Sharps-Nut
"am building an ar kit and would like to shoot 52 grain bullets. The gun will be a varmit style gun used from 100-250 yards."
I am of the same frame of mind as you, I prefer the 52 gr HPs for varmint hunting with an AR. I have been hunting with the .223 cartridge since '72. I have used barrels of 7, 8, 9, 10, 12 and 14" twist. With the lighter HPs the 7 & 8" twist barrels always gave some problems with RPMs and associated bullet disintegration in flight. Also the higher the RPM of the bullet the more exagerated effect any defects will have on the pitch or yaw of the bullet decreasing accuracy at the longer ranges. The 9 & 10" twists are a decent compromise and give good accuracy most often but if we are not using the heavier bullets why compromize? The 12" twist always worked well with the 52 HPs and still allowed accurate shooting with the 55 gr M193 military ammo. The 14" twist would be an excellent choice IF only the 52 HPs were going to be used.
I was involved in testing match barrels some years ago for use in ARs for service rifle competition. The focus was on match bullets of course out of the 20" SR barrels. A Leupold 6.5x20X scope was used on the flat top recievers to eliminate as much aiming error as possible. I also took the opportunity and did considerable testing of the 52 gr HPs (I used the Sierra 52 gr HPBT and the Speer 52 gr HP) in the various twists from 100 to 600 yards (500 yards is a stretch for hunting larger varmints with the .223 out of a 20" barrel). I found accuracy to be problematic with the 7 & 8" twists for the reasons mentioned. The 9 & 10" twist produced compareable accuracy to the 12 & 14" twist out to 200 yards. Beyond 200 yards the 12 & 14" twist showed a marked accuracy edge and the 14" twist proving the most accurate at 500 yards. Again, this was with the 52 gr HPs. With heavier bullets of 62 to 80 gr the 7 & 8" twist were of course more accurate with the 9" twist barrel holding it's own with bullets up through 70 gr.
I chose to go with a 1-12" twist in my varmint hunting AR and I mostly use the Speer 52 gr HP over 26.5 gr of H335 with the Sierra 52 HPBT being a close second. Accuracy is always excellent (sub MOA for 5 shots)and terminal ballistics are impressive. I have stretched a couple shots to right at 500 yards on rock chucks with one shot kills and had good results on a couple coyotes in the 300 yard range. In my bolt action M700V with 12" twist and 55 gr SXs I have done well beyond that on rock chucks and prairie dogs. However, I believe the 12" twist is the best choice for your AR application and is my recomendation
Larry Gibson
