Using The Bob Green Bullet Comparator

[mikecr]

I use Wilson seaters, which provide desired local CBTO without issue.
That's CARTRIDGE BASE to ogive, not CARTRIDGE SHOULDER to ogive.
My shoulders are bumped 1thou HS.
And before anyone suggests that primer striking re-bumps my shoulders -> that doesn't happen with me.

 

[ckaberna]

Thanks T-Shooter I have some more. Keep in mind both these bullets weigh in at 142.1 with a RCBS digital I have confirmed with my beam.
You should be able to see the "rings" from both the seater and the hornady 4-25 bushing. Bushing made contact @ .248 bullet OD.
The bullet OD where the seater made contact was .183
The closest I can measure the rings without building a jig is about .008" difference (between upper and lower) in the two which translates about the difference I was measuring while seating.
I must assume between lots there may be this much difference. Never again will I mix them.
I still want to know if Bobs tool would allow me to sort these, if so I will have one ordered before the week is over.

 

[Ned Ludd]

I have measured the base to shoulder and all case were within.001 or I bumped them back to where they were before loading. As I mentioned I am developing a load using what was new Lapua brass. The issue was only noticed when I was reloading these. The first time I didn't bother to measure every CBTO, I assumed once the seater was set all would be the same. Now I know to not "assume".

In my hands, setting the seating die micrometer so that some of the loaded rounds will give you the desired measurement on the first light stroke of the press and the rest will be seated .005" to .001" long has worked best. I measure every loaded round after seating and even on my best days, the variance may be as high as .002" to .003" after the first stroke. That's why I set the mic to seat bullets at no more than the desired seating depth or just a tick long. I can always put a round back in the press and barely touch it again to get it where I want, but if it's too short, I don't ever try to pull it and start over. Too much chance for upsetting neck tension or damaging the surface of the bullet.

 

[ckaberna]

After two afternoons I THINK I have a solution to my problem. I call it the o-give to seater comparator. I can sort bullets to achieve a consistent seating depth before going to the bench. See pics:
It uses MY hornady comparator insert and a stem bored the same as mine on my Redding seater. Haven't loaded yet but I will update- success or fail.
Kevin

Thanks for all yalls help

 

[Bart B.]

Two things keep resized case headspace to a minimum spread:

• Uniformly lube all cases so each has the same amount all over. I like to use a 50-50 mix of STP engine oil treatment and Hoppe's No 9 bore cleaner, several drops in a large coffee can lined with foam then put in 50 cases. Tumble them in a Thumblers Tumbler while full length sizing an earlier batch of lubed ones.

• Use a Redding competition shell holder the right height above the .125" standard then set the die to let it stop against the die bottom with the ram topped out gently camming over. Keep it up for 3 to 4 seconds to let press springback pull the die down that last thousandth from where it pushed up sizing the case. Bump case shoulders back .002"; .001" if their headspace spread after sizing is less than .001" and the rifle's bolt face is squared up right.

A .002" spread in case headspace is very good.

 

[ckaberna]

Two things keep resized case headspace to a minimum spread:

• Uniformly lube all cases so,each has the same amount all over. I like to use a 50-50 mix of STP engine oil treatment and Hoppe's No 9 bore cleaner, several drops in a large coffee can lined with foam then put in 50 cases. Tumble them in a Thumblers Tumbler while full length sizing an earlier batch of lubed ones.

• Use a Redding competition shell holder the right height above the .125" standard then set the die to let it stop against the die bottom with the ram topped out gently camming over. Keep it up for 3 to 4 seconds to let press springback pull the die down that last thousandth from where it pushed up sizing the case. Bump case shoulders back .002"; .001" if their headspace spread after sizing is less than .001" and the rifle's bolt face is squared up right.

A .002" spread in case headspace is very good.

Thank you for your input, I like the foam and STP idea..never thought about that. My head space sizing is going good. I do not have a problem with that, I am annealing after every firing though. This dang seating depth is whats driving me nuts.I set the dies to "slightly/gently" cam over for all processes...Not sure if that is correct or not but seems consistent.
Thanks,
Kevin

 

[Bart B.]

This dang seating depth is whats driving me nuts

A few thousandths spread is good enough to shoot sub MOA groups at 1000 yards. Remember the chamber throat erodes away down the barrel .001" for every half to few dozen rounds fired depending on charge weight and bore diameter. Are you going to adjust bullet seating depth that often?

Good rifles will shoot good ammo sub MOA at a thousand over .050" change in bullet jump distance to the rifling. Or soft seat bullets .020" long then single load them so they gently push back by the throat and all have zero jump to the rifling and center better, too.

 

[308BAR]

What dial indicator range does the BGC tool uses or could it use any based on the precision you're looking for? i.e. 0.05"range x 0.0001" or 1.0" x 0.001" etc.... trying to learn more about the tool and if i need to purchase another dial indicator. What do you use?

 

[T-shooter]

In my hands, setting the seating die micrometer so that some of the loaded rounds will give you the desired measurement on the first light stroke of the press and the rest will be seated .005" to .001" long has worked best. I measure every loaded round after seating and even on my best days, the variance may be as high as .002" to .003" after the first stroke. That's why I set the mic to seat bullets at no more than the desired seating depth or just a tick long. I can always put a round back in the press and barely touch it again to get it where I want, but if it's too short, I don't ever try to pull it and start over. Too much chance for upsetting neck tension or damaging the surface of the bullet.

Same here. I check every round. My press doesn't cam over. I set the die so usually it will be .001-.002" long when I just feel it bottom out, then I can give it a slight bit more pressure and get it right. If I go over I pull them back a bit and reset. I don't think my collet die does anything to the surface of the bullet and I only have to use minimal clamping force on it. If you are worried about neck tension or bullet damage, an impact puller would not cause any runout or tension issues I could thing of. Just a couple light taps to move the bullet maybe .005" and reseat. Pulling them clear out and reseating does seem to lessen neck tension.

 

[mikecr]

Pulling them clear out and reseating does seem to lessen neck tension.

It doesn't. You could pull & reseat new bullets in a neck (a thousand times) and it would not affect tension at all.
It could affect friction/seating force(which means nothing directly to ammo/shooting results).

 

[T-shooter]

I just did a seating test using a 208g Hornady A-Max and a new never fired Hornady .308 case. The case was expanded, neckturned, and F/L resized with a Forster die with an expander ball. I went through several cases to pick one with less runout on the neck. No lubricants were used. I used a Mitutoyo micrometer measuring to 1/10,000 inch. Each was measured in several places.

Bullet diameter ... .3083" - .3084" (never changed)
Turned case neck O.D. ... .3344" (before seating the first time)
Neck O.D. with bullet seated ... .3361" - .3362" (never changed)

After 1 seating the neck is .3348 - .3349 (+ .0004" - .0005")
5 seatings the neck O.D. is .3351 - .3353 (+ .0007" - .0009")
10 seatings the neck O.D. is ..3353 - .3354 (+ .0008" - .0010")
20 seatings the neck O.D. is .3353 - .3354 (+ .0008" - .0010")

After the first seating and pulling the bullet, the O.D. of the neck grew (less springback) by about .0004" to .0005"

After 20, no difference in the springback but the bullet was easier to seat and pull, partially due to the wearing and polishing of the surface inside the neck and due to the necks not springing back after repeated seatings which expands nearly .002" the first time.

So after 10 seatings and pullings, the neck interference fit is about .001", approximately 1/2 of what it was the first time.

 

[kvd]

What dial indicator range does the BGC tool uses or could it use any based on the precision you're looking for? i.e. 0.05"range x 0.0001" or 1.0" x 0.001" etc.... trying to learn more about the tool and if i need to purchase another dial indicator. What do you use?

The dial indicator that came with mine is 0.2" X 0.0001". Attached is a picture.

Ken

 

[308BAR]

The dial indicator that came with mine is 0.02" X 0.0001". Attached is a picture.

Ken

View attachment 1016795

Thank you for the reply.

 

[paulT]

Regardless of merchandising or misunderstandings, the BGC does not establish consistent CBTO. That's not what it's for.
The BGC is purely for comparative measure of ogive radius variances.
Once you've established bullet groups matching in ogive radius, i.e. qualified your datums, further measures like CBTO become credible.
But you still have to measure CBTO for every round loaded to establish matching CBTO(which is affected by seating forces).

Keep in mind also that a given CBTO is usually taken from a point different than actual land contact, which is affected by throat angle to ogive angles,, not just diameters. And bearing does not begin anywhere near land contact.

There is also a gualifying measure prior to ogive radius comparison with a BGC. That is, bullet diameter at bearing end/ogive begin. Without considering this, you could match ogives with bullets that don't actually have matching ogives. That doesn't change CBTO directly, but it would affect meplat trimming taken from a high ogive datum.
Meplats should always be trimmed from ogives to obtain same meplat diameters,, not from bases merely to get same OAL..

Would checking the bullet ogive radius with the bob green custom ogive comparator offer more uniform meplat BEFORE Bullet Trim and Pointing Process.

 

[rkittine]

After sorting by weight and length, I then sort by baring surface.

 

[mikecr]

Would checking the bullet ogive radius with the bob green custom ogive comparator offer more uniform meplat BEFORE Bullet Trim and Pointing Process.

It would if your meplat tools take datum off the nose (like Hoover).
It would not if acting w/resp to bullet base (like Whidden).

 

[paulT]

It would if your meplat tools take datum off the nose (like Hoover).
It would not if acting w/resp to bullet base (like Whidden).

Thanks for info,
I have previously batched my bullets from bullet base to Ogive before Trimming and pointing process with the sinclair bullet base to ogive stand tool & dial indicator however i notice the sinclair tool measures the Ogive closer to bullet bearing surface to ogive junction verses the bob green tool which appears to measure the ogive area which is in contact with bullet seater stem which should yeild even better results when batching bullets for pointing process with Hoover system.