I just finished developing loads using 223 cases for my Lar 15, I was successful in meeting my goal of developing loads that shoot groups under one inch and reaching 3000 fps safely with a 16 inch barrel. My next project is to get the same results with 5.56 cases, I have on hand about 300 once fired LC headstamp cases and about 50 cases head stamped PSD. I was under the impression that 5.56 cases were heavier than 223 cases, I weighed a few of the LC cases and they weigh about the same as the Winchester 223 cases that I used to develop my 223 loads.

Being the cases weigh almost the same can I use the same starting load that I used with the 223 cases. I am probably going to stick with just two bullets, 50 gr Nosler ballistic tip and 50 gr Barnes Varminator, that was the only bullet weight that gave me 3000 fps safely only when used with H 4895 powder. I have some 748, H 335, H 4895 Benchmark and Vihtavouri N-135 on hand, the N-135 disappointing, I was getting pressure signs early and way below max load. Benchmark gave the best accuracy with my 223 loads. I appreciate any help or advice.

I'm curious how you determined how loads were safe and loads were showing pressure signs?

LC 5.56 cases typically have more capacity than commercial cases.

?

Any load that showed higher velocity than what my loading manuals show with the same powder charge I consider to be unsafe. I had two loads that showed ejector marks along with flat and cratered primers, sure sign of excessive pressure.

Denton is correct, it is a myth that 5.56 cases are heavier and have less case capacity then civilian 223 brass.

This is from Sierra.

The conventional wisdom to reduce loads with military brass is familiar to most reloaders and is generally good advice. The rationale here is that the military cases tend to be somewhat thicker and heavier than their civilian counterparts, which in turn reduces capacity and raises pressures. This additional pressure normally requires a one or two grain reduction from the loads shown in most manuals or other data developed with commercial cases. While this is most often the situation with both 308 Winchester and 30-06 cases, it is less true with the 223 brass. We have found that military cases often have significantly more capacity than several brands of commercial brass. Again, take the time to do a side-by-side comparison of the cases you are working with and adjust your load as needed. There may be no need for such a reduction with the 223. Know your components and keep them segregated accordingly.

http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfm

There is also this, scroll down to Case Weight vs Capacity

http://www.6mmbr.com/223rem.html

And this.



Here is my current stash of 223/5.56 brass.

GFL(223) dry weight-102.4gr
With H20-131.4
Case capacity in grains of H20-29gr

Remington(223) Dry weight-95.2gr
With H20-125.1gr
Case capacity in grains of H20-29.9gr

LC(5.56) Dry weight-96.3gr
With H20-126.7gr
Case capacity in grains of H20-30.4gr.

How can you compare velocities listed in the manuals that use 24 inch barrel to the velocities from your 16 inch barrel?

Ejector marks are not always a sure sign of pressure in an AR and "Flat" primers is can be caused by a lot more things then high pressure. In fact reading primers is about the least accurate method of determining "high" pressure.

http://www.shootingillustrated.com/index.php/8720/case-head-swipe/

I am comparing the loads to a 16 inch barrel, I have 16 inch barrel data from a source. I have compared data from 16 inch barrels and 20 inch barrels, there is plenty of information on this subject online. Depending on the powder used there is about a 100 to 140 fps difference between a 16 and 20 inch barrel, slower powders have a larger velocity difference.

That is a great article on Case head swipe, I put it in my favorites, it appears that I do have a CHS issue with some of the loads that I tried, the issue occurred only with H335 and Vihtavouri N-135 powder, with the N-135 load CHS appeared early, only about 1/2 grain above starting load, with the H 335 load the issue occurred much later. I thank you for that article, it puts my mind a little at ease.

According to this using the same rifle, More like 150-200fps between 20 inch and 16 inch.

http://www.accuratereloading.com/223sb.html


Also according to Quickload using H-4898 in a 223 has a velocity loss of 180fps with your Barnes bullet from 20 inch to 16 inch.

Looking at the case capacities confirms what I have thought for a long time, that the various 5.56 cases can pretty much be mixed, which they are if you buy comm'l reloads. In a real good varmint rifle, you MIGHT be able to notice a difference in group size. I have a kitchen trash can full of 5.56 brass that I've picked up at the range, almost all of it is never reloaded LC/WCC/IMI brass cause the primers are crimped in. I have never bought brass for one obviously.

Has anyone used this powder when loading 5.56 cases. I tried to work up a load with this powder with 50 and 55 gr bullets and ended up with higher than normal speeds. The load data that Vihtavouri used was developed using Lapua 223 cases and a 25 inch barrel with a 1 in 12 twist, my gun has a 16 inch barrel and 1 in 9 twist. my gun averaged 2970 fps with 24.5 gr, Vihatvouri data shows 2983 with 24.3 gr. With 50 gr bullets I got 3037 with 24.5 gr, their data shows 3077 with 25 gr, I should be losing at least 300 fps with my short barrel.

I talked to tech experts from three bullet manaufactures, and got three different answers. One guy said I have a fast barrel and nothing to worry about, another said don't use those loads, another tech said the fact that I have a 9 inch twist is probably the reason, it creates higher pressures than a 12 inch twist. I don't think that using 5.56 cases would make that big of a difference, what do you guys think.