SIG 556 SWAT Sighting in | SIG Sauer 556 Forum

SIG 556 SWAT Sighting in

Discussion in 'Technical Discussions & Troubleshooting' started by DeepDiver16, Jun 5, 2020.

  1. DeepDiver16

    DeepDiver16 New Member

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    Hi Everyone,

    I know accuracy has been discussed on here before but I would like to get some opinions. I have a sig 556 swat manufactured on June 2009 (Serial number JS 037XXX). I have a Nikon Prostaff 3x9x40 mounted with a Burris PEPR scope mount. I tried sighting it in with 55g .223 ammo of several brands (Federal, PMC, and American Eagle). I understand that this rifle seems to like heavier bullets but I have also read some reports of this rifle shooting fine with 55gr ammo. Anyhow, at 100 yards, bullets are hitting within a 5 inch diameter around the bullseye. For the most part, the bullets seem to group at around 1.5 to 2 inches within the 5 inch diameter. Some group a little high, some group a little low from the bullseye but still within the 5 inch area. Not much change in windage (maybe an inch from center of bullseye to the right and left), primarily elevation. All brands do the same pretty much. The rifle is clean, no sign of canted top rail (mine does not have a single piece rail), no sign of peening, etc. Rifle cycles just fine. At 25yds, rifle is accurate (I can hit a can just fine). What do you all think about this? Ammo perhaps? I checked the scope and the scope appears to be OK. I figured if the scope was bad, I would be all over the place. I did install an O-ring in the front take down pin to minimize upper and lower wobble. Also, I was shooting from a caldwell lead sled. Any input would be highly appreciated. Thanks!
     
  2. CGRBB

    CGRBB Active Member

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    I want to make sure I am understanding this. So your rifle is printing 2 inch groups within a 2.5” radius of your POA, but the groups aren’t piling on top of each other, as you’d expect? You’re not making any scope adjustments, or changing any other conditions between these groups? Are these 5-shot groups?
     
  3. DeepDiver16

    DeepDiver16 New Member

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    Hi CGRBB,

    That is correct. I am doing three shot groups and the groups are not piling on top of each other. However, the groups do remain within a 5 inch diameter area. For example, three shots will group below the POA and the next three will group above the POA. Sometimes, this happens consecutively. However, sometimes one shot will hit below POA and the next shot will hit above POA.

    I got to thinking last night and I think I may have figured it out. I would like to get your opinion on the following. About a year and a half ago, I was having the same issue. I blamed it on a wobbly bipod. I removed the bipod and used a sandbag and started hitting the bullseye (see attached picture). I went ahead and bought a Harris bipod and had same issue. Then, I tried a lead sled and still had the same issue. Somehow, I'm think that attaching a bipod to the barrel end of the hand rail or using a lead sled is affecting bullet trajectory. Like I said, this doesn't happen when I used the sandbag and placed it closer to the magazine end of the hand rail. The picture attached shows how the bullets were landing around the bullseye and then how I was hitting the bullseye when using a sandbag. What do think? Thanks!
     

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  4. CGRBB

    CGRBB Active Member

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    That would certainly make sense to me. Considering these aren’t free-float guns, any load exerted on the handguard could potentially affect POI. Still interesting you manage to exert the same load across the three shots, but not multiple groups. I am a fan of 5-shot groups, as I consider them to be better indicators of both the gun and the shooter. I’d be curious to see your results shooting five rounds per group.
     
  5. DeepDiver16

    DeepDiver16 New Member

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    I think I got it. Went out to the range yesterday and tried the sand bags. The rifle was still not grouping. To minimize variables, I took the scope off and flipped up my MBUS back up sights and moved the target to the 25 yd line. 5 shots, all landed in the bullseye. 4 shots went into the same hole pretty much. I think this confirms the rifle is accurate. Therefore, I either have bad mounts or a bent scope tube. I will be getting new mounts and see how it does. Hopefully this will fix it. Otherwise, the scope is going back to Nikon. I have no way of checking for a bent tube so I'll have to do some trial and error. I did recently adjust the scope as it was a bit canted. I did this by loosening the screws and rotating the scope. I guess I could have screwed something up by adjusting the scope. Who knows. I'll report back once I try new rings. Not sure what the local walmart has in stock but that is the only place I have to shop on a Sunday. If I find some rings, I'll go out to the range this afternoon and see what happens.
     
  6. hooch

    hooch New Member

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    5" with 55 grain sounds pretty dead on, as I said in my other post, load up so projos in the 70 grain weight, and youll see it close to around 2-3" groups
     

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