I went to the range today to finally sight in some of my ARs at distances further than 50 yards.
First up was my BCM M16A4 clone at 300 yards. I had it “zero’d” at 36 yards so it was on paper at 300. It was shooting about 8" low and 6" left. I attempted to zero it, but it just wasn’t working…the smallest 5 shot group I got was about 5-6" which is not where my shooting abilities are at from a steady bench rest and a steady trigger pull. However, I was using Federal M855 which is not the most accurate ammo so I can understand.
I brought the target in to 200 yards and switched to my 14.5" BCM midlength with T1. This was only “test” zero’d at 50 yards and it was dead on at 200. With an unmagnified red dot all 10 rounds could be covered with a baseball. It was really good, I almost didn’t even believe it. (Lets keep this on topic, I don’t want this deviating into a “Thats impossible” thread)
I went back to the 20". Still, even with a 4x ACOG, couldn’t get a group smaller than 4-5" which didnt make any sense at all given what I had just done with the Middy.
Then I moved it in to 100 yards. After a few adjustments I had a 3 shot group that was right at the tip of the chevron you could cover with a quarter. Should be relatively zeroed now right?
Well, then I shot a 5 shot group at another target. I was now shooting a 3" group that was about 2" high.
Sorry for the lengthy “story” but I wanted to give the background so I could get an accurate reply as possible. I was shooting on a very steady rest, and using a very steady trigger pull. I don’t see it being the shooter.
I didn’t feel the ACOG loose at all, but that doesnt mean it wasn’t.
Federal XM855 isn’t exactly the most accurate but why was it great with the Middy?
To wrap it up, what kind of groups should I be expecting with this setup? and what is the best way to make sure I don’t have an issue with the upper or the optic?
5-6" at 300yds is roughly 1.5-2MOA. Well within the accuracy spec for M855
As for your T1, your group was also within the same accuracy range as a baseball is 3" in diameter which is 1.5 MOA at 200yds. People get hung up on this belief that aimpoints and other unmagnified optics can’t be accurate. User Molon on TOS did a great write up on that.
As for your POI shifting around like that, after you zero the ACOG you need to smack it. It sounds crazy but it helps set the reticle and get the prism to cooperate.
How are you supporting the 20" A4 clone on the bench? If using standard handguards, placing pressure on them will shift the point of impact. Shoot from exactly the same position with the same supports and inputs to get consistent results.
You’re right. I am so used to free floating handguards, it makes sense that when I had the handguards on the rest that it would change the POI depending on the amount of pressure I put on the handguards. Sometimes in order to steady the rifle even more, I would grab the handguards over the top and press it down into the rest. Other times, I wouldn’t. Guess I need to go back to the range.
I just got out of the Marine Corps, I never shot less than a 235 on the KD course and my highest was 246 without pit love, I am a Marksmanship coach instructor trainer, and did pretty well at the Pacific Division Rifle Matches I’ve been to. Thats about the extent of my formal training, the rest has just been me messing around with rifles since I was around 9.
Looking back, I understand that M855 is a 4-5 MOA ammo so a 5" group is really decent at 300 yards.
I guess the issue I’m concerned with is the shifting zero at 100 yards, but that could have been caused by what I mentioned above.
A little pressure can easily cause a few inches of shift at long range.
I asked about your training simply to ensure that you are proficient with fundamental marksmanship and NPA, which as a CMT I am sure you are aware are common stumbling blocks. Also, the 4x RCO doesn’t do much to improve precision either, not enough magnfication for truly precise hold at longer ranges. Really, the two things that the magnification does is improve ID and allow the shooter to see the BDC.
You seem suprised that your 14.5 is shooting better than your 20, don’t let that get into your head. Precision is not linked to barrel length, barrel quality is, but if you are getting 2 MOA out of M855, give the god of war a wink, cuz the bastard is smiling at you.
I bet you’ll find that your problem is inconsistent pressure on the handguard. That, and definitely give the ACOG a rap after you make adjustments. I use a wooden hammer handle cut to half length that I keep in my range bag for just this purpose. Don’t Hulk Smash it, just a tap straight down on the top. Don’t forget to mark your scope mounts with a paint pen so you can see if there is any movement.
I guess I bought into the “If the 14.5 shoots 1.5 MOA at 200 yards, the 20” should easily shoot 1 MOA" fallacy.
I’m gonna head down there next week (Its a good 1hr drive to the 1000yd range) I’ve got a couple fixes so far:
Shoot a 10 shot group on a clean target for confirmation, its hard marking previous shot holes at 300 yards even with a 60x spotting scope.
I’m going to lower my expectations. Maybe its because I was shooting my Rem 700 getting 2" groups and went to my AR that caused me to think something was wrong. I will make an 8" circle on the target and if I can get 10 consecutive rounds in the circle I will consider in zero’d at 300.
I’ll also remove pressure from the handguards while firing and let the weight of the handguards only sit on the bench, similar to when its resting on the support hand.
I’ll bring a camera too, because it was a good time and its a shame I don’t have any art to remember it with.
Rap the ACOG, as the other gentlemen stated, after any adjustment to settle the prism. Then shoot your group. I like to give it a rap from the top and side on the turret covers.
Get that support hand off the barrel an on to the butt stock to steady it snugly into the shoulder. Any additional pressure on the non-free-floated hand guards is going to affect POI, both from direct movement of the rifle during the shot and from dampening the barrel harmonics. The more you clamp down, the more the barrel harmonics will change.
Doesn’t sound like your groups are in any way bad as is. Another factor not yet mentioned here yet is the wind - at 50 yards and even 100 yards, the wind effect on 5.56 ammo is negligible. When you push that out to 200 and 300, it increases exponentially - figures will vary with ammo, barrel etc etc etc, but even with something as gentle as a 5mph breeze, at 100 yards the effect is not worth worrying about - half an inch or so, but that can be worth nearly 3 inches at 200 and 6-7 inches at 300. And by the time you are out at 400, that 5mph breeze is pushing the round 12 inches off. So unless you had an absolutely “dead in the water still” day, even slight variations in breeze and gusts can certainly have an effect in pushing your groups larger, even if its not enough to constantly shift the entire group.
To troubleshoot with the optic (as well as the tactics already discussed) - why not swap the optic onto your other rifle and see how that goes on there, and then back again - while there are still some holes in that approach which it may not prove, it should give you a bit of an indication.
You fellers that are giving your ACOGs a rap- Have you tried rotating the adjustment knobs a few clicks past, then coming back? It works on other optics for settling the reticle
From the TA33 manual: “To ensure a consistent zero, it is best to fire one shot off-target to allow the recoil to stabilize the adjustment mechanism after an adjustment has been made, and then fire a three shot group on the target.”
It’s the roof prism that gets “settled in.” A rap to the turret is also effective without taking a shot. I think the rap is more predictable from my experience.
The same is true for other optics as well. After making adjustments with the turrets, it sometimes takes a shot or two for the reticle to settle into it’s true position. It’s been found that if the turret is first adjusted a few clicks past the desired setting, then returned, it settles the reticle before shooting.
For example, the shooter takes a shot and discovers the impact is high and left four clicks. Shooter then adjusts the elevation about six clicks down, then 2 clicks up and the windage six clicks right, then two clicks left. It takes out the slack so the reticle settles in its true position before shooting. Just wondering if it’s have tried to see if it works with the ACOG
I carry a piece or two of 3/4" dowell rod about 8" long in all of my bags for the scope “rapping”. I generally tap in several different axes to make sure the reticle is settled.
Dowell rod is cheap, I think it is like $4 for a 3’ long piece at Lowe’s.
I have seen it make a difference. Ain’t no telling how much ammo that $4 has saved me over the years.
Very interesting discussion on “rapping” the scope. Great info. Does this work with an RDS as well?? I just saw ACOG mentioned so that is why I ask. Might need to do this with my Aimpoint. Thanks for the great info!!
I rap everything, even my T-1. Heck…what does it hurt. Might even save a bullet or three. I generally rap about 5 or 6 times in several different planes.
I tried a “box test” with a Vortex Razor 1-4X the other day without rapping. It was dead-on at 100-yards making an almost perfect 8" square…but…it cost a little more than most scopes.
Like lifebreath said - get your hand OFF your handguards and use that off hand to support/adjust the buttstock/bag. Let that forend float on the front bags and that will be your most reasonable way to reduce the harmonics on that non-FF front end. ALSO, if you are in a wind situation - the closer the wind is to you the greater its impact will be down range. It is usually this closer wind that affects drift and surprises shooters more often than not - that is why bench shooters tend to spend more time reading and waiting on the closer flags.