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Bullet seating mystery

722 views 12 replies 9 participants last post by  noylj 
#1 ·
Ok I'm working up a new load for my G26. I'm using my Dillon SDB. I have my seating depth set to an OAL of 1.154. After I accumulated a dozen or so completed rounds, I measured them with my caliper. I'm getting numbers similar to this:

1.1585
1.164
1.162
1.1495
1.158
1.1575
1.1535

Etc.

Now I realize that OAL will vary simply because each bullet might vary. But here is the part that has me scratching my head: If I take one of the longer rounds and run it through the seating die again, it pushes down further and I end up in the 1.5xx range, which is what I want. Why aren't they seated fully the first time?? I pull the handle completely to the end of its stroke. Is it necessary to pause for a second or so when seating? Is there even enough of a range in my numbers to cause issues with pressures when shooting through my Chrony?
 
#3 ·
1) Cast Boolits or FMJ? On cast, the lube can build up and change OAL.
2) Does the seating stem match the projectile profile? Should have a flat and a round. Pick the one that matches the profile.
3) Are the dies tight? Tool head tight? Press will behave differently if only one station is loaded vs all stations full.
4) Finally, have you called Dillon? They answer questions like this all day long. Their customer service dept is great.

Bullet length has nothing to do with OAL. When seating, you are pressing the top of the bullet down to a fixed location. Bullet length will determine how deeply the bullet is seated; but not the OAL. Or put another way, a longer bullet will have more bullet in the case than a shorter bullet. OAL will be the same though.
 
#4 ·
Ok I'm working up a new load for my G26. I'm using my Dillon SDB. I have my seating depth set to an OAL of 1.154. After I accumulated a dozen or so completed rounds, I measured them with my caliper. I'm getting numbers similar to this:
1.1585
1.164
1.162
1.1495
1.158
1.1575
1.1535
Etc.
Now I realize that OAL will vary simply because each bullet might vary. But here is the part that has me scratching my head: If I take one of the longer rounds and run it through the seating die again, it pushes down further and I end up in the 1.5xx range, which is what I want. Why aren't they seated fully the first time?? I pull the handle completely to the end of its stroke. Is it necessary to pause for a second or so when seating? Is there even enough of a range in my numbers to cause issues with pressures when shooting through my Chrony?
Between your longest & shortest numbers you are looking at 0.015" difference. For general range ammo coming out of your G26, this difference I doubt you will ever notice or feel the difference in your hand. As far as your target accuracy (providing you have had too much coffee that morning) you may notice a difference of "perhaps" a quarter inch or so... again depending upon how steady your hand is. Will this cause any measurable rise or drop in pressure... none that will effect your G26 in any way.

There will all ways be slight variances in every step of the reloading operation. What your have described about in very minute in the over-all result. I use a LEE Classic Turret Press w/LEE Dies and I too get slight variances from round to round, most of which is too slight to even be concerned about.

If you are using these rounds in your G26 for Home/Personal defense, take them to the range and run them through your Chrono and put them through sever different accuracy tests. This will give your a better Idea if their is any real difference that should give you some concern.
 
#5 ·
You are right, bullet shape can account for 0.005"+. The issue is likely you are not completing the stroke, that & mixed brass affect oal the most. The range you are getting affects little in Pressures or accuracy, as long as you are not into the lands.
 
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#6 · (Edited)
Unless you are shooting beyong 50 yds, COL variation like that just doesn't matter. It doesn't even represent a 0.1" larger group.
Bullet length can affect COL, if the seating stem only contacts the ogive (which, in general, produces better accuracy despite any COL variations).
Bullets in a box of 100 will have variations in meplat and ogive (and length, of course).
One of the better ways to improve this is to get a seating stem custom made to fit the bullets.
You can try a seating die with no crimp section. Lower the die so the press cams over slightly and then set yout COL. This takes all flex out of the system.
For piece of mind, you can experiment. Sort rounds by COL, including several groups of mixed COL and prove to yourself that it doesn't matter.
 
#7 ·
Also, for me, seating & crimping in separate steps always produces more uniform OAL. Again though, even 0.010" isn't changing things much, especially in handguns.
 
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#8 ·
If the bullet is not being seated straight you can end up with larger COAL variations. Adding some more flare usually helps to correct that along with a seating stem that fits the bullet properly.
 
#9 ·
I called Dillon. They are sending me a new blue friction plate (mine is 28 years old). Also they suggest making any adjustments on any station with all stations full, i.e. don't adjust your seating depth without also having a casing in stations one and two and four
 
#10 ·
One thing to consider is that the seating die contacts the bullet with a circumferential footprint. There is some irregularity in the bullet's profile. If you were to cut the bullet into radial sections, they would not all be the same. When you run the round back through the seating die a second or third time, it wont be in the same radial orientation as before, so contact between the die and bullet will also be different. This tends to average out the OAL deltas that come from inconsistencies in bullet shape. Of course there are also other deltas, such as from the cases - especially if you are using mixed range brass.
 
#13 ·
Note: the whole worry about COL variations began with an article about 8 years ago or so about the danger of bullet set-back (it had "bit" a few LEOs who kept chambering the same round day-after-day for a year or more). The change in COL they covered was ¼" (0.25") and not 0.01" (say, a change in COL from 1.100 to 0.850"). The data in this article showed a 9x19 round going from 35 ksi to just over 60 ksi from the bullet pushed in the case 0.25" deeper. So, just as a first "guess," lowering the COL by 0.01 would raise the pressure by maybe 1000 psi.
Currently, one to the manuals warns about a 0.1" variation, but when I asked for pressure data, they no longer had the report or knew where to find it, so it is information with no provenance.
 
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