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New brass trashing bullet jackets, any fix?

M

Mr_Happyface

Huge Dork
Full Member
Minuteman
Mar 13, 2006
285
76
I bought a bunch of new Hornady brass off of Gunwerks for my 7LRM rifle. Unfired, the neck tension is incredibly tight and completely trashes a jacket while seating.

Hoping to cure this I ran them through a Sinclair oversized expander mandrel (typically used prior to neck turning) to open things up some. The neck tension is still way too tight, I measured the mandrel itself and it showed .283, so accounting for springback that puts the neck I.D. at .281 or so? Measuring the bullets themselves showed .284. I'd like to get it to .286 or so, so I can resize it right off the bat to the tension I intend to use for subsequent firings.

Calling Sinclair the best they could offer was a .308 mandrel that I could have turned down, but that's really not an option for me.



I have 400 pieces of this brass so I can't just have the first firing through them be a throw-away.

Any ideas?
 
Are you chamfering the case mouths so the bullet starts easier?
 
Yes. That alleviates the jacket scraping, but the tension is still WAY higher than I'd ever use.
 
The expander should have eased things up, I don't know.
 
It did, but like I said, the expander itself is .283 which is about .003 to little.
 
I know a lot of people don't like using them, but one option might be to molly coat your bullets. I know that you hear horror stories of moisture retention, but I clean my guns after using them and never had any problems.
 
Lube them up, use a 30 cal ball expander, then neck back down in your bushing die to the correct neck tension. Anneal if you like. Need to check bullet dia and neck thickness for your chamber. What is that caliber? If some other cal was necked down, you may need to neck turn your brass.
 
You could use a Lyman 7mm "m-die" used for prepping brass for use with cast bullets. It will lessen the tension. So what (in thousandths) is the neck tension of a loaded round now at?
 
rth1800 said:
Lube them up, use a 30 cal ball expander, then neck back down in your bushing die to the correct neck tension. Anneal if you like. Need to check bullet dia and neck thickness for your chamber. What is that caliber? If some other cal was necked down, you may need to neck turn your brass.
Click to expand...

That seems like a hell of a jump in diameter, I'm just looking for a extra few thousandths. 7LRM is basically a .375 necked down to 7mm, I chose it because I wanted a non-belted 7mm that would fit my .300 AW's bolt face and mags without modification. These are cases made in that caliber by Hornady, they appear to be freshly annealed.


I may have to call Lyman to ask about that die, never heard of it before, looks like it may be the fix though!

I think the tension now is at .004 to .005
 
We anneal all our brass before sizing. When we use Barnes 223/243 we use an M Die to bell the mouth before seating the projectile. Barnes haves a long shank and this avoids both initial resistance and shaving the shank. No issues with neck tension.
 
Ok ,
You will need a custom expander mandrel, which you were trying to avoid. Most shops can turn one for you.
Good luck,
RTH
 
rth1800 said:
Ok ,
You will need a custom expander mandrel, which you were trying to avoid. Most shops can turn one for you.
Good luck,
RTH
Click to expand...

I'd have no problem doing it, but I thought it would be difficult finding someone.

Just get a .308 and turn that bitch down? Who can do it?
 
If you take a tight wound Q tip and rub some moly grease into the fibers ,you can rub the grease on the mouth of the case and on the boat tail of the bullet and they will seat a lot easier .It takes very little to work.
 
If you're running them through an 7mm expander mandrel, I would be inclined to just shoot them. That should open them up. What brand of bullet? Maybe try a different brand of bullets.
 
I have the same problem, my shells have an ID of .260 after sizing and my bullets are .264. So my jackets are scraping off even on chamfered cases necks.
 
I wonder if the neck expanders Sinclair has would work .The ones for sizing a neck to turn them to fit tight neck chambers .
 
Mr_Happyface said:
Yep, this is what I'm currently using, they mic at .283... not sure what's oversized about them.
Click to expand...

They are .001" bigger than the regular size to fit over the neck turning pilot with less resistance.

You are going to spend $200 to fix a $10 problem.
 
I think once you fire your brass, you'll be fine.
One guy said to anneal, it sounds like your brass is work hardened already. Get it all fired and see.
It's going to one kick ass round!
 
918v said:
They are .001" bigger than the regular size to fit over the neck turning pilot with less resistance.

You are going to spend $200 to fix a $10 problem.
Click to expand...

I know, I've used this setup in the past to turn necks. I already have the die and both mandrels, all I need is a .308 to turn down to .287. What's the $10 fix I'm missing?

I have 400 pieces of new brass. 72gr of powder each, $176 worth of projectiles, and wasted barrel life on an overbore caliber is nothing to sneeze at!


I'd like to have neck tension consistent from the get go, rather than waste the first firing.
 
So anneal the necks and shoulders, use the .283" expander mandrel, the brass won't spring back more than .0005" and you'll have perfect neck tension for a bolt gun.

A micro torch is $5 and you already prolly have a power drill to spin the case.

If you buy a .308 mandrel and pay a shop to turn it down you'll have to do it prolly twice to get the neck tension right because you have no idea how much the rate of springback is.

If you have annealed necks, you know the rate of springback is insignificant.
 
Damn, I've never annealed before. I'm surprised it'll decrease springback by that much.
 
It's easy. I use a micro torch to keep the temperature controllable. I spin the case while moving the flame back and forth the length of the neck and shoulder. I keep the nozzle about a quarter inch away from the neck. I count seven alligator and done!

It's real hard to burn a case with a micro torch.
 
918v said:
It's real hard to burn a case with a micro torch.
Click to expand...

I'd get the brass expanded and shoot it first. To me, your brass was under-annealed at the factory.
You may look into bushing dies for neck tension also, easy way to control neck tension after firing.
 
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