Bullet comparator diameters

harrygrey382

Well-Known Member
What diameter are bullet comparators - do they match the groove or rifling? E.g. for a 243 are they 0.243" or 0.236" (6.17mm or 6mm)?
 
Harry, I use the Sinclair nut shaped comparator Sinclair says that the holes are reamed the same as your chamber and as near as I can meassure my 6mm hole is tapered from .240 to .236
 
Yes the hole is tappered the same as the rifles leade, the earlier models hole was .240 straight
 
Harry.
Hornady measures out at;

.22 .212
.24 .230
.30 .296

They are all straight. hope this helps.

Spiker
 
Thanks guys. Sounds like they vary between makes then. Those Hornady ones are way under bore (rifling) diameter then...
 
Not only do they vary between makers, they vary within makers. The within-maker variations are relatively small, but not insignificant. Small variations in the diameter - as I'm sure you are aware or you wouldn't be inquiring - can result in large differences in cartridge overall length depending on the ogive of the bullet.

If you are 'serious', you can cast or slug your throat/leade/neck area and have your index reamed to the exact land diameter. When I cut a new chamber, I use the reamer used to cut the chamber to set the diameter of my Comparator index. All of the Hornady indices I have measured are 'conservatively' dimensioned.

Paul
 
I guess so long as the curveture of all the bullet noses are the same, it doesn't matter what diameter they are... But that is a big ask and I doubt they are. Although if they are very close (which I'd say they would), the actual difference in length you're measuring will be very small indeed - like less than calipers could measure I would have thought? You know, sine rule etc..

Basically I would have thought, so long as you use the same comparitor, and only using it for comparing to a reference (or a few) dummy round it'll be close enough even for match shooting, let alone hunting. But I guess it's even debatable you really need it for hunting at all.
 
But I guess it's even debatable you really need it for hunting at all.
That depends both on your attitude about precision reloading and whether or not you subscribe to the premise that seating depth (or distance from the lands), is an important factor in precision reloading.

I couldn't agree with you more that having the exact land diameter in your comparator is rendered moot for many uses as long as you stay to using one comparator. (Simply keeping things relative.) However, if you want to be a specific distance from your lands (manifested in a specific cartridge overall length), then knowing exactly - not relatively - where your lands are is imperative. Personally, I don't find it possible to be more consistent than about 0.003" in cartridge-to-cartridge lengths (ogive length). Given all of the other variables (between cases capacity variation for one big one), 0.003" is sufficiently precise for my 'mental health'.

Paul
 
Well Paul I can safely say I agree on all fronts. If I'm within 3 thou length for my hunting loads I'm pretty happy.
 
Gentlemen.

Hornady is in the bin and my new set of Sinclair inserts will arrive later this week. After posting the above I borrowed a set of Sinclair inserts and was slightly concerned.

It seemed daft to have paid for the chambers to be reamed for a particular bullet only to find I was a long way into the lands in .243 and way out in .308. back to the drawing board.
 
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