308 win bullet/OAL comparator

[m102404]

I used to have a bullet comparator...but it's vanished. I'd like to just make one this time around. Does anyone have the inner diameter of their comparator when measuring to the bullet ogive for a 308 win?

 

[flashman]

Well, you're measuring to the point on the projectile where it will engage the lands, so.... .300" or 7.62mm if you want to go metric.

 

[rookie wildcat]

Well, you're measuring to the point on the projectile where it will engage the lands, so.... .300" or 7.62mm if you want to go metric.

So, what would the groove dimensions be, if the lands are .300"? Because none of my 30 cals measure .300" across the lands.

 

[m102404]

Different barrels/rifling/etc would have different land/groove depths wouldn't they? I have tried to look it up but then the articles went all secant this and ogive degrees that...so I was just hoping someone would mic thiers and I would go with that...lol.

 

[SND]

There's pretty much 3 kinds as far as I know, some are about .307, some closer to the middle at .304 and I make mine .300.
It's only for comparative measurement, so it doesn't really matter so long as you always use the same one after you touched off from the rifling with the new gauge and each type of bullet you shoot, write down the reading and go from there for how much jump you roughly want and see how they shoot. It's not in any way an "exact" measurement, but plenty close and much better than measuring from the tip.

 

[flashman]

So, what would the groove dimensions be, if the lands are .300"?

.308, or 7.82mm.

Because none of my 30 cals measure .300" across the lands.

They sure should, unless you have non standard target barrels. Bore diameter should be .300 in a standard .308 Win tube, .004" for the grooves, for .308 groove diameter. That's SAAMI standard measurements.

 

[flashman]

Different barrels/rifling/etc would have different land/groove depths wouldn't they? I have tried to look it up but then the articles went all secant this and ogive degrees that...so I was just hoping someone would mic thiers and I would go with that...lol.

SAAMI standard tubes will be .300 bore, .308" groove. There is no need to mic. A comparator you buy from Brownell's will be .300

Tell you what, #### it, I'll go measure mine. BRB.

Ok, I'm back. It's .300"

Some target barrels may be .299 bore, .308 groove. If you have one of those, I suspect you would already know the answer to your question.

Groove and bore depths for .308 Win are standardized by SAAMI and CIP. Kind of hard to make commercial loads and bullets that will work - and be safe - in all the .308 Win rifles made if that weren't the case.

Secant vs tangent ogives are just particular kinds; it has to do with the portion of a circle's circumference they correspond to. The type of ogive is irrelevant to a bullet comparator, as they hit on the bore diameter. Bore diameter is bore diameter regardless.

http://www.accurateshooter.com/ballistics/tangent-vs-secant-vs-hybrid-ogive-bullets/