What the heck is going on here?

[Rider47]

What the heck is going on here?
I am experiencing this phenomena with my new .223 Wylde AR-15 build, but also to an extent with my other two AR’s. Shown below are five 5-shot groups shot today at 100 yards. (Ammo used includes 69gr. and 77gr. SMK handloads, shot from a bench with a bipod and a rear bag through a 30X scope.) What I am seeing, virtually every time, is that the first shot from a magazine, where the first round is fed by closing the bolt, has a point of impact about a full inch higher than the next four shots which are fed by bolt cycling upon firing, which form a nice group ~1” below the initial shot. The first three targets show this. The next two targets were shot by holding an aiming point an inch below the center of the target for the first shot, then holding on center for the next four shots.

Targets with the first shot aiming point 1” low

This is not a case of cold bore POI change as the rifle these groups are shot when the rifle is fully “warmed-up”. It also has nothing to do with my hold – I’m an experienced enough shooter to know my rifle holds are pretty much equivalent on all shots. It seems to be something to do with how the round is seated(???): start of a mag from the open bolt position vs. bolt cycling by firing.

Two questions.
1) What is causing this?
2) How can this be eliminated?

I am wondering if over or under gassing can cause this? As I use a brass catcher to catch my cases I can’t really say what clock direction the cases would go without the gas catcher. Note that these are NOT hot loads. Any insight into this would be appreciated.

 

[Clint H]

Dumb question, but is the 1st round sitting in the chamber for a while before you shoot, or are you dropping the bolt and immediately going at it?

I've seen similar patterns happen when the first round is chambered, and then left for a minute or two in a hot rifle while the shooter settles in. The round then gets heat soaked more then the subsequent ones, and depending on the powder, can pick up enough velocity to shoot slightly flatter.

Like I said, dumb thought, but it's the only thing that immediately came to mind.

 

[tomme boy]

It happens with a semi auto sometimes. I have several 1022's that do this. Sothe first shot is always into the dirt. It is because of how the gun feeds. You are feeding the round different thn the gun feeds it.

 

[Rider47]

Thanks for the thought. The first round is not held in the chamber for any significant amount of time, and not usually any longer than between the other shots. Also, powders are Hodgdon "Extreme" H4895 (69grSMK's) and Varget (77gr.SMK's) which are supposedly much less temperature sensitive. It would take some MV difference to increase POI 1" at 100 yards.

 

[mark5pt56]

I don't have an explanation for this. Try pulling the charge handle FULLY to the rear and release like a sling shot verses releasing via the bolt catch/release. The BCG will have more velocity and the feeding, chambering and locking will be different.

 

[ZY100]

Are you chambering the first round using the bolt release and letting it slam forward?

Or are you riding the charging handle and chambering it “slower”?

That can make a difference.

Also, load an extra round and don’t fire it after a string of 5. Pull the round from the mag and measure CBTO…check for bullet setback.

ETA—mark5 types faster…

ZY

 

[Rider47]

"Are you chambering the first round using the bolt release and letting it slam forward?"
Yes - this is my normal start for a fresh mag.
"Or are you riding the charging handle and chambering it “slower”?"
Tried this - no difference.
"Try pulling the charge handle FULLY to the rear and release like a sling shot verses releasing via the bolt catch/release."
I thought I'd tried this as well, but will do it again.
I will also try backing off the gas (adjustable gas block) until it doesn't cycle, and then open it just until it cycles properly.

 

[Cr1775]

Had same issue with a FN FAL , never did find the reason after checking rounds after ejecting rounds after chambering both 1st round and later.

 

[ZY100]

If it with different loads and multiple ARs, I think its ammo related.

Confirm you are not getting bullet setback during recoil. Whats your neck tension? Do you crimp?

Try a box of factory ammo…same issue?

ZY

 

[mark5pt56]

Fiddle with one more thing-magazine capacity and spring tension, it will be greater on the first round, fully loaded magazine and slowing BCG velocity. Does it matter--No clue but check one thing at a time.

 

[joe777]

This is the kind of shit that will drive a man crazy. Can you give more info on the build parts including scope, suppressor, etc.

 

[Rider47]

I don't use factory/commercial centerfire ammo. Not for 20+ years in many different cartridges and rifles. Rounds are precision loads. No crimp, minimal neck tension, cases resized with Redding small base die (necessary as the chamber is quite tight) with +.010" Redding competition shellholder followed by neck sizing and bullet seating with LE Wilson arbor press dies. Powder is weighed to the granule (don't ask). Lapua brass not available at this time, so cases are LC. Primers are CCI400, as mentioned, powders are Hodgdon H4895 (21.4gr with 69gr. SMK's, Varget (23.4gr. with 77gr. SMK's).
Mags are steel 15-round mags, loaded with only 5 rounds at a time. Spring tension appears good, rounds appear to chamber properly.
Build details: Aero lower, Anderson upper, AR Stoner BCG/bolt, Wilson (not Wilson Arms) SS heavy 16" Varmint barrel (.900 muzzle) in .223 Wylde free-floated with a 9" ohhunt lightweight handguard, RRA Varmint 2-stage trigger with JPE reduced power trigger spring set, no thread/suppressor, scope is cheap Mueller set at 30X (scope is temporary for load development only - lower power scope will be permanent). (Money spent on barrel and trigger.) Shooting from a relatively stable range bench with a bipod and rear bag. The gas block is adjustable and I likely have it set at somewhat over gassed. This will be varied next range session.

 

[mark5pt56]

Try some Magpul 10/20 rounders, the rounds will feed with less resistance or polish the steel feed lips. There's usaully more drag on steel mags.
Will leave the neck tension for someone else.

 

[B Man]

What the heck is going on here?
I am experiencing this phenomena with my new .223 Wylde AR-15 build, but also to an extent with my other two AR’s. Shown below are five 5-shot groups shot today at 100 yards. (Ammo used includes 69gr. and 77gr. SMK handloads, shot from a bench with a bipod and a rear bag through a 30X scope.) What I am seeing, virtually every time, is that the first shot from a magazine, where the first round is fed by closing the bolt, has a point of impact about a full inch higher than the next four shots which are fed by bolt cycling upon firing, which form a nice group ~1” below the initial shot. The first three targets show this. The next two targets were shot by holding an aiming point an inch below the center of the target for the first shot, then holding on center for the next four shots.

Targets with the first shot aiming point 1” low

This is not a case of cold bore POI change as the rifle these groups are shot when the rifle is fully “warmed-up”. It also has nothing to do with my hold – I’m an experienced enough shooter to know my rifle holds are pretty much equivalent on all shots. It seems to be something to do with how the round is seated(???): start of a mag from the open bolt position vs. bolt cycling by firing.

Two questions.
1) What is causing this?
2) How can this be eliminated?

I am wondering if over or under gassing can cause this? As I use a brass catcher to catch my cases I can’t really say what clock direction the cases would go without the gas catcher. Note that these are NOT hot loads. Any insight into this would be appreciated.

"Are you chambering the first round using the bolt release and letting it slam forward?"
Yes - this is my normal start for a fresh mag.
"Or are you riding the charging handle and chambering it “slower”?"
Tried this - no difference.
"Try pulling the charge handle FULLY to the rear and release like a sling shot verses releasing via the bolt catch/release."
I thought I'd tried this as well, but will do it again.
I will also try backing off the gas (adjustable gas block) until it doesn't cycle, and then open it just until it cycles properly.

OP I have a rifle started doing this. Started, as in It wasn’t before. The exact same scenario you are having and I have tried everything you are. It’s an easy sub moa rifle usually in the 3/4 range. It has been driving me nuts to figure this out!!! So I’m glad you’ve brought this discussion up.

Try some Magpul 10/20 rounders, the rounds will feed with less resistance or polish the steel feed lips. There's usaully more drag on steel mags.
Will leave the neck tension for someone else.

This is something I haven’t tried. I did just get alot of 20rd steel mags in I use randomly but I have used the same one best of my knowledge here recently. I’ll be trying two 10 rd mags I was using before.

 

[Holliday]

Just skimmed the thread so if this is redundant, ignore. Have you tried manually loading and shooting 5 rounds?

Could one or the other ie first round loading or mag loading be changing the bullet seating?

 

[hlee]

Could one or the other ie first round loading or mag loading be changing the bullet seating?

No crimp and minimal neck tension, you say?…

 

[Cr1775]

Had this problem with my FN FAL, was a true .5 moa rifle but 1st shot always made it 3 moa. When i loaded 1 round at a time it was 3 moa or more. I checked for runout and overall length and nothing changed with the milsurp ammo did see slight changes in my ammo. The best i or anyone could explain what was happening was the way the bolt would lock up chambering the 1st round.
That issue made me go nuts.

 

[tylerradke]

No crimp and minimal neck tension, you say?…

Red flag to me as well. Like someone else said, load one at a time in magazine and drop bolt with release on every round and see if that changes things for you. My guess is you will have a 5 shot group 1" high. I think you might need to either adjust tension or get a Lee factory crimp die and just kiss them a little with it. Should be enough to eliminate any setback or recoil induced COAL changes. Also are your feed ramps nice and smooth with no copper shavings or dust on them? A sharp corner or burr on them can cause issues

 

[NHR]

I and this exact issue with an AR years ago. 1st round loaded by CH would have a different POI. I was shooting IMI 77.

I can't explain why, but for me I traced it back the the OG straight 20rd Magpul PMAG I was using. I tried a 30rd M3, Lancer, and GI 20 Rd aluminum mag. It only occurred with the 20 Rd straight Magpulal mag.

It was very consistent.

This was 2 separate 3 round groups. Both first shots(used bolt release to load) are touching and then shots 2 and 3 from both groups are stacked low left.

Fired at 100 yards.

 

[Rider47]

I got the same results using four different mags, so doubt the issue is mag related. (But still possible.)

To clarify - the "minimal neck tension" used in these rounds is created by using largest neck sizing bushing that will produce all 50 rounds in a batch such that the bullet cannot be moved in/out or rotated by gripping the case in one hand and the bullet in the other and twisting, pulling and pushing. This has been done to maximize rifle precision as I have found it to be a critical loading parameter for precision loads. (Note that while the rifle is somewhat of a "value build", it is capable of good precision excepting the 1st shot flyer issue.) But this is an interesting point to follow up on, and I will load the next batch of ammo with both the same and tighter neck tensions to compare and I will report results. As stated earlier, I will also vary gassing amount to determine if there is any effect.
Thanks again to all those posting ideas.

 

[B Man]

I got the same results using four different mags, so doubt the issue is mag related. (But still possible.)

To clarify - the "minimal neck tension" used in these rounds is created by using largest neck sizing bushing that will produce all 50 rounds in a batch such that the bullet cannot be moved in/out or rotated by gripping the case in one hand and the bullet in the other and twisting, pulling and pushing. This has been done to maximize rifle precision as I have found it to be a critical loading parameter for precision loads. (Note that while the rifle is somewhat of a "value build", it is capable of good precision excepting the 1st shot flyer issue.) But this is an interesting point to follow up on, and I will load the next batch of ammo with both the same and tighter neck tensions to compare and I will report results. As stated earlier, I will also vary gassing amount to determine if there is any effect.
Thanks again to all those posting ideas.

Adjusting gas hasn’t helped my issue. I’m going to run a small test amount in my Lee factory crimp just to see the effect. Another thing I have read was on a custom bolt rifle is that after the rifle sat a minute to cool for the next group but still warm he noticed if he ran a patch or bore snake down the bore the problem went away. Something to the effect of the powder fouling sitting in the bore fluffed and shot one smoothed it out then the remaining shots went as they should. If he ran a few dry patches or bore snake it did the same thing as shot one did and he noticed his problem solved.
I’m not sure as other rifles I have have never had this issue but I’m willing to try.

 

[Rider47]

Found the cause of the problem.
After several range sessions varying just about everything the cause of the 1stShotHigh issue turned out to be the POS AR Stoner bolt. What a POS! The firing pin hole was .070" (should be .058-.060") and was showing pierced primers from not-hot loads and apparently locking up weirdly when fired. Replacing this POS (did I mention that?) bolt with a spare RRA bolt resulted in an immediate disappearance of the issue. Not only that, the rifle shot a .320" 5-shot group at 100 yards! (Don't ask me to ever do that again.) I am now thrilled with my build.