Trapdoor front sight replacement

8.2K Views
Last Post 16 March 2014

CBA Member

tlkeizer posted this 11 February 2014

Greetings,

The Trapdoor 45/70 I have written about in other threads shoots to the right (which it did before and after the barrel lining was done), and I need to align the sights with the bullet strike. The verticle adjustment was made by making a taller front sight out of a dime (if the government objects I will pay them with a couple nickles) using hand file and hone. To adjust the lateral strike of the bullet @ to the sights, I plan on filing a piece of metal to look like a stair step with the below and above back plates in the front and back. Any better ideas? I am not a machinist, don't have milling equipment, and of all the things I am not dextrous is near the top of the list.

The model 1873 has fixed sights in front and back, the front sight has a welded/soldered base for the post to fit in. The later model 1884 had adjustable sindage, so the problem was known back in the late 1870's, but the sight attachment bases are different.

I will include photo's, and if I don't get all on this entry, I will make a couple posts so you can see what I have done and what I need to do.

Thanks.

Attached Files

4570 sights 001.jpg

13 Comments

Order By: Standard | Newest | Votes

Standard Member

onondaga posted this 12 February 2014

I recommend you complete load workup and get a good grouping load before you modify the sight or change it. You can measure your sight radius and use a formula to precisely figure windage and height change needed from the point of aim to your desired point of impact.

Gary

Attached Files

CBA Member

RicinYakima posted this 12 February 2014

Your project will work just fine, except I would take Gary's advice and find your load first. After I had a load for the my TD, I made the front blade like yours and filed it down at the range for elevation. Then I just bent it side ways to adjust for windage. Mine was a very small adjustment as the load was close to the black powder 1873 load spec's. HTH< Ric

Attached Files

CBA Member

tlkeizer posted this 12 February 2014

Greetings,

Thanks for the responses. The load (s) I have are good, see my photo's in the trapdoor excursion thread. Now I need to bring the group to the sight. It shoots 4 inches right at 50 yards, so a bit much for bending the sight. The elevation is good with the sight I put on and filed to heighth. So, I think I will put my arithmetic to use for windage.

Using a rough MOA of 1 inch per hundred yards, that is 1/2 inch at 50, converting to 8 MOA; going down to 42 inch barrell length minus distance from breech to back sight minus distance from front of barrel to post............................

Thanks again. I will send another photo after filing and shooting again. As this morning it was all the way up to minus 28 when I got up, I think I have time to file and hone before getting back out to the range. Another log for the fire beats another heavy coat. All you guys in the lower 48 and out east have my sympathy for your unruly winter, I have experienced a few in South Dakota and when I was living in Virgina while stationed in D.C.

Attached Files

Standard Member

shjoe posted this 12 March 2014

nice math problem. once youve determined the amount to move your rear sight, should put it nicely in the center. my rifle had the windage adjustable rear sight. on one rifle with a non windage adjustable ladder sight, i bought a “spare” sight ladder and machined/filed the side of the ladder which made contact with the sight base “ears” to where i wanted bullet impact to drift to. then re-installed the sight ladder, pushing it to the left direction. if rifle shoots right - file the left side of the ladder, it will then be off-set in the right direction to move bullet impact. i also used an 1903A3 springfield front sight blade for mine, then filed it down for elevation correction. best, john

Attached Files

Standard Member

onondaga posted this 13 March 2014

http://www.castbulletassoc.org/view_user.php?id=6948>tlkeizer:

Sorry If I left you in the dark, here is the easy formula:

Formula:

amount of error x sight radius, divided distance to target = sight correction needed

Example At 100 yards, your shot is 6” low and the distance between your front and rear sight is 19.5". Remember 100 yards =3600 inches, all measurements are in inches in the formula. 6” X 19.5” divided by 3600” = .0325” Since you are shooting low, you would need to lower your front sight by .032". Left and right calculations are done the same way

For rifles, you measure the front sight height from the bottom of the dovetail to the top of the sight. For pistols you measure the height of the blade only. This is true unless stated otherwise in the sight specifications.

Remember the FORS rule for the direction to move the sight to move POI toward the bull: Front opposite rear same .

Your specific problem has the rifle with a 42” barrel shooting 4 inches to the right. I will assume your sight radius is 2 inches less than the barrel length or 40 inches, so:

4.0” times 40” = 160 160 divided by 1800” = .0888"

Your front sight needs to be moved .088” to the right. The .088” is not too far to drift a sight it is about 3/32” You may not have to bend at all, just drift .088” to the right.

Gary

Attached Files

CBA Member

tlkeizer posted this 13 March 2014

SHJOE AND ONANDAGA, Greetings, Thanks for the reply's. My math after measuring the center of the last two groups and the sight difference gave me 0.089 also, same as 0.0888 rounded up. Now all I have to do us get out the file and dremel to work on a piece of brass I was given by a friend who has is priorities right. He has an old brass drift pin, so cut off a piece from the hammered end with a hacksaw. I have enough to make two sights if I choose. So, I think I will make the first, then see how close I came to what I need. I can't drift the sight on this rifle, so a little shop time will be spent over the next few weeks as I find time to get some filing in. Got a nice group that was repeated at 100 yards, I will put a photo out after I get this sent, can't seem to get my photo attached here. TK

Attached Files

CBA Member

tlkeizer posted this 13 March 2014

Greetings,

Here goes for a photo attachment try. Shot sunny day, no wind, +25. Used 55 grains GOEX FFG, Lee 405 HB cast with straight wheel weights, SPG pan lubed, CCI large rifle magnum primer, bullet seated to seating ring. I also used new prescription shooting glasses so I could see the sights clearly (I have heard that seeing the sights helps).

The lines are actually 0.87 inches apart, they don't print out as one inch. I called the low shot to the right. I had another group just slightly larger, only about a 10th on an inch larger.

Attached Files

Feb 45-70 100 yds 002.jpg

CBA Member

tlkeizer posted this 13 March 2014

Greetings and OOPS,

attached the wrong picture, right one here. Still, I am not ashamed of either group. Hopoe this comes through.

Attached Files

5 Mar 14 002.jpg

Standard Member

shjoe posted this 14 March 2014

wasnt able to open and view your pictures, (i must be on double secret probation) but, seems like you are headed in the right direction. best, john

Attached Files

Standard Member

onondaga posted this 14 March 2014

http://www.castbulletassoc.org/view_user.php?id=6948>tlkeizer

I haven't been able to open any of your pix either. Are you copying and dropping the JPG picture code in your text? Copying and pasting an image does NOT work, using the IMG code Does work. Mobile operating browser systems don't work well for this. Are you using a cell phone or a laptop/desktop computer? I use the newest Firefox browser on my Win 8.1 touch Toshiba laptop.

Even if you use the thumbnail code from Photobucket we would get a thumbnail to click on and see full size pix.

I'd sure like to see your pix.

IMG code size: http://s30.photobucket.com/user/rhymeswithwhat/media/P5290148_zps7d55dbf1.jpg.html>http://s30.photobucket.com/user/rhymeswithwhat/media/P5290148_zps7d55dbf1.jpg.html>

Attached Files

CBA Member

tlkeizer posted this 16 March 2014

Greetings, Guys, sorry the pictures did not come through from my desktop. I will be sending it in for update from Windows XP to Windows 7 more than likely. Anyway, will try again later after updates. Thanks again. As an aside, I should be done filing the new sight about the time I get the computer back and make sure it (the computer) is working right. TK