Carter
Member
I currently have my 12.5 sbr zero'd for 50 yards with xm193. How much would my poi change if using 77 gr otm within 25 yards?
POI difference
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Carter
Member
I plan on testing it if I bought some. Just wanted a general idea of what to expect before buying pricier ammo.
wally
Member
Its kind of like asking how much will my POI/POA change when I add a suppressor? Basically no way to tell other than to try.
The shorter the range the less likely it is to be bad enough to make you miss unless shooting really small targets, but for some guns the shift is minimal enough to be no more than you might get swapping lots or brands of nominally the same ammo, with others its large enough that I zero it for suppressed or unsuppressed and then only shoot it that way until I can re-zero.
The shorter the range the less likely it is to be bad enough to make you miss unless shooting really small targets, but for some guns the shift is minimal enough to be no more than you might get swapping lots or brands of nominally the same ammo, with others its large enough that I zero it for suppressed or unsuppressed and then only shoot it that way until I can re-zero.
FL-NC
Member
Expect it to hit high. Also, 25 yard zeros will lie to you. Best to zero at 50 or 100- I prefer 100.
wally
Member
I prefer 50. The groups will be smaller for more precision finding the center, and for most non-magnum calibers it ends up being close to a "point blank zero" and wind errors will be smaller.
7.62x51 Mil surp ammo
50 yard zero, will then be approximately 1.5" high at 100, 1.8" high at 150, 0.7" high at 200, 1.9" low at 250, then things really start dropping but the hold overs are "reasonable" about 0.6 mil at 300, ~1 mil at 350, and ~1.5 mil at 400 yards. Basically the same for 5.56 out to 300 yards but the drop is ~2 mil at 400 yards.
Double Naught Spy
Sus Venator
That is an interesting way of looking at 25 yard zeroes. I always figured it was the shooter engaged in self deception, failing to to account for the slight differences at 25 yards turning into significant differences a much greater ranges.
Getting back to the OP, the POI difference at 50 yards may be small or inconsequential, as noted, but that difference will be more notable with distance and will be further exacerbated by the differences in velocity and BC.
Carter
Member
I planned to keep my zero at 50 yards with xm193 for my regular ammo. I mentioned POI difference at 25 yards because I wanted to use 77gr otm as an hd round only, and 25 yards seemed like a good reference point.
Furthest actual distance in my house is probably 15 yards.
Furthest actual distance in my house is probably 15 yards.
Destructo6
Member
Well, at muzzle contact distance, it will be about 2.5" low, assuming standard AR sight height...
That assumes everything is typical AR...
That assumes everything is typical AR...
doubleh
Member
The only way to really know the POI is to shoot the gun at that distance. Trajectory tables and speculation will get you close. Actual shooting will get you there.
Varminterror
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I shoot the 50 JHP UMC load quite a bit to get my rifles on target before I swap to my reloads. On my latest outing in doing so, I ran out to 500 with the JHP’s? Then swapped to 73 ELD’s, and was within 0.2mil on a 66% IPSC. That 0.2mil at 25yrds would be something on the order of 0.2” at 25yrds. Shooting 50grn through 75grn pills in load development, I typically don’t see much more than an inch at 100yrds... again, something around 1/4” at 25yrds.
Remember, a bad guy at 25yrds (let alone 30ft in your house) is a gigantic target. A 4moa shift is an inch, which would move you from one side of the sternum to the other...
Remember, a bad guy at 25yrds (let alone 30ft in your house) is a gigantic target. A 4moa shift is an inch, which would move you from one side of the sternum to the other...
FL-NC
Member
In that case, I wouldn't even change the zero. Just fire a few supported at 15, or 25, or whatever to test for reliability in the rifle, and just see what the group does. Done.
ontarget
Member
Like the others said, at HD distances, you wont even notice. And I agree with FL-NC fire the HD rounds for reliability check and sleep well knowing you are well protected.
As stated there is NO way to know except test. In my experience many ARs in 5.56/223 don't change POI much between loads at moderate distances. I have a 30/06 that puts most loads of various bullet weights into the same group at 100 yards......I also have a pair of 7mm 08s same brand and model purchased on the same day. Some loadings coincide in POI.....but two loads that one rifle will put within an inch at 100 yards the other gun groups 5 inches apart.
Llama Bob
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It's not uncommon for it to change several MOA, possibly both vertically and horizontally. The harmonics of the barrel are different with a different load.
Coal Dragger
member
At 25 yards with a 50 yard zero you’re going to be approximately 1-1.25” low as the bullet is still below the line of the sights.
I typically zero all my 5.56X45 carbines at 200 yards. This coincidentally gives an essentially perfect 50 yard zero as well given the tall sight over bore height. Some refer to this as the 50/200 zero, but too few actually move out to 200 to confirm and get better data on windage and fine elevation adjustment. Starting at 50 yards and getting a “perfect” zero I usually get out to 200 and discover I need to make a few minor adjustments to truly dial everything in. This tweaking has essentially no affect on the 50 yard point of impact because 50 yards is so close that the .5-1.0 MOA correction typically needed to get a solid 200 yard zero barely registers at 50 yards.
I typically zero all my 5.56X45 carbines at 200 yards. This coincidentally gives an essentially perfect 50 yard zero as well given the tall sight over bore height. Some refer to this as the 50/200 zero, but too few actually move out to 200 to confirm and get better data on windage and fine elevation adjustment. Starting at 50 yards and getting a “perfect” zero I usually get out to 200 and discover I need to make a few minor adjustments to truly dial everything in. This tweaking has essentially no affect on the 50 yard point of impact because 50 yards is so close that the .5-1.0 MOA correction typically needed to get a solid 200 yard zero barely registers at 50 yards.
Caliper_Mi
Member
For HD, why even change? OTM doesn't expand like a hollowpoint handgun bullet. The 55gr with higher velocity should do better for fragmentation/tumbling and help prevent overpenetration. If you are concerned about a criminal wearing some sort of body armor, switch to XM855. My understanding is that OTM 77gr stuff is designed for terminal performance well beyond HD ranges...
The 60's style 55g effects were caused by understabilized bullets fired at high velocity through 1:14" twist barrels. Most modern barrels have a higher twist rate so the bullet will simply drill a nice clean hole through the "target".
On a different note, at 25 yards, you probably want zero magnification sights as close to the barrel as possible to eliminate the parallax. If you can get iron sights 1" above the center of the barrel and zeroed at 50 yards, you'll be no more than 1" low at all intermediate distances. Scopes, red dots and flip up sights will all sit higher and cause your short distance shots to be that much lower.
For instance with a sight 2" above the center of the bore and zeroed at 50 yards with a 3000 fps 55g bullet, you will be 0.9" low at 25 yards. Switch to a 75g bullet with the same max pressure load (less powder so let's predict about 2650 fps MV) and you'll be 1.3" low at 25 yards.
On a different note, at 25 yards, you probably want zero magnification sights as close to the barrel as possible to eliminate the parallax. If you can get iron sights 1" above the center of the barrel and zeroed at 50 yards, you'll be no more than 1" low at all intermediate distances. Scopes, red dots and flip up sights will all sit higher and cause your short distance shots to be that much lower.
For instance with a sight 2" above the center of the bore and zeroed at 50 yards with a 3000 fps 55g bullet, you will be 0.9" low at 25 yards. Switch to a 75g bullet with the same max pressure load (less powder so let's predict about 2650 fps MV) and you'll be 1.3" low at 25 yards.
Llama Bob
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While it's far from ideal, I believe 77gr SMK loads actually have somewhat better terminal performance than M193 because the jackets are thin and fragment more. It was designed for accuracy and long range, but the improved terminal performance seems to be a side effect of the match jacket.
Nether gives terminal performance anywhere close to your basic hunting JSP in any reasonable grain weight.
1/2" or less? Never tired it that close.
Carter
Member
I ended up ordering gold dot 75gr soft points. Plan to check reliability and poi once they arrive.
View attachment 785545 Carter:
Your thread made me ponder the same regarding the .300 AAC, when zeroed at 50 yards, comparing 125 and 165 grain projectiles. I decided to see.
I loaded some 125 grain SSTs and some 165 grain GMXs, just for curiosity.
I zeroed at 50 yards with the 165 grain GMXs, and fired 9 shots. Next, and leaving the zero unchanged, I fired 6 rounds of 125 grain SSTs. I was amazed at the lack of POI shift.
Target attached. Cool thread! Thanks for giving me an idea of something fun to try.
Geno
Your thread made me ponder the same regarding the .300 AAC, when zeroed at 50 yards, comparing 125 and 165 grain projectiles. I decided to see.
I loaded some 125 grain SSTs and some 165 grain GMXs, just for curiosity.
I zeroed at 50 yards with the 165 grain GMXs, and fired 9 shots. Next, and leaving the zero unchanged, I fired 6 rounds of 125 grain SSTs. I was amazed at the lack of POI shift.
Target attached. Cool thread! Thanks for giving me an idea of something fun to try.
Geno
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