I'm reloading a bunch of once shot nickel placed 5.56 brass.  I'm going to be loading it with Speer Gold Dot 55g SP bullets.

These bullets do not have a cannelure and have a flat bottom.  

When I sized my brass I used a Forster full size bushing die, with the expander ball removed and the smallest bushing to get .004 neck tension.

I now realize that it's going to be tough seating the flat bottom bullets without either chamfering the inside of the case necks with a VLD chamfer tool or
maybe, just run all the brass thru a Lyman M die to 'flare' the top of the neck a little so it's easier to seat the bullets.

My question is, I can't find anything they hints at why kind of neck tension you would end up with the Lyman M die in 5.56 brass?

Sites selling the Lyman M-Die say it "expands the case neck to just under bullet diameter for precise neck tension in first step. Second step flares case mouth to bullet diameter or slightly over for proper seating."  What does "just under bullet diameter" mean?  Anyone have anu idea what kind of neck tension I would get with this die?

 

Plenty of neck tension.  I think mine measures at .222" so 2 thou neck tension on a .224 bullet.  Never had an issue with setback, both crimped or uncrimped.  I use a FCD set light enough to just give the case a kiss to close the light flare.

Just FYI, Speer crimps the Gold Dot in their .223 LE loadings.  

So I would just do that at the last die with a Lee FCD.  

I also dealt with enough non-crimped .223 projectiles used in AR’s, causing issues during training, that I always will crimp mine anyhow, so that is an easy decision there if it was me.

The Gold Dot 55gr bullets Speer uses in the .223 LE loadings have a cannelure but the new Gold Dot 55gr bullets don't have a cannelure and I haven't been able to find any for sale with a cannelure.   OK, so I figured just to be safe I would set the neck tension to .004 with a Forster neck bushing die.  The problem with the Lyman M Die is it's going to expand the entire neck out to a .002 neck tension and then flare the top of the neck.

So now I'm looking at the Lee Neck Expansion die. It looks like this die only flares the end of the neck without resizing the entire neck.  So, I'll still have my .004 neck tension and the top of the neck flared.  

I agree 100% that the M die is superior.

OP - it wouldn’t be difficult to reduce the diameter of the M die expander by a few thousandths to increase neck tension. Just chuck it in a drill and use emery cloth.

Not that long ago I was seating 50gr frangible bullets using a m-die to expand first. I noticed neck tension was less than 0.002" and many times only 0.001".

Disassembled the mdie and found the expander was slightly loose. Applied some blue loktite and tightened down the expander,

Neck tension became 0.002-0.003" consistently after that. This was with mixed brass.

What issues were you having with the regular expander ball?

I use the M die after the regular expander to just kiss the case mouth enough to prevent copper shaving when seating a bullet.  I know this isn't the normal intended use case, but it works for me for blasting ammo.

I've never used them (yet) but if you really need to fine tune neck tension, I know there are mandrel sets out there that come in .001 or smaller steps.
I haven't crimped a rifle round in I don't even know how long.  If your neck tension isn't holding the bullet, I would look to solve why that is, and not hope and pray band-aiding it with a crimp will fix it.

What caliber M-die is that a picture of? The shank on the expander head looks pretty short! Would that be enough length to expand an entire case mouth all the way to the shoulder transition?

Out of curiosity I just pulled the center rod out of my 223 M die, and the main rod part is .222, while the expander step at the top is .226.
Also mine doesn't seem to have any threaded on part that I can tell at least?  Looks like one solid piece to me.

So that should be .002 of neck tension using the M die for its intended purpose, right?

Now I need to measure the expander balls in my FL dies...

I was using a Forster bushing neck die.  The expander ball in a bushing die really doesn't make any sense because the ball will make the neck the same regardless of how much smaller a bushing you use you use.  Finally called Forster and they said to remove the expander ball if you want more neck tension.  When I removed the expansion ball I started getting .004 neck tension with the smallest bushing.          

Im thinking its 30 Carbine.  I use that one for 300 BO, but could used for x39 stuff as well.

I remembered your posting on this and it was the reason I used loktite to secure the threads.

Initially thought the mandrel OD was too big, but it measure at 0.221 with my calipers. Thought to try your suggestion of loktite on the threads and it worked!

Surprised me that a loose mandrel would oversize neck expansion.

Not seeing what those would do that the RCBS belling spud they include in their pistol die sets would not already do.



Do your Hornady pistol die sets not come with anything that does belling? (serious question as I do not own any Hornady pistol die sets - Hornady rifle yes but Hornady pistol no)

The Hornady pistol expander is really(!) blunt and is why I used the M-die for pistol for a long time.  For PTX's in my Hornady drops I do use the RCBS as its the same size, works great and offers close to the same profile as a M-die when belling.  
I use the M-die for rifle in 223 and 308 on the progressive as it helps eliminate a step and is good enough for blaster ammo on brass that has been SSTL tumbled.

I am using the Lee expander but replaced the sizers with NOE expander plugs for my various calibers.  It provides similar results to your M die.

The Hornady 9mm PTX (for my LNL AP) does the same, just bells and kinda sucks. I then got a Double Alpha PTX that does expand and slight flare… it’s awesome! Definitely an upgrade!