Handloading the AR-15 .223 with 1-in-7 twist Pt. 3
Date: Mar 30 2008
In the two previous articles on “Handloading the AR-15 .223 Remington,” we offered tips and data for rifles with barrel twist rates of one turn in 12 inches and one turn in 9 inches. Now let’s look at rifles with the one-in-7-inch twist.
The 7-inch twist is intended primarily for heavier bullets ranging from 62 to 80 grains, which it stabilizes very well. With a match grade barrel and heavyweight match bullets, it has proven a worthy contender at 600 yards, effectively beating the .308 Winchester at its own game. (Just for reference, barrels featuring one turn in 8 inches have become popular in AR-15s, which stabilize bullets up to 80 grains. For those wanting an even heavier bullet, rifles fitted with a barrel featuring a one-in-6.5-inch twist will stabilize bullets up to 90 grains, such as the Sierra HPBT-Match. Both the 8- and 6.5-inch twists can be used with today’s data.)
In my mind, rifles fitted with a one-in- 7-inch twist are somewhat specialized, intended primarily as long-range target rifles (which is not to say they won’t work with select 55-grain bullets). While handloads can be assembled with an overall cartridge length of 2.260 inches, which is within SAAMI specifications and will function and feed reliably through the action, better performance and improved accuracy can be obtained by seating bullets out for an overall cartridge length of 2.550 inches. Due to their excess length, cartridges loaded in this fashion will not fit into the magazine and become specialized “single shots” for competition. Some competitors modify magazines by cutting a slot into the front for the bullet tips to protrude, but the receiver box becomes the limiting factor. The rifle used in this article limited that length to 2.380 inches. Seating bullets out increases powder capacity and allows for greater velocity but also places bullets closer to the rifling, which usually improves accuracy and will allow one to finetune the load for a given rifle.
When using the accompanying data, take note of the overall cartridge length listed with each bullet, as they
were assembled “long” for use in the “single-shot” mode. If bullets are seated deeper (to SAAMI specifications) than the listed length, powder charges must be reduced 7 to 10 percent. Failure to do so will result in loads that produce substantially greater (and even dangerous) pressures. The data presented here was developed in commercial Nosler- Custom cases, which have greater capacity than military cases. Do not use the accompanying data with military brass, or pressures exceeding SAAMI guidelines will probably result. Commercial cases also vary in capacity. The point being, never begin with maximum listed loads, but rather begin with the starting loads, carefully measuring fired cases for signs of excess pressure (and case head expansion) before increasing the powder charge. And when working up powder charges, keep in mind that the .223 Remington case is small and a .5-grain increase will noticeably raise pressures, especially when used in conjunction with heavier bullets weighing 75 to 80 grains.
Most commercial .223 Remington cases are of good quality, but to obtain the consistency that match shooters seek, most will need the flash holes “uniformed” and deburred, then the overall case length trimmed and deburred inside and out. With the volume of handloading projects that I tackle, it proved a timesaver to order NoslerCustom unprimed brass for this project, which has all the above features and is ready to load right out of the box, and they certainly assisted in obtaining accuracy.
Before discussing these loads, it should be mentioned that the data presented with 65- to 75-grain bullets in the last edition of LoadData.com for the AR-15 rifle with a one-in- 9-inch twist are suitable for rifles with a one-in-7-inch twist. Those loads will prove of interest to folks wanting loads that function and feed correctly in the semiautomatic mode. For that reason the focus of today’s data is with 75- to 80-grain bullets seated to overall cartridge lengths that exceed SAAMI specifications. It is suggested to not seat bullets that actually touch the lands, but rather to be seated from .015 to .001 inch off the leade.