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7 saum unexpected velocity

 
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  #15  
Old 04-11-2012, 08:36 PM
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Re: 7 saum unexpected velocity

I only use benchrest/match primers. I don't know if they make much difference. But, I sleep better.

You may be able to reduce your ES/SD with some extra case prep and by tweaking seating depth. Consistent neck tension is a biggie. If your neck wall thickness varies a lot, you may want to neck turn just enough to shave the high spots, and then get a bushing die or collet die that will allow you to size necks to about .002 below caliber.

I'm not sure I believe the actual velocity readings. But, it really doesn't matter if your drops confirm what you need to know.

Either way, your long range groups will tell you if high ES/SD is going to cause you grief due to vertical stringing. So, keep taking notes and collecting data.

-- richard
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  #16  
Old 04-11-2012, 09:39 PM
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Re: 7 saum unexpected velocity

Quote:
Originally Posted by XTRTITAN View Post
I think i am getting closer to finding my rifles happy place. I set up today with the chrony at 10ft from the muzzle. I brought my 6 dasher as a baseline for the chrony speeds. It shot a nice little ragged hole with velocity for 5 shots being 3083,3086,3097,3071,and 3068. This is normal for this gun and the jbm trajetory matches these numbers well.

Now for the 7saum.i loaded 5 180 vlds at the original 54.5 grains of h4350 and the velocitys were 3057,3000,3093,3123,and 3118. These produced a 100 yd group around 3/4".

I also loaded 5 180 vlds with 52.5 grains of h4350. The velocitys came in at 2941,2923,2917,2919,2953. This produced a 3/8 inch ragged hole a 100 yds. Extreme spread of 36. I had 5 more rounds at 52 grains with almost identical results.

This seems like a lot of speed for 52.5 grains of powder but if the trajetory matches it i guess that will be ok.

Would you guys accept an extreme spread of 36 or change primers or any other tricks to lower the extreme spread? Accuracy seems to be good here. I really dont want to wear this barrel out before i get it tuned.
I may not have read everything so forgive me if I missed something. Have you weighed your brass and sorted to two grains or less? Do you have consistent neck thickness? Have you annealed your brass? Are the lengths consistent? Have you checked your runout? If you have done these things as well as played with seating depth, you might try a different primer to see if that makes a difference. If you haven't yet done all this, a primer change will not likely tell you much.....Rich
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  #17  
Old 04-12-2012, 08:34 AM
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Join Date: Mar 2012
Location: BLACK HILLS SD
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Re: 7 saum unexpected velocity

The last time i shot was the second firing on new remington brass. They have been sorted within 2 grains and necksized with a forster non-bushing neck die. It seems like there is more neck tension than i am comfortable with. Does anyone make a collet die for a 7 saum?

I havn't turned the necks yet but it is on the list of things to do. Flash holes have been deburred but not uniformed. Dont know if uniforming makes a difference.

Dont have a concentricity gauge but i have been rotating the case as i am seating to reduce runout. I have been looking at the hornady concentricity gauge but dont like how it measures from the rim of the case instead of the body. Anyone have any experience with this product?

I dont have any match primers to try right now. Which ones would you purchase to try? (reg or mag. And which brand)

thanks again
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  #18  
Old 04-12-2012, 11:18 AM
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Location: New Bern, NC
Posts: 609
Re: 7 saum unexpected velocity

I had some similar issues with my 7SAUM. My advice to you is leave the chrony at home. They aren't nearly accurate enough to pay that close attention to what they spit out. Double check your scope height for your drops, if it's off your velocity will be off as well even with the drops matching. I have my 7SAUM zeroed at 300 yds and I'll find a load that groups the best, then strech it out to 600+. If the load still maintains a good group, it's a keeper. I'll then shoot it out to 1000 yds, gather my data, and imput it into Exbal and have it calculate the velocity. But as long as the load shoots for me, I don't really care how fast it's going.

180 Hybrids
62 gr H4831sc
CCI BR2 primers
Norma brass
3047 fps
My best 3 shot group with this load was .5" @ 604 yds
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  #19  
Old 04-13-2012, 10:50 AM
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Re: 7 saum unexpected velocity

I agree! b.c., velocity, etc. is what you use to get you on paper. The data you get from your own rifle, scope, load combo is the data that works!.......Rich
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  #20  
Old 04-13-2012, 01:09 PM
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Re: 7 saum unexpected velocity

Quote:
Originally Posted by XTRTITAN View Post
[...]Dont have a concentricity gauge but i have been rotating the case as i am seating to reduce runout. I have been looking at the hornady concentricity gauge but dont like how it measures from the rim of the case instead of the body. Anyone have any experience with this product?[...]
I have the NECO and the Hornady.

The NECO will frequently detect .003-.005" TIR in situations where the Hornady only registers .000-.001". The NECO is also configurable to measure a variety of other things such as case wall thickness and case head squareness, etc. I highly recommend the NECO.

My Hornady is shiny, like new, and in the box with all the paperwork. I will gladly sell it. Perhaps someone else knows better than I how to get the most from it.

-- richard
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  #21  
Old 04-14-2012, 03:04 PM
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Location: BLACK HILLS SD
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Re: 7 saum unexpected velocity

I will look into the neco. Sounds like that might be the way to go.
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