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Old October 7, 2018, 01:48 PM   #1
rebs
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changing seating depth ?

I am reloading 223 69 gr SMK with 24.5 of reloader 15, to over all length of 2.250. What would happen to pressure if I seated this same load to 2.230 ? I am loading these to shoot in a 5.56 AR using LC 5.56 brass.
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Old October 7, 2018, 02:58 PM   #2
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You are pushing really high on the powder charge. Close to if not over a bit at the upper range.

You increase initial pressure but might gain a bit overall being further from the lands so its a toss up.

Drop a half grain would be prudent.
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Old October 7, 2018, 05:59 PM   #3
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What RC20 said
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Old October 7, 2018, 08:23 PM   #4
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according to Sierra manual 25.7 is the max load, I am under that by 1.2 grains. Should I still load down 1/2 grain ?
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Old October 9, 2018, 02:25 AM   #5
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That is good data on that bullet if it's from the Sierra manual, 1.2 grains below max, I wouldn't think a single thing of loading 2 hundredths shorter.

Load up a few and test them if you feel like being overly cautious, but if you have already tested this load I don't even think that's necessary. There's probably a deviation of 2 hundredths naturally between the differences of bullet length between lot numbers and seating stem etc.

Loading shorter to fit a mag?
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Old October 9, 2018, 04:15 AM   #6
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Small case capacity(overall). Be carefull shortening COAL.

I'm thinking your running a touch short to begin with. Should be 2.260" per the Sierra manual.

You just trying to tighten up your groups?
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Old October 9, 2018, 05:06 AM   #7
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Yes looking to tighten up the groups. I have found a sweet spot in OAL for my Colt AR at 2.230 for all 55 gr bullets and would like to try the same OAL for the 69 gr SMK to see if it shrinks the groups for this bullet too.
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Old October 9, 2018, 05:26 AM   #8
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I believe getting closer to the lands is generally better for accuracy than further, but, if you can't go longer because of magazine, going shorter may be worth a try.

Powder charge going to make more of a difference than OAL in this case, I will assume you have already done that and now are adjusting OAL?

I would not compare the OAL as very meaningful with these two bullets of different weight and design, and OAL is likely set (by Sierra) more to fit a magazine than for accuracy in this case.

Still. I wouldn't sweat that. Doubt it helps but it's gonna be safe at 1.2gr under book max and if Sierra recommends 2.25" or 2.26" and you only go to 2.23"
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Old October 9, 2018, 10:57 AM   #9
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Rebs: What I am looking at is other correlating data that says its about maxed out.

The tough part of a semi is you don't know if its getting a bit sticky.

I have seen some data that is 3-4 grains difference in the max, so just being cautious.

In a 30-06 that much capacity reduction is nothing, in a 5.56 is proportionately quite a bit more.
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Old October 9, 2018, 02:44 PM   #10
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Thank you for all the replies, I appreciate it. I loaded and fired five rounds at 2.230 and show no pressure signs. It did reduce the group size considerably. I don't know why but this AR prefers an OAL of 2.230
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Old October 10, 2018, 01:21 PM   #11
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That is what counts!

I don't know how sticky a semi auto bolts gets vs a bolt action but the sticky bolt is one of my first hints things are up too high.
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Old October 11, 2018, 05:09 PM   #12
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I'm a bit late to the party but a 5.56 throat/leade is long which means you have all kinds of play . I know we're talking seating deeper but you need to consider when the primer ignites , a non-crimped bullet often moves forward before pressures really starts to spike . This mean your COAL is actually growing and increasing internal volume as the pressure starts to rise . So even though you are reducing initial case volume . As the bullet moves forward with no resistance your case volume is actually growing until the bullet stops/slows as it hits the lands . Unlike having the bullet jammed into the lands where the bullet is stuck in place and you basically have a fixed internal volume .

So seating deeper in this case would seem to me to be perfectly safe .

Quote:
I have found a sweet spot in OAL for my Colt AR at 2.230 for all 55 gr bullets
Quote:
Thank you for all the replies, I appreciate it. I loaded and fired five rounds at 2.230 and show no pressure signs. It did reduce the group size considerably. I don't know why but this AR prefers an OAL of 2.230
You are talking two completely different bullet profiles so even though the COAL is the same . The difference of each of those bullet profiles means there distances off the lands is very different even though they have the same COAL . My point is don't get caught up on what your 55's coal is because they have no relation to the 69's .
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Old October 11, 2018, 08:17 PM   #13
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Thank you, it did work safely and groups did shrimk
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Old October 12, 2018, 01:01 PM   #14
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That's why I always take the time to do the Berger seating test when starting a load workup. It at least gets me in the ballpark for the load testing, never can tell ahead of time how much jump a particular barrel likes
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Old October 12, 2018, 02:14 PM   #15
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I take my RCBS junior press to the range and seat the first bunch long or to what worked best last (sometimes both)

Then I adjust identical loads to fine out what works.
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Old October 12, 2018, 03:29 PM   #16
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Quote:
I take my RCBS junior press to the range and seat the first bunch long or to what worked best last (sometimes both)

Then I adjust identical loads to fine out what works
That is how I do my fine tuning on depth if needed, sometimes I get a .5 load just with the rough tuning.
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Old October 14, 2018, 10:29 PM   #17
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I made a small change to the depth of my casull and the groups touch each other
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