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changing seating depth ?
- Thread starter rebs
- Start date
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?
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?
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"
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"
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.
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.
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 .
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 .
So seating deeper in this case would seem to me to be perfectly safe .
I have found a sweet spot in OAL for my Colt AR at 2.230 for all 55 gr bullets
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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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.