Sinclair Turning Mandrel question

[jepp2]

Found the book by Brennan. $150

A product of being out of print and high demand. I bought mine new from Amazon for around $22 many years ago.

 

[Willie]

I'll take a stab at this. Even though it'll be my first post. I have been experimenting with neck sizing, using an expander mandrel, for a little over a year now and I have come to a few conclusions. I neck turn all my brass with K&M tools, so I use their die bodies and expand mandrels for getting consistent neck tension. I am going to use a new 6.5-284 w/.296" neck as an example. I expanded and turned necks on new Lapua brass to .014" and neck sized with a .290" bushing. I did not anneal until after fireforming. I cleaned and bumped .0015" and neck sized w/.290 bushing. I then checked ID with pin gauges and there was very inconsistent felt tensions, some being +/- .0003". I set 5 of the random cases aside and loaded them with a known load of Retumbo @ my high node. For comparison, I then took 5 random cases and ran a K&M .262" sizing mandrel thru the necks and loaded the same charge. All were pushing BTO sorted 140 gr Berger HVLDs at exact CBTO of 2.4145". The bushing sized only cases shot a .780" group, sd-14.6 ed-20 @ 100. The 5 cases that were sized with the .290" bushing AND then with the .262" mandrel shot a .276" group, sd-3.3, ed-6.0 in same conditions. It will take a lot more rounds to verify if the sizing mandrels will be a consistent improvement in neck tension, but I have had similar results in a custom .280 rem, consistently shooting .2". It's a start. The real questions I have at this point are: 1] Will the neck concentricity be effected by the unsupported " mandrel die"? 2] How often will cases need to be annealed to off-set differing amounts of spring-back? My limited testing seems to lean towards annealing after every firing. By the 3rd firing, there seems to be no difference between results. 3] Is it worth the extra equipment and added steps involved? That will be up to each shooter.

 

[mikecr]

The real questions I have at this point are: 1] Will the neck concentricity be effected by the unsupported " mandrel die"? 2] How often will cases need to be annealed to off-set differing amounts of spring-back? My limited testing seems to lean towards annealing after every firing. By the 3rd firing, there seems to be no difference between results. 3] Is it worth the extra equipment and added steps involved?

Not sure what you mean by unsupported, the die is supported by your press, and I would want the mandrel itself floating a bit from there(my Sinclair does). Your tension, lower/consistent as annealed, should be declared to you by your load/barrel testing.
So if annealing every cycle shoots best for you, then that's what I would pay for. I'd get the best annealing system I could in that case.
If your system likes higher tension then I would manage it as consistent through minimal sizing. That would begin with less than your 4thou of neck clearance.
But it sounds as though you're homing right in on best for you. Keep going

Oh, and I would part with that [Precision Shooting -Reloading Guide] for half the going (AMAZON) rate!

 

[Willie]

You are right on about annealing. Got all my pilots in today for the AMP [excepting a couple of special ones]. The unit, hopefully in a few days. Been using a friend's AMP for awhile. I was referencing the fact that most of the mandrel dies are made for multiple calibers. Kind of a one size fits most deal. I was hoping to expand in my Co-Ax press for the float, but K&M die won't fit, so using the T-7. I've not had a problem (yet) with neck concentricity, was just wondering. Who can measure how much float? It's trial and error for me. haha I know that it'll be awhile before I can say yes or no, as to how it will work out for me. I do like the Sinclair die, in that it would fit in the Co-Ax, but I don't believe it will take the K&M mandrels and Sinclair does not have a wide range of mandrels for testing a variety of tensions. It is an interesting method. Expanding necks on new brass for fireforming can sure result in some very low EDs. That's why I'm into trying this.

 

[mikecr]

You can adjust tension with a neck bushing. That is, length of your downsizing(not diameter reduction).
I don't see how you would adjust tension with an expansion mandrel, as these are difficult to partial length expand with.

Let's say you have .300" of seated bullet bearing. You could adjust the length area of spring back against that bearing. Reasonable would be ~.125 to.300 bushing sized length. That is the area you choose to grip that bearing, regardless of pre-seating/expansion.
For way higher tension, you could size more length of the neck, putting spring back in a bind against bearing/base junction. But this will greatly increase tension variance, especially where bringing donut area into that tension. This is useful for underbores running extreme pressure loads, that take them deep into diminished returns(which is also diminished variance). No good for LR capacities, as these will be affected by tension variance.

Pre-seating(mandrel expansion) is useful to drive thickness variance outward away from seating bullet bearing. It also reduces seating forces for better precision in CBTO. I built a loadcell into my Sinclair mandrel die for measuring pre-seating forces. This provides opportunities for me to adjust neck sizing lengths as needed to match these forces. While my necks have a consistent carbon layer(friction coefficient), seating forces correlate, comparatively, with tension.

That's the best I can do, but it's still important to understand that nothing about this directly indicates actual tension. There is still diametric area(cal), and gripping geometries that influence the forces needed to release a bullet.
.250" length of full spring back gripping a bullet, is more in 30cal than 22cal, and 40deg shoulders hold a neck hoop tighter than 20deg shoulders, etc.
Expansion mandrel use plays no role in this.

 

[rgmeddn]

Just a relative newcomer asking a question. Hopefully not a dumb one. Which dimension is more important? Is it concentricity of the inside diameter of the neck or concentricity of the outside diameter of the neck with the centerline of the bore?
I realize that neck turning should make them both be equal but it seems that the mandrells result in the most perfect alignment with the centerline of the bore.
So then couldn't you use the bushing depth of the neck the way you do except maybe a little bit tighter and then use just the right custom mandrel for the narrowed section to more perfectly center on the bore?

 

[mikecr]

The best we can do is make straight ammo. This won't be perfectly centered to the bore, as chambered, but it won't be under chambered tensions either, provided normal shoulder bumps. If you're implicating a false shoulder(minus crush fit) for centering, bushing/partial neck sizing of fire formed brass provides for it.
And brass is consistently straightened, at least some, only through firing it in your chamber.
Don't count on a mandrel, bushing, or any type of sizing die to straighten ammo. The best these can do is not add runout to those straight rounds pulled smoking from your chamber.

When you seat a bullet, thickness variance is driven outward just as it is with a mandrel. Problem is that the side forces to do this affects straight seating.
If you have a 1/2thou of thickness variance around your neck, run a mandrel through for pre-seating, then seat a bullet, you would read most of the 1/2thou as runout on the loaded neck(with a v-block type measure). But, you would read little to no runout with the indicator on exposed bullet bearing. Short of turning, this is the best you can do with necks.

Since you can't turn the bodies, and if body sizing, mitigating banana production means culling away all cases with thickness variance right from the git-go. Then, minimally sizing using a custom/well fitting die.

 

[Willie]

You can adjust tension with a neck bushing. That is, length of your downsizing(not diameter reduction).
I don't see how you would adjust tension with an expansion mandrel, as these are difficult to partial length expand with.

Let's say you have .300" of seated bullet bearing. You could adjust the length area of spring back against that bearing. Reasonable would be ~.125 to.300 bushing sized length. That is the area you choose to grip that bearing, regardless of pre-seating/expansion.
For way higher tension, you could size more length of the neck, putting spring back in a bind against bearing/base junction. But this will greatly increase tension variance, especially where bringing donut area into that tension. This is useful for underbores running extreme pressure loads, that take them deep into diminished returns(which is also diminished variance). No good for LR capacities, as these will be affected by tension variance.

Pre-seating(mandrel expansion) is useful to drive thickness variance outward away from seating bullet bearing. It also reduces seating forces for better precision in CBTO. I built a loadcell into my Sinclair mandrel die for measuring pre-seating forces. This provides opportunities for me to adjust neck sizing lengths as needed to match these forces. While my necks have a consistent carbon layer(friction coefficient), seating forces correlate, comparatively, with tension.

That's the best I can do, but it's still important to understand that nothing about this directly indicates actual tension. There is still diametric area(cal), and gripping geometries that influence the forces needed to release a bullet.
.250" length of full spring back gripping a bullet, is more in 30cal than 22cal, and 40deg shoulders hold a neck hoop tighter than 20deg shoulders, etc.
Expansion mandrel use plays no role in this.

 

[Willie]

Mike, you're spot on about length of bushing sized necks setting the amount of neck tension. What I have experienced with the bushing, is when checked with a pin gauge, not every ID will show exactly the same fit.

My first step is to use the bushing sizer to set the length of bushing reduction on the neck, then gauge it --- looking for ANY inconsistencies in ID. Those cases get resized with the mandrel. It will not size the neck below what I have sized with the bushing.

This experiment is time consuming and not without it's disappointing moments, but I'm finding there is no measurable run-out induced and there is a slight reduction in the already single digit EDs. I'm at the point where I'm most likely the limiting factor. Just thought it was worth trying for the heck of it.