View Full Version : sighting in a scope
December 30, 2008, 09:20 PM
hi everybody, new to the site,looks like a great to find a lot of information,, i have a basic question that i need a little help understanding, i have a springfield m1a with a springfield government model scope 4x14x56 it zeroes at 200 yds. i dont have a range closeby that i can take it to, so i can site in the scope,,,i do have a small 100yd range out back,,,my question is,,,how do i zero the scope here on my own range how many inches should it shoot high or low to get a close zero at 200yds any help would be greatly appreciated,
thanks for your time,,,
December 31, 2008, 12:18 AM
More information would be needed to give a real good approximation , i.e, type of bullet (match, ball, hollowpoint, 150gr, 162, gr, 170gr, 180gr...etc.) A fair rule of thumb would be to start at 2" high at 100 yrs - this would get you in the ballpark of most combination,
December 31, 2008, 05:49 AM
FYI, from ChuckHawks:
.30-06 (150 BT at 2910) MRT = 3"@145 yds
.30-06 (180 Sp at 2700) MRT = 3"@125 yds
December 31, 2008, 01:25 PM
Welcome to the forum.
When I took classes at Gunsite, the 200 yard zero was what Jeff Cooper taught for all medium and high power rifles. He actually had us sight in by adjusting the sights to produce a group centered 2 inches high at 100 yards. This was regardless of specific caliber, much less the specific load. You will find this keeps the gun within the kill zone of a deer-size animal to about 230 yards without having to adjust the sights. We then learned sight picture range estimation to hold high at 300 and 400 yards and to estimate in between.
Use that 2" high POI (point of impact) as your starting point. Some flatter shooting guns will climb another fraction of an inch beyond 100 yards point and be good to 240 yards or a little more, and some slower shooting rounds will only be good to 220 yards or a little less, but within the limits of human estimation and hold error it works for all of them.
I carried the M1A through the Gunsite 270 rifle class just using unmodified standard issue iron battle sights and sighted 2" high at 100 yards with some surplus 147 grain loads I had dragged along. I used that sight setting without change when I switched to some 168 grain hand loads I brought for the longer ranges and for the shoot-off match at the end of the class. I won the shoot-off.
January 1, 2009, 01:39 PM
I don't know what the Chuck Hawks data is about? I've never seen a 200 yard zero run 3 inches high at mid-range. It would have to be going much, much slower than mentioned.
Assuming a scope axis 2" above the bore axis of the rifle:
A 150 grain BTFMJ fired at 2910 fps sighted 2" high at 100 yards will actually be zeroed for 193.5 yards. It is at its apogee (high point in the trajectory), and drops about ¼" low at 200 yards. To be exactly on at 200 it would need to be sighted about 2⅛" high at 100 yards from the muzzle.
A 180 grain spire point flat base sighted 2" high at 100 yards and fired at 2700 fps will have more drop. Its actual zero will be at 181 yards. It will hit its apogee at 99 yards and fall about 1" low at 200 yards. For it to be dead on at 200 it will actually need to be sighted about 2½" high at 100 yards.
I have a attached a PDF file with the trajectory tables from the published G1 BC numbers for two sample bullets of these types (a Speer 150 gr BT and a Hornady 180 gr SP). There is also a zero range table for each out to 500 yards (pages 3 and 6). I think you get the idea, though. Cooper's 2" high sighting strategy gets most rounds to within about an MOA or so at 200 yards. Close enough for your starting point and more than close enough for minute of deer.
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