A buddy just started reloading and asked if I could come over and help him get started.  He is reloading 30-06, something I don't reload, and has lead bullets with a copper cap on the bottom.  When we re sized the rounds everything was fine untill we seated the round.  There is a gap between the bullet and the rim of the neck.  I was wondering if this is due to the copper cap on the bottom, and if a factory crimp die would resolve it?  We are trying to keep the chamber pressure down, and that's why I was trying to avoid crimping.  Any help would be greatly appreciated.

The copper cap is a gas check. If properly installed, being as to how it is attached as the bullet is sized, will not have a larger diameter then the rest of the bullet. If the gap is very obvious, I personally would mic the bullet, just to satisfy my own couriosity, and if it miced out appr. .309, then yes, Id' run it to the die until it just bumped the crimping ring enuf to close that gap.
Allen

Yaaa grandpops, there are a few of us cheap, miserly types that shoot lead in guns that really need a good jacket bullet. I've been shootin' lead thru my .30-30s' .300Sav. and .30-40 for over 60 years I do have 8 differant bullet mould just for the .30s' and with the exception of the 130gr, that I use in my .30 carbine, all are gas checked.
When ya just like to shoot, weather it be a grey digger, deer or bear, ya try to use the cheapst method. Ya gotta realize, back in the '50s--'60s, a good quality jacketed bullet figured out a smidgen over 3 cents a piece. Lotta money for a youngster tryin to raise a family!
Indeed Dale, the base of a gas checked bullet does have a smaller base just for the purpose of crimping on the gas check, and when properly resized, the gas check are is the same dia. of the bullet body.
In my experments, I have found that I can load up to 2200fps, before I start noticeing any signs of heat distortion, on a gas checked bullet. However, once I exceeded 2200fps, the distortion rapidly got worse.
As heat starts to melt the lead(The distortinon I mentioned), the lead will become a vapor, as that vapor excapes down the barrel, it will again solidify, normaly on the lands between your rifleings. I assure you, it is not an easy job to get that lead out, once ya get it in there. Your best bet is to be carefull and do not exceed that magic number of 2200 fps, in my cases!
To this day, my wife and I still shoot primarly lead, and we do get a average of 4 deer a year. we do probably shoot well over 1500 rounds a year, just becaus we like to shoot!
Allen

Posted By finepoint on 12 Nov 2012 11:32 AM
Gas checks are pretty much required for velocities over 1400 FPS. Your dies are probably flaring the case mouth slightly to ensure you do not shave the lead bullet during seating. Lyman "M" dies do this as a matter of course. As long as the ammo chambers properly, it really doesn't matter. You can iron this out with the judicious application of a Lee factory crimp die. An actual crimp is not necessary on cast bullet loads in rifles. It will not effect pressures significantly.
Lead bullets can be problematic in gas operated weapons with lead fouling of the gas port. Just a problem to be aware of.