Collapse bottom bar
Subscribe

Guns & Ammo Network


Ammo Ballistics Competition Tips & Tactics

Power Factor & Recoil: Bullet Weight & Compensators

by Brad Miller, Ph.D.   |  November 5th, 2014 2

reloading_bullet_weight_compensators_FPrevious tests show that light bullets have more recoil and muzzle rise than heavy bullets when driven at the same power factor, because light bullets need more gunpowder for their required higher speed. The greater amount of gunpowder produces more gas that adds to the recoil force. 

Power-Factor_recoil_bullet_weight_F
related

Power Factor & Recoil: Which Bullet Weight Gives You the Edge?

Many organized shooting sports require ammunition to achieve a minimum power level to qualify and be scored in a specifi...

What happens when you put a compensator on the barrel? A compensator uses gas to reduce muzzle climb. Tests show that the extra gas provided by a gunpowder that uses a larger charge weight reduces muzzle rise more, even though they produce the same velocity with the same bullet . The additional gas provides more force to counteract the muzzle rise more effectively. 

Figure-1-compensators-Pressure-or-Gas
related

Compensators: Pressure or Gas?

We often hear arguments that high pressure is required to make a pistol compensator work properly. Some people claim tha...

This suggests that a compensator might reverse the effect of lighter bullets on recoil. Because lighter bullets require more gunpowder, this provides more gas to counteract muzzle climb, and they might have less muzzle rise than heavy bullets when loaded to the same power factor.

This was tested in two calibers, the .38 Super and .45 ACP. The .38 Super is commonly used in competition pistols where compensators are allowed. The .45 ACP is less common in a compensated competition pistol because the larger diameter round reduces magazine capacity, but it was included here to make a direct comparison with data from the previous article on bullet weight and recoil. Both guns have three-port compensators with ports only on the top (Figure 1).
reloading_bullet_weight_compensators_1

The .38 Super ammunition compared 115-, 124- and 147-grain Hornady XTP JHP bullets (Figure 2) loaded to a cartridge overall length (COL) of 1.240” in Starline 38TJ brass (a rimless version of the 38 Super) with three different charge weights of Vihtavuori 3N38 and Federal 205 (small rifle) primers.

Bullets used for these tests. The Berry’s 185-grain bullet is a round nose hollow base design. Click to enlarge.

Bullets used for these tests. The Berry’s 185-grain bullet is a round nose hollow base design. Click to enlarge.

The .45 ACP ammunition compared 185- and 230-grain RN Berry’s plated bullets loaded to a COL of 1.240” in Sellier and Bellot brass with three different charge weights of Winchester 231 and CCI 300 primers.

The gun was fired from a Ransom Rest. Measuring the distance that the gun moves in the Ransom Rest indicates relative recoil. The rocker arm that holds the gun pivots upward when the gun is fired. Since the compensator ports vent the gas upward, the gas produces a reciprocal downward force that reduces muzzle rise by reducing how far the gun pivots. Thus the Ransom Rest provides an objective method to measure gas effectiveness with a compensator. 

Cover-Figure-Ransom-Rest-Brad-Miller
related

How to Measure Relative Handgun Recoil

Can a Ransom Rest be used to measure recoil? Analysis of 3,500 rounds of .38 Special, 9mm Luger, .38 Super, .40 S&W,...

Linear regression was used to calculate gun movement and gunpowder charge weight at a power factor of 165, the power factor for Major scoring in USPSA practical shooting.

Results
As expected, light bullets required more gunpowder to achieve their required velocity. In the .38 Super, the 115-grain bullets required 9.5 grains of Vihtavuori 3N38, the 124s required 8.7 grains and the 147s required 7.2 grains. The 185 grain .45 bullets required 6.3 grains of Winchester 231, while the 230 grain bullets required 4.6 grains.

Velocity, gunpowder charge weight and calculated recoil force for a power factor of 165. Velocity to reach a power factor of 165 is rounded up to the next whole number. Gun weight used for the calculations was 2.5 lbs (40 oz). Click to enlarge.

Velocity, gunpowder charge weight and calculated recoil force for a power factor of 165. Velocity to reach a power factor of
165 is rounded up to the next whole number. Gun weight used for the calculations was 2.5 lbs (40 oz).

The result of lighter bullets requiring more gunpowder means that they produce more recoil force. The calculated recoil force for both calibers is shown in Table 1. In the .38 Super, the 115-grain bullets had 3% more recoil force than the 124-grain bullets, which in turn had 6% more recoil force than the 147-grain bullets. In the .45 ACP, the 185-grain bullets produced 7% more recoil force than the 230-grain bullets.

.38 Super
Even though light bullets produce more recoil force than heavy bullets at the same power factor, the compensator uses the additional gas provided by the extra gunpowder to reduce their muzzle climb more than heavy bullets. In the .38 Super, the 115- and 124-grain bullets had 21% and 13% less muzzle rise, respectively, than the 147-grain bullets (Figure 3). The 115-grain bullets had 9% less muzzle rise than the 124-grain bullets.

Muzzle rise with three different bullet weights at 165 power factor in the compensated .38 Super pistol.

Muzzle rise with three different bullet weights at 165 power factor in the compensated .38 Super pistol.

.45 ACP
The .45 ACP demonstrated the same greater reduction in muzzle rise with the lighter bullet. The 185-grain bullets had 6% less muzzle rise than the 230 grain bullets.

The .45 ACP test in “Power Factor & Recoil: Which Bullet Weight Gives You the Edge?” used the same Berry’s bullets and Winchester 231 gunpowder, which allows a direct comparison of how much muzzle rise was reduced with a compensator. With no compensator, the 185-grain bullets had 9% more muzzle rise than the 230-grain bullets, compared to the 6% less muzzle rise with a compensator in this experiment.

Figure 4 shows data from the previous article compared to data from this experiment. Note the reversal of muzzle rise with the light and heavy bullets with the use of a compensator. Crunching the numbers shows that the compensator produced a 30% reduction in muzzle rise with 230-grain bullets and a 40% reduction with 185-grain bullets.

Muzzle rise in the .45 ACP with light and heavy bullets at a power factor of 165. With no compensator (left), the 185-grain bullet has more muzzle rise than the 230-grain bullet (data from bullet weight and power factor article). That effect is reversed with a compensator (right), and the 185-grain bullet now has less muzzle rise than the 230-grain bullet. Click to enlarge.

Muzzle rise in the .45 ACP with light and heavy bullets at a power factor of 165. With no compensator (left), the 185-grain bullet has more muzzle rise than the 230-grain bullet (data from bullet weight and power factor article). Effect is reversed with a compensator (right), and the 185-grain bullet now has less muzzle rise than the 230-grain bullet.

Muzzle pressure
More gas volume should translate into higher gas pressure at the muzzle when the bullet exits the barrel. This can happen even if the larger charge weight does not produce a higher peak chamber pressure, as demonstrated when comparing two gunpowders with different burning rates.

Higher gas pressure at the muzzle should indicate greater upward force deflected by the compensator’s baffle plates and ports. This would produce more downward force to reduce muzzle rise. QuickLOAD software (version 3.8.0.2) was used to estimate gas pressure at the muzzle to see if it corresponded with the greater reduction in muzzle rise with the light bullets. It did.

Muzzle pressures as calculated with QuickLOAD software using the data from this experiment. Whatever brand of bullet was selected for the .45 ACP comparison (Speer, Nosler), there was always more muzzle pressure with 185-grain bullets than with 230-grain bullets.

Muzzle pressures calculated with QuickLOAD using data from this experiment. This shows there was always more muzzle pressure with 185-grain bullets than with 230-grain bullets.

Calculations with the .38 Super data showed that the light bullets had higher muzzle pressure than the heavy bullets. The 115-grain load had 10% more muzzle pressure than the 124-grain load, and 34% more than the 147-grain load (Table 2). QuickLOAD does not have the Berry’s .45 caliber bullets in its database, so I substituting 185- and 230-grain Hornady HAP bullets for the calculations.

Note: QuickLOAD’s calculated pressures are estimates. The actual pressure can be different, but the trend of pressure differences (more, less) between bullet weights should be the same. The calculations showed that the lighter 185-grain bullet had 45% higher muzzle pressure than the 230-grain bullet (Table 2). Thus, higher muzzle pressure can overcome what would normally result in more muzzle rise with no compensator to produce less muzzle rise with a compensator.

Summary
A compensator changes how a gun responds to light and heavy bullets when loaded to the same power factor. Light bullets produce less muzzle rise because they use more gunpowder, and that means more gas to enhance the compensator’s effect. This is just the opposite of what happens when you don’t have a compensator where light bullets have more recoil than heavy bullets. If you’re loading ammunition for a compensated pistol, light bullets combined with a gunpowder that provides a lot of gas (large charge weight) will produce the least muzzle rise.

Load Comments ( )
back to top