Polish Inside of Seating Stems to Avoid Ring Marks on Bullets
Here’s a helpful hint for hand-loaders from Sierra Bullets. While this article focuses on Sierra’s new Tipped Match-King bullets, the recommended solutions apply to other bullet types as well. The article explains how sharp edges on a seating stem can cause a ring to be pressed into the bullet jacket — especially with compressed loads that resist downward bullet movement. Here Sierra technician Rich Machholz diagnoses the problem and provides a solution.
Solutions for Ring Marks Caused by Seating Stems
by Sierra Bullets Ballistic Technician Rich Machholz
Now that the new Tipped MatchKing® (TMK) bullets are being shipped and shooters are putting them to use I have received several calls regarding marking on the bullet ogive from the seating stem.
The cause can be traced to one of several things. In the .223 and especially with the long, 77 grain TMK seated at 2.250” or even 2.260” most loads of Varget® and Reloder® 15 are compressed loads, sometimes heavily compressed. This puts a great deal of pressure on the bullet through the seating stem. The result of all this pressure is a mark of varying depth and appearance on the ogive of the bullet. [Editor: We have seen this issue with a variety of other bullet types/shapes as well, including non-tipped VLDs. The solution is profiling the internal cone of the seating stem to match your bullet shape.]
Some older seating stems might even bear against the tip of the bullet which can make a slight bulge in the jacket just below the junction of the resin tip and the copper jacket in a compressed load. If this is the case there is not a ready fix other than calling the die manufacturer and requesting a new deeper seating stem.
Polish Your Seating Stem to Remove Sharp Internal Edges
If the seating stem is of proper depth the culprit most generally is a thin sharp edge on the inside taper of the seating stem. This is an easy fix that can be accomplished by chucking a spare 77 grain bullet in your drill, coating it with valve grinding compound or even rubbing compound or in a pinch even tooth paste.* Remove the seating stem assembly from the seating die. Turn the drill on and put the seating stem recess over the spinning bullet with the polishing compound to break or smooth the sharp edge that is making the offending mark. This might take more than one application to get the proper polish depending upon what you use, but the more you polish the better the blend of angles which will [ensure the stem matches the bullet contours, not leaving a sharp ring].
If the above is a little more than you care to tackle you might try very fine emery cloth twisted to a point that can be inserted into the mouth to the seating stem and rotated to polish the inside to eliminate any sharp edges that might be present.
Load Advice for 77gr TMKs in the .223 Rem
And last but certainly not least. Actually, even though we don’t say you need additional data for the TMKs, remember you are dealing with heavily-compressed loads in some cases because of the additional bullet length. Due to the additional length of these new bullets and in the interest of gaining some room in the case you might consider trying a slightly faster extruded powder like BenchMark or the 4895s or an even more dense powder like the spherical H335®, CFE223 or TAC. The extra room will allow for trouble free bullet seating also.
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Tags: bullet, Rich Macholz, Seating Stem, Sierra Bullets, TMK
Good lord, I’d look at neck tension before I started polishing stems.
Editor: Actually, we saw this with some 6mm bullets with relatively minimal neck tension. I quick spin with some polishing compound removed the sharp edge of the stem — problem solved. Another benefit was that the round-to-round bullet seating force seemed a little more consistent, though that is hard to quantify.
What a coincidence! I’ve been working up a mid-range mag-length AR load using the new Sierra 69 gr TMK (I love it!) and I’ve encountered just this problem. I’ve had some deformed bullets that looked even worse than the one in the picture.
In my case, lapping the seater stem to match the bullet’s nose profile helped but didn’t completely solve the problem. (HINT: I ordered some 3.5 micron diamond lapping paste from Amazon for $8 and that worked MUCH better than valve grinding compound from the auto parts store.)
The biggest contributor to my problems turned out to be excessive neck friction, which resulted in very high seating force. Once I solved that issue, the marks from the seater stem essentially went away. So, if you’re getting marks from the seater, make sure that your neck tension (friction), seating force, and bullet removal force are “reasonable”.
I still haven’t got to the root cause of my problem, but it’s probably due to the processing techniques used by my brass supplier. I’m using once-fired Lake City brass that has been sized, cleaned, and trimmed by the supplier. On the outside it looks beautiful, but the necks are tight and VERY “grabby”, perhaps due to their cleaning process. So, watch out for “etched” necks that are “too clean”. (There, that ought to set the hornets buzzing…)
This is a good idea but horrible execution. Spinning the bullet against a stationary, hand-held seating stem is almost guaranteed to create an eccentric cavity in the stem. Instead, chuck the stem and rotate it against a hand-held bullet.
Editor: Your suggestion is a good one. However, the method shown actually works OK. In practice, it doesn’t take long, the lapping compound provides a bit of a barrier, the stem naturally self-centers.
This just happens to me with new 6.5 Creedmoor Lapua brass. Great article! Thanks for the tip!
Great. I’ll be trying this. Ran into this issue with 136 grn Lapua Scenar-L’s while loading up a few different bullets to try. It was NOT too much neck tension or a compressed load causing it – and the 3 other bullets were fine. It was also giving grief with consistent seating depth. I had to back off ten thou and turn down each round.
Then you have David Tubb’s nosering:
http://www.davidtubb.com/index.php?route=product/search&search=nose%20ring
https://www.warner-tool.com/product/338-285gr-flat-line/ – Tubb ring mod option
VLD stems like those I use from Redding don’t solve this problem? I also thought these rings had no effect on bullet flight.