177 Slug Ballistic Coefficients – The First Results
As Hard Air Magazine continues to expand our already-huge range of BCs for airgun projectiles, we now have the first results for 177 slug Ballistic Coefficients. These BCs are for Field Target Tech slugs manufactured by Tom Holland.
For background, check out this previous HAM post on Tom’s slugs.
These 177 slug Ballistic Coefficients were generated in our usual fashion. They were all shot using the same FX Impact air rifle in the regular location, at the same session, by the same people. The FPS data was recorded using Ladradar and analyzed using the same methodology.
Today’s slug BC data bears some similarities to the .22 caliber data we published last week, although there also some differences.
Below, there’s an obvious difference in size and design between these slugs and it shows in the vastly different BCs. One the left is one of Tom’s 12.04 Grain Rebated Boat Tail slugs. The one on the right is a 23 Grain Cup Base slug. They both have hollow points, 2S Ogive heads and .1775 caliber.
The basic similarity is that – in general – BCs tend to increase with increasing slug weight. When fired from the same gun in the same caliber, that is. The red dotted line in the graph below gives a “trend line” that’s calculated by the spreadsheet software.
The difference is that Tom manufactures four designs of slugs all at around the same weight of 15 Grains. These give very different Ballistic Coefficients as we can see from the graph below.
As we can see, Tom’s “15 Grain” slugs have BCs that vary all the way from 0.014 to 0.030, for almost identical weights. The difference has to be attributable to the design of the slugs, as everything else about the testing was identical and the results were analyzed in the same way.
Comparing the “same weight” slugs with the highest and lowest BCs does – indeed – show a significant difference in design, as we can see below.
The Hollow Point, Flat Nose slugs (right) are of more conventional airgun slug design. They give a 0.030 BC. The “Field Target point” slugs (left) are of a very unusual configuration and deliver the 0.014 BC.
Here’s the “hard data” from these tests.
|MAKER||NAME (If red, click for full HAM review)||WEIGHT||HEAD DIAMETER||BALLISTIC COEFFICIENT||SECTIONAL DENSITY||FORM FACTOR||MUZZLE VELOCITY||30 YARD VELOCITY|
|Field Target Tech||Slug 2S Ogive H/P Cup Base 23 Grain .1775||23.00||0.1775||0.043||0.104||2.43||771 FPS||707 FPS|
|Field Target Tech||Slug 2S Ogive H/P Rebated Boat Tail 12.04 Grain .1775||12.04||0.1775||0.014||0.055||3.78||921 FPS||704 FPS|
|Field Target Tech||Slug 2S Ogive H/P Flat Point Hollow Base 14.96 Grain .1775||14.96||0.1775||0.025||0.068||2.74||874 FPS||747 FPS|
|Field Target Tech||Slug 2S Ogive HP Flat Base 15.04 Grain .1775||15.04||0.1775||0.030||0.068||2.27||873 FPS||766 FPS|
|Field Target Tech||Slug 2S Ogive Flat Pt Flat Base 15.04 Grain .1775||15.04||0.1775||0.019||0.068||3.54||880 FPS||721 FPS|
|Field Target Tech||Slug 1/2 Ogive HP Rebated Boat Tail 20.04 Grain .1775||20.04||0.1775||0.019||0.091||4.73||773 FPS||640 FPS|
|Field Target Tech||Slug 2S Modified Special FT Flat Nose Flat Base 15.02 Grain .1775||15.02||0.1775||0.014||0.068||4.89||883 FPS||673 FPS|
As with the .22 caliber BCs, there’s no necessary correlation between Ballistic Coefficient and accuracy. That’s going to be a function of the complete “shooting system”, primarily the slugs and barrel characteristics.
The “sea of slugs” shown in our heading photograph at the top shows a mass of Tom’s 14.96 Grain, Flat Point, Hollow base slugs. The BC is 0.025.
For more information – and to buy – .177 caliber slugs from Field Target Tech, click through to Tom’s website at fieldtargettech.com.