can't get consistent number from same bullet ogive

[taseal]

I just got the hornady comparator and set it up on my digital caliper.

well I'm running into a problem...

when I seat the bullet in the 8-30 insert (.30 cal I guess) it's just not gonna fall perfectly vertical. there is maybe a 1 degree (or even .5 degree) can't on the bullet when it goes in the insert. I try to line it up best as I can with my fingers, but then when I push the caliper claw on it, if it's not perfectly vertical I can see it, so I get a bad reading. then I straingen the bullet and do it again, but now the bullet from the caliper claw got pushed in about .0001 or so, and now I'm getting a totally off reading everytime I push the caliper claw down to see.

I just can't even get the same number from the same bullet. it's varying way too much. and my caliper is accurate to +/- .0005 so I'm limited to at best .0005. but at this rate, I can't even get the same damn bullet to stay in .001

any help here? ideas? the caliper is perfectly calibrated at 0 with the comparator in place

 

[Shady_Jay]

Re: can't get consistent number from same bullet ogive

Spin the round in the insert with slight pressure on the back of the round with the caliper blade until it levels out.

 

[taseal]

Re: can't get consistent number from same bullet ogive

ok, what I did was sort of like what you said. but instead of spinning it, i just wiggled it ligthy horizontally and it sat it in place without any downward pressure. most were .6500 some .5490 and very few .6525

 

[bohem]

Re: can't get consistent number from same bullet ogive

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: taseal</div><div class="ubbcode-body">ok, what I did was sort of like what you said. but instead of spinning it, i just wiggled it ligthy horizontally and it sat it in place without any downward pressure. most were .6500 some .5490 and very few .6525 </div></div>

I'm assuming you mean:

.6500 some .<span style="text-decoration: line-through">5</span><span style="font-weight: bold">6</span>490 and very few .6525

Calipers are really a tool for measuring +/-0.002 on good calipers. Yes, they read out on yours to 0.0005 but due to the design restrictions they're generally not something you want to bank on inside of 2 thousandths.

Any tool and die maker or good machinist is going to tell you the same thing.

The numbers you got are not entirely surprising, I'm very confident that if you took a box of bullets and measured each one like that (especially SMK's) you will find a variation of around 0.010" across the box...

CKA's advice on spinning it is akin to what I was going to say, which was "wobble it in the jaws until it tightens up and stabilizes".

 

[Shady_Jay]

Re: can't get consistent number from same bullet ogive

In my reloading classes I teach to cull one round from your box and use that round to measure your lands every time. Keep your "Magic Bullet(s)" in the same box as you keep your comparator inserts.

As Bohem stated, they vary. If you don't use the same projectile every time you could get false readings. The variation is also the reason why loads that have a .005 jump will sometimes actually be in the lands and you can feel it when you close the bolt.

 

[vman]

Re: can't get consistent number from same bullet ogive

This is slightly off topic, but has anyone here used the sinclair bullet sorting stand?

I have been curious to know if it suffers from the same problem of not being level... or bullets not sitting in level, and hence lots of variation in readings.

 

[bosulli]

Re: can't get consistent number from same bullet ogive

I was having the same issue. I shoot a gas gun, and they are rougher on bases. I believe most of my variance was coming from bases that had been swiped or not as level as new. I bought another comparator base and insert, and as TresMon describes, measured the bearing surface of the bullet. Found SMKs vary .002 or so, and occasionally a little more. So, for me, measuring the ogive from the base is not always reliable.

 

[YAOG]

Re: can't get consistent number from same bullet ogive

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: taseal</div><div class="ubbcode-body">I just got the hornady comparator and set it up on my digital caliper.

well I'm running into a problem...

when I seat the bullet in the 8-30 insert (.30 cal I guess) it's just not gonna fall perfectly vertical. there is maybe a 1 degree (or even .5 degree) can't on the bullet when it goes in the insert. I try to line it up best as I can with my fingers, but then when I push the caliper claw on it, if it's not perfectly vertical I can see it, so I get a bad reading. then I straingen the bullet and do it again, but now the bullet from the caliper claw got pushed in about .0001 or so, and now I'm getting a totally off reading everytime I push the caliper claw down to see.

I just can't even get the same number from the same bullet. it's varying way too much. and my caliper is accurate to +/- .0005 so I'm limited to at best .0005. but at this rate, I can't even get the same damn bullet to stay in .001

any help here? ideas? the caliper is perfectly calibrated at 0 with the comparator in place </div></div>


taseal,

I use the same tool and this is how I set them up. Set your comparator base and holder on the large thick part of the caliper jaws loosely being sure the little grub screws on the back of the base and holder are not touching the caliper jaws. Also make sure your ogive insert is not tightened in the holder yet. Next line up the base, insert holder and insert while closing your caliper jaws on the comparator and get all three bits lined up in a straight line and hold the caliper jaws closed. Lightly snug down the large brass locking screws and then the small grub screw for the ogive insert but do not touch the rear grub screws. Once you have done this zero your digital calipers and try it again.

HTH!