.223/5.56 compressed loads

[kyle528]

I just worked up a load for my AR chambered in 5.56 using 223 brass. 26 grs of RE-15 and a 77 gr nosler custom comp. However, the other night I noticed when loading more that when I use 223 brass, I get an ever slightly compressed load, but when using 5.56 brass, the entire case is filled to the neck with powder, giving me as much of a compressed load as possible. I know it is not my meter, as I weigh all loads on a scale before dumping into case. My question is with such a compressed load am I going to get over pressure or significantly different velocities? Thanks for input

 

[sermonator]

Careful about switching brass! If you haven't worked up to it, it can get all bad quick.

However, to deal with compressed loads, some use a vibrating tumbler and just set their hand up on in for a couple of seconds, settling the powder.

I like a drop tube. I used them all the time when loading black powder cartridge and use them when loading 77 in the .223, also. It still has a little crunch, but not bad.

 

[kyle528]

So should I unload the 5.56 cases and use only 223 brass for the heavier load?

 

[CharlieNC]

What is the difference in water capacity of the brass? My Lake City 5.56 brass has higher capacity than commercial 223 brass, which is normal. It sounds odd that you have the reverse; what brands are you comparing?

 

[gunsnjeeps]

If you worked up a load with one case and it fills a different case differently than there is a going to be a change in velocity and pressure. You're load sounds a little hot but may not be. I'm loading 24 grains Varget and RL15 is vary close. I'd guess you're in the 2800 foot per second neighborhood with your normal load. Compressing it in a smaller case will increase velocity and pressure. 24 grains of Varget and 77 SMK's are compressed, but not much.

Anyhow, when you change cases you will probably have to rework your load.

 

[Sniper Uncle]

What is the difference in water capacity of the brass? My Lake City 5.56 brass has higher capacity than commercial 223 brass, which is normal. It sounds odd that you have the reverse; what brands are you comparing?

Charlie, I think you may want to check your case capacity again, because by spec, the 5.56 has LESS capacity than the .223, by a factor of 28.5/28.8----not much, but the 5.56 is the smaller of the two.

 

[BoilerUP]

In my opinion...

223 or 5.56, using Varget or RL15 with a 75/77gr... don't fear the 'crunch'.

26gr of RL15 with a 77 @ AR mag length sounds damn hot, however.

 

[kyle528]

Yes, 77's with 26gr re-15 seated at AR mag length is indeed a hot load. Throws the case about 2 feet farther than factory loads. However, with the 223 brass, I got no pressure signs at all, not even flattened primers. My main concern is will the difference in compression of the two cases be enough to throw off consistency for steel shooting out to 600 yards?

 

[bigedp51]

Charlie, I think you may want to check your case capacity again, because by spec, the 5.56 has LESS capacity than the .223, by a factor of 28.5/28.8----not much, but the 5.56 is the smaller of the two.

Actually Lake City cases have the most case capacity.

Below is a Lake city case at 30.6 grains of H2O case capacity and 25 grains of H335 at 44,000 psi

Below is a generic case with 28.8 grains of H2O case capacity with the same 25 grains of H335 at 50,000 psi. (6,000 psi increase)

Your load of 26 grains of RL15 is 65,000 psi using a Lake City case at 30.6 H2O and 10,000 psi over max pressure, the Nosler manual shows 24 grains as the max load. Your load is more than a little hot, it is dangerous. Your load at 28.8 H2O is 80,000 psi and 25,000 psi over max pressure.

 

[CharlieNC]

Biged, that chart from Accurate Shooter is exactly what prompted my question regarding which brands of brass??? I run a similar load but with 75 Horn BTHP that gives moderate pressure based on Quick Load using LC brass, which I check very close at 30.7 WC. The impact of water capacity from different brands, and even bullet design for a given weight, is quite revealing using Quick Load and unfortunately not so obvious from reloading manuals alone; I continue to learn a lot using it!

 

[gstaylorg]

I noticed the same thing. Running Quickload with 30.0 gr case capacity and 26 gr Re15 gives way more than a 10% compressed load. Dude, you'd best be cautious cramming that much powder into a case without knowing anything definitive about your case volume. Your eyes are yours to do with as you please...but the guy sitting next to you probably likes his the way they are.

Here's a helpful reloading tip: when you switch to a new case and your previous powder charge fills the new case all the way to the neck>>>BAD IDEA. Start low and work your way up...always.

 

[Bender]

Pull em apart and try again.

 

[kyle528]

my loading manual states that the average 223 chamber pressure is 52,000 CUP. using the CUP>PSI conversion -17902+(1.516•CUP)
comes out a little under 61,000 PSI. considering that most reloading manuals are very conservative, this leads me to believe that my load of 26 grains should not be dangerous. Turn the page in the manual, and the maximum charge is 27 grains. however, this is for a .223 case, so pressures would be normal. but surely compressing a load cant produce 25,000 psi over "max" could it? not saying you are wrong, not saying im right, that is just my way of thinking, please correct me if i am wrong, here to learn.

 

[bigedp51]

The max rated chamber pressure for the .223/5.56 are:

52,000 cup SAAMI copper crusher
55,000 psi SAAMI transducer method
62,000 psi European CIP transducer method with the pressure measured at the case mouth and not the midpoint of the cases as SAAMI cases are.

Below are the milspec requirements for commercial contract 5.56 ammunition made for the military.

MIL-C-9963F
15 October 1976
SUPERSEDING
MIL-C-9963E
12 May 1970

MILITARY SPECIFICATION
CARTRIDGE, 5.56MM, BALL, M193

3.7 Chamber pressure.

3.7.1 Measurement by copper-crush cylinder.-The average chamber pressure of the sample cartridges, conditioned at 70° ± 2°F, shall not exceed 52,000 pounds per square inch (PSI). The average chamber pressure plus three standard deviations of chamber pressure shall not exceed 58,000 PSI.

3.7.2 Measurement by piezoelectric transducer.-The average chamber
pressure of the sample cartridges, conditioned at 70° ± 2°F, shall not
exceed 55,000 PSI. The average chamber pressure plus three standard
deviations of chamber pressure shall not exceed 61,000 PSI.

You load is over max by Alliant Powder data, Nosler loading data, Sierra load data and Quickload data with all being in the 24 grains maximum of reloader 15.

Your pressure conversions are incorrect, all three pressures listed above are the same identical pressure measured three different ways. The only pressures that concern us as reloaders are 52,000 cup or 55,000 psi using American SAAMI standards.

 

[Bunnypunter]

Not to hijack this thread, but I have a question along the same line. Hornaday Reloading manual sets max Varget load for 5.56 75gn BTHP at 24.6, while the Hodgdon site sets max at 25.0. I realize we're only talking 0.4gr; however out of curiosity, which do you follow? I performed and OCW test last week working up to 25.0 and had a node set in between 24.5-25.0. While I like the idea of sending that round out at 2900 fps, am I over pressuring? I did not see any over pressure signs at 25.0 but I'm not real stoked about blowing myself up. Shooting a Colt CRP-18 with 1-8 twist.

Pretty new to reloading so forgive the newbie question.

Thanks y'all.

 

[gstaylorg]

As has been mentioned, the key is starting low and working up. That way you should get warning signs before critical pressures are reached. It's still no guarantee, but much safer than jumping right up to the high load.

As far as kyle528's load, I come up with 71,259 psi and 111.1% fill using Quickload with a 77 gr Nosler CC pushed with 26 gr Re15, 2.250" COAL, 16.0" barrel, and 30.0 gr case capacity. Using 28.8 gr case capacity, it jumps up to 80,790 psi. With a highly compressed load, even relatively small changes in charge weight, case capacity, seating depth, etc., can lead to large changes in pressure very quickly. The more compressed the load, the faster the pressure goes up. Little things that ordinarily wouldn't be an issue in a load that is slightly below max can be all it takes.

I'll be the first to acknowledge that Quickload, or your average reloading manual for that matter, tends to be pretty conservative. The better your input with regard to total volume of the pressure vessel (ie. fired case capacity), powder burn rates (which undergo pressure-dependent change), etc., the better the numbers predicted by Quickload will match your actual results. However, I've had at least one experience with IMR4320 in a .308 where predicted max WAS the max. I loaded up one 0.3 gr increment higher because I'd had results using Varget and H4895 where the predicted max load was much lower than the actual max. Fortunately, that 0.3 gr incremental increase I had loaded up was only enough to cause one blown primer out of 3 rounds. Between the blown primer and the wildly erratic MVs for those 3 rounds, I left the rest unfired and pulled them when I got home.

By starting low and working up, I avoided reaching a critically high pressure before I became aware it was an issue. If you start low and work up, you can always go home and load an increment or two higher if you're certain you haven't yet reached the upper safe limit. Sure, it takes a little more time and effort, but it's worth it IMO.

 

[Sniper Uncle]

Bigedp, thanks for the charts and the spec on the ammo. I was reading spec diagrams from Quickload which tracked with what I had been told previously that "most mil-spec ammo has thicker brass, so less case capacity." Obviously, i was mis-informed. Thanks for the correction.

For those of you who have Quick-Load, you have probably tried seating depth changes of even small amounts, and watched the changes in expected peak pressure. They can be quite an eye-opener. I have found that when you go into compressed loads, a 0.1 gr difference makes a slightly larger difference in pressures than it did while un-compressed. For those who don't have access to QL, do proceed with caution as you reach the upper maxes published in the books. I often reference three or four different sources to find how they match each other before I foray into a "ladder type test" to find max safe pressure for a given rifle.

On a side note, you may want to get some measuring tools to measure max trim length of the chamber of your rifle and max COAL for a given bullet. Case in point, I took the data for Swiss GP-11 Ammo and made some rounds up for pressure testing in my K31 and my uncle's K11. Mine showed pressure signs way earlier than his did. When I measured the chamber to find max COAL, I found that my K31 had a much shorter throat than his K11. Even though I had loaded the loads by the book, the book didn't show Ogive length, and the ogives of my bullets didn't match the Swiss GP-11 bullet ogive. Thus, I was loading jammed cartridges and seeing pressure signs. With a little work, I shortened my COAL, and the pressure signs dis-appeared. Little things, like a hard jam versus a small jump, or a seating depth difference, or a compressed load can make rather large pressure differences that you might not expect.