Mandrel size Alpha OCD 6 bra

[Rebel Rooster]

Hey guys,

I am having my first 6 BRA built, and I have purchased the Short Action Customs 6 BRA sizing die with both .267 and .266 bushings, but I am wondering what size expander mandrel guys are using with Alpha BRA brass. It's and impact action with a stutteville barrel with a .135 freebore. Is this just something I will have to wait and see for, or can I purchase the collet and mandrel beforehand? Also, is the mandrel really even needed with the SAC bushing die? Thanks in advance for helping a noob.

 

[Feniks Technologies]

Whatever size you want the inside diameter to be + .001 or so.

If you want a .241 ID for .002 interference fit, get a .241 and .242 (and a .2415 if available). That should cover it with not much spring back or a bit of spring back.

Typically only using bushing is reserved for neck turned brass. And that’s when it doesn’t hit the ground and get dinged up.

Non turned and/or brass allowed to fly around, I’d use the mandrel if you want best results.

If you’re using a mandrel, you need smaller bushings than you want the finished OD diameter to be as you need it sized down smaller to allow the mandrel to expand it back.

 

[Rebel Rooster]

Perfect man, thank you!

 

[Choid]

Whatever size you want the inside diameter to be + .001 or so.

If you want a .241 ID for .002 interference fit, get a .241 and .242 (and a .2415 if available). That should cover it with not much spring back or a bit of spring back.

Typically only using bushing is reserved for neck turned brass. And that’s when it doesn’t hit the ground and get dinged up.

Non turned and/or brass allowed to fly around, I’d use the mandrel if you want best results.

If you’re using a mandrel, you need smaller bushings than you want the finished OD diameter to be as you need it sized down smaller to allow the mandrel to expand it back.

So I am kind of new to mandrelling, and noticed this bushing issue today. I was resizing with a .290 bushing for 6.5 Creedmoor, and it was giving me about 2 thou of neck tension as measured with pin gauges, but running my .001 over mandrel felt like it didn't have the differential to do anything about an imperfect neck. So I am thinking to go to .289 to give the mandrel a better chance at making a bigger difference. Does this seem right?

 

[Feniks Technologies]

So I am kind of new to mandrelling, and noticed this bushing issue today. I was resizing with a .290 bushing for 6.5 Creedmoor, and it was giving me about 2 thou of neck tension as measured with pin gauges, but running my .001 over mandrel felt like it didn't have the differential to do anything about an imperfect neck. So I am thinking to go to .289 to give the mandrel a better chance at making a bigger difference. Does this seem right?

Just so I make sure I have it right. You’re using a .262 pin gauge. And using a .290 bushing to get that.

You’re trying to get to .263 ID?

What size mandrel are you using? More than likely will need a .264 mandrel. Or maybe a .2635.

Usually see .0005-.001” spring back. Depending on annealing and other such stuff.


IMO, the less you have to size, the better you are. Not as much for working the brass, but just for ease of use on the press. Much easier to move faster without a lot of resistance.

 

[Choid]

Just so I make sure I have it right. You’re using a .262 pin gauge. And using a .290 bushing to get that.

You’re trying to get to .263 ID?

What size mandrel are you using? More than likely will need a .264 mandrel. Or maybe a .2635.

Usually see .0005-.001” spring back. Depending on annealing and other such stuff.


IMO, the less you have to size, the better you are. Not as much for working the brass, but just for ease of use on the press. Much easier to move faster without a lot of resistance.

Yes. Well, I am not sure if I want to be at .263 or .2625 but I am coming out of the .290 bushing at .262 with a pin gauge, and out of the .263 mandrel at just about .263, but I imagine I am not getting much springback because the mandrel is only .001 larger than the neck before mandrelling.

If that small amount of change isn't a problem, I can just go for it. It just seems so easy in the press, which is actually why I worried. Especially compared to virgin brass with the same mandrel, which is kind of a slog and requires graphite.

 

[Feniks Technologies]

Yes. Well, I am not sure if I want to be at .263 or .2625 but I am coming out of the .290 bushing at .262 with a pin gauge, and out of the .263 mandrel at just about .263, but I imagine I am not getting much springback because the mandrel is only .001 larger than the neck before mandrelling.

If that small amount of change isn't a problem, I can just go for it. It just seems so easy in the press, which is actually why I worried. Especially compared to virgin brass with the same mandrel, which is kind of a slog and requires graphite.

If it’s getting the desired ID, I’d go with it.

IMO, when it’s easy like that, you’re doing it the “optimal” way. As in minimally sizing down and minimally sizing up.

And ya, virgin brass either has smaller OD and/or more friction since it’s completely clean. Depending if you leave carbon in or lube fired brass, it will definitely feel different.

 

[Choid]

Thanks dude.