Comparators explained please

[Texas Solo]

I've used an OAL gauge before to measure my bolt face > lands and then subtracted .010". I ended up with a very accurate load that would only single feed because it was longer than my magazine would allow. In that rifle, I switched from Nosler BT to Sierra BTHP and gained some space from not having the plastic tip on the bullet. ie: the ogive was closer to the lands than the Nosler BT when the OAL was shortened to fit the mag.

I'm not sure how a comparator works or what is to be gained from it's use. Can someone explain it so I can understand?

[82boy]

A bullet comparator, measures the bullet by ogive. So you can measure bullets and match them up by ogive length, and with loaded rounds, you can find where a bullet's seating depth works, and if you switch bullets it will give you a guide where to go on the new bullet.

[skypilot]

The comparator holes(on the Sinclair Comparator) are cut with a throating reamer to allow someone to measure from the case head of a loaded round to the largest part of the bullet that would touch the rifling.
A comparator will confirm the length you have determine by other methods and allow you to accurately measure that length and compare other loaded rounds to that measurement while you are reloading(seating bullets). That allows you to be more consistent with the jump or jam.

The Sinclair happens to be a 1" hex nut with holes for different calibers, so you would need to subtract 1" from that measurement to get the actual case head to ogive length.

EDIT: I was writing about the same time as 82boy. He explains it well.

[Texas Solo]

OK, so if I load to a given length with bullet"A", then to the same length with bullet"B", I'll be able to see witch bullet places the ogive closer to the lands.
If that's correct, I get it.

[82boy]

No, you are measuring the bullet at the ogive, this is the section where the bullet contacts the lands. So if you measure bullet A, which is .010 off the lands, (Lets say it is 1.825) if you set bullet B at the same length (1.825) it should be at the same place from the lands (.010 off).

[Texas Solo]

I get that. In my last post, I meant to say that if bullet "A" and bullet "B" were set to the same OAL, then the length from base to ogive could be different...given two different bullet makes/shapes.
By using the comparator, both loads would be .010" off the lands, but OAL "could" be different. Which, I could care less about as long as it fits the mag.
Is this correct?

[Trent]

The biggest reason for using a comparator is so that you aren't using the tip of the bullet as a measuring point. The tip of the bullet is generally the least consistent part of a bullets construction (especially with the polymer tips). You can have two bullets of the same make/model/lot that both measure exactly the same from the base to ogive and still end up 0.010" different in the length from base to tip.

Also, keep in mind that comparators aren't all the same. If you measured a factory round with your comparator and I measure it with mine we will more than likely be close, but not the same in our measurement. It's not a magic device by any means. Its just a piece of metal with a hole in it. A very slight variance in the hole size will make a big difference in where it contacts the bullet. As long as you always use the same comparator from your tool box then it doesn't matter.

[WuzYoungOnceToo]

I get that. In my last post, I meant to say that if bullet "A" and bullet "B" were set to the same OAL, then the length from base to ogive could be different...given two different bullet makes/shapes.
By using the comparator, both loads would be .010" off the lands, but OAL "could" be different. Which, I could care less about as long as it fits the mag.
Is this correct?

Bingo. :cool:

[John_M]

Trent, Let me add my "Bingo" to that of WuzYoungOnceToo.

[M.O.A.]

So really it would be easy to make a comparator out of some bar stock or some thing of that nature