300 blk brass / general reloading question

[qorban88]

I purchased a jug of 300 blk brass from brassguys.com, which is made from LC 5.56 brass. Overall the brass looks great, but during my checks with a Wilson case gage I found the head spacing is .008 below the minimum step, meaning the headspace is too short, which seems like a lot to me.

I'm not a reloading expert, but I suspect this is a general reloading question. So, is the headspace on this brass too short to be used safely? And if it can be used safely, will it perform well enough to be worth the expense? Thanks.

 

[iH8DemLibz]

They had to use the correct dies to reform the brass. So I would say the brass is fine.

Head spacing isn't determined by the brass. It's determined by the distance between the back of the case head and the face of the bolt.

I would say the issue is with the gage.

.008 is not a lot, but I would be concerned with a firing pin being long enough to properly strike the primer.

Buy a Go-Gage and drop it in your other case gage and see what that looks like. If you still get a .008 reading, the case gage is the problem.

 

[Klunatic]

.008 or eight one thousands of an inch is not much. Brass by its nature is designed to expand to fit the chamber and create a seal.

 

[BUFF7MM]

They had to use the correct dies to reform the brass. So I would say the brass is fine.

Head spacing isn't determined by the brass. It's determined by the distance between the back of the case head and the face of the bolt.

I would say the issue is with the gage.

.008 is not a lot, but I would be concerned with a firing pin being long enough to properly strike the primer.

Buy a Go-Gage and drop it in your other case gage and see what that looks like. If you still get a .008 reading, the case gage is the problem.

I believe the case has something to do with headspace, don't most bottleneck semi rimmed and rimless cases headspace off of the shoulder? With the exception of belted cases headspacing off the belt.

 

[lmorrison17]

If your chamber is on the big end of sami tolerance you may have problem.
I'd prime some cases and if they go off your golden.

 

[iH8DemLibz]

I believe the case has something to do with headspace, don't most bottleneck semi rimmed and rimless cases headspace off of the shoulder? With the exception of belted cases headspacing off the belt.

The reformed brass can go into the resizing die only so far because of the top of shell carrier coming into contact with the bottom of the sizing die. At that point, the shoulder is formed and can't be pushed back any farther. If it wasn't pushed back far enough, his case heads would be above his case cage. Then it would be a problem with the brass.

The 300 BLK has a fairly substantial shoulder with a shoulder diameter of around .355 inches. The neck, with a bullet present, measures around .333 inches. So it does head space off of the shoulder.

I wasn't saying ALL brass when talking about head spacing because straight walled semi-rimless cases like the .45 ACP, .30 Carbine, etc. head space off the case mouth. Which is why you taper crimp these cases and not roll crimp them.

 

[smdub]

Idon't most bottleneck semi rimmed and rimless cases headspace off of the shoulder? With the exception of belted cases headspacing off the belt.

Yes.

I have a wilson gauge and I THINK I have 300 go/no-go gauges. I'll dig them out and test tonight.

Edit: Dug in my box and I don't have 300 go/ng gauges I should probably order some from Manson.

 

[qorban88]

That's a good idea to test with a Go Gage.

I checked the gage against brass I've made and factory ammo and it reads within the limits, so it doesn't seem to be the gage.

I know brass is meant to stretch to fill the chamber when fired, but .008 or more seems like a lot. Why would they make a test gage with minimum readings if it didn't matter that much?

I put a call into Brassguys.com and they said to send them some to test.

 

[John from MD]

All gauges have min max tolerance plus you have the differences from using a new cherry vs an old one. Tolerance stacking happens.

Your AR firing pin, if it is spec, will protrude enough to light off your rounds and the brass will form to your chamber and your problem will go away. The next time you reload it will go back to SAAMI, unless of course if you again run into tolerance stacking.

I wouldn't sweat it in the 300 black as they are pretty low powered rounds.

John

 

[Jmorrismetal]

I have a Wilson casegauge and have to size the cases about the same (too much) to fit the chamber of my 300.

 

[fa18hooker]

No safety issues, more of just function issues (and I doubt even that). .008 is actually not that much, when you consider larger rounds (say M118LR, which can spec as low as .010 below headspace) which actually have a true shoulder to blow forward, pulling brass from the web of the case, and potentially causing case head separation...the BLK has such a marginal shoulder, it doesn't "pull" much brass, but rather case forms from the side. Once you've fired one in your chamber, you can measure and compare how far the shoulder actually moved.

 

[Pinecone]

The way the web gets thinned is when the firing pin hits the primer, the case is driven forward. How far depends on headspace.

The powder then fires, and the case is pushed out against the chamber wall and sticks. And the back of the case gets pushed backwards until the head hits the bolt face.

Since the front of the case is held by pressure, the case head moving back, pulls brass from just in front of the case head.

BTW, the case head does not expand like the forward aprt, due to the thickness and the web.