Carbine bullet trajectory? Need info!
Printed From: The Carbine Collector's Club
Category: The Club
Forum Name: General Discussion
Forum Description: Carbine Related
URL: http://www.uscarbinecal30.com/forum/forum_posts.asp?TID=6188
Printed Date: Apr 18 2024 at 8:26pm
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Topic: Carbine bullet trajectory? Need info!
Posted By: skunk62
Subject: Carbine bullet trajectory? Need info!
Date Posted: May 11 2022 at 8:03am
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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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Replies:
Posted By: David Milisock
Date Posted: May 11 2022 at 8:46am
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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.
------------- David Milisock |
Posted By: Matt_X
Date Posted: May 11 2022 at 9:06am
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Discussed and graphed a bit here. http://www.uscarbinecal30.com/forum/forum_posts.asp?TID=5139&PID=45079&title=range-results#45079" rel="nofollow - http://www.uscarbinecal30.com/forum/forum_posts.asp?TID=5139&PID=45079&title=range-results#45079 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.  |
Posted By: floydthecat
Date Posted: May 11 2022 at 10:01am
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https://www.federalpremium.com/ballistics-calculator" rel="nofollow - 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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Posted By: Sawbones
Date Posted: May 11 2022 at 12:31pm
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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 ------------- "Always do sober what you said you'd do drunk. That will teach you to keep your mouth shut." Ernest Hemingway |
Posted By: dutchgunman
Date Posted: May 11 2022 at 4:27pm
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That is a very nice calculator! Also possible to make it metric,perfect! (I live in europe
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Posted By: skunk62
Date 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!!! |
Posted By: skunk62
Date Posted: May 12 2022 at 5:39am
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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Sawbones wrote:Posted By: skunk62
Date Posted: May 12 2022 at 5:48am
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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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Posted By: skunk62
Date 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. |
Posted By: skunk62
Date Posted: May 12 2022 at 5:57am
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Posted By: floydthecat
Date 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. |
Posted By: GotSnlB28
Date 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. |
Posted By: skunk62
Date 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. |
Posted By: David Milisock
Date Posted: May 13 2022 at 10:36am
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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. ------------- David Milisock |
Posted By: floydthecat
Date Posted: May 13 2022 at 11:20am
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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Posted By: W5USMC
Date Posted: May 13 2022 at 11:30am
??? 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. FORS
------------- Wayne USMC Retired NRA Life Member |
Posted By: floydthecat
Date Posted: May 13 2022 at 11:44am
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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Posted By: skunk62
Date Posted: May 14 2022 at 8:22pm
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Posted By: Sawbones
Date Posted: May 20 2022 at 9:35am
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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. ------------- "Always do sober what you said you'd do drunk. That will teach you to keep your mouth shut." Ernest Hemingway |