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Posted: 11/19/2003 5:57:48 PM EDT
Maybe you can help me here. A weird thing happened today when I took my AR to the range to confirm the zero. I am using the same sight adjustments I use for my match ammo, (69gr SMK over 24.2rgs W748, vel approx. 2875fps.) for my deer slaying ammo, (64gr Winchester powerpoints over 25grs of W748) and found the point of impact had drastically changed. I ended up having to drop the rear sight 12 clicks (1/4 clicks, 3"@100yds) to get sighted in. I know different ammo will have different zeros but this seemed like a heck of a lot of difference to me. If I had any of my match stuff I could have checked if the original zero still was good but since I didn't, I couldn't.
Does this big of POI change sound right to you? If not do you have any ideas what it might be other than somehow I banged up my sights?
Thanks!
Link Posted: 11/19/2003 6:59:05 PM EDT
Sounds right to me - the recoil from shooting heavier bullets will often cause the point of impact to rise on a 100 to 200 yard target.

I didn't believe myself the first time I saw it; Ron Hoehn confirmed my observation.
Link Posted: 11/19/2003 7:24:33 PM EDT

Originally Posted By AeroE:
I didn't believe myself the first time I saw it; Ron Hoehn confirmed my observation.


Ron Hoehn? You are a benchrest member aren't you? (So am I, I wonder if we have ran into each other there and don't know it)
Link Posted: 11/19/2003 7:39:54 PM EDT
I don't know if we've crossed paths or not - I always look for a likely candidate with surplus rifles, but haven't seen you. I sort of fell off the wagon and have been shooting sporting clays all year and haven't gotten as much rifle shooting as I like.

I recall that you had a K-31 and I wanted to look one over and talk to you about them.

Anyway, the best way is to just set a day and time.
Link Posted: 11/19/2003 7:45:33 PM EDT
Gary,

I found the 64gr Winchester ammo also shoots higher on my gun. About 2-3" higher at 50 yards out of my M4 carbine (my deer slayer for this year). My M4 was zeroed using M193 type ammo. I know an SS109 shot out of this gun also hits higher, but not by much ... 1-2" maybe. I guess the Winchester ammo is a bit hotter than the old milsurp ammo.

Since your rifle is sighted for a 69 SMK load, I dont think shooting a 64 gr Winchester load will cause the POI to increase. The only factors I could think of is the Winchester may have more powder and/or the OAL is shorter. Match shooters like to use a rather long OAL to minimize the free-space the bullets must jump through before biting the rifling. Commercial ammo OTH, tend to keep it as short as possible but still longer than minimum OAL. They do this to insure that their ammo is usable in most rifles out there both magazine fed semi-auto and bolt gun. Shorter OAL means the bullet must be seated a bit deeper into the casing causing the volume to decrease. I found this to translate to a higher pressure and higher muzzle velocity. But you will also observe less accuracy since the bullet now has more free-space to jump through before the rifling bites. This is just my personal observation ... maybe I am off the mark by a mile.
Link Posted: 11/20/2003 4:05:07 AM EDT
AeroE, if you ever drop in on one of our MoDCC meets remind me to bring the K31, I have taken once or twice and would love to show it off ands even let you try out a magazine or two.
Mousegun, I knew you would have some idea of what was happening. The PP is most definitely seated deeper than the SMK. I hadn't thought about the case capacity in relationship to the primary pressure increase but it does make sense it would be higher. I am glad you have also experienced something similiar to this because I was really worried I might have beaten my rifle up and not even known about it. The funny thing is with my rifle M193 and the SMKs hit about the same spot, no need for any sight adjustment. (They are not exactly the same POI but close enough since all M193 shooting is plinking type for me)
I am guessing I have nothing to worry about and the SMK zero should be the same as usual.
Thanks everyone...
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