Expanding Mandrels

[Lawnboi]

I’m curious if dinged necks will cause any issues if nothing is used. I normally end up with 10% of my brass having a dent in the neck depending if it got stepped on or hit something hard.

 

[wind gypsy]

I’m curious if dinged necks will cause any issues if nothing is used. I normally end up with 10% of my brass having a dent in the neck depending if it got stepped on or hit something hard.

Man, i'd sure think so and I think that is a different case.

 

[Lawnboi]

Man, i'd sure think so and I think that is a different case.

Did you ever get your 223 not denting necks? My 223 is still denting 75% after 7k rounds through the action.

 

[wind gypsy]

Did you ever get your 223 not denting necks? My 223 is still denting 75% after 7k rounds through the action.

Yeah, I had a gunsmith trim the spring to reduce the force it was pushing the case against the receiver on the way out. Cases just kind of dribble out of the action now but they always make it out. For long term reliability i'm not sure it's great but I haven't had any issues and its probably been 3 years and 1500+ rounds since i had it done.

Kind of nice when shooting from a bench too. Brass stays on the bench and doesn't fall to the concrete.

 

[SDHNTR]

hope to get to the range this weekend to see if expander vs not makes a difference on the 2nd firing of this Peterson dasher brass.

I have two loads I’ll shoot 5 of each with expander mandrel installed vs not.

For what it’s worth at this point, I noticed no difference, to maybe the slightest perceptible difference in seating pressure required between them. If it was anything it was slightly harder to seat bullets on the brass I did not use expander ball.

Also my calipers have been off for a hot minute. At least as far back as when I ordered the .264” bushing - I measured .266” loaded, and these show .267” now that I’ve calibrated.

It sure still feels very easy to seat bullets though, so I doubt I’ll go up a bushing size unless I can’t get the gun to shoot.



This won’t be a huge sample, but if I can’t tease out the difference in 5 shots, I’ll run a 20 shot comparison once I’ve picked a load.

Get a Mitutuyo caliper.

 

[wapitibob]

I’m curious if dinged necks will cause any issues if nothing is used. I normally end up with 10% of my brass having a dent in the neck depending if it got stepped on or hit something hard.

I turned down a larger caliber button and use it to expand the dinged necks to the same dia as my fired brass.

 

[J_Jacobson]

You mind sharing cartridge, neck diameter of loaded brass, bushing diameter if used, and mandrel diameter?

Just had a look at my 6BR.
Loaded Neck Diameter: 0.2685
Bush: 0.265
KM Precision 0.003" Custom Mandrel: OD 0.2415

 

[wind gypsy]

KM Precision 0.003" Custom Mandrel: OD 0.2415

What am i missing? 0.2415 is 0.0015" smaller than 0.243. Accounting for a 1.5 thou spring back?

 

[WhoGarrDen]

What am i missing? 0.2415 is 0.0015" smaller than 0.243. Accounting for a 1.5 thou spring back?

Maybe there's almost no spring back with the mandrel (holding it for a second or so?) and he's aiming for 1.5 thou neck tension? I agree it doesn't make sense that a 0.003" mandrel is not 0.003" under caliber, but he did say custom....

 

[J_Jacobson]

@wind gypsy It's supposed to be a 0.003" neck tension mandrel, when you order from KM you order by desired neck tension and not the diameter of the mandrel (in this case it is 0.2415"). Which I know doesn't make sense, as spring back will differ between brass lots and brands. However, I think it's pretty close, 1.5thou + a little bit of spring back. Either way, I generally always use their 0.003" NT custom mandrels across all my rifles and it has worked really well.

 

[Lawnboi]

SAC actually has an interesting calculator now on their site for mandrel/bushing size choice.