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..

sent from my typewriter

[pope]

On the grip, not the bag. I can't figure out how changes at 100 yards wouldn't also show up (maybe even more dramatically) at 200.

[JLS]

I would check the action screws and the scope mount screws.  Flinching typically manifests itself in shooting low and left for a right handed shooter because you are anticipating and "leaning into" the recoil.  It could be flinching, but I highly doubt that it would cause you to shoot 3" high without some deviation side to side.

I wouldn't even clean it.  Get another box of ammo and reshoot.  Don't worry about temps.  I've shot my AR to the point that smoke was coming OFF of the barrel, and the POI didn't change any significant amount.

Is your barrel free floated, or does it have a pressure point?

[Don Fischer]

So what was the group size's at each range? I can't see how what happened could happen. Nothing changed in the ammo at all that you know of. even if it had, it would have also shown up at 200yds, not just 100yds. Even if the action screws were loose or you encountered some new bedding problem, both ranges would show the change. If it was the scope, same thing. Change at both distances. You can run a box test on  the scope and all that will tell you is if your adjustment's are working well. I think most don't really do all that well but unless your using a scope with turret's, it doesn't make that much difference. If something was going on in the scope that caused the change, it would do the same at both ranges. Now if it is a much older variable, POI was known to change going up and down through the power setting. Possibly that could be happening to you but it would require changing the power setting at the different ranges. Even then the difference shouldn't be three inch's.

No offense but I believe I'd check out shooter error. That's what it sounds like to me.

[biggfish]

Do you usually shoot on clear days when its cool?  If that is the case a muggy day is usually cause from increased barometric pressure and that will play with bullet travel

[Don Fischer]

Do you usually shoot on clear days when its cool?  If that is the case a muggy day is usually cause from increased barometric pressure and that will play with bullet travel

Problem is it changed at 100yds but not at 200yds. It would change at both ranges if it were most anything other than shooter error. Keep in mind, it only changed at one range, the other had no change.

[JLS]

Do you usually shoot on clear days when its cool?  If that is the case a muggy day is usually cause from increased barometric pressure and that will play with bullet travel

Problem is it changed at 100yds but not at 200yds. It would change at both ranges if it were most anything other than shooter error. Keep in mind, it only changed at one range, the other had no change.

It also isn't going to change it several inches.

[mazama]

Having had the same experience i was going to post about it,this is a common problem that happens to many people,by changing the position of sand bags or putting soft rest under gun at one range,then hard rest will change poi,i used sandbag at 200,switched to pillow rest at rear shot at 300was high,went back to sandbag group moved 4in down.Try an expermint,use a coat or pack for a rest then shift to sandbags.

[pope]

I appreciate all the comments and suggestions. I agree with Fischer that shooter error is likely. Nothing else seems to explain. Maybe it was an off day. I've been solid with fairly tight groups in the past. My groups were a little wide left to right but on vertically. I'm shooting a Remington 721 which probably dates to the late 1950's or early 1960's. I'll look into all the suggestions and straighten this out. Could be I need less scouting and more trigger time. Thanks again.

[Fl0und3rz]

More trigger time in any event.  My guess would be inconsistent hold between the 100 and 200 groups.

[Jolten]

Question are you using the exact same bullet? Type/construction/ grain as in your original set of grouping?

[OnHoPr]

Other things to consider. Did you change x power on the scope when you changed distance, some variable power scopes can change POI if the x power is changed. You mentioned that you shot at the 200 yd target first and then went to the 100 yd, if you didn't let the barrel cool down your point of impact could have changed. I had a 06 760 that after 3 shots would move POI about 3" to the 4:30 position on the target but a lot of times you will get walking up on your shots. You mentioned factory ammo which is only 20 rounds to the box. If you opened another box for your shooting the it is possible that the cartridges weren't from the same lot. One box could have been loaded with 760 and the next with another powder or different charge weight. Possibilities of mirage and bright target (bright sun) or cloud cover or shade could of cause an issue as well.

[Alchase]

Scope rings nice and tight?

[pope]

My neighbor is offering to help. Heck of a nice guy, and although he doesn't brag about it, I found out he had some kind of sharp-shooter designation in the Army. This summer he was desperate because a scope he ordered through e-bay didn't arrive and he was supposed to leave the next day for an Oregon prairie dog hunt. He went to Walmart and bought a (don't laugh) $20-dollar scope. He mounted it to the semi-auto 22 he's had since age 16, and we went to a gravel pit on road 70 (White River). He dinked around with it for 20 minutes, then set up 5 empty shotgun shells on a sawhorse at 50 yards. He took 5 shots in 10 seconds and hit four. That's when I got him to admit he's had some serious training.

Anyway, he's going to help me make sure everything is tight with the scope and gun, then we're going to find out if it's me or the gun. We're both going to shoot it to see if we can produce a tight group. Great to have a good neighbor and good friend.

[Bob33]

I'll bet good money he won't be able to reproduce your results.