Does a difference of 7 grains really make a difference?

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Okay, so I usually shoot 62gr M855 out of my Sig556. It currently sports an EoTech 551 and is very accurate. (well enough for me)

I recently tried out some 55gr Federal HP rounds that I keep loaded for home defense to make sure they cycled fine.

However while shooting the first 5 rounds of this ammo (the rest of the mag had the M855 in it) I could not hit the cans I was aiming at from 80 yards. Once they were out and I was shooting the M855 I was hitting exactly where I was aiming.

So not being a super accuracy person (I just like to blow off steam and plink) should there be a huge POI change between the two ammo types?



FYI my sig has a 1/7 twist barrel.
 
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its not just 7 grains, it's entirely different loads and, more importantly, its different pressures... you were probably missing high or low.

but if you take two different 55gr loads, you'll get a noticeable POI shift.
 
OP
W
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Thanks for the info.

The reason I ask is that I want to get into reloading my own but I plan on saving up to be able to do that. In the mean time Ill need to be buying bulk and the cheapest Ive found is silver bear at a great price. Problem is its 55gr.

I LOVE the 62gr green tip LC ammo Im using now but the 36 cents a round minimum is not too enjoyable. At 20 cents a round the Bear stuff is much better priced. Considering it'll just be used for plinking... but 4 inches!?! I might have to save up and just get the good stuff....
 
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If it is just for plinking, why not shoot the cheaper 55gr and re-zero your red dot or irons for now? Then when you get into reloading and find a load you like zero it again for that and keep it there. Just my $0.02.
 
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Some of the accuracy results may come from your barrel twist too. My Colt AR has the heavy 1:7 barrel, and likes 62 grain rounds. It tends to 'fly' 55 grain rounds a bit, nothing drastic, but enough that I don't get nice tight groups. If I am going to shoot my AR, I just shoot the good stuff. I agree, the Lake City M855 is great stuff. If I just want to plink, out comes the 10/22!
 
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I re-load .223 for shooting sage rats and coyotes. Once I switched from 55 grain nosler plastic tip (balisitic tip) to 55 grain sierra plastic tip (blitzking) keeping everything else the same and the POI changed up and to the left by over an inch. It made hitting a 1" wide sage rat at 100 yards pretty hard.
 
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You mentioned Silver Bear ammo. This ammo is steel cased and not reloadable. You wil be able to get it cheaper but will not be able to save the brass for your future reloading. If this is the rout you are going I would suggest staying with brass cases. I am also a fan of LC brass. They just take a bit more time to process. The LC brass has a crimp ring that needs to be sweged to allow for new primers to be installed.
 

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