Heat mirage and hot barrel on accuracy

[broadhead]

Ok so I'm new to "precision" shooting and even though I've lived in southern Arizona the last four years, it wasn't until this year that I decided to get back into rifle hunting. I had a weird thing happen on Sunday while I was alternating three shot groups between 143 grain ELDX and 147 ELDM from my 6.5 PRC off the bench out to 200 yards. The ELDX, which has consistently grouped around .6 MOA at 100 yards suddenly started going all over the place. The ELDM on the other hand grouped very well, keeping under 1 MOA. The only thing that changed was since I started shooting the mirage had become much worse and also the sun had moved around to the front of the range so that the barrel was in the sun the entire time. I did not shoot a final group with the ELDM after the sun moved around and the mirage got bad, which might explain why I didn't see the ELDM groups go south too. One thing about the erratic group was that all the rounds ended up between 2.5 and 3 inches high and were spread out left and right, which is also uncharacteristic for that rifle and cartridge before now. I've read mirage can cause shots to go high and drift and a hot barrel can cause all kinds of accuracy problems but I'm wondering if the conditions would account for such a big deviation in accuracy.

Can anyone with experience shooting in these conditions shed some light on what was going on? Thanks!

[10Turkeys]

The first question I would ask is what kind of magnification do you have on your scope? If it is relatively low you were probably picking up heat mirage off your barrel. Warm day, warm barrel and you keep putting rounds down range probably not the best for shooting good groups. If you have a scope that has a lot of magnification, you could be picking up barrel heat and mirage down range. On a hot day let the barrel cool and turn your magnification down. If you are seeing mirage down range and the waves are going straight up, you are seeing what's known as a boil, most competitive shooters if they have time will wait for the mirage to start moving one way or another before they fire their round. Mirage can be a good indicator of what the wind is doing with a bullet on its way to your target. Some people read the mirage at their target, but doing that your bullet is already there. I usually try to read it about half way to the target. Long story short the mirage off your barrel could have messed with your group, shooting a high BC .264 bullet probably didn't affect your group too much at 200, unless the mirage was bouncing around left right and if you shot in a boil. Just my two cents.

[recurveman]

What contour barrel are you shooting.   The thicker the barrel the less the heat will change your POI.   I notice that after about 6-10 shots I start to see heat coming off of my barrel and typically I stop shooting and let things cool off (I have time and don't need to keep shooting).   My father in law shoots F-class and they put a material about 2" wide that goes down the length of their barrel.   Kind of looks like a mini blind that they velcro to the barrel to stop the heat from going up and looking at it through their scope.    The heat is still there but they can still see good.   

Learning how to read the mirage is super helpful.  If you want to read the wind at distance it is a must to learn.    There is a difference between the mirage off of your barrel and the mirage between the shooting line and target.   

If you have time just let your gun cool.   If you don't have time then put a cover over your barrel.    

[10Turkeys]

If anyone is interested in learning the basics of shooting in conditions this book is a good place to start. Also pick up a couple tips on shooting! His web site has these books about 10 bucks cheaper than Amazon. He has another book also, but I found that it's more about selling his rifle than shooting.

[broadhead]

Thanks for the feed back, fellas. To answer a couple of the questions I have a 3.5-18 scope and it was all the way up so yes, the magnification was high. Thanks for the info, too. I didn't really appreciate mirage and hadn't even thought about mirage off the barrel but now it seems pretty clear there were a few things at work that were influencing a normally very consistent shooting gun. I think the thing to do is to make a point to get out and shoot when it's still cooler and try to eliminate as many variables as possible. This makes me feel better about things.

[lancetkenyon]

Mirage has no impact on barrel accuracy.  But it makes a huge impact on perceived POA.  Mirage will cause your aim to wander greatly, seemingly causing errant shots, when in actuality, it is just Point of Aim issues.

Light direction can cause this as well.

Hot barrels can and will definitely cause shots to walk.  I usually only shoot 3 shots in 30 minutes or so.  When at the range, I always have 2-4 rifles I alternate 3 shot strings between.  Let the barrels "cool" (relative term if the barrel is sitting in direct sunlight in 113* temps) between 3 shot strings.  I shoot almost every weekend, and it takes me 5-6 hours to shoot 12-18 rounds in each of 3 rifles.  I see guys all the time shooting 40 rounds in an hour and wondering why their groups suck.  Well, when you shoot 20 rounds in 15 minutes, yeah, POI is going to wander.  Let alone the mirage from the barrel screwing with POA.  

[broadhead]

2 hours ago, lancetkenyon said:

Mirage has no impact on barrel accuracy.  But it makes a huge impact on perceived POA.  Mirage will cause your aim to wander greatly, seemingly causing errant shots, when in actuality, it is just Point of Aim issues.

Light direction can cause this as well.

Hot barrels can and will definitely cause shots to walk.  

This is exactly what I was thinking and I think I did a poor job of explaining it in my original post. Based on what you guys are describing I suspect what happened was a combination of the perceived POA and the rounds freaking out because the barrel was getting hot at the same time. A few weeks ago I was running out of time and wanted to plug a few more shots to end my day. I fired multiple shots from the prone with a bipod and squeeze bag at 100 yards - well executed shots too - and they were all over the map.

Thanks again for all the input. This is all very valuable information to me!

[broadhead]

Well, this was disappointing. I guess I'm at the point where I can't trust the 143 ELDX as far as accuracy past 200 yards, at least until I see what happens at 300 when I can get to the longer range. But based on what I've been seeing at 200 I can't be optimistic.

This morning I got out earlier and was shooting by 8:00 am to beat the heat. Little to no mirage and I waited about 4-5 minutes in between shots while keeping the barrel in the shade. Top target below is ELDX, bottom pic is ELDM. Three shots ELDX in 15 minutes, 10 minute break, three shots with ELDM and did that twice. Only six shots with each load total. The pics say it all. It should be noted that the shots outside the 2 inch orange on the 147 grain were 100% my fault. I'm hesitant to use the ELDM on my mule deer hunt but from what I've ready even though Hornady doesn't recommend it the ELDM does just fine on deer sized game, especially with the added velocity from the PRC. Looks like it's time to finally start playing around with some hand loads until a few more PRC rounds hit the market and I can find out what else this rifle likes.

 

[PRDATR]

So is one target ELDM and the other ELDX?

[10Turkeys]

If they were grouping and now there not, something is wrong. I would check all the screws, action , scope rings and bases.

[broadhead]

4 minutes ago, PRDATR said:

So is one target ELDM and the other ELDX?

Smaller group is ELDM, shotgun spread was ELDX.

Turkeys - that's the problem. The two targets shown above were three shot groups alternating back and forth between the 143 and 147 respectively.

[recurveman]

I've shot the 147 ELDM, 143ELDX, 140ELDM all the same time with the same powder charge.    All shot well under MOA out to 1000 yards.   All of those bullets will do their job if the load is right, gun is right and the shooter does their part.   I worked up a load this weekend for the 143's that was crazy.   Basically it took 8 shots before I didn't hit the bullet hole of the previous shot at 100 yards.   

If you had good groups and now you don't have good groups something changed.   Either with your loading or your gun.   Something changed.   I've shot the 140 ELDM's at deer and I will not shoot that bullet at deer again.   It didn't perform well and took multiple shots to kill the critter and that happened to multiple deer.   I've seen good results with the ELDX on deer.    The ELDX bullets will perform great once you find the right load and it should be very, very close to the same load as the ELDM's.   

[10Turkeys]

When was the last time the barrel was cleaned with some sort of copper removing agent?