expanding button or mandrel

SJB358 · Mar 28, 2019

I have been using the Sinclair Expander Mandrels for a few years now. Dr. Mike turned me on to them. I buy the expander mandrels .002 under size and use the pin gauges to check for how much neck tension I am getting. Typically I have about .003 neck tension with good brass that isn't work hardened. Even using the Redding Bushing Dies I will use the expander mandrels for my Mashburn and 338 Win Mag. I have no idea what is best, but I tried neck turning and prefer not to do it. I have to inside neck ream my 7mm Mashburn Super brass after the first or second firing, in order to get rid of the donut that comes out from forming, but after that, I just shoot the stuff.

For me, going to RWS, Lapua, Alpha and similar has been a big money saver for me. Most of it is straight and concentric, with very little inconsistency right outta the box and if I am not firewalling my stuff it would blow your mind how many loads I get out of a piece of brass.

While being more expensive up front, it lasts longer, less fiddling to make it perfect and uses less components since I am not having to burn through as many components before finding great loads...

Great topic.

DrMike · Mar 28, 2019

Yup, I like the Expander Mandrels a lot. Scotty gave an excellent summation of their use and shout out for quality brass saving a lot of time and effort.

gerry · Mar 28, 2019

Very interesting information, I'll be rethinking how I do things from now on and can see adding some of the Sinclair mandrels in the future.

jimbires · Mar 29, 2019

for the guys wanting to play with this . 21st century is going to sell sets .

http://forum.accurateshooter.com/thread ... s.3975815/

TackDriver284 · Mar 29, 2019

jimbires":2une1v28 said:
for the guys wanting to play with this . 21st century is going to sell sets .

http://forum.accurateshooter.com/thread ... s.3975815/

I saw that earlier, I may want to get the .0025 and the .003 mandrels for a more tighter neck tension. Would those mandrels work in the Sinclair Gen. II expander mandrel die?

jimbires · Mar 29, 2019

replies #11 - 13 say these will work in the sinclair die . the same 3/8 diameter shank .

TackDriver284 · Mar 29, 2019

Thanks Jim. I hadn't read that comment there before I saw yours. :grin:

jimbires · Mar 30, 2019

TackDriver284":c4pm6qcu said:
Thanks Jim. I hadn't read that comment there before I saw yours. :grin:

no problem Mark , I see you got your answer right from the guy . you've got to weed through , but there is some good info on that forum .

I don't read there much any more , for awhile it was like nonstop fund raising for the forum .

RAD57 · Apr 7, 2019

I use expander mandrels and Forster FL dies honed to the diameter that I want. My honed FL Forsters are kissed (.0005-.001") by the expander button while the neck is still supported by the die. Using the Forster dies this way provides me with the lowest runout in most cases. I've found that with very thin brass as found in the 22 Hornet and 38-55 that using a mandrel can overexpand just one side of the brass, especially when you only can slightly neck turn to clean up about 50% of the case neck.