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 Post subject: Rem 7 mag
PostPosted: Sat Jul 27, 2019 4:29 pm 

Joined: Thu Jul 25, 2019 6:17 am
Posts: 2
New to this forum and have a question on Chronograph testing. Im shooting 160 gr.accubonds 59grs.IMR4350 cci magnm primers out of a model 70 winchester. With a 5 shot string and letting barrel cool down 10+ minutes in between shots I got.278.3 279.3 277.0 279.3 280.4. The Nosler 8th edition says my muzzle velocity should be 2943 +. Is this normal first time I had any of my rifles chronographed. Thx for any replys. (y)


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 Post subject: Re: Rem 7 mag
PostPosted: Sat Jul 27, 2019 4:37 pm 

Joined: Wed Nov 08, 2006 2:49 pm
Posts: 32113
Location: Northern British Columbia
Welcome to the forum. Not at all unusual to witness such disparity. To achieve parity with published data means that all components are identical (or nearly so). The disparity you note can be accounted for by differing lot numbers of the various components, differentials in barrel specs between your own firing system and that employed by Nosler. etc. To achieve the extra one hundred fps (or so) that would match the published data, you can try to gently up charge weights, watching for pressure signs until you reach the velocity you want. On the other hand, if accuracy is there, there is little change that any game you choose to hunt will notice the slight difference in velocities. Again, welcome aboard.

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 Post subject: Re: Rem 7 mag
PostPosted: Sat Jul 27, 2019 4:43 pm 

Joined: Thu Jul 25, 2019 6:17 am
Posts: 2
Thank you Dr.Mike for the reply. Im at 59grs now and the max is 60 so Ill leave it there. When I got home and pulled out the Nosler book and saw the differences I said wow Im off over 150 mv whats going on here. Thx for explaining it better. (y)


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 Post subject: Re: Rem 7 mag
PostPosted: Sat Jul 27, 2019 7:32 pm 

Joined: Sat Feb 13, 2016 10:16 am
Posts: 1232
Same issue happened to me, and could be more than just the burn rate being off. The bullet seating far out to to reach the lands also reduces volume and you get less pressure and speed. I used RL-19 with the 139 grain SST Interlocks and was getting 3,125 fps which was 65.5 grains and book max was 3,318 fps with 65.5 grains as well but the bullet was seated far out to be .005" off the lands. So I carefully worked up a ladder up to 72 grains and was at 3,320 fps. without pressure signs. It's 6.5 grains over book max. Always work up a ladder for this test , be sensible and observe brass for pressure signs. I, indeed, was nervous when it was at 6.5 grains over. :mrgreen:

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