Newb question

Separated for different twist rates in older “service rifle” barrels that are 1:12 twist probably

Modern AR-15 style service rifles fit a pattern based on the rules of the game. As such, they have a particular 20" barrel profile and most competitors will shoot both magazine length at 200 and 300, and then single feed (too long for the magazine) at 600.

Service Rifle loads tend to become Pet Loads that use match bullets and favorite powders. The chambers on popular rifles like WOA and CLE, are a hybrid design of a Wylde Chamber. They can take full 5.56 NATO pressure loads and ammo, where that isn't recommended for 223 REM.

Of course there is always a pressure overlap between those two (5.56 and 223) when the twist is common. Most Service Rifles will run twist at 8 or faster with 7 being common. This allows using 69 - 77 grain bullets at magazine length, and then switching to ones like SMK 80 or similar for the 600 yard line. BTW, many SR loads are hard on brass to the point where four cycles usually retires the case.

RegionRat said:

Modern AR-15 style service rifles fit a pattern based on the rules of the game. As such, they have a particular 20" barrel profile and most competitors will shoot both magazine length at 200 and 300, and then single feed (too long for the magazine) at 600.

Service Rifle loads tend to become Pet Loads that use match bullets and favorite powders. The chambers on popular rifles like WOA and CLE, are a hybrid design of a Wylde Chamber. They can take full 5.56 NATO pressure loads and ammo, where that isn't recommended for 223 REM.

Of course there is always a pressure overlap between those two (5.56 and 223) when the twist is common. Most Service Rifles will run twist at 8 or faster with 7 being common. This allows using 69 - 77 grain bullets at magazine length, and then switching to ones like SMK 80 or similar for the 600 yard line. BTW, many SR loads are hard on brass to the point where four cycles usually retires the case.

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A point of clarification on the pressure comment. 223 Remington pressure is tested per specifications based on SAAMI and the 5.56x45 NATO round is tested based on EPVAT test which is a different measuring system (basically CIP. The testing methods yields a different pressure hence the apparent difference in pressure, not a actual difference in design pressure. CIP (similar to EPVAT) lists the 223 max as 62,000PSI while SAAMI is listed as 55,000PSI.

@NJRaised I will only add a few pointers as you go down this rabbit hole of handloading the 223 Remington
don’t mix your brass headstamps
used the same primer brand, whatever brand you start with stay with during your load development a magnum is not needed in the 223
don’t use the COAL method
Use the CBTO method
Good luck wishing you very small groups