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.223 vs 5.56 Chambers - HUGE bullet jump?

 
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  #8  
Old 12-28-2010, 08:38 PM
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Location: SW Idaho
Posts: 193
Re: .223 vs 5.56 Chambers - HUGE bullet jump?

Thanks for the advice Kevin. I want to load in the magazine, so I'll forget about the jump and press on. I wasn't so much hung up on the jump as I was concerned that there was something wrong with my chamber. I'll assume everything is fine as is and move on.

Just loaded some rounds with Sierra Match King's and Varget...ensuring bullet runout is 0.003" and less.

I'll give these a go in the next couple days and see what I get. If it still won't shoot, then I'll be back with more questions

Thanks again.
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  #9  
Old 12-29-2010, 08:41 AM
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Re: .223 vs 5.56 Chambers - HUGE bullet jump?

Bookworm,

If you're fairly new to the gas guns, it might be worthwhile for you to take a look at Glen Zediker's book, "Handloading for Competition." Glen deals with Service Rifles at length, and it really is a very different world than loading for bolt guns. Some things which we take as critical for "normal" reloading become completely irrelevant, and in some cases, downright problematical. Others, which you have some latitude with in bolt gun reloading, suddenly become critical (such as full length sizing, shoulder bumping, etc.). Bottom line is, they're different, and can't be approached the same way.

The AR is an inherently accurate little rifle, and with a few refinements (such as the float tube and a decent trigger), they're simply phenomenal. They've completely displaced the larger 30 caliber Service Rifles in competition these days, and they serve as the basis for some very accurate varmint guns. A friend of mine, John Feamster, actually shot one in a registered BenchRest match some time back. This wasn't well received by the other competitors, who tried to throw up some roadblocks to keep him out of the match. Nothing in the rulebook prevented it, ans when he cheerfully agreed to use a brass catcher to prevent his ejected cases from annoying the other shoters, they grudgingly let him pay his entry fee and shoot. They were even less amused when during one of the first relays, he fired an "Official Screamer" group; a group fired in a registered match measuring less than .100" at 100 yards, .200 at 200 yards, etc., for which an award is made. He didn't win the match, but he did beat several bolt gunners, and placed somewhere in the middle of the pack. Not too bad, considering the company. They also made it plain that he wasn't really welcome at future matches. Hey, some folks just can't deal with progress.
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  #10  
Old 12-29-2010, 09:13 AM
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Join Date: Dec 2005
Location: Longmont, Colorado
Posts: 325
Re: .223 vs 5.56 Chambers - HUGE bullet jump?

Have a look at this page (223 Rem + 223 AI Cartridge Guide). There is also a link to the sierra loading guide for the AR. I have a 20" RRA upper, and with the 69 gr match kings, I can shoot 1/2" groups without too much trouble. I have an 8" twist, so the 60-70 gr bullets work fine. I have also found some good loads with the 53 gr bullets, both boattail and flat base.

One of the things I love about shooting the AR at varmints is that you can load a 20 round magazine up, and get in a good position for many shots without having to manipulate anything (bolts). Makes for quick follow up shots on those crowded mounds.
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  #11  
Old 12-30-2010, 07:01 PM
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Join Date: Dec 2008
Location: SW Idaho
Posts: 193
Re: .223 vs 5.56 Chambers - HUGE bullet jump?

Kevin - I'm about 2/3 of the way through Zediker's book right now...very informative and entertaining read.

I went out and shot today and got mixed results with various loads. I varied the charge from 24.5 to 26.0 grains of Varget (at half grain increments), and shot two separate sets of 3-round groups for each load.

Overall I was a bit disapointed with most of the groups coming in at around 1.25 - 1.5" at 100 yds. The one exception was the 25.5 grain loads, which both grouped at just over 0.5"...so it gave me some hope to build on.

One question I have for you: the loads above (26.0) and below (25.0) opened up significantly - to around 1.5". Since 0.5 grains is quite a bit this was not a huge surprise. I also loaded 3 rounds at 25.3 grains and I was surprised to see those throw a group also near the 1.5" range. Is it possible that 0.2 grain difference (25.5 to 25.3) could make a group open up from 0.5 to 1.5 inches? Seems to me it should not be that sensitive.

Other possibility is that my two 25.5 groups had some luck involved. Interested in your thoughts.

visigoth - thanks for the link. The 6mmbr site is a good one - I'm always amazed at the amount of good info on that site.
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  #12  
Old 12-30-2010, 10:19 PM
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Join Date: Apr 2010
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Re: .223 vs 5.56 Chambers - HUGE bullet jump?

25.3 is Sierras best accuracy load with the 69smk. No surprise you fall right in that
range.
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  #13  
Old 12-31-2010, 03:14 PM
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Join Date: Dec 2008
Location: SW Idaho
Posts: 193
Re: .223 vs 5.56 Chambers - HUGE bullet jump?

Loner - what is surprising to me is that my two best groups were with 25.5 (at 0.5") and that 25.3 opened up to 1.5".

I would have thought that 0.2 grains would not have shown such a large difference.
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  #14  
Old 12-31-2010, 05:26 PM
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Join Date: Apr 2010
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Re: .223 vs 5.56 Chambers - HUGE bullet jump?

It's a small case so .2 is a large jump percentage wise. If it were a mag round it would be like a .6 jump.
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