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Carbine bullet trajectory? Need info!

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skunk62 View Drop Down
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    Posted: May 11 2022 at 8:03am
For some reason I can't find info to answer this question on google. My question is if you have a carbine sighted in at 100 yards, at what point does the bullet first pass through the line of sight before it then falls back down due to gravity at 100 yards? I find my old age vision no longer allows precise sighting in with iron sights any more past about 40 yards. Whatever that distance turns out to be, that is what distance I'm  going to sight my carbine in. Better than nothing.

I was able to properly site in my SA58 (FAL clone) from DSARMS at 28 yards (25 meters) because the gun is supposed to be sighted in at 200 meters. No way I was going to see good enough to sight a gun in at 200 meters, let alone find a range where I could anyway. So I found out that the 7.62x51/.308 Winchester bullet first hits the line of sight at 25 meters, then goes above the line of sight only to fall back to the line of sight at 200 meters. I also sight in ARs (A2 sights -.223/5.56mm) doing it this way (but different range). This is as good as I can do it these days.
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David Milisock View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David Milisock Quote  Post ReplyReply Direct Link To This Post Posted: May 11 2022 at 8:46am
My experiance with sighting my 2 carbines is this. Because the sight placement is so low to the center of the bore the 30 Carbine if sighted at 100 yards crosses the line of sight between 15 and 20 yards.

I'm an old FUDD as the kids call us today and I sight in so that at all functional ranges the target appears above the sight.

I use 9" paper plates, hold 6 o'clock on the outer ring, group center is then 4 1/2" high at point of aim. At 50 it's nearly at the top of the plate, if the target is at 200 I pull my ramp sight to the top and hold bottom of chest.

The 30 Carbine is a very handy rifle at those ranges and proof that modern is not always better.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Matt_X Quote  Post ReplyReply Direct Link To This Post Posted: May 11 2022 at 9:06am
Discussed and graphed a bit here.

It seems the original production sighting was for zero at 150 yards, which worked out to a 6 oclock hold on a 10" bullseye at 100 yards.  
See the second table 35 Whelen posted there for bullet rise of 2.5" at 50 yards when zeroed for 150.
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Edited by Matt_X - May 11 2022 at 9:34am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: May 11 2022 at 10:01am
https://www.federalpremium.com/ballistics-calculator

Very handy and you can easily plug-in the variables. Set the increments to 10-yards and notice the bullet should cross line-of-sight at about 25-yards on a 150-yard zero.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sawbones Quote  Post ReplyReply Direct Link To This Post Posted: May 11 2022 at 12:31pm
Ditto the old age dilemma.  Here's an old Indian trick:  I am able to remedy the problem by aiming thru reading glasses.  Sharpens the post focus on the target at any distance.  Give it a try and get back with us.

Peace is that glorious moment in history when everyone stands around reloading---Jefferson
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dutchgunman Quote  Post ReplyReply Direct Link To This Post Posted: May 11 2022 at 4:27pm
That is a very nice calculator!
Also possible to make it metric,perfect!
(I live in europeWink)
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 5:25am
Looks to me to cross at right around 25 yards for a 100 yard range. I want it zeroed closer to 100 yards, not 150. I have also heard that if a front sight was newly installed when they went to the arsenal after the second world war it might shoot too low, which would complicate things a bit. So I'll see what happens at 25 yards. Then figure out more later. Thanks for all the info. The thought of filing down the front sight is not happy one, but it is what it is. The sight does indeed look like it's never been filed down so what the heck!!!

Edited by skunk62 - May 12 2022 at 5:40am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 5:39am
Originally posted by Sawbones Sawbones wrote:

Ditto the old age dilemma.  Here's an old Indian trick:  I am able to remedy the problem by aiming thru reading glasses.  Sharpens the post focus on the target at any distance.  Give it a try and get back with us.

Peace is that glorious moment in history when everyone stands around reloading---Jefferson
I've never had reading glasses but now I might buy a pair and try what you're saying. With my particular vision, if I wear my regular long range glasses (I'm near-sighted) set at 20/20 from about five feet to infinity, then I can't focus on close up stuff closer than a foot from my face. But if I just take my glasses off, I can see fine up really close without needing reading glasses. My old age presbyopia is apparently not as bad as most my age. No glasses at all has been great for me for up close. 

But either with glasses or no glasses on I can't focus on both a front sight and the sight picture of any target down range very far. But shooting up to 50 yards not too bad with my glasses on, past that forget about it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 5:48am
I also read somewhere (not here) that most old wood stock rifles, including the carbine, will need to be re-zeroed if you take the gun apart and put it back together, basically every time you do so. Is that the experience with you folks here at this forum?

 More modern guns with polycarbonate or composite stocks are not so bad with disassembly and reassembly. And of course free-floaters are the best. Of course don't think too many out there have a carbine with a free floating barrel!! Would not be too original. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 5:54am
For that Federal ballistic calculator, would would the sight height of a M1 carbine be? Looks to be an inch or under to me, looking at the end of my bore to the top of the front sight post. 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 5:57am
Originally posted by skunk62 skunk62 wrote:

Looks to me to cross at right around 25 yards for a 100 yard range. I want it zeroed closer to 100 yards, not 150. I have also heard that if a front sight was newly installed when they went to the arsenal after the second world war it might shoot too low, which would complicate things a bit. So I'll see what happens at 25 yards. Then figure out more later. Thanks for all the info. The thought of filing down the front sight is not happy one, but it is what it is. The sight does indeed look like it's never been filed down so what the heck!!!
Quoting my own post here since I was too late to edit it. But I change that to 20 to 25 yards for the upward crossing point. Probably a lot closer to 20 yards going with a sight height of one inch.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 8:17am
With an adjustable rear, run the elevation up to a point that it might zero and don’t worry about what range it’s set on. If one insist it has to be set on 100 and shoots too low, your only option is to get a front sight with a shorter post….or file it. Sights with varying post heights are out there. I’d just rather not go filing on a USGI sight. Get a repo and grind it all you desire, but I would not do a thing until I ascertained the barrel is not bent….it happens.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote GotSnlB28 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 8:37am
Provided the carbine has been rebuilt at some point I wouldn't worry about targeting it by filing the front sight as necessary. I have done it to mine before. Unless you've got some rarer mfg coded sight, it's about a $25-35 part and worth more to have it properly sighted IMHO. Doesn't take much so take it slow.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 12 2022 at 9:42pm
Anyone know the approximate sight height of the carbine? And I have no idea how rare my front sight is, it has no discernible markings on it.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote David Milisock Quote  Post ReplyReply Direct Link To This Post Posted: May 13 2022 at 10:36am
Just my opinion but even though the design is 81 years old a well maintained 30 Carbine is still the cats meow in terms of a defensive rifle.

With that said the most accurized 30 Carbine is close quarter combat accurate at best. From a bench with a good rest a minute of coke can at 100 yards.

I get a sight setting with factory issued sights at 200 yards, I find out where it hits at 100, 50, 25 and 15. I then practice moving and making hits at the different ranges,  shooting and scooting. What the 30 Carbine does best.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: May 13 2022 at 11:20am
Originally posted by skunk62 skunk62 wrote:

Anyone know the approximate sight height of the carbine? And I have no idea how rare my front sight is, it has no discernible markings on it.

They are all over the place. I would not rely on trying to find a sight that works. If you decide to file, .010 up-or down will move the point of impact at 100-yards up-or-down by 1.67”. At 25-yards, 1/4 of that. I can’t claim to be the guy that determined this, but his math seems solid. You can use the shorter range of 25-yards to move the POI where it’s suppose to be at 25-yards for your particular zero.

You can use this figure to determine about how much you can take off the post. If it is shooting 4-inches high at 100-yards you need to plan on taking off about .024. Divide the number of inches by 1.67 then multiply by .010.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote W5USMC Quote  Post ReplyReply Direct Link To This Post Posted: May 13 2022 at 11:30am
Originally posted by floydthecat floydthecat wrote:

[QUOTE=skunk62] If it is shooting 4-inches high at 100-yards you need to plan on taking off about .024. 
 

??? if you are already shooting high, don't think you want to take anything off of the front sight post. Front sight needs to be taller to lower the impact of the rounds.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote floydthecat Quote  Post ReplyReply Direct Link To This Post Posted: May 13 2022 at 11:44am
Originally posted by W5USMC W5USMC wrote:

Originally posted by floydthecat floydthecat wrote:

[QUOTE=skunk62] If it is shooting 4-inches high at 100-yards you need to plan on taking off about .024. 
 

??? if you are already shooting high, don't think you want to take anything off of the front sight post. Front sight needs to be taller to lower the impact of the rounds.
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Right you are Wayne. Got my ups and downs mixed up. If POI is high….need to add post height. The 1.67 holds true for up-or-down though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote skunk62 Quote  Post ReplyReply Direct Link To This Post Posted: May 14 2022 at 8:22pm
Originally posted by floydthecat floydthecat wrote:

Originally posted by skunk62 skunk62 wrote:

Anyone know the approximate sight height of the carbine? And I have no idea how rare my front sight is, it has no discernible markings on it.

They are all over the place. I would not rely on trying to find a sight that works. If you decide to file, .010 up-or down will move the point of impact at 100-yards up-or-down by 1.67”. At 25-yards, 1/4 of that. I can’t claim to be the guy that determined this, but his math seems solid. You can use the shorter range of 25-yards to move the POI where it’s suppose to be at 25-yards for your particular zero.

You can use this figure to determine about how much you can take off the post. If it is shooting 4-inches high at 100-yards you need to plan on taking off about .024. Divide the number of inches by 1.67 then multiply by .010.
I understand that a carbine is not a sniper gun. But I want it to average close to center bullseye at 100 yards. A 5 inch group would be nice. Wouldn't a 5 inch group be 5 MOA? Which is pretty good for iron sights on most guns. 8 inches would be acceptable for me.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Sawbones Quote  Post ReplyReply Direct Link To This Post Posted: May 20 2022 at 9:35am
Well, went up the hill to my shooting range and while setting up for a shoot my reading glasses fell to the ground and I stepped on them. RATS!!  So I went down to the house to fetch my computer glasses to substitute for the readers (cheaters).  WOWSER!!  Computer glasses (bifocals w/ different dioptors than my regular bifocals) were better'n the cheaters!  VERY sharp focus image of aperture/front sight on down range target.
Give it a try.
"I know worrying works, because none of the stuff I worried about ever happened." Will Rodgers
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