Recently I got my hands on an FDAC(Field Density Altitude Compensator) from ACTS(Adaptive Consulting and Training Services), a new vendor here on the hide. In a nutshell the FDAC is a ballistic chart for the 308 shooting a 175SMK. What makes this ballistic chart different is that it takes into account "Density Altitude" which is the altitude in the International Standard Atmosphere at which the air density would be equal to the actual air density at the place of observation, or, in other words, the height when measured in terms of the density of the air rather than the distance from the ground. So this allows the shooter to take into account shooting in various temperatures along with altitudes from sea level or a combination of both.
Many of us have dope for our rifle but this dope is usually set up for our "home range". But how good is that dope if you travel to different altitudes and temperatures? I live at sea level with temperature ranging from high 20's to low 100's. So what would happen if I gathered dope during the middle of winter (40*'s) at sea level and went shooting in the summer (80's) in Colorado at 4500'? A miss is what would happen by using, what amounts to essentially, the "wrong" dope. This is where the FDAC really shines. The FDAC would allow me to take into consideration the change of temperature and altitude and see how it will affect my dope.
When I received the card the first thing I noticed is that it seems to be a durable unit. Designed to be waterproof, the first test was the pre-schooler durability test. This test consists of giving the product to a child and seeing if it withstands the punishment. A few hours later after observing the FDAC become a car ramp, a garage roof, a frisbee and a ninja star (briefly) I picked up the FDAC and there was not a scratch or ding on it. It looked the exact same as when I pulled it out of the package. Durability test #1 easily passed. Test #2 the water test. It's obvious the FDAC is waterproof as all the cards are laminated but being a firm believer in Murphy's Law, I know that if there was the slightest opportunity for water to affect it, I would discover it in the first rain range outing. So for the water test, again, I solicited the testing skills of the previously mentioned pre-schooler at the appointed bath time. 15 minutes of submersion and about 15 seconds of air hose rendered, again, the FDAC as good as new.
So with the durability tests out of the way, it was time to get down to business at the range. Not having shot 308 in some time and having no dope at all, I was 100% reliant on this card to get me on steel. With any density altitude compensation you need to have an air temperature to start. Although you can fudge it with a huge (10*) margin of error, we happened to have a Kestral handy and got an accurate temp. In about 5 seconds I was able to see that even though I was at sea level, I needed to use the dope for 2K+' due to the hot weather. I slid the range card to 2K, looked down to 600 yards, dialed my dope and sent the shot. A bright splash and a thud let me know that my round had found the steel. I worked my way around from 300 all the way out to 800 yards and the FDAC had me right there. Even the wind chart on the card was putting me on steel.
The card I used was for a 175SMK at 2650. I picked this card as the ammo I was shooting (Corbon SHC 308) was loaded for 2650 however the FDAC comes with three different cards, all for the 175smk; 2600, 2650 and 2700, covering virtually 99% of the velocity spectrum for a 308 175gn. bullet. With these choices, the maximum velocity difference between your round and the ballistic chart should be 25fps at most. 25fps at 1000 yards is virtually indistinguishable and therefore not a factor in any adjustments.
Durable, accurate and handy are just a few of the ways to describe the new FDAC. It's impressive and well thought out as well as extremely versatile. I'm not a proponent of a lot of kit but this FDAC is well worth the investment and should be a part of anyone's gear that shoots 308 w/175gn. I know it's now a permanent part of my gear.
Many of us have dope for our rifle but this dope is usually set up for our "home range". But how good is that dope if you travel to different altitudes and temperatures? I live at sea level with temperature ranging from high 20's to low 100's. So what would happen if I gathered dope during the middle of winter (40*'s) at sea level and went shooting in the summer (80's) in Colorado at 4500'? A miss is what would happen by using, what amounts to essentially, the "wrong" dope. This is where the FDAC really shines. The FDAC would allow me to take into consideration the change of temperature and altitude and see how it will affect my dope.
When I received the card the first thing I noticed is that it seems to be a durable unit. Designed to be waterproof, the first test was the pre-schooler durability test. This test consists of giving the product to a child and seeing if it withstands the punishment. A few hours later after observing the FDAC become a car ramp, a garage roof, a frisbee and a ninja star (briefly) I picked up the FDAC and there was not a scratch or ding on it. It looked the exact same as when I pulled it out of the package. Durability test #1 easily passed. Test #2 the water test. It's obvious the FDAC is waterproof as all the cards are laminated but being a firm believer in Murphy's Law, I know that if there was the slightest opportunity for water to affect it, I would discover it in the first rain range outing. So for the water test, again, I solicited the testing skills of the previously mentioned pre-schooler at the appointed bath time. 15 minutes of submersion and about 15 seconds of air hose rendered, again, the FDAC as good as new.
So with the durability tests out of the way, it was time to get down to business at the range. Not having shot 308 in some time and having no dope at all, I was 100% reliant on this card to get me on steel. With any density altitude compensation you need to have an air temperature to start. Although you can fudge it with a huge (10*) margin of error, we happened to have a Kestral handy and got an accurate temp. In about 5 seconds I was able to see that even though I was at sea level, I needed to use the dope for 2K+' due to the hot weather. I slid the range card to 2K, looked down to 600 yards, dialed my dope and sent the shot. A bright splash and a thud let me know that my round had found the steel. I worked my way around from 300 all the way out to 800 yards and the FDAC had me right there. Even the wind chart on the card was putting me on steel.
The card I used was for a 175SMK at 2650. I picked this card as the ammo I was shooting (Corbon SHC 308) was loaded for 2650 however the FDAC comes with three different cards, all for the 175smk; 2600, 2650 and 2700, covering virtually 99% of the velocity spectrum for a 308 175gn. bullet. With these choices, the maximum velocity difference between your round and the ballistic chart should be 25fps at most. 25fps at 1000 yards is virtually indistinguishable and therefore not a factor in any adjustments.
Durable, accurate and handy are just a few of the ways to describe the new FDAC. It's impressive and well thought out as well as extremely versatile. I'm not a proponent of a lot of kit but this FDAC is well worth the investment and should be a part of anyone's gear that shoots 308 w/175gn. I know it's now a permanent part of my gear.
