The Russian Mosin Nagant Forum

Mangrove wrote: ↑Wed Mar 16, 2022 11:17 am

Austin26 wrote: ↑Mon Mar 14, 2022 10:14 am How would one acquire a (much) taller front sight post? I don't see a difference of 28 grains being enough to drop an additional approximate 20" at 300 yards. But regardless if I had a taller front sight post it would fix this problem.

For precise calculations, I think you should first try shooting a few shots at 50, 100, 150 or 150 metres using the corresponding sight. You may then use the table below to estimate how taller the front sight should be.

From Finnish Defence Forces booklet "Ohjeita ampumakouluttajille kivääriperusammuntakoulutusta varten" (1949), pages 12, 13 and 14. Translation from Finnish to English by me:

"The distance between the notch and the post in the m/39 rifle is such that if the notch is elevated by 0.1 mm, the mean point of impact will rise by 50 mm or one circle in the [international] target (not quite but effectively). The following table shows the elevations in the sight notch as the slide moves notch by notch from the basic position up to 600 metres.
[...]
The table contains calculated mean point of impacts corresponding to each elevation at the target located at a distance of 50, 100, 150 and 300 metres. The table also shows the tolerances allowed in the manufacture of the sight. This will give an idea of how carefully and accurately the sights are made.

Let's assume that the shooter has fired 3 test shots [...] to a target at a distance of 150 metres. The sight has been set to position 2.6 (i.e. in the 6th notch ahove the 200 metres position). Once the mean point of impact has been determined, it is found to be 1½ circles (75 mm) too high. From the table, we see that the sight must be set to position 2.2 (i.e. the second notch ahove the 2) in order for the mean point of impact to descend to the correct height. [...]"

Tähtäimen asento = Sight position
Hahlon nousu = Sight notch rise
Sallittu valmistustoleranssi mm = Allowed manufacturing tolerance in mm
Tähtäimen siirron aiheuttama iskemäkeskipisteen nousu mm = Rise in mean point of impact (in mm) caused by moving the sight

Austin26 wrote: ↑Mon Mar 28, 2022 2:24 am Are there various height front sight posts made for the M39? How would I solve the problem once I identify the height discrepancy?

Mangrove wrote: ↑Tue Mar 29, 2022 1:46 am

Austin26 wrote: ↑Mon Mar 28, 2022 2:24 am Are there various height front sight posts made for the M39? How would I solve the problem once I identify the height discrepancy?

According to Ministry of Defence (of Finland)'s m/39 blueprint 46-4-2, dated 22 October 1940, front sights were originally available every 0.2 millimetres from 6.4 to 8.4 millimetres. However, it seems they later made taller sights available. If the m/39 is shooting high, you have two options to try to solve the problem. Either you lower the rear sight or make the front sight taller. It is usually better option to change the front sight since you can't lower the rear sight enough if the discrepancy is too high.

Let's say you are using 2.9 (a notch below 300 metres) sight setting at 300 yards and you are aiming at the centre of the target. Your mean point of impact is 15" or around 380 millimetres too high. Reading from the table I produced earlier, you should lower your rear sight a notch lower than 150 metres setting, which is of course impossible.

The second option is to raise the height of the front sight by 0.7 millimetres. If you are using 7.8 millimetres front sight, your new sight should be 8.5 millimetres.