Paul Harrell On AR Platform Barrels: 10.5″ vs 16″ vs 20″
BY Herschel Smith
4 years, 5 months ago
You are currently reading "Paul Harrell On AR Platform Barrels: 10.5″ vs 16″ vs 20″", entry #24630 on The Captain's Journal.
This article is filed under the category(s) AR-15s and was published June 21st, 2020 by Herschel Smith.
If you're interested in what else the The Captain's Journal has to say, you might try thumbing through the archives and visiting the main index, or; perhaps you would like to learn more about TCJ.
This article is filed under the category(s) AR-15s and was published June 21st, 2020 by Herschel Smith.
If you're interested in what else the The Captain's Journal has to say, you might try thumbing through the archives and visiting the main index, or; perhaps you would like to learn more about TCJ.
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On June 22, 2020 at 8:10 pm, The Wretched Dog said:
What were the barrel twist-rates?
The 20-in A2 should be 1:7. I expect that the 16-in is a 1:9. I have no idea what the common twist-rate is for 10.5-in barrel lengths.
Why the 55-gr XM-193? The 1:7 A2 twist-rate was designed for longer, heavier bullets. M855 62-gr green-tip isn’t even ideal for a 1:7 twist-rate. I use 69-gr.
I assume Mr. Harrell knows all this, so I am curious as to his choices.
TWD
On June 22, 2020 at 9:12 pm, Georgiaboy61 said:
Around the time M855/SS109 was being considered for standardization by the U.S. Army and then NATO, testing was done using a variety of barrel twist rates and lengths to determine which combination worked best. The 1:9 RHT was found to be the most-versatile, offering excellent accuracy with M193 55-grain Ball/FMJ, but also with heavier projectiles such as the then-new “green-tip” 62-grain Ball/FMJ (with an internal steel penetrator or cup to enhance its effectiveness against the standard sheet metal helmet at 500m). However, the fly in the proverbial ointment was that 1:9 twist would not stabilize the heavier and also substantially-longer 64-grain FN L110 tracer round. Hence the move to 1:7 twist barrels. Why didn’t the army test a 1:8 barrel instead? It would have offered the necessary stabilization for the 64-grain tracer while providing better accuracy than the faster 1:7 rate.
On June 22, 2020 at 9:24 pm, The Wretched Dog said:
Georgiaboy61: Yes, indeed – all is as you say.
Thus my question – why use the short, light-weight 55gr. M193 ball for an ‘accuracy’ test of the 20-in A2 barrel, given its 1:7 twist-rate.
Other than that question, I always enjoy Mr. Harrell’s presentations.
Loved the design of the “meat” target.
TWD
On June 23, 2020 at 9:05 am, Bill Buppert said:
A longer barrel isn’t only related to ballistic characteristics but the effective “driveability” of a rifle servicing multiple targets laterally with varying degrees of elevation. Your support hand is most useful drawn out than tucked in doing so.