Do 9mm bullets "size up" when fired?

[zero]

I've never noticed it shooting factory 9s before, but recently i pulled some standard 9mm fmj to load in a 357(no bullets) and noticed they had a slightly concave base. I expected them to be not as accurate as. 357 bullets but found them to be every bit as accurate as any others i've tried from 38s and 357. So i'm wondering, does the concave base help them size up similar to what a hollow base does?

[mechanic]

9mm bullets are generally too small for a 357 or 38.  9mm should be .355-.356,  357 are .357-.358.  With a concave base, (not all bullet designs have such), it's possible they will "bump up", but I would think optimum accuracy would come from bullets more correctly sized.
 
When there is a shortage of what you need, obviously you have to use what you have.
 
Ben

[geezerbiker]

I seriously doubt the bases blow out to bore size like say a mini ball in a muzzle loader.  Some .357's do shoot the slightly smaller .356" 9mm bullets ok.  Both of my S&W have a slightly tight bore.  I don't know about my Colt, I never got around to slugging the bore...

Anyway there was a time when I was broke and I could get bulk FMJ 9mm bullets for half the price of anything jacketed for .357 so I bought a couple pounds of them.  The shot OK but I had to use more care in crimping them in since they weren't as tight in the case.

Tony

[Savage]

A fired jacketed 9mm bullet will mic out pretty much the same as unfired, assuming no deformation.  I had some 147 gr TCFP .355 bullets I loaded in .38 spl cases for plinking. Turns out they shot as well or better than the .358 dia LSWC bullets I normally used. They were accurate enough that I used them for NRA Falling Plates until they were gone. Don't shoot the .38 much anymore, if I did I'd be happy with them in it.
Savage

[wncchester]

Any fast bullet will tend to 'upset' when fired, especially soft or thin jacketed bullets that hit the rifling early the way pistol bullets usually do.  It's easy for them to swell one thousanth - or more - in a hot load and the form of the base will have little to do with it.

[Flynmoose]

I was given a bunch of 9mm bullets a while back. I loaded some in 38spl cases and used a 9mm
die to put a crimp on them. They shot well from my T/C G2 carbine and pistol barrels. I am glad I still have a couple hundred of them with our present situation.
FM

[corbanzo]

I've loaded .356's into 38/357's with success. 


At hundgun ranges, an as much surface area a .35 caliber has contact with the bore and rifling with, shouldn't make a huge dent in accuracy as it is. 


I have a blackhawk 9mm/357 convertible, using the 9mm cylinder I haven't seen any drop in accuracy.