Do I have a neck tension problem??

[PaulieV]

Folks,

I'd really appreciate your help with a question that has been bugging me relating to the neck tension on my 6.5 Grendel brass. I'm not hugely experienced with reloading bottle necked cases; most of my experience to date has been straight walled pistol rounds (38/357 & 40 S&W), however it feels to me that there might be too much tension on my projectiles - as they are seated as there is a bit of pressure and I am getting faint rings on my projectiles from the seating die, not to mention I struggled removing one bullet with a kinetic bullet puller. The rounds work no problem at all with no pressure signs and acceptable accuracy when I do my part.

A bit of info below to help with the diagnosis:
Brass: Hornady once fired (factory American Gunner/Black)
Projectiles: 123gr ELDM
Dies: Forster Full length sizing/Bench rest seating. I've also checked the sizing ball is 0.264" and located in the right place per the info with the dies.
Brass thickness at the neck: ~0.015"
Unsized neck diameter: enough for a projectile to drop into
Sized neck diameter internal: ~0.258"
Sized neck diameter outside: ~0.288"

My real question is this normal for this brass, or should I be adding another step to get the internal neck diameter to closer to 0.260" through either outside neck turning the brass or something like a 0.264" KM expander mandrel? I know I should have probably started with Lapua brass but 200x American Gunner loaded ammo was cheaper than 100x Lapua brass.

Thanks in advance.

Paulie

[SCJim]

Are you happy with your groups. Do you damage your bullets when seating?

I personally size all my brass to a ID of .002-.003 below bullet diameter but as long as you are not damaging the bullet with your current setup then go for it. In Modern Advancements in Long Range Shooting Vol. 2, chapter 6 Bryan Litz found .003 to be optimum neck tension for .223, .243. and .308 so I just run with it for everything. If you want to expand your necks a bit 21st Century https://21stcenturyinnovation.com/ has a great line of expander mandrels and the die needed.

[grendelnubi]

Good advice. Couple more things to be mindful of.

1. Check outside neck diameter before and after seating the projectile. 2 to 3 thousands is what I am seeing.
2. Chamfering will help reduce the pressure required to seat.
3. Flat base projectiles generally require more seating pressure than boat tail projectiles.
4. You may see a slight ring in the projectile casing after seating depending on projectile jacket thickness. For example I see this if using nosler 129 ABLR projectiles.

[Klem]

Paul,

Yes, that is a lot of neck stretch, but not necessarily tension.

123ELD measure .2642" in diameter. Plus two lots of 0.015" neck thicknesses = 0.2942" OD when loaded. The difference between a loaded and sized case is 0.2942 - 0.288 = 0.0062". As Jim is saying, Litz thinks .003" to be optimum however it will be down to the action and other things like brass ductility, case thickness, and how much surface area is gripping the shank.

I use 0.004" on an annealed case to grip as much as possible. The reason being that semi-autos need a lot of grip to stop the bullet from shifting when fed and slammed into battery.

Your .0062" does not necessarily mean a stronger grip on the bullet. It depends how ductile (elastic) that brass is. As the case gets work hardened from multiple expansions and contractions it loses elasticity. It gets to the point that although getting stretched .0062" the bullet now comes out easily with a kinetic hammer. You can restore a lot of elasticity by annealing. Or simply swap out the brass. Right now however it is the opposite, being gripped more than necessary. Great for semi-autos. Shouldn't affect anything however, except case life. Those rings from forcing the bullet in, again, shouldn't affect anything because they will be concentric. If the bullet ring caused by the seating die influences external ballistics then all bullets will be similarly influenced, so it doesn't really matter. Regardless, those ring marks from seating will do almost nothing to bullet flight.

Lapua cases are 0.0135" neck wall thickness. Yours are thicker which accounts for the difficulty. You could neck turn them if you want. What you shave off directly reduces neck tension.

In your shoes I'd wouldn't worry unless it affects accuracy. A soon as you swap out that brass for a brand with thinner necks it will be more normal.

[VASCAR2]

I use a RCBS case mouth deburring and chamfering tool which helps in seating bullets. It really helps to chamfer the mouth when seating flat base bullets. The only down side with to much bullet tension might be crushing the shoulder of the case or deforming the case mouth when seating bullets. On many military rifle cartridges the bullets have an asphalt sealant to keep the bullet from moving when being fed in semi autos. The sealant also helps seal the cartridge from moisture or other contaminants.


Personally I’m more concerned about bullets jammed into the lands than the tension on the bullets. Jamming bullets into the lands can spike pressure and pull bullets from the case when trying to extract a live round. I found 29 grains of TAC loaded behind a 95 grain V-Max was not a good thing dumped into the action of my AR-15. I had seated the V-Max to long and it was stuck in the chamber. Mortaring pulled the case, dumped the powder and left the bullet stuck in the barrel. I’ve only made that mistake once, but once was enough.


The RCBS tools seem to be out of stock but here is a link to Hornady’s deburring tool.

https://www.midsouthshooterssupply.com/i...eburr-tool

[SCJim]

Paul,

Yes, that is a lot of neck stretch, but not necessarily tension.

.

That statement is spot on. It depends on the amount of work hardening your brass has accumulated. Damon Cali of Bison Ballistics explains it better than I can

At first, the bar stretches linearly with the force applied - for every x pounds of force that you apply, you get y inches of stretch. If you were to stop pulling somewhere in this linear region, the bar would immediately snap back to its original size, unharmed. This is called elastic deformation. Elastic deformation does not permanently alter the material.

But if you keep pulling, you will hit a point where the line noses over. This is called the yield point, and indicates the point at which the material will no longer return to its original shape. If you let go past this point, the bar will snap back a little (the elastic portion of the deformation remains reversible), but there will be some permanent (known as plastic) deformation remaining

https://bisonballistics.com/articles/the...-annealing

Just my opinion here but I find the easiest way of getting consistent velocity and eliminate a lot of unexplained flyers is to only stretch the brass .003 during the seating process and anneal after every firing. Again just my opinion because other excellent shooters get good results with other methods, this is just what works for me

[GREYBUFF]

I found that after having three cervical discs fused that I have too much neck tension......

[PaulieV]

Thanks Gents, this is fantastic advice and has put me at ease. A great example of the wealth of knowledge we have on this site!

Klem/SCJim, this is great info which is going into my knowledge bank. I think I'd come across that article in my searches but had worried that I was meant to meet that yield point. I know I'm not going to get heaps of loads out of this brass so will keep an eye on that tension v stretch differentiation which I hadn't realised existed .

Nubi/Vascar that chamfering/FB point is great, I hadn't chamfered the brass yet as it was all within spec so hadn't needed to trim but now had planned to include that regardless. I'm not worried about the lands yet as I seem pretty far away so far despite my COAL. I'm using a Howa Mini action and had seated them right out at mag length with no indication that they are touching yet (was looking out for it when I was testing the chamber fit).

Greybuff, suggest you anneal with a good wheat pack in the microwave for a couple of minutes and then neck application for 15 mins.

Cheers

Paulie

[SCJim]

if you want to see how much compression you are getting just seat a bullet, measure the OD of the neck, pull the bullet and remeasure.

[kmon]

An easy way to check for the bullet contacting the lands is color the bullet with a sharpie and chamber it. If it is contacting the lands you will see marks in the sharpie coloring. Back when I learned reloading we did it with a candle or match to coat the bullet in soot then chamber and look for the rub marks. Worked but sharpie is easier. That was in my first reloading manual from Speer as was case annealing using a propane torch and a pan with water in it. Stand up the cartridges in water and heat the mouth and neck of the cartridge with the torch. Not the best method but worked