Drastic changes in my 600yd dope in a week?!

[hyl3ridtheory]

Been reading these threads for a while, hoping someone can shed some light on what I have going on!

Rifle: Remington 700 chambered in .308 20 inch barrel/Right 10
Scope: Vortex Viper PST Gen II 5-25X50
Ammunition: Federal Gold Medal Match 168g Sierra Matchking BTHP

So Ive been at this for about a year. Finally shot my first competitions in the past few weeks. I was able to chrono exactly a year ago at my home range getting an average of 2603fps at 70 degrees clear weather. Was able to collect dope throughout the year from 100-600yds at the home range. Everything was working great, was recording all of my data.

4.7mils/600yds at 69 degrees

Fast forward to my first two matches. Of course my first stages are shots at 600 yards. Both matches ended up being hot hot days, closer to 100 degrees. Ended up with an elevation of 4.5 mils to hit 1 and 2 MOA targets. It dawned on me that my DA had changed and after consulting my data book and researching the Lindy Sisk DA articles I was sort of able to confirm what went wrong there and am prepared to work that out next match or venue.

Today is what is prompting this post. Returned to my home range to shoot a couple of 100yd zeros and get out to 600yds. Temp was 72 degrees, 94% humidity, 29.79" and on and off rain. Shot a few groups at 100yds to check zero ended up around .5moa which is about the best i ever do. Worked my way back to 600yds and dialed on 4.7 mils. Now the hits were low! Using the reticle I was able to make corrections and ended up with 5.2 mils elevation.

Now I get it.....temp humidity etc is going to change my elevation but a .7mil shift from the match and a .5mil shift up from the same range, same temp, diff humidity just doesnt make sense to me. What am I missing?!

 

[stello1001]

How many total rounds on barrel and how many rounds since bore last cleaned?

 

[hyl3ridtheory]

How many total rounds on barrel and how many rounds since bore last cleaned?

237 rounds since the last cleaning

Total round count is around 1500 since 2014

 

[TRG65]

if it was .2 or .3 I'd say mirage if one day was sunny and the next was shade. could it be a combo of mirage and da?

 

[hyl3ridtheory]

if it was .2 or .3 I'd say mirage if one day was sunny and the next was shade. could it be a combo of mirage and da?

Mirage would def be a factor for the match days were I had to take some off. It was boiling hot and the mirage was pretty bad at 6-700. It was raining today and I wasnt catching the normal amount that I would have seen.

 

[Deleted member 10043]

Just one of those days. 10" barrel? Really?

 

[hyl3ridtheory]

Just one of those days. 10" barrel? Really?

Typo haha, 20 in

 

[Dthomas3523]

Likely shooter error in data and fundamentals. Combine that with lighting and mirage.

Few small problems stacking to make for one large problem.

 

[doninreno]

Has the rifle maybe been dropped or fallen over with a HARD hit on the scope?

 

[hlee]

Your 100 yard zero looks low...

 

[PAYDIRT]

Your 100 yard zero looks low...

I'm with you.

 

[onetopgun]

Check your action screws. I had a .7 mil jump at 700 yards when the rear action screw on my M40A6 worked loose. Once I loosened both screws and re-torqued rear to front, my zero went back down .7 mil.

Regards

JHC

 

[morganlamprecht]

same lot of ammo since a year ago? and during the match? a 50-75 fps change would put you in your current dope range at 600...not uncommon among various lots of factory stuff

combined with your zero being slightly low, and added in shifts you could incur from sunny mirage conditions vs cloudy rainy...easily COULD all add up if your lot of ammo isnt the same or you havent chrono'd again

for what its worth, ive seen plenty of screwy things on rainy/cloudy days...especially instances where the sun is popping thru the clouds every now and then....seen entire groups of shooters have to adjust .2-.4 up during a light shower...then 30 min later the clouds clear up and everyone is back to normal...just happens sometime...other times shot in heavy rain and seen no effects down range

outside of any of the above, id be looking mechanical

 

[magtech]

I went through something similar this spring. Since I was shooting from reloads I knew that wasn't my issue.

I ended up having to torque my scope to the high end of the torque specs. My scope was slipping ever so slightly.

I also discovered that my Barrel shoots considerably worse after 100 rounds.

It was with a 300WM though.

You could rechrono the rounds just to check something off but your fps would have to be way off... You never know.

 

[fdkay]

Down here where I am, at 600-700 yards, DA begins to play with your dope a lot.
I have seen DA shift between -500 to 2500 ASL in a matter of a few hours.
Our actual altitude is approximately 20 feet.

 

[PracticalTactical]

I'm thinking its box to box variation in the ammo... along with smaller environmental factors.

Not in a match but first chance, I would suggest that you run a Labradar along side and confirm speeds and take that into consideration.

Sometimes even at the match they have one set up somewhere for guys having problems.

 

[1moaoff]

Shooter error possibly and possibly ammo lot and data discrepancy

 

[PracticalTactical]

I was thinking about this while out for my walk last night and I've been wondering about the terrain in the area where this problem occurs.

If its hilly or mountainous, up drafts and down drafts can have a significant effect on your come ups.

I live in a flat farming area and I remember shooting across a valley at a match in West Virginia where there was a head wind so I held a bit high, like I would here at home, but the wind hitting the face of the valley in front of me was actually creating an up draft causing me to hit much higher.

I wonder if something similar might be happening with the Op.

 

[hyl3ridtheory]

Has the rifle maybe been dropped or fallen over with a HARD hit on the scope?

I can safely say it didnt have a significant impact. Stores and travels in a pelican type case

 

[WB300]

I'm sure you've already checked it, but I didn't see it above so....

Cheek/head pressure on the stock. I chased a 1 1/2 moa wandering zero up and down because i was inadvertently changing cheek/head pressure. I THOUGHT i was immune to recoil.

Keep us updated with what you find.