Is it safe to headspace on bullet instead of case mouth?

[shawnba67]

Specifically loading 40 s+w brass with heavy weight bullets at 166 power factor but at 10mm OAL. Wouldn't this eliminate the free in chamber detination worry of just shooting 40 in a 10? 180 MG hp hit my rifling at an oal of 1.280, haven't tried to see if 40 brass has enough grip left on bullet loaded that long yet, but if it cant be safely done that part wont matter.
So rundown 40 long and weak in a 10mm chamber???

 

[giovani]

I think I would leave this one up to Myth Busters!!!

 

[shawnba67]

I would love to watch that red head shoot some, or do just about anything for that matter. But back on topic.

 

[sloughfoot]

No it is not safe. Since I couldn't figure out what you were trying to say in the body of your post, this is my answer to the question in the heading.

 

[shawnba67]

No it is not safe. Since I couldn't figure out what you were trying to say in the body of your post, this is my answer to the question in the heading.

Since I'm seeking info here, any particulars on the unsafe parts?

 

[giovani]

40 sw brass in a 10mm chamber = no headspace

there is no such thing as headspacing off of a bullet

 

[rvb]

.40 ... shooting for 166PF.... IPSC load?

I suspect (iow 'speculation,' I've not done it), even if you loaded it so you met your PF goals w/in a safe peak pressure, you'd see wild variation over the chrono. Bullets just aren't that exactly formed... a little difference in the ogive and one round has a couple thousandths jump to the lands and the next is wedged in tight. You could even cause some issues w/ going to battery if the ogive of a particular bullet hit the lands a little early. sounds like a bad idea.

in typical loads, the bullet gets a jump out of the case, then hits the lands, so it takes less pressure to get it started. For a given load/velocity, it just seems you are going to possibly up the pressure w/ no real benefit.

best case, you save yourself the cost of a .40 barrel. Worst case, you blow up your gun.

-rvb

 

[CountryBoy19]

40 sw brass in a 10mm chamber = no headspace

there is no such thing as headspacing off of a bullet

While there isn't such a thing as head-spacing off a bullet, there is such a thing as zero jump, ie no jump to the lands, or bullet touching the lands. This, IMHO, would be an unreliable way to "headspace" but may be possible. Take into consideration the many things that you need to do when loading a zero-jump load and start low and work up and see what happens. The most common problem is when doing a zero-jump load there will most certainly be a pressure spike. In a normal load the pressure drives the bullet forward and the momentum forms the bullet to the rifling. In a zero-jump load the pressure drives the bullet forward AND forms the bullet to the rifling. This takes a lot more pressure and you will definitely see some increased pressure so keep that in mind.

Disclaimer: I'm not condoning this, it may be dangerous in the 40/10mm, but it isn't uncommon in rifle loads so take that for what it's worth?

 

[IndyGunworks]

Sorry bud, gotta disagree w/ you on this one. Loading into the lands is NOT the same thing as HEADSPACING. when loading to the lands you are still putting the proper size brass into the proper size chamber allowing proper expansion and sealing. Putting a casing into a chamber that is not headspaced for it is a recipe for disaster.

You can load into the lands, but the casing must still be headspaced properly to the chamber.

 

[timsdl72]

Sorry bud, gotta disagree w/ you on this one. Loading into the lands is NOT the same thing as HEADSPACING. when loading to the lands you are still putting the proper size brass into the proper size chamber allowing proper expansion and sealing. Putting a casing into a chamber that is not headspaced for it is a recipe for disaster.

You can load into the lands, but the casing must still be headspaced properly to the chamber.

+1

 

[shawnba67]

This was stolen from the glock talk forum, I'm fairly certaim 95 percent of pistols "headspace" off the extractor. I just checked my 9mm and a case at .760 would not go into battery .755 would but could feel it wasn't normal. .753 went like always. Most of my once fired resized brass was .745. What is the extra .010 doing to hold my case mouth. 40 loaded this long would keep it from slipping past the extractor and going off unrestrained in the chamber would it not?

 

[giovani]

Like I said , no such thing as headspacing off of a bullet.

headspace dosen't even require a bullet to be present to be checked.

bullet seating depth is something entirely different

 

[giovani]

They head space off of the case mouth , that is why you taper crimp auto rounds and roll crimp revolver rounds as a revolver head spaces off of the rim

 

[Leo]

I know this seems like a silly question, but why don't you just get some 10mm brass to match the 10mm barrels chamber?

 

[giovani]

What I bet your friends at the glock forum are doing is having a 40sw barrel deep throat cut to accept the longer bullet while retaining the 40 sw head space.

 

[shawnba67]

They head space off of the case mouth , that is why you taper crimp auto rounds and roll crimp revolver rounds as a revolver head spaces off of the rim

How does a .745 long brass headspace in a .755 deep hole??

 

[IndyGunworks]

This was stolen from the glock talk forum, I'm fairly certaim 95 percent of pistols "headspace" off the extractor.

No sir. No pistol heaspaces off the extractor. revolvers headspace off the rim, autos headspace of the mouth of the case.

What I bet your friends at the glock forum are doing is having a 40sw barrel deep throat cut to accept the longer bullet while retaining the 40 sw head space.

I would agree that this is probably what is going on also.

you NEVER headspace ANYTHING off the bullet.

 

[IndyGunworks]

How does a .745 long brass headspace in a .755 deep hole??

The rear part of the case is extra thick and reinforced. Invariably you will have just a little of the casing sticking out of the chamber. this is what the extractor and breach face are pressing against. The casing is forced into the chamber until the mouth of the case runs against the area of the chamber that's properly cut for it to go up against.

 

[shawnba67]

I know this seems like a silly question, but why don't you just get some 10mm brass to match the 10mm barrels chamber?

40 brass is lying all over the range for free, 10mm brass is $22 per 100. Until you shoot it then it is also all over the range free for everyone else. At end of USPSA you only get to police your stage so you'll only get back 30 or so pieces of your brass. I'm only entertaining the thought of Why you cant use 40 brass at 40 loadings in a 10mm at 10mm OAL. I havent done it, I am just challenging the common believe of case mouth headspacing. Having been told something your entire life doesn't make it true, only beleived. The pressure spike from the short jump to rifleing might be completely negated by the longer length of the 40 "long"

 

[shawnba67]

The rear part of the case is extra thick and reinforced. Invariably you will have just a little of the casing sticking out of the chamber. this is what the extractor and breach face are pressing against. The casing is forced into the chamber until the mouth of the case runs against the area of the chamber that's properly cut for it to go up against.

.755 is deeper than .745 what is sticking out??