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Old September 20, 2011, 10:06 PM   #1
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a size question

I have a 9mm beretta and also a taurus, both barrels slug to .357 my cast bullets come from the mold .001 larger than this at .358 and squeeze through my dies a bit when crimping. we all know that exessively large bullets will cause the chamber to pinch the case and cause unacceptable pressure, is there a way to know that this might be happening when you chamber the round before you shoot it? ive noticed that even factory 9mm at .355 diameter sticks out of the chamber a bit until the slide knocks it in just as my cast bullets do. is there anyone with experience in this?
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Old September 20, 2011, 11:35 PM   #2
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ive noticed that even factory 9mm at .355 diameter sticks out of the chamber a bit until the slide knocks it in just as my cast bullets do. is there anyone with experience in this?
Are you saying they won't seat on the case mouth and are seating the bullet against the lands/cone? If so, that can cause big pressure spikes depending on the load and powder.

If the cartridges will drop into the naked bbl chamber and seat on the case mouth with a "clink" and drop out when you turn the chamber down, then they aren't hitting the lands.

"Short cases" may not seat on the case mouth when feeding, but shouldn't be contacting the lands, leade or cone.

Usually hollowpoints, flat nose or conical nose bullets loaded too long for the pistol's chamber are the culprits causing this sort of problem. Most pistols using fmj ball (or lead with the same shape) will load and feed with "load-data oals"/long.

My CZ won't feed some hollowpoints/flat point using load data oals or some factory ammo. It has a shorter chamber than many.

Last edited by 1SOW; September 20, 2011 at 11:49 PM.
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Old September 21, 2011, 12:06 AM   #3
chris in va
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My CZ 75BD slugged at about 356. All of the 356 bullets I tried went in sideways, and someone suggested I try the Lee 358 bullet mold.

Bottom line, I load 3.8gr of Universal at 1.01oal with that bullet profile. Anything longer and it won't chamber all the way.
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Old September 21, 2011, 01:28 AM   #4
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Your worrying about oversizing too small to matter. The military, for example specs .30 cal rifle barrels .3065"-.03095" groove, and bullets .307"-.309". So you can get a .3065" bore shooting .309" bullets and there isn't even enough performance difference to affect the sight settings. And that's in high power rifles where pressures are already a lot higher. Then you get into the Euro-30's and their various diameters from .308" up to .314" (with some even bigger exceptions), and people cross bullets between them frequently. I've got a French MAB with a .309" groove barrel for shooting the standard 0.312" .32 ACP. No problem, and that's a jacketr bullet in a fairly light barrel.

When you get to cast bullets, they are usually soft enough to shoot an even further oversized bullet than the jacketed ones above. For years, .45 Colt revolvers were chambered for the old .454" diameter ammo, but sported a barrel in .451", so as to be compatible with both bullet diameters (though the extra loose chambers don't help accuracy). The main reason not oversize your lead bullets too far is accuracy. Lots of guns, lever guns in particular, and many revolvers, seem to shoot better with cast bullets .002" over groove rather than the usual commercial .001" over. However, once you get to .003" over groove, many seem to start to have their groups open back up. Not sure why .002" is such a special number in them.

Anyway, you're nowhere near a danger zone. If these were 0.010" or more over, I'd start showing some concern. And that wouldn't be because of pressure so much as concern that if a bullet that fat will chamber in your gun, there is likely a chamber dimension problem with it.

P.S., I know a lot of folks measure slugs with calipers, but it's easy for them to be off a thousandth or even two, sometimes (though the modern digital ones do surprisingly well at this point). Anyway, if you haven't got one, go to Harbor Freight or Enco and for around $20 you can get an OD thimble micrometer with .0001" Vernier scales. These are much preferred for measuring slugs both because of the greater resolution and precision, but also because the wider measuring surface gives you a more precise feel on touching down on the slug. Using a cheap micrometer stand makes it even better.
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Last edited by Unclenick; September 22, 2011 at 01:38 AM. Reason: typo fixes
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Old September 21, 2011, 09:50 PM   #5
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Thank you all again for your replies. this is a great forums to be able to post to. Unclenick always has great things to read. I was refering to the bullets diameter in respect to the way it affects the headspacing of the round itself as i am aware that many times a larger bullet will expand the case mouth some causing the chamber to squeeze the bullet inside its case thus causing excessive pressure and possibly a realy bad day. it does not appear that the bullet itself is engaging the lands at all as there are no marks on the bullet and my loaded rounds are actualy a few thousandths shorter than factory at the moment (maybe .003). We know that automatics can be more particular about these kinds of things. I was wandering if anyone here had ever had any tight rounds, looks as though my questions have been pretty much answered though. Perhaps Unclenick is right, perhaps .001-.002 isnt a big deal. I know i couldnt tell the difference when i put the round in and the gun didnt act any different.The round was not hard to chamber or to extract so maybe it isnt too tight. Oh and about the callipers I have those as well as 0-1" mics and i work at a machine shop so i have certified standards at my disposal whenever i need not to mention lathes and cnc mills if i want i can play with on weekends. A great fringe benefit to have for a guy like me. great conversation thanks again.
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