Caliber and Actual Measurements

[682bear]

This is not (entirely) true. They have a very slightly differing spec with regard to headspace, which is usually over-emphasized in the literature. Their pressure difference is largely irrelevant (and for the most part everything loaded for one, works for the other). The same is true of .308 and 7.62 Nato. In theory a .308 minimum chamber *could* have a throat shallow enough that a 7.62 round would be constricted at the neck and generate excessive pressure. In practice, every .223 chamber I've seen is throated so deeply that either round can be fired with impunity. Those desiring extra confidence in a chamber to fire both can use the .223 Wylde. I can attest that this chambering has negligible deleterious effect on accuracy. My Wylde chambered competition gun shoots sub-0.75" off the bench and could probably do better if I wished to make the trigger more bench friendly.

GsT

I prefer the .222... can't be fired in either one, but is generally more accurate than .223 or 5.56...

Just stirring the pot... lol!

-Bear

 

[pdentrem]

other than the projectile diameter those are completely different rounds....

Yeap. Just a short history.

 

[rwm]

I am seeing some diagrams that indicate the projectile is .308 and some that indicate .309". Clearly they are not machinists! I did see one that said .309 (-.0003")

 

[pdentrem]

My first rifle I bought is a Win Model 70 short action in 222 REM. Very accurate but my Sako 6mm PPC beats it most of the time.

 

[RJSakowski]

Are 38 and 357 really the exact same projectile? Or just very close? I measured a 7.62 x 51 and it is .308". Is a 300 WM really .300? I don't have one to measure.

According to the Hornady Reloading Handbook the 300WM shoots a .308" (30 caliber) bullet.

 

[pontiac428]

I'd caution about the use of absolutes in this discussion. When you chamber your own barrels with reamers made to your spec to load cartridges for a single rifle, all this nonsense goes out the window. Most of this discussion applies to factory rifles shooting boxed, mass-produced ammo that come from big companies with many lawyers who caution them to throat their barrels long and load their ammo short to avoid lawsuits from this exact sort of confusion.

Look at the SAAMI and CIP chamber prints and you'll see there is no difference in the case or neck of a 5.56 vs. a .223, but the reamers are different. The difference comes in the leade/throat to accommodate the longer, heavier bullets you can buy in a box. NATO only deals in two bullet weights for the caliber (and really just retains the 55 grainers for old Vietnam era rifles with 14-twist barrels like the ones they supply Contras and Sudanese insurgents with), but the warehouse sporting goods store has dozens.

Sport shooters often stuff the bullets into the lands and run necks larger than spec to save time on the reloading bench when repeatedly loading the same brass. Many of us still have the use of both eyes and most fingers.

 

[GeneT45]

I am seeing some diagrams that indicate the projectile is .308 and some that indicate .309". Clearly they are not machinists! I did see one that said .309 (-.0003")

Cast lead (including moly coat and plated) bullets are often 0.001" larger than their jacketed counterparts. Are you, perhaps, looking at a lead (unjacketed) projectile?

GsT

 

[rwm]

Cast lead (including moly coat and plated) bullets are often 0.001" larger than their jacketed counterparts. Are you, perhaps, looking at a lead (unjacketed) projectile?

GsT

No idea. These were just online drawings claiming to be specs for 30 caliber.

 

[RJSakowski]

When I was reloading, the Hornady Handbook of Reloading was my bible. It has case dimensions and bullet dimensions as well as loads vs. muzzle velocities for various powders and exterior ballistics.

 

[GeneT45]

Hornady's bible, and that of every other manufacturer or standard ammunition is SAAMI (Sporting Arms and Ammunition Manufacturers Institute). Their specs are free to view:
SAAMI cartridge and chamber drawings

As Pontiac noted, there are custom chambers and corresponding cartridges available to those that roll their own which are not SAAMI spec, but anything you buy from a major manufacturer *should*. (I am convinced that on at least two occasions I have purchased firearms with smaller-than-spec chambers, but that's another matter.

GsT