COSteve beat me to it. Spherical formulations often benefit from changing to a magnum primer. The deterrent coating on them makes the outer layer of each grain slow-burning and harder to ignite. Hornady used the Winchester WLP in their development of these loads and it is a magnum primer (dual use, actually, as Winchester makes just one LP primer for both standard and magnum loads, but to work in large magnum cartridges, it has to make as much start pressure as a magnum primer does).
From SAAMI's glossary:
LOAD, SQUIB
A cartridge or shell which produces projectile velocity and sound substantially lower than normal. May result in projectile and/or wads remaining in the bore.
So "squib" applies to undercharged as well as empty cartridges, and the term certainly applies in this instance.
Laymenshooter,
If your primer is milder than the Winchester and if you have any high primers (inadequate seating—you generally want to seat primers fairly hard for best ignition consistency) you may be getting slow or erratic ignition that gives time for building pressure to push the bullet out of the case and into the throat before the powder has made much of its gas. That means it is burning in a bigger volume, which drops the intial pressure significantly. This will be especially true of the short nose profile bullet, as it will have a long jump to the throat as it leaves the case. While that is happening, the case expands, but not always hard enough to seal the chamber well, so a lot of the pressure can bleed off, causing the squib.
Another thing that affects pressure and ignition, especially in a short powder column cartridge like the 45 Auto, is bullet seating depth. The Hornady RN FMJ is a short bullet for the type, having a more spherical nose than the military bullets which have more elongated elliptical noses. As a result, Hornady recommends a COL of just 0.210" for their 230 grain RN FMJ bullet, where the military cartridges I've measured are usually at about 0.270", closer to the maximum of 0.275" in the cartridge drawings. You did not state what COL you are using, but if you are seating to the SAAMI drawing number of 1.275", that would explain a lot of the pressure difference. A chronograph would quickly confirm that your velocities are low (after correcting them for your barrel length) and this would indicate your pressures are lower than Hornady got.
Hornady will have loaded their test rounds with off-the-shelf powder, whose burn rate can vary plus or minus several percent. They could have had a lot at the fast end of the burn rate tolerance, while you may have one at the slow end, explaining part of the problem. These kinds of variables are why loads have to be worked up for your component combination and powder lots.
The bottom line is, you don't have enough heat and pressure to keep the powder burning properly in your chamber. That much is certain from the squibs. Your chamber is not going to be as tight as a SAAMI standard pressure and velocity test barrel, so it is possible for a load tested in these standard devices to fail in your looser production chamber.
Check that your primer is a WLP or another magnum primer and that it is seated firmly. Check that your bullet is seated to 1.210" cartridge overall length. If that doesn't correct your problem your chamber is just too much looser than the Hornady chamber was and you need to increase your powder charge as already advised.
