Excessive bullet drop

RobG

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I need to go back out to the range but this is haunting me...

Last night my rifle was 1.5" low at 200yds and 20" low at 300yds. I don't remember what it was at 100yds - ball park +1.5".

20" is way too low. The box says -8.4" if zeroed at 200yds. My Federal ballistic chart says it should be -11.6" if drop is -2.3" at 200yds.

I'm shooting 180gr Barnes VOR-TX tipped TSX BT 30'06 factory ammo. The gun is a 1939 Savage bolt action, 24" barrel. It was cleaned by a gunsmith. I shot 6 normal jacketed bullets to foul the barrel and this was after about 15 shots with the the all-copper TSX bullets.

Why would it be so much lower at 300yds?
 

npaden

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Completely anecdotal, but if you are 1.5" high at 100 yards it shouldn't already be 1.5" low at 200 yards should it?

If I'm 1.5" high at 100 with my 7 mag I'm dead on at 200.
 

RobG

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Completely anecdotal, but if you are 1.5" high at 100 yards it shouldn't already be 1.5" low at 200 yards should it?

I agree, it seems to be dropping off even at 200yds, however I was a tad low at 100. The ammo specs say it will be zeroed at 200 if +2" high at 100yds, still, I would think 0.5" low at 100 would translate to -1.5 at 200yds.

Would a "worn out" barrel do this? Copper fouling? I was thinking my groups would spread out from those. The groups at 100 are about 2".
 

Mthuntinfool

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Are you still good for windage? If they are all over there is the possibility that the throat might be burned out. If they are only low, there is the possibility that they were under-charged at the factory. Just my thoughts...
 

cowboy

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You either have some really poor factory ammo (which I doubt), you've got something loose (bases, rings, etc), you've got a bad scope, you've got a rifle with a bad throat/rifling or the nut behind the bolt pulling the trigger had a bad day. I would double check all your mounting screws etc to make sure nothing is loose and then try it again. You may also want to double check the srews in your stock to makle sure you have proper tension on them holding your barreled action.

FYI: I have found with many rifles that mixing different bullets after a thorough cleaning of the barrel is bad joo joo. Different bullets have different consistancy in copper, hardness, shape and dimensions and some bullets will have more or less tendency to fowl a barrel as is travels down the tube in a differnet way than another. Once you fire a number of Brand A bullets down a barrel and then switch to Brand B bullets that is where true accuracy can have some effect. Keep in mind that this has been proven many times by the bench rest shooters - but then again they measure accuracy by how big one hole is on the target.

I do not know how many rounds have been down your barrel but I know a guy that is pushing 8000 rounds down a .308 and he has to fire at least 5-8 rounds after a thorough cleaning to get that rifle to settle down to the accuracy he is accustomed to.

Good luck - things can be frustrating at times with any setup.
 
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300stw

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chronograph the bullet and then look at the ballistics ,,,
 

RobG

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Are you still good for windage? If they are all over there is the possibility that the throat might be burned out. If they are only low, there is the possibility that they were under-charged at the factory. Just my thoughts...

Windage was pretty good, see the attached. My group is the 4 shot with big holes below the 2nd target, plus the one at -4.5U,2L of 2nd target. I was aiming at the top diamond. The holes are large because I had a board holding up the target and the shots were through that board. The shot in the far bottom left was there previously.

I also wonder if it was the ammo not being up to spec. I hope the next time I get out to the range the guy with the chrono is there...
 

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Gr8bawana

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It's very unlikely bad ammo. I would check everything suggested by the other posters.
 

npaden

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That's a really good group at 300 yards I think. Good thing you made an extra tall target or you wouldn't have even seen them hit the paper!

That really doesn't seem like a loose scope or anything like that to me.

I have a friend that just picked up a box of .30-06 factory shells that were smoking out at 3,100 fps when they were supposed to be shooting at 2,800 ish. Maybe he got your extra powder?
 

Mthuntinfool

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Unless your scope mounts are loose, or your scope got knocked off, I would lean towards it being the ammo. Do you have some other type or brand you could run through the rifle to check and see what the results are? That would be the easiest thing to check first, and then get more in depth if it doesn't solve the problem.
 

npaden

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I shot with a friend with a chronograph this weekend and my shoots averaged 3,160 fps when the specs say they should be shooting 3,200 fps. Pretty close and some actually ended up at 3,210 as the barrel warmed up. The first shot was the slowest at 3,115 fps.

No idea what that means to trajectory, I was shooting at 100 yard paper.
 

belly-deep

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Shoot it over a chronograph.

Also, do your ballistic calculations with actual data, not "what is on the box" because there's a world of difference between the two.
 

Southwind

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1.5" low at 200 yards with that load and bullet your 300 yard drop should be 10.4"
2700 fps/ .484 bc 180 grain ttsx

At 20" low his velocity would have to be only 1800 fps with this bullet
 
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RobG

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1.5" low at 200 yards with that load and bullet your 300 yard drop should be 10.4"
2700 fps/ .484 bc 180 grain ttsx

At 20" low his velocity would have to be only 1800 fps with this bullet

That's crazy for ammo to be off that much, but it doesn't sound like it could be anything else except shooter error. If it were 400 yds it would explain it but I'm sure the target was 300 yds. I guess I'll have to recheck with different ammo and bring out the lead sled.

Thanks.
 

Bambistew

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Could be a miss-aligned scope... meaning the scope is not parallel to the bore. Your smith might be able to see the miss alignment, not sure how though. It could be out of alignment 1.5-2" at a 100 yards and mess you up that much at 300.

Shoot through a chrono, and sight in for what the expected drop is at 300, and then see where it hits at 100. I have a rifle that is slightly miss aligned. Changing the POI at 100 about an inch set me up where I needed to be at 300 for the expected drop.

Another option is to get a set of burris rings with inserts.

Not uncommon... the bore may not be in the center of the barrel. I highly doubt its slow ammo. The difference in drop would have be signifficant velocity loss to get that far. Assuming the point of aim is the same in relation to the bore at each range is a poor assumption.

Good luck!
 
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