Gregory Gauvin
New member
I am a former competitive shooter, on all types of military rifles, but started and ran with a Match AR-15, being vastly familiar. I acquired a PreBan Colt Sporter (1978), to me, appeared to have approximately 20 rounds through it. It's in pristine condition - via bolt face and the apparent lack of wear marks on the bolt carrier, bolt lugs, and brass deflector - I know this gun was barely shot. I had not fired it until today. I wanted to get a 100 yard zero.
I began at 50 yards. I believe it had previously been sighted for 300 meters, as it hit very high. I brought POI to about 1.5" high at 50y and was 1/2" left (if I recall) left windage, with 2 clicks windage (1/2 MOA clicks) was dead center on windage at 50y. I shot a couple of 3 shot strings. Windage was taking out the vertical grid line.
Stepping it out to 100 yards, carbine shot near top of black ring of SR1 Military Target (6 1/4" black circle). I brought up the front post 2 clicks and got my elevation inline with X ring. I was limited on time as the range was preparing to close, however, I am dumbfounded to find the carbine hitting 3-4" left when it was rock solid on at 50y. There was no crosswind - even so, at this range would be negligible... As a trained competitive shooter, I know this windage error being off so much from 50 to 100 was not me.
Is it possible, that when adjusting elevation at 100, the two clicks on the front sight post through off the windage via the post not being truly square?
Secondly...The barrel is a 1:7 twist. I was firing my "plinking" handloads. 25grns of H4895 under a 55 grain. I know 1:7 is best suited for heavier bullets, I found this load to be accurate in my other ARs with 1:8, and 1:9 twists, as well as my mini-14 with a 1:12. No rounds keyholed. This is a Hodgdon minimum load with estimated velocity of 3191, out of a 16" barrel, probably achieving somewheres around 3100. OAL measures 2.240". The twist rate wouldn't have a torquing effect to throw my windage off that much would it?
How could I explain having proper windage at 50 yards and being off by 4" at 100 yards? 1 or 2 clicks I could understand...but 4"?? I'm going to bring the rifle back to 50yards to verify windage there next range session. If I'm off...I know front post is not true. Unless someone else has any thought?
I began at 50 yards. I believe it had previously been sighted for 300 meters, as it hit very high. I brought POI to about 1.5" high at 50y and was 1/2" left (if I recall) left windage, with 2 clicks windage (1/2 MOA clicks) was dead center on windage at 50y. I shot a couple of 3 shot strings. Windage was taking out the vertical grid line.
Stepping it out to 100 yards, carbine shot near top of black ring of SR1 Military Target (6 1/4" black circle). I brought up the front post 2 clicks and got my elevation inline with X ring. I was limited on time as the range was preparing to close, however, I am dumbfounded to find the carbine hitting 3-4" left when it was rock solid on at 50y. There was no crosswind - even so, at this range would be negligible... As a trained competitive shooter, I know this windage error being off so much from 50 to 100 was not me.
Is it possible, that when adjusting elevation at 100, the two clicks on the front sight post through off the windage via the post not being truly square?
Secondly...The barrel is a 1:7 twist. I was firing my "plinking" handloads. 25grns of H4895 under a 55 grain. I know 1:7 is best suited for heavier bullets, I found this load to be accurate in my other ARs with 1:8, and 1:9 twists, as well as my mini-14 with a 1:12. No rounds keyholed. This is a Hodgdon minimum load with estimated velocity of 3191, out of a 16" barrel, probably achieving somewheres around 3100. OAL measures 2.240". The twist rate wouldn't have a torquing effect to throw my windage off that much would it?
How could I explain having proper windage at 50 yards and being off by 4" at 100 yards? 1 or 2 clicks I could understand...but 4"?? I'm going to bring the rifle back to 50yards to verify windage there next range session. If I'm off...I know front post is not true. Unless someone else has any thought?