New bullet design testing?

[Fast14riot]

I was given some newly designed bullets to test for target shooting and was wondering if beyond basic metrics of load testing and range testing, is there anything else I should be looking to record?

The bullets are a monolithic, higher BC projectile for AR15 sized cartridges. I will be testing a .277 120gr HPBT in my 6.8 which is my prone match gun (mid range out to maybe 800 yards). It has a G1 BC of about .440, far better than the current match bullets available for the 6.8, (I currently shoot 110gr BTHP with a stated G1 of .360)

Other than velocity and correcting BC based on actual dope, along with ability to tune a good load at magazine length as well as long loaded, what else should I be looking for?

-Alexander

 

[Berger.Fan222]

Published BC numbers should be based on an accepted BC measurement method that measures velocities over a set distance or near velocity and time of flight over a set distance. Inferring BC from drop has too many confounding factors and introduces too much error to be reliable.

Try a google search, I think there are some web pages and publications that describe it in detail, including how to use the LabRadar to do it.

Monolithic bullets can have pressure issues at charges that are fine for jacketed lead bullets. I cringe a bit when people publish load data deemed safe with little more than inspection of the brass. A bullet manufacturer is probably subjecting shooters to risk of harm and themselves to liability lawsuits when they do this.

There are industry standards for measuring load pressures that bullet manufacturers should use. Most do, but some of the boutique companies do early work with guinea pigs, er, volunteer hobbyist testers. In the absence of proper industry standard techniques (a universal receiver with a proper pzt based pressure measurement system), hobbyists can make some progress by:

1. Using a hobbyist pressure measurement system like this one:
https://www.shootingsoftware.com/pressure.htm

2. Not just inspecting, but carefully measuring and inspecting brass for pressure signs and continuing to check after several firings for things that may not show up on one firing (like loose primer pockets). There are some good articles on detecting pressure signs out there. Read them.

3. Using a hobbyist tool like QuickLoad to estimate peak pressures with carefully determined values for all the entry fields. I would double the shot initiation pressure of a jacketed lead bullet of similar length or use the shot initiation pressure of an original Barnes X bullet of the same caliber and weight as an estimate for that of a monolithic solid. Using the shot initiation pressure of a newer X bullet (with the grooves) or a jacketed lead bullet will give overly optimistic results.

 

[Fast14riot]

The bullets have been tested and no load data is being published yet, I was going to be testing more of performance. These bullets have reduced bearing surface compared to similar weight lead bullets.

I appreciate the information.

 

[Berger.Fan222]

The bullets have been tested and no load data is being published yet, I was going to be testing more of performance. These bullets have reduced bearing surface compared to similar weight lead bullets.

I appreciate the information.

Reduced bearing surface may or may not translate to reduced friction compared with similar weight lead bullets. Further, things that are done to reduce friction in the barrel (grooves like Barnes TSX and TTSX) often have negative effects on aerodynamics. Each edge at the front and back of each groove creates a shock front in supersonic flight that increases drag. The longer lengths of monolithic bullets also decrease stability which can increase drag in marginal twists. Longer lengths also increase drag of there is any bullet wobble.

Your intent may only be to test performance, but a lot of small bullet companies go public with load and BC data provided by performance testers before they ever perform the more appropriate kinds of load development, pressure testing, and BC determinations described above. If they do not want to take the time or spend the money to do proper testing, what is to prevent them from using your data? Especially if you are a sponsored shooter, how are you going to prevent them?

 

[Fast14riot]

I do know that a lot of initial testing has been done on these bullets before they were even released for public sale. I'm testing mainly because I shoot a 6.8AR in mid range matches and they're aren't many of us who do, so I will be trying out this makers target bullet.

I do appreciate the info, as far as sharing load data, I will share my load publicly (with typical disclaimers) but not through the company. The maker has already declined from sharing any load data. I have been crunching numbers in QL for a few days finding safe starting loads with my powder selections. I'm confident in my safety protocols for initial load work up.