Increasing Your Accuracy With A Bullet Comparator

 

If you are a reloader, the term cartridge overall length or simply "COAL" should be familiar to you. The SAAMI (Sporting Arms and Ammunition Manufacturer's Institute) spec for overall length of a specific cartridge is always listed in a reloading manual. It is the measurement from the base of the cartridge to the tip of the bullet. For reloaders, it's no secret that adjusting the COAL is a variable used to fine tune accuracy.

The problem is that there's another variable hidden inside the COAL variable that some people may not realize. Depending on the bullet and manufacturing process, bullets can vary as much as .025" in length. Due to these variances in the tips of the bullets, reloading based on COAL can be quite unreliable. For people who reload solely for hunting purposes, this probably wont pose an issue. However, for people reloading for accuracy this could be the cause of your occasional flyer or more dangerously, the cause of your pressure spike. 

This is where ogive (pronounced O-Jive) comes into play. Ogive refers to the curved section of the bullet from the bearing surface to the tip. The variances on this curve where the bullet begins to touch the lands is much less than the variances in the tip. Because of this, measuring cartridge base to ogive (CBTO) will give you much more consistent readings.

In order to measure CBTO you need a bullet comparator like the one shown above. The Hornady Lock-N-Load Bullet Comparator easily attaches to and set of calipers with the use of a brass thumb screw. I opted for the complete kit which includes just about every insert you’ll ever need. They also sell a basic kit, but if you do a lot of reloading for a variety of calibers, I suggest just getting the complete kit from the get go.

I decided to measure the overall length of these three types of bullets and then measure them again with the bullet comparator. I lined these bullets up for the photo in the order of what I expected to be most consistent to least consistent. I expected the lead tips to vary the most. But much to my surprise, the Hornady lead tipped BTSP and the polymer tipped ELD Match measured quite consistently. With the BTSP all measuring within .002” and the ELD’s measuring within .001”. However, the Barnes HPBT’s varied as much as .010”. A variance that big could definitely affect your group sizes if reloading off of COAL.

I then attached the bullet comparator and remeasured. The ELD’s came in exactly the same with a .001” variances. The BTSP’s had a slight improvement from the overall length measurement and come in at .001” as well. Now where the bullet comparator really showed it’s worth was with the Barnes HPBT’s. That almost sickening .010” overall length variance shrunk to .002” when measured off the ogive. That right there is enough to show the advantage of ogive.

After seeing the variances in overall length vs. the ogive of the bullets I can't see myself using any other method. It has shown me that you shouldn't trust the tips. This is what reloading has evolved to and its almost like using old technology by using the COAL method. Like I said in the beginning, the COAL is probably good enough if you only reload for hunting purposes or if you're loading the Hornady ELD's that appear to be so consistent in both OAL and ogive. But why take that chance when you can achieve better consistency with a simple and relatively inexpensive device?