Seating depth dilema....

[griffgil1]

K, try to make this short- and not leave out important info.
Loading for .308 target rifle, Lapua brass, 175 SMK bullets.
Measuring and grouping all bullets for weight and length to ogive.
Trimming all cases to 2.005. Using .335 neck bushing (.001 down from loaded neck diameter).
Problem is erratic seating depth. About one in ever 3-4 are seated up to .007 too deep- never a problem with too long of a seat. I can live with a a certain amount being off by .001-.002, but 30% or so .004-.007 too deep? Not cool at all.
Can't for the life of me figure out what variable is causing this. I took apart a handful of the rounds in question, re-measured all parameters on the bullets and cases (case h.s., base to ogive length, overall case length, etc), and all measurements or in the green. Also took the seating plug out of the die, placed it on top of numerous bullets, and measured the OAL that way (thinking that the bullet diameter at the seating contact point was varying)- these numbers were also ok, within .001 variance or less.
Tried using both a Redding T7 press and a Forester CoAx, but same problem on both- so it's not a press issue. Took the seating die (Redding competition seater with micrometer dial) apart, cleaned it, readjusted it in the press, and still the problem is there.
PLEASE HELP!!! I'm a smart, very mechanical guy, and not new to reloading, but I can't figure this out. Thanks

 

[Toby Bradshaw]

Not enough neck tension -- go with a bushing 0.003 under the loaded neck diameter and I'll bet that your seating depth problem goes away.

 

[griffgil1]

Interesting....I do notice that the lever pressure required when seating is kind of "all over the place"....some slide in like butter and some I can almost "feel" the friction. Less of this issue when using virgin brass- go figure. I will try going down in bushing size by .001 increments and see if it works. Thanks.

 

[/VH]

Probably what tobybradshaw said but while you had the seater plug out did you check to make sure the bullet tips are not bottoming out in the plug? Check it with several bullets, if not.

 

[Toby Bradshaw]

Less of this issue when using virgin brass- go figure.

That's because the virgin brass is softer, and springs back less after sizing. After a couple of firings, it's pretty common for brass to spring back 0.001, so when you're sizing with a bushing just 0.001 below the loaded round diameter, the springback is enough to let some bullets slide too deep because the inside of the neck is barely (if at all) smaller than the bullet shank.

If you were using an arbor press instead of a bench-mounted press, you'd be better able to feel the difference in bullet seating force.

 

[6BRinNZ]

Check out Erik Cortina's youtube channel for another reason that causes inconsistent seating depths.

https://www.youtube.com/watch?v=cM4JwC5Wj8U&list=PLJm6jq3qGs_oaO4dv90BapFpmvj2kzb71

 

[Joe Salt]

If your seating stem is wrong and touching the point like the other guys said. And are you using any Lube inside the neck like Moly or graphite.If not you are galling the inside of the neck when you push the bullet in dry. If you don't lube the lugs on your bolt the same thing will happen!

Joe Salt

 

[lpreddick]

Varying resistance when seating bullets(single stage old rcbs) will always get me varying depths! My problem is when a bullet is "hard" to seat it will always be long and when "easy" it seats deeper. The tip of the bullet (hard ones) go INTO the seating stem a few thous leaving a noticeable ring on the bullet's tip, whereas the easy ones get pushed into the neck with a very small mark on the bullet's tip. Neck resistence is at play here whether it's due to old brass(work hardened and needing annealing) or too tight a neck(varying neck thickness needing turning or too much sizing). Sizing .001 under loaded neck diameter lessen this problem whereas sizing .002+ can worsen the situation. I'v tried filling the seating stem with an assortment of materials such that the bullet can't enter it but this has been a technical failure. Annealing and neck turning (the two tasks I enjoy the least) seem to keep this occurrence to a minimum. One other observation...if a bullet seats long, set it aside for a few minutes, then run it back thru the press, with no changes, and it will often seat to the desired depth! I think the overly tight neck has relaxed just under the bullet's base.

 

[Erik Cortina]

It is likely due to inconsistent neck tension. Do you chamfer your necks?

 

[bill123]

6BRinNZ,
Looks like an interesting device but I thought that the preferred way to length sort was by bearing surface to get more uniform surface contact between bore and bullet.

 

[Erik Cortina]

6BRinNZ,
Looks like an interesting device but I thought that the preferred way to length sort was by bearing surface to get more uniform surface contact between bore and bullet.

Let me answer this one. The sorting way I showed on the video is to obtain consistent base to ogive measurements, bearing surface sorting does something totally different. Bullets have to be sorted in more than one way.

 

[bill123]

Eric, Thanks for the reply!

 

[mikecr]

Measuring and grouping all bullets for weight and length to ogive.

Also took the seating plug out of the die, placed it on top of numerous bullets, and measured the OAL that way (thinking that the bullet diameter at the seating contact point was varying)- these numbers were also ok, within .001 variance or less.

If I read this right, OP essentially covered the function of a BGC,, verifying ogive radius consistency. Good move.

I'm guessing it's big variance in seating forces. This variance is increased with more sizing (not reduced).
The whole purpose of lighter neck tension is to utilize lower variance in it.

 

[Raythemanroe]

I'm gonna ask if you have measured your tool, where does it contact in comparison to the seater? I like or think it is better to have a comparator that is close to bore dimentions. Even if you do get consistent measurement it may not relate to real world bore dimensions therefore giving you a false sense of concentric.


Ray

 

[222 rem]

Aneal cases and clean.
Concur it could be neck tension.

 

[lpreddick]

i was loading NEW brass last night and this nightmare bit me...only .002 thous under loaded neck but pressure to seat bullet was higher than with fired brass...very common. seating stem made quite a dent in bullet's tip and seating depth varied .007!!! tried dry lube on bullets but no change. i don't do this very often but i applied a very light coating of case lube (my own concoction of lanolin,atf and 10-w 30) and every bullet seated with the same pressure and a very slight mark from the seating stem. seating depth was perfect and all the same! that little bit of powder residue in fired cases acts as a dry lube. fired cases rarely give me this problem and when they do , time to anneal. do those using ultrasonic cleaners have this problem?

 

[michaelnel]

do those using ultrasonic cleaners have this problem?

I had that problem both with my Thumler's Tumbler and my ultrasonic cleaner. On the advice of an accomplished shooter here, I no longer wet clean my Dasher brass. I clean the neck / shoulder area with 0000 steel wool, I clean out the primer pockets with a 21st Century uniformer, and I run a rotating 6mm nylon brush inside the neck. Then I anneal, size, and tumble in corncob to get the Imperial Case Wax off the outside.

I too believe the carbon on the inside of the neck acts as a lubricant. The bullets seat smoothly with the above process, and they shoot really well.

 

[Raythemanroe]

I add a bit of graphite to the necks before seating


Ray

 

[lpreddick]

The dry lube I tried was a graphite product...more messy than the lube I used. What ever works.

 

[Elkbane]

Griff,
My $.02.

The one variable you haven't accounted for is variation in the shape of the NOSE of the bullet. As Eric pointed out in one of his excellent videos, the point at which the seater stem contacts the nose is what sets the seating depth (and nothing else - once your dies are set), excepting mechanical/friction variances. The distance from that point to the base of the case is set by the depth you've imposed with your micrometer top. Even if you've sorted the bullets base to ogive, you still have variation in the shape of the nose from ogive to tip. I think that's what you're seeing, the effect of that variation on your measured seating depth. From what I've experienced, SMK's a have quite a bit of variation in nose shape. In fact, in some of my measurements, they were all over the map - I don't shoot them much, only 130g 7mm's so it's not an indictment on Sierra, nor is it a broad sample. .

You can see what I mean if you draw two equal width and height rectangles on a sheet of paper to represent the shanks of two bullets. Now draw a short triangle on one and a long triangle on the other. On the short triangle, divide the height roughly in thirds and draw a line across it at the top of the second third. That represents where the seater stem hits. Measure the diameter at that point. Now find the point on the long triangle where that diameter exists and draw a line across it. That's where the seater stem would hit a bullet with that nose shape. Look at both the lines you just drew. That is the difference in seating depth you'd get from seating those two bullets with exactly the same base to ogive measurements (they are rectangles of equal length) .....


If you want to test a few, you can do it by inking your tips on bullets you've already sorted to ogive, then rotation them inside the tip of your seating stem to mark the ink. Another way is to install a .20 cal insert on your Hornady tool and take some measurements from your sorted bullets with that - use the .20 cal insert as a proxy for the I/D of your seater stem. If those measurements are close, the problem is probably not nose shape. If those measurements show high variation, your seating depth will as well.
Elkbane