Lyman GPR sight picture

[dano2467]

I have been trolling this sight for a while trying to find out what is the correct way to line up the sights on a GPR. I am using the stock buckhorn sight that has a little bit of elevation adjustment on the rear sight (part number is RS-PM-1 on TOW website). Am I supposed to align the top of the front sight to the notch at the bottom of the rear? or do I hold it level between the top of the buckhorns? last time out I was using the top of the horns and put the base of the front sight level with the top edge of the bottom of the horns, I got 2 shots to group low right using this method. rifle is a new, complete rifle and I have taken maybe 75 shots so far.

 

[Zonie]

As you've been looking around here, I'm sure you know the front sight on a new GPR is intentionally left high so the new gun will shoot low?

The idea is it is easier to file off material than it is to put it on and a tall front sight will make a gun shoot low.

Also, the new GPR was shipped with some incredibly tough bore grease that needs to be cleaned out by using disk brake cleaner, lacquer thinner, acetone or denatured alcohol (less effective).
They also need to be shot at least 100 rounds worth before they stop cutting patches.

That said, IMO, the gap between the horns is used for long range shooting.
The horizontal top of the lower area with the notch is the actual sight used for normal shooting.

As you may notice, the V notch is rather shallow.
That is intended to force you to aligh the top of the front sight blade so it is centered in the notch and the top of it is in line with the top of the horizontal area.

With the sights aligned this way (front blade centered and top in line with the rear sight) the gun is considered aimed.

Use a very large target or a smaller target stapled towards the top of a large piece of cardboard so the low shots will show up.

Some people sight their guns in so the sights are pointed towards the center of the bulls eye.
Some people who are planning on doing only target shooting like to hold the point of aim at the bottom of the black bulls eye.
I prefer to use the "aim at where you want to hit" school of thinking.

Remember, raising the rear sight or filing down the top surface of the front sight will raise the point of impact for the group.

Do your first shooting at 25 yards distance.

IMO, that is a good distance to work at until you have adjusted the sights to bring the group up to the point of aim.

Fire at least 5 shots to determine where the gun is hitting while aiming exactly at the same point on the target. Use the center of the pattern as the correct location.

There are several things that can effect the group size and point of impact.
The powder load, the powder type, the patch thickness and the patch lube.

Changing any of these will change the point of impact so, if your gun is a .50 caliber start off with something like a 65 grain powder load.

I'm sure the others will jump in and give you a lot more information.

 

[dano2467]

so is this is the correct sight alignment I need to achieve for 100 yd shots? with the gray spot being the top of the front sight blade.

 

[jethro224]

Yes. IF you have the rifle sighted in at 100 yards.
You could sight it in for any distance you prefer, that is still the correct sight picture.

In my experience, the primitive fixed rear sight that should have come with your GPR makes for a much better sight picture. You will have to peen either the sight base or the dovetail to make it fit tight.

First work up your best load THEN adjust your sights.

 

[Semisane]

Dan, the first thing I do with that sight is file the top flat, and widen the notch to get a sight picture like this.

 

[jethro224]

Hey, that's more like what the fixed sight picture looks like. :wink:
Plus, you don't get all that slop from the spring and hinge in the adjustable rear sight.

 

[Kapow]

If I recall correctly the fixed sight that comes with the Lyman GPR has a very wide notch in it, more so than the adjustable one. For real accurate shooting you might even do better getting a rear sight blank and filing your own narrower notch and sourcing the appropriate narrower silver blade front sight from TOTW. I actually filed the sides of my front blade to remove about a third of the metal and reblued it. It is much more user friendly now.

 

[Zonie]

Yup. That's the picture.

As for sighting the gun in, after you get it shooting at 25 yards, extend the range out to 50 yards and then, if your into 100 yard target shooting, go to 100 yards.

If your into hunting out to a distance of 100 yards with patched roundballs, you might want to consider sighting it in at 80 yards.

With it zeroed at 80 yards a patched roundball will be about 2 inches high at 50 yards and 3 1/4 inches low at 100 yards.

Most roundball shooters agree that 100 yards is about the limit for them. After 100 yards they start loosing a lot of elevation.

If your shooting unpatched slugs the effective range increases but even so, they also start loosing elevation pretty fast.
That's where the buckhorns start to work but you'll have to figure out what they are doing at those extended ranges.

Because the range is so great, the buckhorns need to be fairly close together so the front sight can be centered accurately. Just a little bit of side to side error will really have a lot of effect, most of it bad.

 

[dano2467]

Thanks to all for the help, I have been thinking of getting the the long hawken rear sight from TOTW along with some other mods, but for now I am just trying to make sure I can shoot straight, and consistantly with what I got. Thanks again for all the help.

 

[HuntAway]

You can use the full buckhorn sight as a ranging sight.

The sight picture shown above could be your close range sight picture.
Your second Mid Range with the the top of the front sight centered in the "horns".
Your long range sight picture with the top of the front sight between the tips of the horns.

One load. Three sight pictures. Three ranges.

HA