Odd drop issue

[b0nes]

So last weekend i fired my test loads from my first batch of reloads. Started at 69 grains and worked up to 71 grains which is that max load listed for 270 WSM and retumbo with a 140 accubond. 71 grains was the best load by a slight amount. The range i was at only went to 200 yards and i shot approximately a 1.5 inch group at that range. This weekend i went out to a different local range that allows you to stretch a rifles legs out to 1000yds. From everything i have read i was working off a dope sheet that would put me about 3200 FPS per the reload data i found with retumbo, BUT at 600 yards and that speed i should have needed to to use 8.9 moa with a 200 yard zero at 600 yards. I had to back it all the way off to 7 moa to hit the target at 600 and i had a spotter and that put me right on for elevation at that range. Im using a nightforce shv sfp with no turrets. Is my reticle that far off or am i running wayyyyy faster than i should be? I punched into my calculator 3400 fps and it was still to slow to account for 7moa at that range. Also today was raining and got all my gear wet but i did have a slight amount of stiff bolt lift but did not last weekend when it was dry. What gives?

 

[Harvey_NW]

200 yard zero, reticle holdover, generic dope sheet, and using velocity per load data paints a pretty clear picture to me. My first suggestion would be to fine tune that zero at 100 and make sure all of your inputs are correct. Then make the numbers match the physical ballistics. Shoot groups at 300 and 600, adjust values accordingly.

 

[Pro953]

If you are just looking at the velocity estimates in the book you could we WAY off. You would need to run it over a chrono to get a more accurate answer.

If that’s not a option then keep shooting from 300 on out to 1K and build a dope sheet from that. Not perfect by any means but at the end of the day it’s not what the computer says, but what the rifle and shooter can do.


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[willfrye027]

1) get a 100 yard zero, 5-10 shot aggregate. Being off even slightly at 100 yards throws your drop data wayyy off. More that you would expect. Your 100 yard zero should have the bullseye obliterated..that’s how you know it good enough!

2) shoot for drops at 600 again and record the actual drop required to get there. If you do not have a chrono, you can use a ballistic calculator at this point to get close enough. If you are within 50fps or so, all your data from 0-600 should line up

All this does not matter if you do not have a perfect 100 yard zero. I do a lot of load work up for my guns and most of my buddies. Its almost always a 100 yard zero issue when the trajectory is not lining up!

 

[Cahunter805]

You have been given some solid advice above especially checking your zero.
3200 with a 140 and Retumbo sounds about right for the WSM.
Did you have the scope on Maximum power? Also why not use turrets?

 

[rootacres]

All good points on here. Also something to look at is what your scope over bore calculation is. How far your scope sits over your bore can change the outputs of a dope chart. It won't be a 2 MOA difference but it will cause a slight change.

 

[nhyrum]

Remember that SFP scopes need to be at a certain power for the scale to be what it says it is. If you change the power, you'll change the scale.

Get a chronograph.

Build your own dope sheet

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[Dioni A]

Just to clear up the earlier mentioned actual 600 yard drop. That's measured drop using your 100 yard zero. Measure from point of aim to actual impact. I have used a 4x8 sheet of plywood with Good results

 

[b0nes]

First of all thank you guys for the replies. My scope is a SFP Nightforce SHV 3x10x42 and yes I was at max magnification. I do not currently have a local range that lets you shoot paper past 200 yards which makes the big piece of paper tactic a lot harder to accomplish due to I personally don't like lobbing rounds cross canyon in the woods when the archery season is in full swing. I also don"t plan to shoot at anything any where near 600 yards this season as i just haven"t shot enough to be comfortable at that range. I would however like to stretch out to 450 if the occasion arises but would obviously like to be way closer. It just seemed odd that 400 was right in there and so was 500 and then 600 seemed to be substantially off. There have been some great suggestions here that i fully intend to try but i just don"t think i will have time before 0ct 10th due to I'm out of Retumbo and Accubonds and cant find anymore. I only have 25 loaded rounds to last me through this season as of now. I've always zeroed at 200 and ran my drops off of that and that is what I did this time also. I shot a confirmation round at that range first before stretching it out and I was 1/2 inch low and windage was pretty much perfect. Could this be a rifle fouling issue? I've never used Retumbo before now and I kind of always used to make a point to never really clean my rifle spotless because it seems to change POI and leading up to hunting season i don't want to have to shoot 10 rounds at the range just for POI to return. Thanks for all the great advice I will try to keep this thread updated when I can shoot some more/find more components. Hopefully in a few weeks I'll have a picture of one of the giant whitetail on the ground I found cross canyon while archery hunting over labor day weekend. Sorry for the run-on paragraph.

 

[b0nes]

Rootacres to your point I did use a very generic 1.5 inches for the dope sheet which I should verify. Nhyrum, I looked at a magneto speed and OUCH! A little pricier than I can afford right now with a newborn, just bought SEAK stormtight gear, boots, and a zoleo. Hopefully I can find some components and I can refine this by spring.