Expander Mandrel?

[papajoe222]

I've read a number of posts where an expander mandrel is ecommended for obtaining consistent neck tension. I've searched a number of suppliers for one in .308, but my search comes up empty. Is there another description that they are sold under?

 

[Scott Harris]

I suggest a carbide "turning" mandrel, available from Sinclair/ Brownells, PMA Tool and many others. The turning mandrel is .002 under bullet diameter. An expander mandrel is only .001 under bullet diameter: too little neck tension for my tastes.

 

[chuckshooter]

I think you're talking about the K&M expanding mandrel kit. I don't have one but I'd like to. If you do a Google search. Search for " case expanding mandrel.". That might help

 

[Willie]

I use K&M expander mandrels. They are available in .0005" increments, I believe they start at .0010 under caliber. I have .002, .0025 and .003 under for each of my hunting rifle calibers. You'll need a die body ( works for all their mandrels). They will also grind any diameter mandrel, you may need. Or you can buy the Porter collet die and use cheaper pin gauges to expand to desired neck ID.

I use FL dies, without the expander ball, to size the neck down and the mandrel to set neck tension. Works great for consistency.

 

[newbieshooter]

another reference/source (5/14 bulletin): http://bulletin.accurateshooter.com/2019/05/precision-expander-mandrels-from-21st-century-shooting/

 

[ToddKS]

I like the 21st Century mandrels better than the K&M personally (own both). 21st century offers them in .0005 increments.

 

[B23]

I use FL dies, without the expander ball, to size the neck down and the mandrel to set neck tension. Works great for consistency.

I think this works well, particularly, when you want a specific neck tension and you don't have a bushing die, and, in theory, if brass isn't neck turned and of equal thickness all the way around, by using a mandrel as your final step to set neck tension, it will push any thick spots to the outside of the neck instead of them being on the inside.

 

[Howland]

I like the 21st Century mandrels better than the K&M personally (own both). 21st century offers them in .0005 increments.

I went with the 21st Century mandrels and am very pleased. I read one review of the K&M where the user ordered 0.003" tension (Yes, they actually list the mandrels on their website in tensions, not mandrel size.) and was disappointed to measure the same 0.002" under that he already had with his expander ball. He called their customer service and was told they allow 0.001" for springback.

I observed erratic velocity ES with my .338LM and theorized it might be due to insufficient neck tension. Using the 0.3350" mandrel got my groups from .61 MOA previous best down to .51 MOA new best. I bought 0.3340" to 0.3355." I guess my rifle just likes that .003" interference fit.

Now I just need to figure out why that nut behind the buttstock won't stay tight.

 

[Ned Ludd]

For a time, I processed .308 Win and .223 Lapua brass using bushings that were approximately .002" under that necessary to give ~.002" neck tension (interference fit). I then opened the necks up in the second step using a carbide neck turning mandrel that was .002" under bullet diameter. My reasoning for switching was that I do not turn necks. I figured any imperfections in neck wall thickness will be pushed to the outside, and if anything, the necks might even end up a bit straighter.

Bottom line - in my hands this approach generated no detectable improvement to the brass than the use of FL resizing die with the appropriate bushing. It is, however, twice as much work. After realizing this, I went back to using the bushing die. Some people love the mandrel approach and swear by it. To each their own. The only difference I could actually detect was that using a neck turning mandrel .002" under bullet diameter actually gave me ~.0025" to .0028" [average] neck tension, because the spring-back works in the opposite direction when you under-size necks, then open them up from the inside, than it does when you simply squeeze them down from the outside with a bushing die. The loads obviously had to be adjusted to account for this difference.

My recommendation would be to try the mandrel approach first on a small number of cases. Compare them directly to cases that were prepped by your previous method and determine whether you can actually shoot a difference, before you attempt to prep a large number of cases. If you are happy with the approach, you can subsequently prep your remining brass the same way. If not, you won't end up with a few hundred cases that have to be loaded/fired before you can go back to your previous method.

 

[SamLS]

i bet you could put an expanding mandrel with a hole in it on the decapping pin and not need a seperate step in the reloading process.

 

[Rich S]

+1 for the Porter Precision mandrel die. It uses standard er collets and pin gages. They can be bought from MSC or other sites in 0.0005 increments pretty cheap. 0.001 increment mandrels are abot $3.50 and around $7 for 0.0005 increments.

The only issue I have with the Porter die is it is a little long for BR cases. He recommends dropping the pin lower in the collet. That works, but I trimmed some off the bottom of mine.

I got frustrated trying to get bushings to get the neck tension I wanted. When I switched to the mandrels, I just use a bushing that runs 0.001 to 0.002 small and expand to desired size with a mandrel. My seating pressure became pretty consistent.

 

[338 dude]

I've read a number of posts where an expander mandrel is ecommended for obtaining consistent neck tension. I've searched a number of suppliers for one in .308, but my search comes up empty. Is there another description that they are sold under?

Check Sinclaire international search for expanding mandrel or turning mandrel possibly