optimum minimum 223 case length

[foxx]

Somewhere I read there was an advantage to not trimming below a certain length. Dont remember the reasoning
Does anyone know what I might be talking about? Of course I realize there are practical limits. I am looking for somethinv more haviing to do with affects on chamer or bore.

[BillPa]

Trimming less then the recommended length really isn't problem other than a little more gap space, the distance from the case mouth to the start of the freebore. Its one of the places powder residue and burnt oil (carbon) can buildup and should be cleaned the same time as the bore. Of course the smaller the gap the less room there is for the crap to collect and buildup.

http://i49.tinypic.com/j96k1u.jpg

You can see the where the case mouth would be compared to the chamber cast. Its also easy to see why trimming is necessary. If the cartridge neck was too long when a round is chambered the "Step" or the start of the free bore would essentially crimp the bullet then ugly things could happen!

Bill

[foxx]

okay. Thanks.

I suppose that's why the necks on my shorter cases get more crud on them, huh?

BTW, I always trim (but first sort-out significantly longer ones) to uniform length, but now that I've accumulated 400 or so, I am getting a sizable number of various lengths and am tempted to try to avoid trimming the longer ones thinking maybe there is an advantage to having a batch that are longer. I suppose that's a waste of time and effort? Just trim them all down to the same size and quit trying to gather a supply of the long ones?

[davemuzz]

If your shorter neck cases are getting more "crud" as you state, then they are not expanding enough to seal off the gases when you fire the case. It's likely that's because the case neck is too short, or your firing low end loads.

I don't know what your definition of "short" is, but if they are too short, I would consider tossing them and just trim the brass to the SAMI spec. I find, at least with the .223 brass, the easiest thing to do is just use the Lee hand trimmer. I use a small battery powered screwdriver type gizmo and simply buzz 'em down until the stop hits the holder. That way all of the brass is trimmed to the same length, and for consistent velocity, that's what you want.

FWIW

Dave

[foxx]

my short ones are 1.753 SAAMI is 1.760

Maybe I should not trim them till they get to 1.760. Still, it does not seem like that big of a difference. Dave, you're not thinking I should throw out 1.753 are you?

Just thinking out loud... but am I thinkin' right?

[BillPa]

my short ones are 1.753 SAAMI is 1.760

Maybe I should not trim them till they get to 1.760.

They're not short. At 1.753 they're only .003" over the trim length of 1.750", the SAAMI max length is 1.760". The SAAMI cartridge spec is 1.760-.030" or 1.730"(min) to 1.760"(max), a .030" difference. http://www.saami.org/PubResources/CC_Drawings/Rifle/223%20Remington.pdf

If .003" is a concern trim them all to 1.750".

Bill

[davemuzz]

Now that we know the length, I'm agreeing with Bill. However, my other question wasn't answered…which may explain why your getting powder burns on the neck or neck and shoulder (you were not specific on that, and if you could post a pic that would be helpful) but…are your loads near the bottom end of the loading data or the top end?

Loads near, at, or a little above the "book" usually will have your neck expand quickly and block any gas from blowing back over the outside of your cartridge.

Dave

[foxx]

Sorry, Dave. I guess I dismissed the low load question b/c I was not at the bottom... Didn't mean to ignore.

Here's what I have and what I am doing:

It is a 26" Varmint Savage barrel. My routine is this:
Start with New Lapua Brass, Then after fire-forming, use Lee Collet Neck Sizing die only for 3-5 firings. Then I anneal, use RCBS FL die, and then neck size next 3-5 times before annealing again. Lately I've been trimming to 1.753 after neck-sizing every time.

Using Lapua Brass, 50 gr NBT's , 25.6 g Benchmark (Nosler book says 24.5 to 26.5) and Rem 7 1/2's. I've tried other powders, Benchmark's the best for me.

At 100 yds, I am getting .333 and better , sometimes even a .25 or better, but not sure if how consistently :)
-That was 'spose to be funny, BTW-

I don't have any examples of the fired brass to take a pic of, b/c I've cleaned them off prepping to reload. When I do, I'll post them. However, I don't know that it is a big concern of mine... I just noticed I get more powder residue on the shorter cases than on longer ones. But it was awhile ago when I made that observation, (I haven't even fired any of the longer ones in a while) I don't know how dramatic a difference it really is.

The only reason the question about case length came up was I had sent out a couple hundred for someone to anneal for me, got them back, and after I FL sized them, I started sorting them again by length... About 1/2 were at or a little above 1.753, the rest were closer to 1.756 and above... So there I was again, looking at a range of case length wondering if I should trim them all down to 1.753 or not...
If there was an advantage to keeping them long, I would not trim them all down so far. Then I remembered something about problems with bore or chamber if cut short... so I posted my question. Then Bill mentioned "crud" or fouling or whatever...

It's probably okay. Will post pics next time. But it will be Dec before I go to the range again. As you said in another post, it is DEER SEASON!

[BillPa]

However, my other question wasn't answered…which may explain why your getting powder burns on the neck or neck and shoulder
Dave

Blow by on the necks isn't all that uncommon. Usually its a result of generous chamber to case neck clearance dimensions. Soot on the shoulders on the other hand is an indication of too light of a charge and or a result of excessive shoulder bump.

How hard the brass is also comes into play, it resists changing shape. When sizing its called "spring back", when you have to run a case into a die two or three times to get the shoulder bumped back to where you want it.

Rarely will one see those conditions using factory ammo or the first firing on virgin brass because of the loading and the brass is soft having been annealed when its was made.

Bill

[davemuzz]

Yeah, I'm agreeing with you on the blow by comment Bill. I think the reason I "jumped in" on this post is because the OP stated he was getting "more crud" on his shorter trimmed cases. So, I was prodding him with questions to find out what he meant by "shorter" and also what he meant by "more crud."

I was going to raise a red flag if shorter meant 1.740 (Yikes!!) and if more crud meant "Ghee…the necks are as black as my new Lincoln's paint". (Double Yikes!!)

That's the only reason I got a little snoopy. I was getting a little scardy-cat that he may be headed down a dark and deep path.

Dave

[foxx]

thanks, guys.

All good stuff. I think I got it now.