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Posted: 6/6/2011 12:25:14 PM EDT
| Quick question, I have some SSA 70gr 5.56...I have it put away for SHTF. Now if my rifled is zeroed for 55 gr 193, and I have to use the 70gr, how far off will I be on my zero? |
| Only way to know is to try. Get zeroed with the 70gr and then see how the 55gr does. You might find it's close enough for your plinking purposes, or you might find that you have to go 3 clicks up and 5 left or something to be zeroed with the 55gr. You can make note of those changes and re-set your zero back to where it needs to be for the 70gr when you're shooting that ammo. But there's no rule about how your POI will shift between different weights. |
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Only way to know is to try. Get zeroed with the 70gr and then see how the 55gr does. You might find it's close enough for your plinking purposes, or you might find that you have to go 3 clicks up and 5 left or something to be zeroed with the 55gr. You can make note of those changes and re-set your zero back to where it needs to be for the 70gr when you're shooting that ammo. But there's no rule about how your POI will shift between different weights. This. I bet you're minute of man at 200 yards if you zero at that distance with either. However, as Eric said, you'll have to try it to know. |
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Only way to know is to try. Get zeroed with the 70gr and then see how the 55gr does. You might find it's close enough for your plinking purposes, or you might find that you have to go 3 clicks up and 5 left or something to be zeroed with the 55gr. You can make note of those changes and re-set your zero back to where it needs to be for the 70gr when you're shooting that ammo. But there's no rule about how your POI will shift between different weights. Well the ammo I have is the Brown Tip stuff that is 70gr IIRC, I only have 840 rnds of it, I wanna use as little as possible to try this, I found a nice stash of the SSA 70rg ammo, from what I read it is the same ammo, correct me if I am wrong, I do have a extra Aimpoint laying around, so I'll probably do the Aimpoint in the Larue mount, as I know the repeatability from those mounts seems to be the best... |
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Only way to know is to try. Get zeroed with the 70gr and then see how the 55gr does. You might find it's close enough for your plinking purposes, or you might find that you have to go 3 clicks up and 5 left or something to be zeroed with the 55gr. You can make note of those changes and re-set your zero back to where it needs to be for the 70gr when you're shooting that ammo. But there's no rule about how your POI will shift between different weights. Well the ammo I have is the Brown Tip stuff that is 70gr IIRC, I only have 840 rnds of it, I wanna use as little as possible to try this, I found a nice stash of the SSA 70rg ammo, from what I read it is the same ammo, correct me if I am wrong, I do have a extra Aimpoint laying around, so I'll probably do the Aimpoint in the Larue mount, as I know the repeatability from those mounts seems to be the best... You should fire ammo from the identical lot number to your SHTF stash to assure zero, not from something you "read is the same". I understand you don't want to shoot a bunch up, but all you need to do is shoot a couple mags to check zero and to be sure it feeds and cycles in your rifle as you would need it to in an emergency scenario. After all, how much ammo do you think you are going to be using in a SHTF scenario? I would rather have 800 rounds of ammo I know functions in my rifles, and I have made sure of the zero than have 840 rounds of something I've never shot but have shot ammo that is supposed to be the same stuff. |
The bullets will likely fly within a few inches of each other out to 300 yards - how far do you think you will need to shoot if the SHTF ? To be sure, test both loads with the same zero. If it worries you, you can chronograph both loads then run the velocities through a ballistic calculator; this, along with the actual test fire data, should allow you to produce a chart showing the relative trajectory of both loads. This is what I have done for my SHTF rifle (16" AR15), through which I shoot both 62gr M855 and 69gr SMK loads. I printed out a small version of this table and stuck it on the inside of my Aimpoint occular lens cover for instant reference:
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Quoted:
I haven't tried the 70 grn stuff but I've shot 55, 69 and 75. They all shoot within 1.5 - 2 inches at 100 yards Agree, The issue for me is do I zero for what I plink with (193) or the TAP I keep for SHTF. Personally, I doubt I'll be taking shots over 200 yds in either situation 95% of the time so I zero'd with the TAP and the 193 is always very close inside that window. I totally disagree with the "minute of barn" claim. It was not even been remotely that much of an issue inside 200 yds. |
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I totally disagree with the "minute of barn" claim. It was not even been remotely that much of an issue inside 200 yds.
It depends on the rifle. My SP1 will change POI @ 100 yds by as much as 8" of elevation and 6" of windage between different *brands* of 55-gr ammo. Fortunately it's quite accurate with Malaysian and I've got a couple of cases of it, leaving the other random other M193 clones to the other children. |
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