Changing open sight elevation

[Ajohns]

Ok
I hope I can explain this right lol.
I'm in the process of building a 257 Roberts on a small ring Mauser. For this build, I decided to stick with open sights, although I D/T'd the side for a receiver sight.
I did all the math for a standard small ring with 7mm, military sight set, measured from the top of the sights to what center of bore would be.
Then, after screwing the new Roberts barrel on measured to center of receiver sight aperture to center of bore.
I'm putting a ramp on for the front sight, and have the math set for what height blade/bead front sight I need by this ratio vs. military, but am leary being identical to military because of those being regulated to 300 meters.
And the Roberts will be a few hundred fps faster than the 7mm.
Any idea how much higher or lower a front sight I'd need? I would assume it would need to be a bit taller because of the gain in fps.
I'm wanting zero to be about 150 yds. And no, I haven't fired the gun yet to even see what's what.
Just kinda wanted to get a good ball park before I pull the trigger.

Thanks.

[Castaway]

I suggest you plug the weight and BC of the bullet you intend to use in the 257 Roberts in a ballistic calculator and do the same for a factory load duplicating the 7mm military load. Then you can compare numbers at whatever distance you decide upon

[Larry Gibson]

All that might work out but probably not. The weight difference of the sporterized M95 to the military rifle plus the recoil difference between the two cartridges is mostly why. An elevation and windage adjustable rear sight [or are you using the military rear sight?] and a front ramp that is dovetailed to allow different height blades is the best bet. I would start with a medium front ramp and epoxy it on the barrel for a few test shots prior to permently affixing it and/or bluing the barrel.

[Ajohns]

All that might work out but probably not. The weight difference of the sporterized M95 to the military rifle plus the recoil difference between the two cartridges is mostly why. An elevation and windage adjustable rear sight [or are you using the military rear sight?] and a front ramp that is dovetailed to allow different height blades is the best bet. I would start with a medium front ramp and epoxy it on the barrel for a few test shots prior to permently affixing it and/or bluing the barrel.

To answer the best I can is,
The only thing the same as the Chilean action I started with is the action itself. I have a Redfield receiver sight D/T'd to the action, and a new McGowen barrel in the Roberts chambering, with a ramp I've installed to put any dovetailed front sight I wish.
I had just started out by measuring sight height from bore center on my military 7mm barrel (from a Chilean) to see what sight actually was. Knowing they are regulated to 300m, I just was trying to figure out how high the front sight on my new (257) setup should be, or try for a start.
The receiver sight is about .180thousandths taller, did the ratio from military front and rear, found the answer to what my front sight height should be. Which is about a .390 height sight on top of the ramp.
But, I'm just not sure how different I should be from that for the 257vs.7mm

[georgerkahn]

All that might work out but probably not. The weight difference of the sporterized M95 to the military rifle plus the recoil difference between the two cartridges is mostly why. An elevation and windage adjustable rear sight [or are you using the military rear sight?] and a front ramp that is dovetailed to allow different height blades is the best bet. I would start with a medium front ramp and epoxy it on the barrel for a few test shots prior to permently affixing it and/or bluing the barrel.

Once again, Mr. Gibson provided the best answer I might think of! Years back I spent (pre-calculater/computer days) many, many hours calculating a front sight height for a .38-40; finished; measured twice before I ground once ; re-measured again; and my mentor silver soldered it on for me. At 50 yards the bullets landed almost a perfect THREE inches low !!!
We re-calculated to get same height as used.
Hence, again, I soooo concur with the epoxy it on first suggestion!
geo

[MostlyLeverGuns]

If you are drilling/tapping for a ramp front sight, just take a tall screw that fits the D/T hole. Use that tall headless screw as a front sight. Shorten as needed until you are sighted where you want it, measure the height of the screw and select your ramp/sight combination. You can take a couple different length screws along to get close then file to where you want your setup.

[Ajohns]

Well, by ballistics done by shooters calculator .com, with all variables (except my front sight height which doesn't matter)
It says if both of the loads, military and mine, sighted in at 300yds (military standard)
the Roberts would be +5.83" at 150,
the 7mm would be +9.16" at 150.

This might not be so relavent, but does tell the path difference.

[Texas by God]

Start with a tall front sight in the ramp and your Redfield bottomed out.
Bore sight it the old fashioned way to see what needs to happen.
My Krag has a Redfield and a front ramp from a Winchester m70.


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[Ajohns]

Have a medium ramp on now, gonna do just that Tex.
Should be ready by next week, I'll post results

[rockshooter]

I have to agree with MostlyLeverGuns- easier than trying to be too scientific about it!
Loren

[Ajohns]

I have a medium ramp (.350) and .375 tall sight. It's close, but still a bit high with the Redfield as low as it will go. Changing to a .406 and my handloads (100gr)soon.
Started with 117 Rem factory's so far. When it's all done I will post heights from bore center just in case someone is interested.

[quack1]

Brownells had a sight height calculator and diagram in their catalogs for years.
Pretty sure Homestead Parts has a free download to calculate front and rear sight heights

[pietro]

.

Measuring the front sight height on the military barrel, then replacing it with a different barrel & expecting the sight height measurement to be the same for the new barrel is an unreasonable expectation.

I would suggest remeasuring with the new barrel then using Brownell's Sight Height calculator to get in the ballpark for a zero.

Here's a Brownell's video on measuring for sight heights:

https://www.youtube.com/watch?v=ZrFat8rix-4

.

[Ajohns]

In all honesty, I wasn't looking to replicate the military sight setting. That was just a known sight height, and zero (300m).
And I have a hard time explaining what exactly it is I was looking for.
Long story short, knowing a cartridge of a slower speed has a certain sight height, how much higher a front sight, with a new rear sight (receiver sight) would have to be to bring it down to zero at half the distance of military, and doing so with a faster fps cartridge.
All I did is what was mentioned above, and I thank the guys who commented. I have it down to maybe one more .030 taller front sight, and it will be on the money.
I will checkout the Brownells diagram and also will post my results in case someone would like to know.

[HWooldridge]

Brownells had a sight height calculator and diagram in their catalogs for years.
Pretty sure Homestead Parts has a free download to calculate front and rear sight heights

^^^This. I would find a calculator and get yourself in the ballpark before installing anything.

[Ajohns]

I watched the video. He is basically starting a baseline for the sights to be parallel with bore axis, then adjust from there.
So, I did all of that. Below is what I had posted.

I had just started out by measuring sight height from bore center on my military 7mm barrel (from a Chilean) to see what sight actually was. Knowing they are regulated to 300m, I just was trying to figure out how high the front sight on my new (257) setup should be, or try for a start.
The receiver sight is about .180thousandths taller, did the ratio from military front and rear, found the answer to what my front sight height should be. Which is about a .390 height sight on top of the ramp.
But, I'm just not sure how different I should be from that for the 257vs.7mm

And being I wanted to be zeroed in half the distance, with a faster cartridge. But as I said, I have it now and will get it sighted in.

[curdog007]

I have always used a temporary front sight electrical taped on - shoot it and get it where you want it. The maths will take you from there.

[Ajohns]

For anybody who's interested, the numbers were as follows

Military rear was .866 high and front was .782 high from bore center.

My 257 Roberts project was .980 high rear receiver sight and 1.010 high front from bore center.

I will do some more shooting to verify how well it is, but so far so good.

[Ajohns]

This is the rifle in question. So far so good for shooting, need to send a few more down range and get it broke in

[Texas by God]

I would think that it handles well with the minimalist stock. What does the front sight look like?
I like the bolt handle and the metal finish.
Did you use a barrel nut?


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