Reloading practices

[Tpb10505]

The problem with using a commercial (i.e., Hornady) "comparitor" to measure CBTO is that the diameter of the comparitor insert is very likely not the same as the diameter of your die's seating stem. Consequently, you will likely not get consistent CBTO measurements after seating. The reason is, in my testing I've found "ogive form" to be very inconsistent, even in what is considered high-quality commercial target bullets. So what I've done to remedy this is to make a comparator insert with a dia. as close as I can to the dia. of my seating stem (neither the original comparitor insert nor the one I made is even close to where the ogive actually meets the rifling). I then use a Sinclair "Seating Depth Gauge" to establish OAL to "touch" (what to "touch" is a different discussion), then using the same bullet, I seat it to the calculated OAL for "touch" and then measure the resulting CBTO, using the modified comparitor insert. That gives me a starting reference point, for seating depth, it also gives me very consistent CBTO measurements.

If you’re using the same comparator to measure both CBTO with the Hornady tool and the CBTO of your loaded round, how would that yield inconsistent CBTO measurements? Ogive form seems to be more of a bullet issue than a tool issue, no?

 

[Chuckhunter]

Well, sounds like I should measure length from cartridge base to ogive as OAL.

Colt, when I log in my data, I have two columns, one is OAL and the other is OALG (#1 is Overall Length and #2 is Overall Length in Gauge). You'll be able to identify best seating depth for accuracy according to your targets and OALG, then the OAL will let you know if that depth will work in your Magazine. Just a suggestion. Good luck.

 

[Bill Norris]

Colt, when I log in my data, I have two columns, one is OAL and the other is OALG (#1 is Overall Length and #2 is Overall Length in Gauge). You'll be able to identify best seating depth for accuracy according to your targets and OALG, then the OAL will let you know if that depth will work in your Magazine. Just a suggestion. Good luck.

Really important to include that data in the log.

 

[COLT45SA]

Really important to include that data in the log.

Good suggestion, but mine is a single shot so there is no consideration of magazine length.
Appreciate you response~!!

 

[wkdickinson]

If you’re using the same comparator to measure both CBTO with the Hornady tool and the CBTO of your loaded round, how would that yield inconsistent CBTO measurements? Ogive form seems to be more of a bullet issue than a tool issue, no?

As I said in my post, the difference comes from the Hornady (or any other) comparitor having a larger diameter than the bullet seating stem. So if the form of the ogives vary the distance between where those two diameters on the bullet are located longitudinally, will also vary. Hence the variance in the CBTO using the Hornady comparitor. Only my opinion, but I've proven to myself many times.

 

[gmr4]

In this video Sam Milliard discusses the methods and differences between the two measurements. He also goes into the issue of length changes between measuring rounds loaded with fired brass and un-fired brass. The one fact that he drives home is the dangers of thinking one might be just touching in the lands BUT in reality jammed completely when flirting with "hot" loads.

Man, I’ve referred many newbys to Sam Millards videos.. 2-3 have followed them and even purchased the same equipment and each is well on there way with reloading. Panhandle Precision rocks.

 

[Tpb10505]

As I said in my post, the difference comes from the Hornady (or any other) comparitor having a larger diameter than the bullet seating stem. So if the form of the ogives vary the distance between where those two diameters on the bullet are located longitudinally, will also vary. Hence the variance in the CBTO using the Hornady comparitor. Only my opinion, but I've proven to myself many times.

So I should see variances in my CBTO on loaded rounds? How large were the variances you found when using a comparator?

 

[drop_point]

Start sorting your bullets if you're seeing drastic differences.

 

[wkdickinson]

So I should see variances in my CBTO on loaded rounds? How large were the variances you found when using a comparator?

Here is what I found when I randomly selected 30 rounds and measured them using the Hornady comparitor. The accompanying picture shows the difference between where the comparitor and the seating stem reference on the bullet.

 

[Tpb10505]

View attachment 1679375

Here is what I found when I randomly selected 30 rounds and measured them using the Hornady comparitor. The accompanying picture shows the difference between where the comparitor and the seating stem reference on the bullet.

Interesting! Appreciate the data! I use a SAC Universal seating die and the stems contact the bullet much lower than what’s typical. Could be why I don’t see much variation in CBTO.

 

[wkdickinson]

Interesting! Appreciate the data! I use a SAC Universal seating die and the stems contact the bullet much lower than what’s typical. Could be why I don’t see much variation in CBTO.

Could be, if I recall, the die I was using was a Whidden. At the time I also did a fairly large study (200 bullets) of BT to Ogive on Berger 105 Hybrids. Here is what I found:

Base to Ogive Berger 105gr Hybrid
Lot#: XXXX	Date: 11/2/21
BTO (in)	Cnt
0.642	1
0.643	14
0.644	50
0.645	74
0.646	49
0.647	12
Total:	200

 

[ELR LVR]

If I trim all my cartridges to precisely the same length and seat my bullets so that the carefully measured final OAL is the same, will that make a significant difference in how the loads group~??

No-
it will only make a significant difference if you are at the correct seating depth and do all those things

 

[ELR LVR]

So I should see variances in my CBTO on loaded rounds? How large were the variances you found when using a comparator?

When using a comparator - differences should be no more than .002" only due to Brass springback and neck tension.
When these two things are cured there should really be no variance when measuring at the ogive.
MAYBE.............. 0.001" once in awhile every 20 rounds or something