Building The 90 Grain AR-15, Part Three

An overview of projectiles and loads for heavy bullet .223/5.56 AR-15s.

by Joe Carlos

All of my 90 grain AR-15 loading data was developed in Wylde chambers, being a good compromise chamber when shooting both 77s at the 200 and 300 yard lines and 90s for 600 and 1000 yard lines. I used new military Western Cartridge Company or Lake City brass with crimped primers in all load development. Always work up gradually from well below any recommended loads, watching closely for signs of pressure. Measure your chamber using a Stoney Point (now owned by Hornady) overall length gauge and an 80 grain Sierra MatchKing bullet.

Yes, I know we are shooting 90s but the standard of measurement was developed ages ago before 90 grain .22 caliber boat tail bullets were even invented. If your chamber is a true Wylde it should measure 2.475” overall, from case rim to bullet tip. Don’t worry much as long as you’re within 0.010”, plus or minus, but be ready to adjust your loads if you have a much larger discrepancy. Shorter chambers require reductions in powder charge weights. Remember, gunsmiths chambering these barrels may work on hundreds a year and reamers wear out. They may order Wylde replacement reamers but not all reamer companies deliver the exact same dimensions. I use competition bullet seating dies with micrometer adjustments so I can vary my bullet seating depth in 0.001” increments to hit the sweet spot.

Read more in our June 2014 issue. Back issues are available.

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