How to Improve Case Concentricity with Standard Seating Dies
Each Wednesday, the U.S. Army Marksmanship Unit publishes a reloading “how-to” article on the USAMU Facebook page. This USAMU “Handloading Hump Day” article, the second in a series on improving concentricity, has many useful tips. If you use standard (non-micrometer) seating dies when loading some cartridge types, this article is worth reading. And visit the USAMU Facebook page next Wednesday for the next installment.
Once again, it’s time for USAMU’s “Handloading Hump-Day!” Last week, we addressed achieving very good loaded-cartridge concentricity (AKA “TIR”, or Total Indicator Runout) using standard, “hunting grade” reloading dies.
We explained how to set up the Full-Length Size die to float slightly when correctly adjusted for desired case headspace. We also cited a study in which this method loaded ammunition straighter than a set of [higher grade] match dies from the same maker. [One of the keys to reducing TIR with both sets of dies was using a rubber O-ring below the locking ring to allow the die to float slightly. READ Full-Length Sizing Die TIP HERE.]
Now, we’ll set up a standard seating die to minimize TIR — the other half of the two-die equation. As before, we’ll use a single-stage press since most new handloaders will have one. A high-quality runout gauge is essential for obtaining consistent, accurate results.
Having sized, primed and charged our brass, the next step is bullet seating. Many approaches are possible; one that works well follows. When setting up a standard seating die, insert a sized, trimmed case into the shell-holder and fully raise the press ram. Next, back the seating stem out and screw the die down until the internal crimping shoulder touches the case mouth.
Back the die out one-quarter turn from this setting to prevent cartridge crimping. Next, lower the press ram and remove the case. Place a piece of flat steel on the shellholder and carefully raise the ram. Place tension on the die bottom with the flat steel on the shellholder. This helps center the die in the press threads. Check this by gently moving the die until it is well-centered. Keeping light tension on the die via the press ram, secure the die lock ring.
If one were using a micrometer-type seating die, the next step would be simple: run a charged case with bullet on top into the die and screw the seating stem down to obtain correct cartridge OAL.
However, with standard dies, an additional step can be helpful. When the die has a loosely-threaded seating stem, set the correct seating depth but don’t tighten the stem’s lock nut. Leave a loaded cartridge fully raised into the die to center the seating stem. Then, secure the stem’s lock nut. Next, load sample cartridges and check them to verify good concentricity.
One can also experiment with variations such as letting the seating stem float slightly in the die to self-center, while keeping correct OAL. The runout gauge will show any effects of changes upon concentricity. However, the first method has produced excellent, practical results as evidenced by the experiment cited previously. These results (TIR Study 2) will reproduced below for the reader’s convenience.
| TIR Study 2: Standard vs. Match Seating Dies
50 rds of .308 Match Ammo loaded using carefully-adjusted standard dies, vs. 50 using expensive “Match” dies from the same maker. Standard dies, TIR: “Match” dies, TIR: AccurateShooter Comment: This shows that, with careful adjustment, the cheaper, standard dies achieved results that were as good (or better) than the more expensive “Match” Dies. |
These tips are intended to help shooters obtain the best results from inexpensive, standard loading dies. Especially when using cases previously fired in a concentric chamber, as was done above, top-quality match dies and brass can easily yield ammo with virtually *no* runout, given careful handloading.
Similar Posts:
- Smart Advice for Reducing Run-Out with Standard Seating Dies
- TECH Tip: How to Reduce Run-Out with Seating Dies
- How to Load Straighter Ammo with Reduced Cartridge Run-out
- Try Using O-Rings with Sizing Dies for Reduced Neck Run-out
- Watch Out for Bullet Nose Contact in Short Seating Stems
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Tags: Concentricity, Handloading, Reloading, Seating Die, Stem, TIR, USAMU
Thanks
Nice artical. I use a fender washer, about .20 at the hardware store to square the die putting it between the ram and die.
I started reloading with LEE product the whole die kit cost 65 dollars and I got really good result with it. Now I have MATCH dies and I get really good result with it. This trick works with all type of dies inexpensive and expensive. And by that … I really want to say, do not get discourage by expensive tool at the start, try the standard dies, less expensive press and just get into it.
My most valuable tool was and still is this website!
Mike
I’ve always found that the amount of neck clearance is the most significant contributor to runout. If you shoot thick neck cases like Lapua, you have less neck clearance in the chamber so less neck reduction is required. Since you are reducing the diameter less, you therefore reduce the probability of inducing runout.
This is the number one case for a tight neck chamber… If you only have 0.002″ of neck clearance then you cannot create 0.003″ runout during the resizing process… its impossible…. unless your dies are messed up.
As someone who worked in the Cold Heading Tool & Die field for over thirty years ; and working in .0001 ( tenths ) I can state that you can achieve a greater bullet TIR than the .002 of the case O.D. TIR of .002 .
If the bullet is pressed into the case slightly crooked to start with, as all bullets are , it may , or may not straighten itself up as it is being pressed to full seating depth . You can check TIR of the case neck , and get .002 or less , and still have a bullet “running out” of eccentric TIR greater than the case . It will chamber in the +.002 chamber , but the bullet will still be out of TIR by at least half the clearance of the chamber , or .003 from Neck TIR .
In simple terms the bullet will be crooked inside the case , and the neck area in the chamber will not straighten the bullet as it is being chambered , because it is still within the Chamber neck clearance . But it will chamber .
This is exactly why Cold Heading Die pieces are made .0005 – .001 under-sized , and final lapped after assembly .
Gene – and who makes such reloading dies?
Would be very interesting to see the results with the “Match” dies set up the way the standard dies were.
To ELR Researcher ;
Cold Heading tooling is all done “in the round”, as are reloading dies . The correlation I was trying to make was bullets , cases and chambers are all also “in the round” and the same geometry and principles apply to both .
Cold Heading tooling is used to make bolts and screws and other fasteners . And generally speaking ; at much tighter tolerances than the average reloading dies . Not quite sure where you came up with the idea that anyone making cold header tooling made loading dies , also . Though it wouldn’t be that difficult .
The response was in regard to a discussion of TIR and the comment Mike made regarding the impossibility of having a TIR greater than the size of the +.002 of chamber over-size . A bullet , a case , and a chamber . A circle within a circle , within a circle . Plus the thickness of the brass that will allow for a bullet to have a greater run-out than .002 …And still fit in the chamber neck area . The neck area of the case will fit in the chamber neck , but the bullet inside the case neck can be tilted by as much as half the thickness of the brass . Which can greatly exceed .002 run-out on the bullet .
When working with relatively thin turned necks, and FB match bullets with pressure rings at their bases, I have found that when bullets are seated to engage the rifling that runout can reduce as the bolt is closed. To learn this I did a test where I intentionally caused a round to have .0035 runout and then chambered it and remeasured it. After being chambered with a neck clearance of about .0015 the round had .0015 runout. IMO the thin neck, relatively short bullet insertion into the neck and pressure ring combined to allow the bullet to pivot in the neck much like a ball and socket joint. Also, BT bullets tend to seat straighter than flat base. For chambers with larger clearances in the neck, and ammunition that is set up so that bullets do not engage the rifling, the entire burden is placed on the quality of the brass and the fit of the dies.
If one has to use a one piece FL die that has not been modified, for loading cases that have not had their necks turned, doing the requisite neck expansion with a separate die and expanding mandrel will give better results. The neck IDs need to be lubed and the work done carefully. Also, when sizing you can lower the ram to some point where the expander is not engaged and turn the case half a turn and raise the ram again. This may improve concentricity. The same sort of thing can be done when seating, by seating half way, rotating and then finishing.
I have tried endlessly to reduce case neck runout but what works best is to run a tight neck chamber.
Measure fired cases from any chamber and the neck is always concentric to the body… until you resize it.
The more you need to reduce the neck diameter the more opportunity to drift off center.
Conversely the less you need to reduce the neck diameter the less opportunity you have to drift off center.
Now short of custom chambers you can always just run thick neck brass like Lapua. That will help reduce the amount you have to reduce the fired neck to fit a bullet.
Since Winchester cases are one of the thinnest, they are also one of the most difficult to keep concentric… for reasons stated above.
This has been the most interesting and useful commentaries that I have read so far.
One question:
Why measure bullet runout near the case mouth?
I measure bullet runout halfway near the tip, I think that I get a better reading using the longer radius from the vgroove support.
No problem with my Forster coax press
I get the same TIR with standard dies and BR dies. I recently learned the press top bushing wasn’t even/level across nor was the die rings. I used 400 and 600 wet sand paper for both. I square off dies for TIR of .001 -.001 BRO seating with standard Redding and RCBS seating dies. Sizing…. .0005 neck TIR, along with .012-.0125 neck thickness. Full length neck TIR is usually
.0005 with turned necks. I have to use neck mandrels 21st century to achieve this.