Before we get too far into this discussion, it will be beneficial to agree on a few specific points. 

  • One important point that should not be in dispute is the fact that with all other factors being equal, a target flying perpendicular to the shot will require the most lead.  That is to say that a target flying across the shooter’s field of view will require more lead than any other target that is either angling toward the shooter or away from the shooter.
  • Another point that we should be in agreement on is the definition of lead, or forward allowance.  I hope that most people would agree that lead is the distance in front of the target, along the line of the target, that the shotgun must be positioned if the target is to be broken with the shot.  Another way to look at it is how far the target will move in the time it takes for the shot to transit the space between the target and the muzzle of the shotgun.
  • For the purposes of this discussion, I will use a standard of a regular clay target, travelling at 45 miles per hour.  I will not adjust for target deceleration – I will presume that the target will maintain its speed of 45 mph throughout the shot.  I will also assume an elevation of 3,500 feet above sea level, and an ambient temperature of 15° C. 
  • Finally, I will assume that the projectile is a pure lead sphere and that it is reasonably round.

A target travelling at 45 mph is going slightly more than 66 feet per second.  From this, we need to determine how long it takes our shot to cover the distance from the muzzle to the target.  For sake of clarity, I will assume my standard 45 mph target is crossing at 45 yards from the shooter – for most shooters, this would qualify as a relatively fast target and a relatively long shot.

45 mph target crossing at 45 yards from the shooter – with #7-1/2 shot:

Muzzle Velocity45-yard velocityVelocity LossTime of FlightTarget Movement
1,200 fps614 fps586 fps0.163 seconds10.75 feet
1,250 fps626 fps624 fps0.160 seconds10.56 feet
1,300 fps637 fps663 fps0.157 seconds10.36 feet
1,350 fps648 fps702 fps0.154 seconds10.16 feet

45 mph target crossing at 45 yards from the shooter – with #8 shot:

Muzzle Velocity45-yard velocityVelocity LossTime of FlightTarget Movement
1,200 fps590 fps610 fps0.167 seconds11.02 feet
1,250 fps604 fps646 fps0.163 seconds10.75 feet
1,300 fps615 fps685 fps0.160 seconds10.56 feet
1,350 fps625 fps725 fps0.157 seconds10.36 feet

45 mph target crossing at 45 yards from the shooter – with #9 shot:

Muzzle Velocity45-yard velocityVelocity LossTime of FlightTarget Movement
1,200 fps540 fps660 fps0.175 seconds11.55 feet
1,250 fps552 fps698 fps0.171 seconds11.28 feet
1,300 fps562 fps738 fps0.168 seconds11.08 feet
1,350 fps572 fps778 fps0.165 seconds10.89 feet

Velocity and its relationship to recoil

Many shooters, particularly newer shooters, can be sensitive to the recoil impulse generated when the round is discharged.  There are many factors that must be considered when dealing with recoil, so I will make a few assumptions to clarify the primary points I am attempting to articulate.  First, I will assume that the firearm fits the shooter reasonably well – an ill-fitting gun can amplify the effects of recoil.  Next, I will assume that the shooter has some shooting experience, which is required when dealing with the effects of recoil.  Finally, I will assume the shooter is somewhat accustomed to recoil, and that there is a threshold that the shooter has for recoil.  There are some shooters that do not feel the effects of recoil whatsoever, but for the majority of shooters, there is a level at which recoil becomes noticeable, uncomfortable or unmanageable.

Using an online shooters calculator, I have determined that a cartridge that sends a 1-ounce payload of lead downrange at 1,200 feet per second, in a 7-1/2-pound shotgun will generate approximately 16.49 foot pounds of energy.  With everything else remaining the same, but the muzzle velocity raised to 1,350 FPS, the recoil energy increases to 20.13 foot pounds, approximately 25% greater recoil.

When we compare a 7/8-ounce load at 1,200 FPS to a 1-1/8-ounce load at 1,350 FPS, the difference in recoil is even greater – nearly twice as much recoil:

Payload (Ounces)Muzzle Velocity (FPS)Recoil Energy (foot pounds)
7/81,20013.07
1-1/81,35024.52

When a shooter does have a threshold with respect to recoil, it is always better to operate below that level.  Besides being uncomfortable, it is distracting and tiring.  Furthermore, the evidence would suggest that all the extra noise, expense and recoil is likely not worthwhile.  If we use the same standard parameters as in the previous section, and we compare a rather sedate load with a velocity of 1,165 fps at the muzzle with a high-performance round that starts out at 1,450 fps, we see the 285 fps advantage at the muzzle shrink to 64 fps at 45 yards.  The difference in the forward allowance is just over a foot, well within the pattern of most shotguns at that range.  The distance the shot drops below the line of the bore at 45 yards varies between 4-1/2” and 5-1/2”, another aspect of shotgun shooting that, like the forward allowance, is obscured within the pattern.

Muzzle Velocity45-yard velocityVelocity LossTime of FlightTarget Movement
1,165 fps611 fps554 fps0.165 seconds10.89 feet
1,450 fps675 fps865 fps0.148 seconds9.76 feet

The Need for Mass (Momentum)

In 2007, I travelled with my wife to New Zealand and Australia, and while there I participated in a large shooting competition.  When I was talking with the fellow who was supplying the ammunition, he was delighted when I said I preferred the #7-1/2 pellet size – he was frustrated with most of the other shooters from North America who insisted on shooting #8 pellets.  His rationale was simply that since most of the clubs used International trap targets as opposed to the standard targets we see at most North American ranges, the #8 pellet will often not break the target, as it lacks sufficient momentum.  The increased number of pellets in the shot column was not sufficient to compensate for the decreased energy stored in each pellet.  The targets used in international trap was subjected to significantly more stress when being released from the trap and are therefore a more robust target.  There were several that my wife was able to carefully stand on that did not break.

During the sporting competition, we saw many instances in which a target appeared to have been hit, but no visible piece came off the target.  In many instances, we would see the target move, but the rules do not allow for the awarding of a “hit” unless a visible piece comes off the target.  After the competition, we found a rabbit target with 13 pellet holes in it, but it was unbroken – it was likely that the shooter was not given credit for a hit on that target, despite hitting it well.

Conclusions

The math reveals that the speed advantage that any shot has at the muzzle is significantly eroded as the shot gets out to 45 yards, and that advantage continues to erode as the range increases.  The reason for this is found in aerodynamics, a fundamental principle of which is as an object travels faster through the air, the drag on the object increases.  Drag on the projectile causes it to decelerate, and increased drag results in greater deceleration.  Lead spheres are aerodynamically inefficient, and they rely much more on mass and momentum to maintain their ballistic advantages over longer ranges.  

Another interesting revelation from the charts above is the importance of momentum, or the benefits derived from additional pellet weight.  The weight of the shot charge in each cartridge is the same, but the larger pellets have heavier individual weights, and therefore are able to maintain their velocity better over distance.    This can be seen in both velocity loss as well as the time required for the shot to cover the distance from the muzzle to the target.  This phenomenon is well-known to rifle shooters, who understand that long-range shooting requires the heavier bullets for the calibre.  It is not unlike throwing a ping-pong ball and a billiard ball.  The ping-pong ball can be thrown very fast, but because it is so light, it will not go very far.  The billiard ball, on the other hand, is quite heavy, and while the initial velocity of the ball will not be as high as the ping-pong ball, it will travel many times further because of its momentum.  It would therefore appear that the size of the pellet a more important consideration when shooting longer range targets than is muzzle velocity.

Add Your Comment

Your email address will not be published. Required fields are marked *