Novice question on trajectory

[pope]

I rarely shoot in the summer heat. In cool temps, my 270 is dead on at 200 yards and 2 inches high at 100 yards, which is I think correct. I went to the range on a warm, muggy day and the rifle was dead on at 200 yards but 5 inches high at 100 yards. What the heck? Same ammo out of same box. These are Remington 270 Winchester Express Core-Lokt 150 grain with a rounded nose.

[Bob33]

Shooter, different bench, diffent ammo. Temperature won't make that much difference.

[b23]

As long as everything with your rifle is the same, I would suspect your POI (point of impact) change is/was caused by the higher ambient temperature.  Most powders are temperature sensitive and as the temp. goes up so will the chamber pressure/s which will spike the fps the bullet is traveling.  This is why long range shooters like to use "extreme" powders because they are less affected by temperature change and that gives them more consistent POI as the temps go up and down.

[pope]

Same ammo. Same range. What about humidity? I can't understand why I was on at 200 yards but unusually high at 100 yards. I was only wearing a T-shirt where typically I'm wearing a coat.

[headshot5]

Did you shoot the 200 yard target first, and then the 100 yard?  There is no reason it would be on at 200 and really high and right at 100.  How many shots?  Just 2?

[Bob33]

Velocity would need to drop by about 800 ft/second to explain that shift due to velocity.

[pope]

b23, that may be the answer. I'm hunting mostly out of tree stands this year (@ 30 yards max) so it's probably not going to matter.

[pope]

headshot, I started at 100 yards. Pretty tight group, just strangely high. It bothered me so I took more than a dozen shots.

[headshot5]

If it was me, I'd run some copper remover through the barrel.  Check how tight the screws are between the action/barrel and the stock, check free float (question: is it a wood stock?).  Then I'd pick up a new box of ammo, and see if the results match between batches (hit up the range in the morning before it get too hot).

If this does not clear it up I'd be looking at the scope.  I'd either run a box test, or swap it out, after making sure the rings/bases are tight.  I don't see the weather affecting it that much to move your impact 3" up and still be on at 200 yards. 

I would not hunt with a rifle that I don't have complete confidence in.           

[rtspring]

No way would temp have that great of effect on said shots. 

[b23]

I just re-read the first post.  If I understand it correctly, your 200 yard POI was unchanged but you were 3 inches higher than normal at 100 yards???

If this is the case, I'm with the others, you've got issues greater than just a temperature change.

My apologies for not reading the first post more closely.   

[pope]

Thanks for advice all. I thoroughly clean the gun every time I shoot. Only difference I can think of is I was wearing a T-shirt. Yes, it's a wood stock with a steel butt. First shot was unusually painful on the shoulder, so maybe I was flinching a little. I'm going early next time and I think I'll replace the steel butt.

[h20hunter]

How about the part about the dozen shots....barrell just get way hot? That could make a big change.

[Bean Counter]

elevation changes affect drop far more than temp

[grundy53]

Was your barrel resting on the sandbag or your fore grip? If it was your barrel then that could explain it..

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