Observations on the Barnes TSX bullets
The Barnes 70 grain TSX is a very long bullet for its weight and caliber. At a nominal length of 1.037” it is longer than the heavier 77 grain Sierra MatchKing.
Besides being a long bullet, the 70 grain TSX has a specific gravity much lower than a copper jacketed/lead core bullet due to its sold copper construction. For example, the Hornady 75 grain BTHP has a specific gravity of approximately 10.3, while the Barnes 70 grain TSX has a specific gravity of only 8.9.
The Barnes 70 grain TSX will be unstable from a 1:9” twist barrel with a gyroscopic stability factor of less than 1 at all velocities. The 70 grain TSX will only be marginally stable in a 1:8” twist barrel with a G.S.F. of 1.05 at 2500 fps. A 1:7” twist barrel will produce acceptable stability with the 70 grain TSX with a G.S.F. of 1.37 at 2500 fps.
Barnes also makes a 62 grain TSX. It is even available in a factory load from COR-BON. Hand-loads using the 62 grain TSX consistently shoot slightly more accurately than hand-loads of the 70 grain TSX, at least in my barrels. The smallest 10-shot group from 100 yards that I’ve fired with the 70 grain TSX hand-loads had an extreme spread of 1.12”. With the 62 grain TSX hand-loads, I’ve been able to achieve sub-MOA accuracy for 10-shot groups at 100 yards.
COR-BON 62 grain DPX
This COR-BON load uses the Barnes 62 grain TSX bullet which has an all-copper construction. The bullet is much longer than a typical lead core/copper jacketed bullet of the same weight. This load had a muzzle velocity of 2963 fps from the 20" Colt barrel. The 10-shot group of record had an extreme spread of 1.75" and a mean radius of 0.61".
As for the possible difference in terminal performance between the two different bullets, here is a quote from Dr. G.K. Roberts on the subject:
“Keep in mind, that with non-fragmenting bullet designs, heavier bullet weights are not necessarily better, especially at closer ranges and from shorter barrels. As long as penetration and upset remain adequate, it is possible to use lighter weight non-fragmenting bullets and still have outstanding terminal performance. Heavier bullets may have an advantage at longer ranges due to better BC and less wind drift.”
The picture below (courtesy of Dr. G.K. Roberts) shows the Barnes 70 grain TSX after being fired into bare gel (on the left) and after first passing through auto windshield glass and then into gel (on the right.) Dr. Roberts states that when the TSX passes through auto windshield glass “the jacket ‘petals’ fold back against the core, or the ‘petals’ are torn off; this results in a caliber size projectile configured a lot like a full wadcutter, leading to deep penetration.”
Silver State Armory’s 70 grain TSX load easily matched the reported muzzle velocity of the 5.56mm Optimized load. From a 16" Colt barrel with a NATO chamber, chrome lining and a 1:7" twist, the SSA load had a muzzle velocity of 2788 FPS with a standard deviation of 15 FPS. From a 20" Colt barrel it had a muzzle velocity of 2899 FPS with a standard deviation of 21 FPS.
As I previously posted, the Silver State Armory 70 grain TSX load had a muzzle velocity of 2899 fps from a 20" Colt barrel. This is a hot load. Factory loads using equivalent weight bullets, for example the Federal Gold Medal 69 grain Sierra MatchKing, generally run around 2750 fps from a 20” Colt barrel.
Since the SSA 70 grain TSX load is such a hot load, I decided not to use my Krieger barrel, with its match chamber, to evaluate the accuracy of the SSA load. Instead, I used my 20” Noveske HBAR which has a chamber designed to fire the military pressure MK262 load safely, on full-auto, in hot environments. This barrel has a 1:7” twist. Using match grade hand-loads, this barrel turned in a 10-shot group at 100 yards that had an extreme spread of 0.726”.
Previous accuracy testing using hand-loads of the 70 grain TSX bullet proved the bullet itself to be capable of some fine accuracy. A 10-shot group fired from my Krieger barreled AR-15 at 100 yards had an extreme spread of 1.12”.
The SSA 70 grain TSX load was tested shooting from a bench-rest at a distance of 100 yards. A Leupold Competition scope with a magnification of 45X was used for sighting. Wind conditions were monitored using a Wind Probe.
Just for kicks, I did something a little different this time. I fired two 5-shot groups! Those groups had extreme spreads of 1.22” and 1.91”. I then fired a traditional 10-shot group, which had an extreme spread of 1.93” and a mean radius of 0.61”. I over-layed the two 5-shot groups on each other using RSI Shooting Lab to form a 10-shot composite group. The 10-shot composite group had an extreme spread of 1.93” and a mean radius of 0.63”.
As I posted previously in this thread, a barrel with a 1:9” twist theoretically will not stabilize the 70 grain TSX. Today, I put the theory to test using a Colt 16” HBAR with a 1:9” twist. This same barrel will marginally stabilize the Hornady 75 grain BTHP, though accuracy is slightly diminished compared to a 1:7” twist Colt HBAR.
I fired a 10-shot group of the 70 grain TSX round at a distance of 100 yards using the 1:9” twist barrel. Accuracy was terrible; the group had an extreme spread of over 3 inches. Several of the bullet holes were slightly oblong in shape and a coulple of the bullet holes were clearly “key-holed” demonstrating that a 1:9” twist barrel will indeed not stabilize the 70 grain TSX.
