7.65 1891 twist rate

[7.65,1891mooseeater]

Hello, I have an 1891 argentine mauser sporterized to 19" and the flip up sight is off so i did the math and failed and failed again so does anybody know how far out 400m would be? it would probably be around 300 i'm guessing. also does anybody know the twist rate on these fine rifles it is very smooth and accurate

[saint_iverson]

Pythagorean theorum... The shorter the distance to your front site, the more radical the angle of elevation/bbl rise. Your barrel is angled higher than before and you will be launching it further, not closer. All things being equal, we would still need to know the original length of bbl the adjustable sight was built for.... I'm not a proficient in kaiser, so forgive me, original at maybe 26-28"? Maybe on your math you have the num and denom flipped?

[saint_iverson]

Also remember burn rate and barrel velocity will be stunted by the lack of extra length to allow for longer powder burn time.

[Larry Gibson]

The twist rate for the 7.65 Argentine is 1-9.8". On my M91s with the rear sight up the bottom elevation is 400m. If that is what yours is then where does it hit at 100M with the rear slide of "4"? Then you'll need to know the drop of your load with a 100 yard zero to determine the elevation increase. You'll need to measure the sight radius to compute it.

Larry Gibson

[7.65,1891mooseeater]

thank you and I meant when the sight was on the 300m line it would be shooting at around 400m or something thank you

[Larry Gibson]

thank you and I meant when the sight was on the 300m line it would be shooting at around 400m or something thank you

That's because the shorter sight radii with the cut off barrel gives a larger angle of departure per range graduation to the bullet than it would with the longer sight radii. Simply put moving the rear sight up 100 meters moves the impact range farther than 100 meters.

However, if the M91 was a 19" barreled carbine to begin with(?) then the sights are regulated. They used a 6 o'clock aiming point with Mausers so the impact will be high (8 - 12" usually) at any given sight setting. If you want point of impact to equal point of aim then a higher front sight is needed. The original can be welded up. reshaped and filed down to bring POI to POA. Or Brownell's has high ones that can be installed and filed down.

Larry Gibson

[leadman]

Larry, isn't the carbine rear sight shorter than the rifle?

When I first got my 91 sporter I installed a Lyman receiver sight on it. Took the front sight off and had my machinist cousin slot it and soldered a new blade in it. This worked real well until the eyes started to go so had my cousin drill and tap it. I bent the handle.

So to the OP if you want a really nice outfit buy a receiver sight for it. Most likely the front sight will have to be made or replaced with a taller one.

[Larry Gibson]

Larry, isn't the carbine rear sight shorter than the rifle?

I don't have an Argentine M91 Carbine but I do believe the sight ladder is shorter as it needs less space between ranges due to the shorter sight radius.

Larry Gibson

[Frank46]

I have an 1891 carbine and the carbine ladder as far as an estimated guess is about half the length of a regular 1891 rifle. Frank

[Larry Gibson]

Thanks Frank, that's what I thought.

Larry Gibson

[Multigunner]

I have a couple of books here that have the formula for fitting a higher front sight to a shortened barrel in order to get the same point of impact from a particular rear sight setting.

It will take awhile but I can try to dig these out later tonight or tomorrow.


PS
Many of the short barrel mausers and enfields have sights that only go to 600 or 800 yards rather than the 1000+ yards of the long rifles.

[frnkeore]

If you divid the sight radius in inches by the yardage in inches (100 yds = 3600), you'll get the amount of ajustment to move the sights POA 1" at 100, 2" at 200 and so on.

i.e. 20" sight radius divided by 3600 = .00555 @ 100, 2" @ 200

Frank