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velocity to low

 
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  #1  
Old 06-23-2013, 10:33 AM
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Join Date: Jun 2013
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velocity to low

hey guys, I just posted over in hunting about this but thought it might get more attention here. Long story short, Im loading for a 7mm rem mag. I have no chronograph so I estimated my mv to be around 2950. Shot at 550 yards dialed in 7.5 minutes and was hitting 9 to 10 inches low. Dialed up to 9 minutes and hit. Im loading 66gr H4831sc over a 168gr berger vld. My scope height is 1.75 and at 100 yards my group (.181) was around 2.18 inches high. I am kinda disappointed bc I was hoping to be right at 3000 fps. but it seems im not even at 2800 fps. Anyone have any ideas as to whats going on? Thanks
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  #2  
Old 06-23-2013, 10:49 AM
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Join Date: Aug 2006
Location: Missouri Ozarks
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Re: velocity to low

Could be a lot of things, book velocity is often not even close. I don't know how you got your estimate but there are a lot of variables that come into play. Even 2 identical rifles will have different velocities, sometimes considerably different. For any serious shooting or load development I consider a chronograph a requirement.

Bob
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  #3  
Old 06-23-2013, 11:37 AM
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Join Date: Jun 2013
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Re: velocity to low

Thanks for the reply Nimrod. My manual only list 65 gr of 4831 and 170gr bullet at well over 2800 and it doesn't list barrel length so I was hoping my velocity would be higher but I guess not. I know I need a chronograph but its just one of those things I haven't got around to buying. Ive been looking at reviews on different ones and am scared to buy anything really. Just about all of them have a bunch of bad reviews so I don't know which one to go with. Do you have a recommendation? Also would anyone recommend switching powders. I like the temp stability of the 4831 but it was just leftover from another gun I loaded for and im almost out of it. So now would be a good time to switch if I need to. I was thinking about Retumbo possibly. I know velocity isn't everything but you would thing with a magnum I could at least hit 2900.
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  #4  
Old 06-23-2013, 01:19 PM
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Re: velocity to low

A book will get you close but you can't count on the velocity across different rifles. A crony would be nice but if you know what the drop is you can use that to figure out what your velocity is. What book were you going by? If I get a minute I will see what bergers book has listed.
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  #5  
Old 06-23-2013, 01:29 PM
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Join Date: Aug 2006
Location: Missouri Ozarks
Posts: 420
Re: velocity to low

The Oehler 35P is the best chronograph IMHO. I had a Pact that worked great for several years and then it quit. Now they refuse to make good on the lifetime warranty. They have had it for nearly a year, their solution was to offer a 30% discount on a new unit, so the warranty is worthless . I'm saving for an Oehler now.

There are several powders that will work in the 7MM Magnum among the ones I have used are H4831, IMR 4350, IMR 7828, H1000 and Retumbo.

Good luck in your quest!
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  #6  
Old 06-23-2013, 02:40 PM
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Join Date: Jul 2011
Location: Near Napoleon,MI
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Re: velocity to low

Apologies I listed a 300 Rem load....

Since you are using Hodgdon powder, why do not use their data from their online web site ? Cartridge Loads - Hodgdon Reloading Data Center - data.hodgdon.com Based on their website, a minimum powder charge is 60gr with a max at 64. At 60gr 24" barrel the velocity is listed at 2731fps and at 64gr it is at 2871fps.

How did you do your load development ? Usually one works up until you start seeing pressure signs, then backs down. Also check the listed cartridge OAL, usually if it is listed then it is a Sami value, you may be able to load longer which will reduce pressure if your throat allows it.


162 GR. HDY SPBT Hodgdon H4831 .284" 3.290" 60.0 2731 43,300 CUP 64.0 2871 49,800 CUP
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  #7  
Old 06-23-2013, 02:47 PM
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Location: Near Napoleon,MI
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Re: velocity to low

It looks like Retumbo may be good for 100fps more. If you can load longer, might be good for even more.
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