Neck expansion

[KY DAN]

So I miked an star machine tool expander plug for 38 special, it was .356 and when used I could feel resistance. I then used a pin gauge set to find what id dimesome 38 special cases were and found .351 fit snug in an resized case.

So I set the plug in the lathe and turned the expander plug to .3495 and polished and blended the bell feature in with the new diaameter. Now my cases on have their necks slightly balled to allow castbollits to be used. I have not done this yet with cast but it seems to works with xtp hollow points.

Does anyone see an issue with this by maintaining a super tight neck tension?

 

[HowieG]

So, you are expanding with a .3495 tool and are probably ending up with an id of .348 or so with spring back? That would give you .009 neck tension for a .357 jacketed bullet and even more for a cast bullet. If that is the case, then yeah, I think that's a problem. Basically a good neck tension for any cartridge is 2 to 3 thousandths. What you are doing is basically using the bullet to do your expansion for you instead of the proper tool. Bullets ain't made for that. Not good for accuracy either. Maybe not for pressures depending on your load. The original expander dimension of .356 sounds good to me. That would probably give you a .355 id with spring back and a .002 tension with a cast bullet and a .003 tension with a .358 cast bullet.

If the initial problem is your sizing die taking the necks down too small and working the brass, a solution would be to have the neck of the die opened up some.

 

[lordpaxman]

If I may, what initial problem are you trying to solve?
With what you did, I don’t see an issue with jacketed (not plated) bullets, in my experience it’s pretty tough to swage them by forcing them in a brass case. Cast bullets would be quite the opposite. I would also expect there’s a relationship between neck tension and pressure, so if you’re near max that may be cause to work up the load again. Good luck.

 

[edwardware]

I then used a pin gauge set to find what id dimesome 38 special cases were and found .351 fit snug in an resized case.

It sounds like that expander, as delivered, was approximately correct for jacketed, and slightly undersized for cast bullets.

By the time you exceed 0.003-0.004" expansion on seating, you aren't gaining any neck tension (just yielding the brass) and you're likely swaging cast bullets smaller. I target 0.003" expansion on seating yo capture some variation.

 

[jmorris]

If I may, what initial problem are you trying to solve?

+1

 

[KY DAN]

+1

No issues just playing with neck tension, i read an article on loading 44 mag on the Los angles silhouette site where the writer used a star to load and had modified the expander to where it belled the case mouth only and did not expand the neck portionwhich retained projectile. He spoke quite favorably of that modification and was using lead bullets.

If it works well with one revolver based handgun cartridge loaded to its intended potential, where should it not do the same in a 38 special or 357 magnum?

 

[KY DAN]

So, you are expanding with a .3495 tool and are probably ending up with an id of .348 or so with spring back? That would give you .009 neck tension for a .357 jacketed bullet and even more for a cast bullet. If that is the case, then yeah, I think that's a problem. Basically a good neck tension for any cartridge is 2 to 3 thousandths. What you are doing is basically using the bullet to do your expansion for you instead of the proper tool. Bullets ain't made for that. Not good for accuracy either. Maybe not for pressures depending on your load. The original expander dimension of .356 sounds good to me. That would probably give you a .355 id with spring back and a .002 tension with a cast bullet and a .003 tension with a .358 cast bullet.

If the initial problem is your sizing die taking the necks down too small and working the brass, a solution would be to have the neck of the die opened up some.

I am not touching the I'd of the case walls at all. I used high spot blue to check and my only contact spots are the bell of the mouth.