Ballistics Report on a Hill Country Rifle Custom Rifle in 308 Winchester

September 15, 2012  11:00 AM

 

I had an interesting day at the Vermillion Pistol Club, recently, shooting my Hill Country Rifles custom .308 over a Pact MKIII chronograph.  Although I got the rifle about fourteen months ago, yesterday was the first time I've shot it over a chronograph.  Antelope season opens soon in South Dakota so I decided it was time to find out what kind of velocities my hunting loads were producing in the HCR. I needed actual measured velocities so I could use Sierra Bullet's Infinity ballistic software (V6.01) to get a better idea of what the bullet path and wind deflection would be like at 300 and 400 yards (not that I plan on shooting anything at 400 yards, but you never know what your opportunities are going to be in the field).

As is often the case, I was the only person at the range when I arrived around 11:00 AM.  It took me a little while to setup targets and get the chronograph ready, so it was close to 11:30 AM before I started testing .308 loads.

My 20 year old Pact MKIII chronograph had acted hinky the last time I used it (about two years ago) with some .44 Magnum reloads, so this time I did everything I could to optimize the chances of getting good readings, including cleaning the conductive surfaces on the sensor plugs and chronograph jacks the day before with DeoxIt. (The MKIII isn’t available from Pact anymore, but  the MKIV is.)

Shooting conditions that day were very pleasant.  The sky was sunny and clear and the temperature was about 80 degrees with around a 10-15 mph cross wind. The wind didn’t concern me as I wasn’t shooting for groups.

I isolated the chronograph unit and sensors from the shooting bench and muzzle blast as much as I could. The chronograph sensors were mounted on an old camera tripod and placed as far from the muzzle as the sensor cables allowed (about 12 feet).  The Pact MKIII unit was on top of my shooting box on the ground next to the bench. I carefully aimed 6-8 inches over the sensors in the center of the area defined by the brackets holding the sunscreens. 

To my relief, the Pact MKIII chronograph worked perfectly.  Many people apparently have a lot of problems getting their Pact chronographs to work reliably (but, to be fair to Pact, many people apparently have no problems with their units).  If the chronograph had failed to work reliably I planned to replace it with a Competition Electronics Prochrono Digital model.

I measured velocities of four different loads before the day was over: three factory hunting loads and one reload that I'd worked up for use as 100 yard practice load.  Here are the results.

308 Winchester Load

Ave fps

Shot 1

Shot 2

Shot 3

Hornady Superformance 165gr SST #80983
Lot 3112133

2748

2741

2742

2761

Federal  Premium 165gr Sierra GameKing BTSP (P308C in old style blue and tan box)

2670

2663

2668

2680

Federal  Premium 165gr Sierra GameKing BTSP (Current production P308C)

2584

2611

2587

n/a

My reload (lot #219), 45.1gr (10-year old) 748, 150gr blemished spitzer from Midway

2192

n/a

n/a

n/a

When I got back to my computer, I plugged the measured average velocities into Sierra’s Infinity ballistic software and  these bullet path and wind drift charts for the older Federal Premium load and the Superformance load:

Bullet Path for Sierra 165gr Gameking SBT at 2670fps 


Bullet Path for Hornady Superformance 165gr SST at 2750fps


Wind Drift for Sierra 165gr Gameking SBT at 2670fps


Wind drift for Hornaday Superformance 165gr SST at 2750fps



This range session confirmed the value in shooting over a chronograph.  If not for the chronograph, I would have never guessed that the older production Federal Premium ammo averaged 90 fps faster than the current production load. Fortunately, a few months ago, my son-in-law picked up 10 boxes of the older Premium load for me at a garage sale at a great price!

Also, if not for the chronograph, I would have never known that my 150gr practice reload was poking along at only 2200 fps!  Now I know that I definitely have to work up a faster load! I’ll probably try 47.0gr of 748 in the next batch.

Finally, it is interesting to me that the Hornady Superformance load is indeed faster than the Federal Premium factory loads--164fps faster than the current production Federal Premium ammo. Hornady advertises a muzzle velocity of 2840 fps for the 165 grain Superformance load, but my HCR rifle has only a 20” barrel, so I wasn’t surprised to not get the advertised velocity.

Hill Country Rifles guarantees that their custom rifles will shoot 0.5” 3-shot groups with specific factory hunting ammunition. When I ordered the rifle, Matt Bettersworth (Hill Country’s General Manager) and I agreed on the Federal Premium ammo with the 165gr Sierra GameKings as the proof load.  When I received the rifle, a test target was included with a 0.4” group that was shot with current production Federal Premium 165gr GameKing loads.  I haven’t been able to duplicate that small a group with Federal Premiums, but I’m still working on my bench technique. Even so, I’ve shot a half-dozen groups close to 0.5” with other ammunition and I’ve shot several 0.75” groups with the Federal Premium load so I have no hesitation in using it for deer.

Right now, my HCR is sighted in with the older Federal Premium 165gr GameKing load so it shoots 2” high at 100 yards. Bullet path should be about dead on at 200 yards, 3.4” low at 250, 8.6” low at 300, 15.8” low at 350, and 25” low at 400.

I may use the Hornady Superformance load for antelope hunting, though because it has a slight advantage in trajectory and wind drift.  With the HCR sighted in for the Federal Premium load, I have to remember that Superformance load shoots a little high and right (2.25” high and 0.5” right at 100 yards).

 

Load

Ave fps

50

100

150

200

250

300

350

400

450

Old Federal Premium 165gr GameKings

2670

0.9

2.0

1.8

0

-3.4

-8.6

-15.8

-25

-36.6

Hornady Superformance 165gr SST Interlocks

2748

0.7

1.8

1.6

0

-3.1

-7.9

-14.4

-22.7

-33.0

 

Product Notes:

The best price I could find on Sierra's Infinity ballistics software was at manventuresoutpost.com.