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first shot high, next shots in nice group 1 moa lower

rockwind1

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Feb 16, 2017
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this had been a recurring pattern while shooting my "precision" ar-15. been noticing it the last 2 days.

the first shot will be all by itself high, then the next 2-4 shots will almost be in a single hole, like at a 100 yds. . it's got to be me somehow, but i can't figure it out. usually will shoot a group and then have a 10-15 minute break. i don't really notice it on other rifles that i shoot.

pretty nice ar i put together myself with JP supermatch barrel, lmt enhanced bcg, elftman trigger, good quality upper lower, and handguard. prs stock, a geissele mount and steiner 5-25 txi, can give all details on ar-15 if necessary but i suspect it is something i am doing with the gun.
 
Fairly common. How are you seating the first round? Pulling the charging handle or bolt release? I get a lot more consistently with the bolt release.

I’m assuming everything is properly gassed.
 
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If I recall, our HMFIC here says that there is no such thing as a "cold bore" shot. In other words, it's not the "cold bore," but rather, a "cold shooter."

The longer I have been at this, the more I believe Frank is right.
 
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I assume you’re not changing anything like adding a suppressor when you get to the range? I ask because I have a lesser quality can and mount that always shifts the first round high 1 moa if I take it off to store the rifle. I assume it’s not that, but in my case it drove me crazy trying to figure out why for a while.
 
Many shooters mistakenly mislabel various phenomenon surrounding precision rifles. Often this ignorance at best leads to a misuse of a term, but at its worse, it can lead to improper technique or even the denial of occurrences. The “cold bore” phenomena is exactly such a phrase that instills much confusion thanks to hundreds if not thousand of the self reported anecdotal opinions of amateur shooters. To really diagnose we need to first define some terms.

"Cold Bore Shift" - Is a consistent and repeatable deviation between a point of impact and the desired point of aim, that occurs when the rifle has be fired in a state in which the temperature of the bore and the ambient environmental temperature is the same.

^This is kind of what it sounds like you have going on but to be honest you hardly have enough data points to correlate a trend. Being that it's an AR, they are also know to sometimes have "first round shifts" which manifest similarly but are not directly linked to temperature. Also note that not every rifle is going to have a cold bore, in fact most don't which is where the second term comes in...

"Cold Shooter Shift" - Is an inconsistent and therefor unrepeatable deviation between a point of impact and the desired point of aim, that occurs due to the shooters inability to engage the rifle in a consistent physical manner. This can manifest itself in variety of relations.


The easiest solution is to map out the rifle and determine what's actually occurring. This process should be then be repeated at least 5 to 10 times (the more precise the rifle generally the quicker process) in order to create a composite that denotes the potential average cold bore shift as to the average mean point of impacts from a warm bore. This averaged angular deviation can then be compensated for via dialing or holding in conjunction with ballistic solutions.

Step 1: With the a previously zeroed rifle (turrets set to “0/0”) that has been allowed to cool to ambient temperature (I normally make this my first rounds of the day), assume a good fundamentally sound prone position and fire one round at the left target.

1.png


Step 2: Shifting your natural point of aim to the right target, fire 4 rounds to determine a mean point of impact.

2.png


Step 3: Using the linear grid, measure the vertical and horizontal shift (if any) from the mean point of impact of the last 4 rounds to the 1st round. Then covert the linear measurement to an angular measurement.

3.png


Again key here is you're looking for consistent and repeatable. If you where to over lay a series of say 5- 10 targets and you notice a trend like this, then your rifle likely has a cold bore shift. If you find that's not the case then its likely you have something else going on.

4.png
 
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If I recall, our HMFIC here says that there is no such thing as a "cold bore" shot. In other words, it's not the "cold bore," but rather, a "cold shooter."

The longer I have been at this, the more I believe Frank is right.

i don't think it was a cold bore issue, cause i had been shooting it all day in intervals, shoot 4 shots about 30 sec - 1 min apart, then 5-10 mninute break, then do it again. i think it was something i was doing or something mechanical with the gun or my attachments.
 
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Fairly common. How are you seating the first round? Pulling the charging handle or bolt release? I get a lot more consistently with the bolt release.

I’m assuming everything is properly gassed.
ironically, i had totally shut off the gas system and was manually running the bolt back with the charging handle after each shot. however, in the beginning i was hitting the bolt release for the first shot,,,,so this occured to me after a bit and i tried using the bolt to also load the first round, it still seemed to do it. i had thought perhaps there was some bolt lug lock up difference with the tiny bit of extra spring action when using the charging handle. my gun is well lubricated and seems to operate fine. this was a recurring pattern that day, at least 8 times (one shot high, next 3 or 4 in a great group 1 moa lower. but,,,, it wouldn't do it every single time so was a bit hard to track down.

the next day, i tried very hard to make sure everything was the same as far as cheek weld, grip, and also tried to really bury it in my rear bag and then squeeze it upwards the same. (per another post i read on this thread) however, since i kinda added in several things, i guess i will never know what helped. the next day i turned the gas back on and where i originally seemed to see an improvement in accuracy by manually running bolt, it seemed to shoot about the same with gas.
 
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Also, which upper and handguard?
it is a m4e1, ( i think) from aero with a jp match barrel, 16" it is the upper that has the special barrel nut, i think the threads are on the inside of the nut,,,and it needs a special handguard. i think its a rifle length tube and the handguard doesn't cover the gas block. it's the thicker style handguard, m-lok, not like some of the newer slim ones.
 
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I assume you’re not changing anything like adding a suppressor when you get to the range? I ask because I have a lesser quality can and mount that always shifts the first round high 1 moa if I take it off to store the rifle. I assume it’s not that, but in my case it drove me crazy trying to figure out why for a while.
no, didn't change anything on the gun. was running a hypertap brake (which i give a thumbs up)

but in the past, on other guns, when switching from suppressor to brake or even removing/adding brake, i have definetly seen a poi shift,,, very large on some guns. this one i had take off a direct thread supressor and put on the hypertap and the poi went up an inch or 2 if i remember but i had done that a week ago so that is not the issue here
 
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it is a m4e1, ( i think) from aero with a jp match barrel, 16" it is the upper that has the special barrel nut, i think the threads are on the inside of the nut,,,and it needs a special handguard. i think its a rifle length tube and the handguard doesn't cover the gas block. it's the thicker style handguard, m-lok, not like some of the newer slim ones.

Make sure there isn’t enough flex when loading bipod for any of the handguard to touch or move anything.

Have seen some guys with gas guns able to load into bipod/obstacles enough to have a POI shift.