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Standard deviation in .223 Rem

 
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  #1  
Old 07-10-2009, 04:11 PM
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Standard deviation in .223 Rem

I'm working with a new .223 Rem with 23" Broughton 5C bbl (12 twist). I am using Lapua brass, Federal 205M primers and 5 different powders with 3 different bullets, 52 Berger, 52 A-Max & 55 V-Max. It seems that whatever I do I seem to get SD's anywhere from 20-40, which reflects some extreme spreads of over 100 ft/sec with 5 shot groups. The only thing I haven't tried was loading bullets into the lands which I prefer not to do with this rifle.

For whatever it's worth, I'm using Redding S FL dies and moving the shoulders back about .002"

Anyone have any idea what could be causing this problem?

Both my .308 and 300 RUM have SD's in the single digits almost every time I fire a group, but this .223 has got me baffled. Accuracy is OK but not exciting.
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Old 07-10-2009, 05:43 PM
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Re: Standard deviation in .223 Rem

Quote:
Originally Posted by Varmint Hunter View Post
I'm working with a new .223 Rem with 23" Broughton 5C bbl (12 twist). I am using Lapua brass, Federal 205M primers and 5 different powders with 3 different bullets, 52 Berger, 52 A-Max & 55 V-Max. It seems that whatever I do I seem to get SD's anywhere from 20-40, which reflects some extreme spreads of over 100 ft/sec with 5 shot groups. The only thing I haven't tried was loading bullets into the lands which I prefer not to do with this rifle.

For whatever it's worth, I'm using Redding S FL dies and moving the shoulders back about .002"

Anyone have any idea what could be causing this problem?

Both my .308 and 300 RUM have SD's in the single digits almost every time I fire a group, but this .223 has got me baffled. Accuracy is OK but not exciting.
VH.

In my experience the very small/light bullets are harder to get single digit SDs but it's possible.

Normally the reason for poor SDs is inconsistent combustion.

Some of the causes = Inconsistent; neck tension,volume of case,bullet seating depth,wrong
powder and primer combination.

My best guess would be the primer. You need to try a different one and see if the problem improves or worsens.(Nothing wrong with the primer you are using it just may not be the one
your loads like.

Next = I would not bump the shoulders unless they are hard to chamber.(When the firing pin
strikes the primer if the round moves to much it will cause inconsistent primer strikes and thus
poor ignition.

the third thing would be bullet seating .It normally effects accuracy more but with the vld's
it is important to seat closer to the lands (5 to 15 thousandths) than with the standard ojive
bullets.

I would work on changing only one thing at a time to find the culprit.

Just a few things to try.

J E CUSTOM
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Old 07-11-2009, 02:57 AM
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Re: Standard deviation in .223 Rem

My .222 rem gives me at most 15fps, and is usually within 10fps with its couple better loads. I am about .010"-.015" off the lands using CCI400 primers. Use IMR-4198 w/40g bullets and IMR-4895 w/55g bullets. Neck sized in a RCBS die. I dont know, I always thought smaller cases were easier to get lower deviations??? Never had a problem with my triple deuce getting low spreads.
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Old 07-11-2009, 05:07 AM
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Re: Standard deviation in .223 Rem

Sometimes rifles with a wide SD spread nevertheless shoot well. I hope you have tried Varget and H335 powders. I would go about 2 grains below max and work up, checking with your chrono each outing. With my Savage LRPV and 7" twist, I use Berger 80 gr. VLD's and load .010" into the lands. I believe that doing so settles the bullet into a more consistent start each time. But, I don't remember my ES or SD; I need to go check my records cause I have not chrono'd my load in a long time.
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Old 07-11-2009, 08:23 AM
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Re: Standard deviation in .223 Rem

VH -are sure your chronos not on the blink? 100FPS ESs for the same powder charge is a lot I think
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Old 07-11-2009, 09:44 AM
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Re: Standard deviation in .223 Rem

Thanks for all the input. A little additional info:

I tried Benchmark, IMR4198, H4895, H335, Varget & RE7. All loads were shot over an Oehler 35P. Most bullets were set .005" - .015" off the rifling. Some of the 40's I loaded .065" off the rifling so that I would have better bullet grip in the neck.

All loads were shot at 200 yds with favorable (am) wind conditions. Average group is about 1.5" with an occasion 1" group but a few that were nearly 2". I also shot several groups with 4 in a cluster and a 5th that may have been 1.5"-2" out??????????????

Funny, but when I had this rifle built I thought that it would be one of the easiest rifles to find accurate loads for. As it turned out, it's proving to be one of the most difficult.

This is an intriguing sport.
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Old 07-11-2009, 10:06 AM
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Re: Standard deviation in .223 Rem

Switch primers. Also anneal your cases. You will be surprised.
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