Help diagnosing low shots at 600yds

[VA_XTC_Shooter]

brand new optic. I find it very odd that the optic would only have an issue 3 times over the whole week and only in slow fire prone. Also, the off call shots formed about a 1.5-2 moa group, just 5-6 MOA low. I would think if the optic was failing I would a) see it in other courses of fire and b) it would not bounce 5 MOA low, back to center, then back to 5 MOA low a few shots later, if at all.
Maybe I dont understand optics though.

 

[JFrank]

Maybe someone cross fired on your target

 

[rwj]

brand new optic. I find it very odd that the optic would only have an issue 3 times over the whole week and only in slow fire prone. Also, the off call shots formed about a 1.5-2 moa group, just 5-6 MOA low. I would think if the optic was failing I would a) see it in other courses of fire and b) it would not bounce 5 MOA low, back to center, then back to 5 MOA low a few shots later, if at all.
Maybe I dont understand optics though.

Could scope parallax be a factor?

 

[memilanuk]

Could scope parallax be a factor?

No

 

[VA_XTC_Shooter]

Cleaned the BCG, focused on the portion where the firing pin goes, rear cavity.
Also replaced firing pin. Tough to get exact measurements with calipers, but appears the new pin is slightly longer.

 

[rwj]

No

If the scope parallax is fixed at a significantly different distance than that being shot, why not?

 

[chkunz]

If the scope parallax is fixed at a significantly different distance than that being shot, why not?

The maximum parallax error possible is much less than the error observed. The error observed is no small thing. It is a major error.

 

[memilanuk]

The maximum parallax error possible is much less than the error observed. The error observed is no small thing. It is a major error.

Bingo

 

[rwj]

The maximum parallax error possible is much less than the error observed. The error observed is no small thing. It is a major error.

What would be the maximum parallax error possible in a scope with its focal plane fixed at 100 yards when engaging a target at 600 yards?

 

[Average joe]

I don't know your loading procedure, but I have on more than one occasion, had powder "bridge" in my funnel, and not fill the case... I did not catch it till I over-filled my next case.
If I had set that funnel to the side, I may not have caught it.

 

[big john 5394]

I was scoring for a guy he was shooting a 223 bolt gun all 10&x and then a 6 it was 125fps slower the the other shots and then it happened again slopping loading might have bumped the case and knocked sum powder out.

 

[Park ranger]

So Jeff says he weighed cases and didn’t see the difference show up. Could be a stacking error, 2 grains lite on powder in a 2 grain heavier case?

I’ve heard bullets getting mixed up from time to time. Possible a 70 vld found its way into a 75 vld Box???? Unlikely, but run jbm to see. Gary is probably right it’s in the optic or mount. Get it fixed before the Maryland Championship!

Roy

 

[ppaul]

brand new optic. I find it very odd that the optic would only have an issue 3 times over the whole week and only in slow fire prone. Also, the off call shots formed about a 1.5-2 moa group, just 5-6 MOA low. I would think if the optic was failing I would a) see it in other courses of fire and b) it would not bounce 5 MOA low, back to center, then back to 5 MOA low a few shots later, if at all.
Maybe I dont understand optics though.

I'd get 2 or 3 boxes of cheap ammo, ex. frontier 75 gr hpbt, shoot it at 100 yd same as you'ld shoot 600. Single feed. If it's your optic it ought to show up.

 

[rwj]

I'd get 2 or 3 boxes of cheap ammo, ex. frontier 75 gr hpbt, shoot it at 100 yd same as you'ld shoot 600. Single feed. If it's your optic it ought to show up.

I’ll add when the shooter switches to the 600 yard target that he moves his head relative to the scope ocular lens and observe if the reticle’s aim point is “moving” on the target.

 

[Whit holman]

I am no expert but I think park ranger got this even though the off shots are low there
Inline. Got to be bullet weight.
Do you have any kids grandkids wife

 

[VA_XTC_Shooter]

I don't know your loading procedure, but I have on more than one occasion, had powder "bridge" in my funnel, and not fill the case... I did not catch it till I over-filled my next case.
If I had set that funnel to the side, I may not have caught it.

dispense each case with chargemaster.
visually inspect case to see powder in case
move to press, under powder cop, again another powder check
seat bullet
check final weight of cartridge to look for any outliers, low powder load, etc.

It would take a lot more than 1 or 2 grains less powder to drop 30" at 600 yds.

 

[VA_XTC_Shooter]

I’ll add when the shooter switches to the 600 yard target that he moves his head relative to the scope ocular lens and observe if the reticle’s aim point is “moving” on the target.

scope has adjustable parallax and I have it set to where there is no movement with head movement

 

[VA_XTC_Shooter]

I’ve heard bullets getting mixed up from time to time. Possible a 70 vld found its way into a 75 vld Box???? Unlikely, but run jbm to see. Gary is probably right it’s in the optic or mount. Get it fixed before the Maryland Championship!

Roy

If a 70 was snuck in my 75s, wouldnt it be going FASTER, not slower than the 75, thus not dropping? I guess potentially an 80 VLD?? Damnit if I have to weigh each bullet for service rifle, im going to be pissed

 

[memilanuk]

If a 70 was snuck in my 75s, wouldnt it be going FASTER, not slower than the 75, thus not dropping? I guess potentially an 80 VLD?? Damnit if I have to weigh each bullet for service rifle, im going to be pissed

Nope. Lighter bullet would go faster... but you'd typically have more powder under the lighter bullet to make it do so. Lighter bullets usually have shorter bearing surface, and don't build as much pressure for a given charge weight, etc. etc.

If you had a heavier bullet over the same charge as you normally use, you'd have the opposite - longer bearing surface, more resistance... and a huge pressure spike, and probably blown primers at a minimum. It'd probably be slower than your normal 75 gn load... but not that much slower. Pretty good chance you'd know it immediately if you had one like that.

TBH, the only time I saw something like this in a match was at a local match and a varmint hunter friend showed up with his .25-06 AI. Every once in a while he'd go from nailing the 10/X, to nerfing one straight down into the 6/5/M range. I did watch his trace on a few of those shots... they were doing some sort of weird cork-screw pattern into the target, not a straight path down the middle. Best guess at the time was he was either over driving the bullets or had a barrel going south, and had borderline jacket failure. How/why that didn't translate into a more random dispersion pattern, I don't know.

Might be worth cleaning your barrel very, very well, and finding a friend with a borescope...

 

[VA_XTC_Shooter]

Might be worth cleaning your barrel very, very well, and finding a friend with a borescope...

Cleaned rifle after the first day with the odd shots, have a bore scope and barrel looks fine. Less than 1K rds on the Krieger.
The odd shots are only happening at 600, which is a different load than my short line. So I feel it is not a gun issue, but ammo issue.
I'm leaning toward poor primer ignition. Would be odd to have 3 primers go south, when I have already shot about 300 of them with no issues. Perhaps I somehow contaminated those three with some oil or something??