M1 carbine 25 yd zero target

asuming point A is the bottom of the bulls eye, try placing the front sight post at the top of the bulls eye. 

The amount you need to shorten the front sight is proportional to the ratio of the sight radius to the distance to the target.

900"(Distance to the target)/E(Amount of error) = 22.25(Sight Radius)/H(Height Correction of Front sight)

So, if the amount of error (E) is 6", then;

900"/6" = 22.25"/H

H = (6" x 22.25")/900"

H = .148"

Thus you need to shorten the front sight .148"

It's wise to make small adjustments and check and see if they give you the expected results. I would start with half of the calculated adjustment and see if you get a proportional result.

I used 25 yards (900" equals 75 feet or 25 yards). I used 6" for the error because you said the POI was 3" below POA and you expected it to be 3/4" to 3" above the POA. So 3"+ 3"= 6"

Jack,

Thanks again and apologize for my initial mathematical error.

No problem Paul. More often than not, carbine owners complain of their carbine shooting unusually high. This is likely due to arsenals replacing flip sights with adjustable sights. The front sight was ground to zero at the factory as Dan so elegantly described in an accompanying post.

http://www.uscarbinecal30.com/forum/front-sight_topic3209_post23178.html#23178

It is believed that the arsenals didn't make any effort to recheck the zero with the replacement adjustable sight. You have the good fortune of possibly having a virgin front sight. Most have the problem of adding height to their front sight. An unfiled sight should measure .785" from the top of the blade to the centerline of the bore. I know this is hard to measure but it should also measure approximately 1.155" from the top of the blade to the bottom of the sight. Of course, different types of sights have varying thicknesses of the cylindrical portion so this measure is approximate. If possible, could you measure your sight and let us know what it is? Also, let us know what type of sight you have. We don't often get to check this measurement. Thanks.

Jack,

I forgot to mention that my front sight is marked POQ and manufactured by Quality Hardware & Machine Co.

Many years ago I went with the 25 yard zero target. It never worked very well for aligning an adjustable rear sight for elevation at 100 yards and beyond.

I think it was used during WWII wartime as a quick and dirty way to confirm combat accuracy for the original rear flip sight. It doesn't work well at all for an adjustable rear sight.

For my carbines, all with adjustable rear sights, I zero POA/POI for 100 Yards with the rear sight set on 100 yards. The best elevation/and filing the front sight, I have found though, is for the rear sight set at 200 Yards zero with POA/POI at a 200 yard range. It does well at 100 yards, 200 yards and 300 yards.

Bonnie,
I feel much better knowing someone else did not find the 25 yard zero target to be useful for aligning the adjustable rear sight. I don't feel comfortable in filing the front sight blade therefore, I plan trying to zero at 100 yards using each of the rear sight yardage markings and run with the one that produces the best groupings. Right now, the rear sight set on 300 yards produces the best group at 100 yards using Sellier & Bellot 110 gr..    

Paul, I've found that most commercial carbine ammo is a little under powered. You may find other brands to be a little hotter and perhaps more accurate with a higher POI. You might try LC or Federal American Eagle for comparison.