If a carbine is zeroed at 100 yds, how high will it be at 50 yds?
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If a carbine is zeroed at 100 yds, how high will it be at 50 yds?
It will be 0.6 inches high at 50 yards with a 100 yards zero with a 110 gr. bullet leaving the muzzle at 1990 fps.
I find the story of the M-1 carbine accuracy amusing because of the variations between original (pre-1944) carbines, that still have the flip sight (150 or 300yrds) and Mid 1944 change to the sliding sight (along with post war made ones).
Item the first. the flip sight or "L" sight wasn't adjustable for windage, or ranges other than the stated 150 or 300 yrd peep sight. The civilian factories when adjusting for windage, adjusted the entire rear sight to center at the 25yd acceptance target. The elevation to get the acceptance 5 of 7 shots in the target area per the target in the original TM 9-1276 was done by *carefully* filing the front sight down from the original height of
.475in height to around . However Irwin-Pederson made carbines, were adjusted by the use of several pre measured sight heights (the I-P sights had numbers stamped to indicate the height the sight was milled to.) Again the sight adjustment was made at the factory and adjusted for the acceptance 5 of 7 in the target dotted area.
Item the second. Once the carbines made it to the troops, then we have the problem of them being sent to CONUS and Overseas Depots for repair or rebuild.
The Depot manual TM 9-1276 states that verifying the sights being correct is done as time and facilities permit. If facilities and time didn't permit, the gaining unit was supposed to verify sighting by zeroing and filing the front sight on a 100yrd range using the 100yrd sight. Kinda hard to accomplish when the 'Flip Sight" is only 150 or 300yrds. Also if the gaining unit signs and issues the carbine and climbs on a transport the next day. Also there's also the problem, of the unit having too much to do, and too little time to do it in.
Item the third. The winter of 1944-45 the 'flip sights' were field depot replaced with the sliding sight, and new manufacture had the sliding sights factory adjusted per the 5 of 7 at 25yrds. Again if the field depot didn't have the time or facilites, the acceptance fire and adjustments weren't done. So the sight at 100yrds would cause the carbine to shoot low. And unit adjustments to 100yrd zero was hit or miss. Also the sight was graduated in 100, 200, 250, and 300yrd positions, and the sight 100yrd position was also for 150yrs, with 'hold over' to get hits.
Note: if your GI spec'd carbine with the *new* sight is original to the stock, and has ordnance rebuid cartouches, it was rebuilt sometime in the USA and may or may not have been adjusted for the final acceptance targeting. If your stock has no cartouches indicating stateside rebuild, again it may or maynot have been adjusted by the field depot.
There's also a comment in a CMP pdf on carbine accuracy, that changing the height of the front sight by as little as 0.006in (six thousandths) will change the impact of the bullet at 50yrds by 1/2in and 1 in at 100yrds.
There is also the comment from a source that I have forgotten, that a trained rifleman could zero his carbine into the area of a half dollar at 100yrds, and a silver dollar at 200yrds. Put his rounds in, or distinguish a target at those sizes, I actually can't remember.
Item the Forth> New build carbines and 60's commercial franken carbines. their zero would depend on the maer using N.O.S. sights or following the specifications of the sight parts, and adjusting for the '5 of 7 at 25 yds'.
So your zero has a bunch of variables. If you start from the 5 of 7 at 25yds target to get it to meet the old GI acceptance standard, you can adjust the elevation by **CAREFULLY** filing the front sight in small increments if and ***ONLY*** if it shoots low. If it shoots high out of the 25yd target, the front sight has to be either totally replaced and "shoot and filed" till it meets the acceptance standard, or metal has to be added to the height and then filed to blend in and then "shoot and filed" till it meets the acceptance specifications BEFORE you can worry about tweaking the sights.
Just a few comments.
R Brown
Thank you Richard for your information. There is one big thing people have to realize and that is that the military started in 1948 with Underwood and Standard Products to rebuild the carbines. BY 1950 the need had accelerated to the point that 6.2 million carbines needed to be checked and updated if needed. All of the armories now started to work on them and they were being shipped to them by the train load. They didn't finish till the mid to later 50's on this. These carbines were thrown together. proof fired and out the door they went. They were not adjusted for the sights. Just about all still had their original front sight adjusted for the type 1 flip sight and not the adjustable rear sights. They also did not fit in the dove tail very well as they were larger then the type 1 sight. The type 1 could be moved to the left if a carbine was shooting to the side. Once the rifle was shooting center the sight was staked in place with a chisel and front sight filled down for the center hits at 150 yards. The adjustable rear sight can be moved within itself like most adjustable rear sights but the base is too wide to be move much at all in the dove tail. Many of the rear sights did not have enough travel to move the peep far enough to the side to adjust the rifle to hit center of the target. The same for the front sights as they were not changed during rebuilding. That is why today some people have carbines that shoot high and shoot to the right.