What Is The Power Loss Shooting Slugs In PCP Air Rifles?
OK, so here’s a question that many airgunners will NOT want to hear about. “What is the power loss shooting slugs in PCP air rifles?”
Power Loss Shooting Slugs In PCP Air Rifles – Background
As we take a first look at this question, a few explanations may be in order:
1. When speaking about “power”, I’m really referring to Muzzle Energy. Not the retained energy downrange.
2. Most people probably accept that the larger bearing surface of a parallel-sided slug against the barrel’s bore is greater than that for diabolo pellets. There’s just so much more surface rubbing against the steel barrel. That must mean that slugs create more friction when fired than pellets. That friction represents wasted power.
3. Here we are comparing the power loss between slugs and pellets of approximately the same caliber and weight. However, this has not been explored widely as most slugs are so much heavier than pellets.
Having recently added the light – 20.3 Grain – Daystate Howler slugs to the standard HAM .22 caliber test review ammunition suite, we can compare their performance against similar weight pellets. 21.14 Grain H&N Baracuda Match pellets, for example.
4. The data presented here is for a small range of air rifles – actually four. They’re all in .22 caliber. But the trend is clear, as you will see…
Power Loss Shooting Slugs In PCP Air Rifles – Pellet Performance
First, let’s start with a demonstration that the Muzzle Energy of almost all PCP air rifles increases with the weight of the pellet fired.
Here’s a chart of the Muzzle Energies from a PCP recently tested by HAM. It’s the Barra 1100z and is exactly what we have come to expect as “normal” performance.
The red dots in the above graph represent the individual Muzzle Energies attained with specific pellets. The black dotted line is a “line of best fit” generated by the spreadsheet software. This can predict approximate power when using different weight pellets.
For example, 18.0 Grain pellets would give about 24.8 Ft/Lbs Muzzle Energy for this gun when read off of the chart.
Power Loss Shooting Slugs In PCP Air Rifles – Add A Slug To The Mix
Now let’s take exactly the same graph from the same gun and add the results from the 20.3 Grain Daystate Howler slugs. Wow! What happened there?
Immediately we see that the Muzzle Energy for the 20.3 Grain slugs is waaaaay less than would be expected for a 20.3 Grain pellet.
In fact, we can compare it to our trend line an see that it’s actually around 3.95 Ft/Lbs less than would be likely for a pellet. That’s the power that was lost due to friction forcing the slug down the barrel.
In fact it’s no less than 16% of the potential Muzzle Energy wasted just by shooting slugs. Ouch!
Now let’s add the test results for three additional .22 caliber PCP air rifle test reviews. (The Diana XR200 has been tested by HAM but the review is not written-up yet).
The black arrows indicate the four Muzzle Energies achieved when shooting the 20.3 Grain Howlers. As you can see, they’re always lower than the trend line for the pellets.
Power Loss Shooting Slugs In PCP Air Rifles – Percentage Variations
Below we have the same chart, this time showing the percentage reduction in each case compared to the trend line.
Here’s the data for those power reductions.
|Air Rifle||Predicted Power for 20.3 Grain Pellets||Actual Power for 20.3 Grain Slugs||Reduction Due to Shooting Slugs||Reduction as a Percentage|
|Barra 1100z||25 Ft/Lbs||21.15 Ft/Lbs||3.85 Ft/Lbs||16%|
|Diana XR200||33 Ft/Lbs||30.78 Ft/Lbs||2.22 ft/Lbs||7%|
|Western Airguns Sidewinder||42 Ft/Lbs||39.75 Ft/Lbs||2.25 Ft/Lbs||5.5%|
|BRK Ghost||43.5 ft/Lbs||42.39 Ft/Lbs||1.11 ft/Lbs||1.5%|
Taking those percentage numbers and charting them against the equivalent Muzzle Energies for shooting pellets (trend line points), it’s interesting to see that the percentage of power lost declines as the Muzzle Energy of the gun increases.
Power Loss Shooting Slugs In PCP Air Rifles – Conclusions
Frictional losses reduce the actual Muzzle Energy of a PCP airgun when shooting slugs, compared to the power that would be produced by an equivalent-weight lead pellet. The reason is friction.
Slug manufacturers obviously know that. It’s likely to be the reason that many slugs are manufactured in different micro-calibers (.217, .218 and so on for nominal .22 caliber barrels). Although not included in this analysis, it’s likely that matching slugs to actual bore diameter will result in both improved accuracy and reduced frictional losses).
That loss of power can be very considerable with relatively low-powered guns – say around 25 Ft/Lb Muzzle Energy in .22 caliber. So, if you have a low power PCP, you’ll likely lose retained energy downrange too, as that initial power loss will not be overcome by the slug’s superior Ballistic Coefficient at reasonable shooting ranges.
The loss of power due to frictional effects falls as the gun’s power increases. Above around 50 Ft/Lbs Muzzle Energy in .22 caliber the loss becomes insignificant.
There’s no strike against the Daystate Howlers in this analysis. Any flat-bodied slug would most likely demonstrate the same results.
True, this analysis is based on just four examples. However the results are consistent enough to be believable, in my opinion.
It’s yet another indication that you need a really powerful air rifle to shoot slugs successfully. If not, pellets may still be your best bet.