Standard deviation in .223 Rem

[Varmint Hunter]

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.

 

[J E Custom]

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

 

[remingtonman_25_06]

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.

 

[Gene]

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.

 

[jmason]

VH -are sure your chronos not on the blink? 100FPS ESs for the same powder charge is a lot I think

 

[Varmint Hunter]

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.

 

[BillR]

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

 

[dwm]

+1 try anealling your cases

Someone once suggested to me that partly cloudy skies can impact the output of the chrony, was the sky clear that day? Cloudy, then clear, then cloudy, etc effects velocity readings or something like that. I have no way to validate that claim though.

They also suggested that if the chrony readings are taken over a long period of time the change in sun angle would effect the chrony readings. Measured velocity in the morning may be different than measured velocity in the afternoon due to a change in sun angle. (using the same chrony setup/location) Again, I have no way to validate that claim either.

Some things to consider though.

 

[J E Custom]

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.

Those are very good SDs !

It is the smaller bullets that are harder to get low SDs because of the weights of the bullets
compared to the velocity.

The smaller the bullet the more it is effected buy any difference in primers, neck tension, seating
depth, temperature and even the accuracy of the bullet weight . For example= If 500gr bullets
vary by 1/10 of a grain the difference will be 2/100 of 1 percent. but if 50gr bullets vary
by 1/10 of a grain then the percentage is 2/10 of 1 %.

It is not hard to get big bore bullets in the 400 to 600gr range down to single digits because slight differences have less effect on them.

The smaller cases do have an advantage in combustion Pressures because of faster powders
and smaller volume's .

J E CUSTOM