Point of aim / point of impact on my 50-90

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firefighter1990
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Point of aim / point of impact on my 50-90

Post by firefighter1990 »

So my 50-90 Hartford is set up with an mva #113 globe set to a mechanical-zero on the barrel. So using my mva soule rear, it's impact is 9 moa left of zero on a no-wind-day. Obviously it's something easily compensated for but out of all four of my Shiloh's, that one is the only one to shoot off from a mechanical-zero. Is this due to spin drift of the left twist and/or torque? It's deadly consistent though! I used it to take first in A class in the Idaho state match, just don't know if it's a common theme with 50's.
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Lumpy Grits
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Re: Point of aim / point of impact on my 50-90

Post by Lumpy Grits »

Have you confirmed your tang sight is 'square', side to side when the bubble in the 113 is centered :?:
Gary
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J.B.
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Re: Point of aim / point of impact on my 50-90

Post by J.B. »

A good point by Gary. I had a similar occurrence on one of my rifles and it was the first to ever exhibit this tendency. It turns out that on its trip through customs and my dealer, the tang sight & base had been removed and replaced several times. This was confirmed after levelling the rifle up in a rest with a number of spirit levels. A 4" level run up along the side of the post confirmed the sight was out by a small amount. I just backed off the screws a little and tensioned them a little at a time and the post 'trued' itself up. The windage I had needed was screwed back to zero and all was well with the world ! :D HTH

J.B.
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Lumpy Grits
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Re: Point of aim / point of impact on my 50-90

Post by Lumpy Grits »

You also have to ck for side to side play in the staff pivot area.
Make sure the pivot screw stays tight.
G.
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Kodiak
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Re: Point of aim / point of impact on my 50-90

Post by Kodiak »

I don't own a trapdoor rifle, but was the rear-sight on many made to lean out of plumb, to compensate for twist/spin?

Jim
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Don McDowell
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Re: Point of aim / point of impact on my 50-90

Post by Don McDowell »

firefighter1990 wrote:So my 50-90 Hartford is set up with an mva #113 globe set to a mechanical-zero on the barrel. So using my mva soule rear, it's impact is 9 moa left of zero on a no-wind-day. Obviously it's something easily compensated for but out of all four of my Shiloh's, that one is the only one to shoot off from a mechanical-zero. Is this due to spin drift of the left twist and/or torque? It's deadly consistent though! I used it to take first in A class in the Idaho state match, just don't know if it's a common theme with 50's.
Unless with the rear sight on zero windage, and you have proven on paper that your Mechanical zero is good, you don't have a mechanical zero yet. Get your Wyoming Sight drifter out, and drift that front sight back to the left, just a tad.
AKA Donny Ray Rockslinger :?
mike herth
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Re: Point of aim / point of impact on my 50-90

Post by mike herth »

I love it when the POI and POA coincide. I can remember all three times that happened to me in the past 8 years. Euphoric!
firefighter1990
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Re: Point of aim / point of impact on my 50-90

Post by firefighter1990 »

I have drifted the front globe over to where poi/ poa were zero and with the rear sight set to mechanical zero as well; it is .09" off center in the front dovetail in oder for it to happen. I have checked the geometry of the dovetail to the raceways in the action to be perfectly perpendicular of one another. Have also set my soule to be plumb to the axis of the bore but I didn't think to plumb it left/right. I always snug the staff screw and mva's tolerances are tight. It might just be an error in tilt. It was a consistent 9 moa at chickens all the way out to rams. Wouldn't a tilt error exponentially amplify as range increase? Either way I'll check it up. Thanks guys!
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Lumpy Grits
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Re: Point of aim / point of impact on my 50-90

Post by Lumpy Grits »

Just plumb the rear sight (side to side), to the front sight's bubble. That's all that counts here. :wink:
Very common to have to put a shim under one side or the other of the tang sight's base.
.09 movement would have that sight hanging out of the dovetail. You sure you don't mean .009? :?
G
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firefighter1990
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Re: Point of aim / point of impact on my 50-90

Post by firefighter1990 »

Finally got some days off and went home and checked the side-side plumb, indeed it was off. I'm not a big fan of shims so I machined off the excess tolerance on the high side to bring everything all together. Now I just need some more days off to collect drop data and confirm. I feel dumb for completely overlooking the side-side plumb :oops: but live and learn; I'll never make that mistake again. Thanks to all for your help!
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Lumpy Grits
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Re: Point of aim / point of impact on my 50-90

Post by Lumpy Grits »

The advantage of using shims. Comes in, if for some reason later on you want to put that sight on another rifle of the same model.
G.
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firefighter1990
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Re: Point of aim / point of impact on my 50-90

Post by firefighter1990 »

Even with well built sights like mva, Baldwin, Stevens, ect. I always dedicate that base to that rifle I fit it for and epoxy bed the underside to the contour of the tang. Same as I do the scope base blocks to my custom bolt guns. If you hold your rifles up to the light, you can see that even with a well built sight; there's never a perfect fit. Just make sure you tape and use release agent where need be. Just my practice and it may not be for everyone.
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Lumpy Grits
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Re: Point of aim / point of impact on my 50-90

Post by Lumpy Grits »

Understand where you are coming from, with the scope base deal.
I do the epoxy deal and I go one step further on my modern bolt guns, by installing 2, 3/16" dia. hardened steel dowel pins through the scope base & into the rec'r to help take the recoil/shock load off the base mounting screws. And this is with # 8 screws also. :lol:
With the 2, 10/32 screws that MVA has for the sight base on our Shilohs. Not sure that bedding with epoxy buys much here.
Is something to think over-- :wink:
G.
"Hav'n you along, is like loose'n two good men"
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