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Mag length 223 77gr seating depth variation

AR mag length 2.260 max.

Been a busy day. Will chase down the parts or turn down a sizing button to get .003 or .004 neck tension. Also trying to figure out a different seating die setup before I ruin my Redding competition seater, if I haven't already. Once I get all that figured out I will report back. Thanks for all the help so far!
 
Jon D said:
AR mag length 2.260 max.

Been a busy day. Will chase down the parts or turn down a sizing button to get .003 or .004 neck tension. Also trying to figure out a different seating die setup before I ruin my Redding competition seater, if I haven't already. Once I get all that figured out I will report back. Thanks for all the help so far!
Click to expand...
Question, and don't let the answer run you down a rabbit hole.

When I saw significant CBTO variation, i also saw extensive run-out. Do you have a concentricity gauge, check the loaded rounds up around the ogive. If you don't have a concentricity gauge, pretend that i didn't say anything.

-Mac
 
Just checked bullet runout of 10 rounds with a concentricity gauge. A low of .001 and a high of .002, with an average of .0015. I went down that rabbit hole previously, it's long and deep!
 
How do they perform on paper? Does the seating feel very different, as in are some very hard to seat and others not? Are there marks from the seating stem on your bullet?
How married are you to the lapua brass? I found it to provide little advantage in an AR chamber and prefer lake city.
What mags are you loading for? There is some variance in them and perhaps with the right mag you can seat them out further.
An electric toothbrush can vibrate powder down if you want to try it.
If it is just over minimum loads where you start to have trouble, that seems odd. Is it with one lot of brass? Have the cases been fired. It just seems like you should not be having this trouble and I wonder if there is something that is way out of whack.
 
I'm still working on it and wondering the same as to what is so out of whack. I did get to measure the case capacity of new unfired piece of Lapua and lake city 17. 29.52gr vs. 29.47gr respectively. The water capacity is almost identical, so new Lake City offers no capacity advantage over new Lapua. Interestingly a piece of fired Lake City has about a full grain more capacity than a fired piece of Lapua, so there is a capacity advantage in once fired brass (30.86gr vs 29.92 gr). At least before sizing. I will have to explore that further. Looking at Hodgon's data they are showing a compressed load at 22.6gr of h4985 and a 77 smk loaded to 2.260, which matches what I am seeing. A berger 77 is .030 longer, not helping things a bit. Still need to chase down decreasing neck diameter.
 
Jon D said:
I'm still working on it and wondering the same as to what is so out of whack. I did get to measure the case capacity of new unfired piece of Lapua and lake city 17. 29.52gr vs. 29.47gr respectively. The water capacity is almost identical, so new Lake City offers no capacity advantage over new Lapua. Interestingly a piece of fired Lake City has about a full grain more capacity than a fired piece of Lapua, so there is a capacity advantage in once fired brass (30.86gr vs 29.92 gr). At least before sizing. I will have to explore that further. Looking at Hodgon's data they are showing a compressed load at 22.6gr of h4985 and a 77 smk loaded to 2.260, which matches what I am seeing. A berger 77 is .030 longer, not helping things a bit. Still need to chase down decreasing neck diameter.
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Normally, loading 223 is ridiculously easy. Is the hodgdon data not made for an ar15? Some manuals have different data for gas guns.
Do you have any 8208 or reloder 15?
 
Just ran the numbers in Gordon's. The extra grain of water capacity in Lake City brass will require about a half a grain more powder to achieve the same velocity in a Wylde chamber. So especially in new brass, one is better off using Lapua if trying to minimize the powder compression and achieve the same velocity. That's pretty interesting and a little counter intuitive to common advice.
 
I'm quickly coming to the conclusion that my best bet is to pull out the most versatile and effective tool, my visa card. I'm done messing around and thinking about this. Ordering up some black hills or Atlanta arms. Both are fast, accurate enough for my purposes, and consistent. If it's good enough for the AMU, it's good enough for me.
 
There are some loads that will work at 2.260 with the 77 Sierra - Have a look at the M262 series on "Johnny's Reloading Bench" on You Tube, where he attempts to duplicate the Black Hills load. Quite informative. Otherwise try some of the quicker and less bulky powders - IMR8208 works well ( I am currently doing some testing for a friends F-Class 223.(OK - Doesn't have the same length restriction - but does have a fairly short chamber- much shorter than the one I specced for my Tikka). Even old H322 may be worth a look, if speed is not too much of an issue.
 
MDT .223 10 Round Polymer Magazines can handle up 2.55" OAL. This is what I run on a bolt gun. If you have an AR and trying to run 77 grainers, good luck.
 
I've shot a lot of Lapua and LC and found 1gr difference in unfired as well, as widely reported. Loading the same has given identical results in spite of the quick load inferences.
 
jelenko said:
FWIW, the issue is not with fitting in a mag, it's consistency from round to round.
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Well, yes and no. The OP said he was having issues with powder compression/crunching, etc.. He thought this was contributing to his length consistency while running 77 gr. projectiles in an AR length (2.25") mag. The simple solutions are to run less powder, a shorter bullet or seat the 77 grainers longer. However, he cannot run the 77's longer because he is limited by his AR mag. He also may be limited by freebore to load the 77's longer. We don't know. Another thought is to run ball powder. It compresses better but has disadvantages we all know of.
 
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Indiana6547 said:
Well, yes and no. The OP said he was having issues with powder compression/crunching, etc.. He thought this was contributing to his length consistency while running 77 gr. projectiles in an AR length (2.25") mag. The simple solutions are to run less powder, a shorter bullet or seat the 77 grainers longer. However, he cannot run the 77's longer because he is limited by his AR mag. He also may be limited by freebore to load the 77's longer. We don't know. Another thought is to run ball powder. It compresses better but has disadvantages we all know of.
Click to expand...
Maybe. Doesn't seem clear from the OP.
In any case, the concern he expressed was the variation in the base to ogive. A longer mag is not related to that.
 
Rob01 said:
What are ACS mags? Did you mean AICS mags? In that case they can take up to 2.550" for the .223 mags.
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