The following demonstration compares the results of firing four 10-shot groups of the same lot of 55 grain Prvi Partizan M193 ammunition from two different barrels; one barrel with a 1:9” twist, the other barrel with a 1:7” twist. The first barrel used in testing was a 16” Colt HBAR with chrome lining, a NATO chamber and a 1:9” twist. The second barrel used in testing was a 20” Colt HBAR, also with chrome lining, a NATO chamber and of course a 1:7” twist. The longer barrel with the 1:7” twist was purposely chosen for the increased muzzle velocity coupled with the 1:7” twist. Both barrels had free-float handguards.
Accuracy testing was conducted from a distance of 100 yards following my usual protocol. The fore-ends of the weapons rested in a Sinclair Windage Benchrest and the butt-stock rode in a Protektor rear-bag. Sighting was accomplished via a Leupold VARI-X III set at 25X magnification and adjusted to be parallax-free at 100 yards. A mirage shade was attached to the objective-bell of the scope. Naturally, the wind conditions were monitored using a Wind Probe. The set-up was very similar to that pictured below.
Four 10-shot groups of the PPU M193 were fired from the 1:9” twist barrel. Those groups were over-layed on each other using RSI Shooting Lab to form a 40-shot composite group. The mean radius of that composite group was 1.08”.
As with the 1:9” twist, four 10-shot groups were fired from the 1:7” twist barrel. Those groups were also also over-layed on each other to form a 40-shot composite group that had a mean radius of 1.01”. The two composite groups are shown side by side for comparison. So much for the often posted nonsense about 1:7” twist barrels making 55 grain FMJ bullets “unstable.”
Quality 55 grain bullets can shoot superbly from a 1:7" twist barrel. Most 55 grain full metal jacket bullets do not fall into the quality category, so any comparison made using 55 grain FMJ bullets with heavier open tip match bullets is nonsense.
The 10-shot group pictured below was fired from a distance of 100 yards from a Noveske barreled AR-15 with a 1:7” twist.
The 3-shot group pictured below was fired from the same 1:7” twist barrel for the Internet Commandos in our viewing audience.
The next 10-shot group pictured was fired from a Krieger barreled AR-15 with a 1:7.7” twist using 55 grain BlitzKings.
Barrels with 1:7" twists can shoot bullets as light in weight as 40 grains without issue, as long as it is a modern, quality 40 grain bullet, such as the Hornady 40 grain V-MAX.
Here's another example of just how well a 1:7" twist barrel can shoot light weight bullets. While the group pictured below was fired from a distance of only 50 yards, it's a 10-shot group fired from a chrome lined, NATO chambered Colt barrel with a 1:7" twist using 52 grain Sierra MatchKings.
The 10-shot group pictured below was fired from a 20" government profile Colt barrel with a NATO chamber, chrome lining and a 1:7" twist. That's about as good as a group as you will see from this type of barrel and it did it with 55 grain BlitzKings.
A 14.5" Colt M4A1 SOCOM barrel,with its NATO chamber, chrome lining and 1:7" twist can shoot quality 55 grain bullets quite well.
Yet another example of how well 55 grain bullets can do from a 1:7" twist barrel. This time from the 16" version of the Noveske N4 light barrel that is also chrome lined and NATO chambered.
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