Explain this

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cdoc42

New member
This sounds so crazy I'm ashamed to post it but I think MAYBE someone will have a real explanation.

I have a .270 win that shoots a 150gr Hornady Spire 1.5" high at 100 yards, dead on at 200 yards and 6 inches low at 300 yards. During two separate trips to the range, under different circumstances everything is the same except the point of impact at 300 yards is 6" low and almost 9 inches to the right. The first trip I thought was caused by the wind, even though it was still dead-on at 200. The second trip there was negligible wind (defined by wind flags). I took more than one rifle and my 6mm PPC, .300 WSM and .270 WSM did not display this problem, so I figured that eliminated me as the problem.

any thoughts?
 
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Edward Horton

Moderator
What length barrel do you have, you are approching the 3200 fps range if your trajectory figures are correct and loading over maximum chamber pressure.

A .270 Weatherby Magnum with a 26 inch barrel can only hit 3000 fps with the 150 grain Hornady.

Maybe your bullets are melting from the super warp speed velocity. :rolleyes:
 
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Jim243

New member
If Scorch is correct, you need to get a bubble level that fits on your scope. It makes the most sense. Or check that the scope is not slightly off on the 270 Win.

Jim
 
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Mal H

Staff
First of all, let's clarify what you are saying: your .270 Win is dead on horizontally at both 100 and 200 yards, but unexplainably shoots 9" to the right at 300 yards? This is with rounds from the same loading session using the same load for all?

How many shots are you shooting for each group at each distance?

As Edward Horton pointed out, it certainly looks like you are achieving velocities with that bullet in that caliber that are next to impossible. I used Sierra's Infinity program, and it determined that you would have to be getting somewhere in the range of 3200 to 3300 fps to get the vertical drops you are reporting. Something's not right.
 
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Edward Horton

Moderator
Mal H

Question: What is the purpose of starting at 10% off of max

cdoc42 wrote below:

Your chamber size, the seating depth, bullet shape and length, type of primer, type of case, all play a part. I suspect the -10% recommendation was made by someone along the line who writes for the mags and had a really bad experience and it just got carried along.

After 34 years of reloading I just adopt the position that I can start a grain below max and work up in half-grain increments, but I still "chicken-out" and don't use the max until I'm sure the lower charges are ok. So I start a half-grain below max as my top load and make 2 others at 0.5gr below each. If I don't get a good group I'm more likely to play with seating depth because, as pointed out here, velocity is not always synonymous with accuracy. I had one load that was obviously an overload in a 7mm Rem Mag with a 110 grain HP. The bolt just could not be lifted without a rubber mallet. No other problems, but that was using my system of increasing charges as described.

http://thefiringline.com/forums/showthread.php?t=429510
 
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cdoc42

New member
Thanks for all the replies. Let me clarify a bit. This load is not new; it was developed by me last year and I have not had any problems with extraction, primer pressure signs, etc. The next chance I get I will chronograph it. I was just shooting the rifle and load while others cooled down as I planned to take it on a Canada deer hunt.

I sincerely doubt if I have the 150 gr bullet traveling 3200 fps; it has not been usual for me to get 130 grain bullets faster than 3000 to 3100. I'm using 56 grains of H4831, a CCI 250 primer, Remington case with the bullet seated 0.015" from the leade.

Nerxt chance I get I'll check speed and pay attention to possible canting.

Thanks again.
 
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Jim243

New member
My personal guess is that your mount srews have lossen up a bit. That's what happen to me on my 270 and wouldn't show up untill the barrel warmed up a bit. Drove me crazzy trying to figure it out.

Jim
 
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Brian Pfleuger

Moderator Emeritus
I'm not sure how a problem with the scope could cause a 9" drift in only 100 yards from 200 to 300.

If the scope was loose, I'd expect erratic accuracy at at all distances. You might be right on one shot, left on the next and center on the next. Or, it could have shifted and remained so but....

If you're 9" off at 300, you'd be 6 at 200 and 3 at 100.

I can see no good explanation for being (consistently) off at one distance but accurate at other distances. If it were erratic, I'd suspect stability issues but an unstable bullet is no going to go the same place shot after shot.

On the question of trajectory that doesn't match the numbers, or suggests an unsafe pressure, I have personally found, in EVERY instance, that my bullets fly flatter than any ballistics calculator would suggest. MUCH flatter.
 
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Archie

New member
I once had a .22 long rifle ...

... that changed windage correction as ranges varied.

After some examination (over a good deal of time and much foul language) I found the scope was mounted a little cock-eyed. The scope and the barrel were not parallel.

Just a thought. Good luck.

I've also had more than one rifle that changed shot registration in the horizontal plane as I increased the powder charge. That does not seem to be the case here. Again, just a thought.
 
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bullspotter

New member
I would check the scope and bases, also watch your level on the gun. Dose your scope have a paralax setting? you may just not be sitting on the gun the same time every shot. it will get worse the farther away the target is, Also I looked at your load data and seems pretty close, your load should be about 2840 fps, 1.52 high at 100, zero at 200, and 6.73 low at 300. According to my books anyways.
 
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cdoc42

New member
Mal H, since this was an established load that previously performed accurately, I was just shooting for fun to cool other rifles down. As such, I started a shot at 200 yards, noted it was still dead-on, then moved to 300. After about 3 misses I began using the thick portion of the horizontal reticle as my sight post (after compensating for drop) and, sure enough, I'd hit the target.

Someone asked about barrel length. If I measure from the muzzle to where it screws into the action, it's 22 inches. A factory barrel.

I may get a chance this weekend to go out again. I'll pay attention to canting, parallex. Just for information, I also set the rifle in exactly the same location on the rest and make sure the rest is in exactly same position as the previous shot.
 
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Jim243

New member
Peetza

Loose "base" srews act differently than loose "ring" screws. Becase of the shape of the top of rifle often bases will come back to true center from shot to shot. A 9 inch vaiance is only 0.025 degrees off from true zero at 100 yards and 0.00833 at 300 yards. I agree with you that one would think you would be consistantly off at 200 yards as well as 300 yards, but life doesn't always do what you think it would. It could be something else, but since it is a simple check, it should be the first thing checked.


Jim
 
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