AR15 Long Advance Bolt Carrier - Expanding Gas System
US Patent No: 10,488,128
Have you ever wondered why a groove appears behind the cam pin recess cut on the inside of all AR15 upper receivers? So did we. But when we asked, we were told that "it’s normal" and “they all do it”.
Well that wasn’t good enough, so with some time on our hands we decided to investigate. The gouge is caused by the cam pin hitting the receiver side wall, and cutting the top off a receiver and high-speed filming the firing sequence revealed this to be the case. But why was it happening? Common knowledge teaches us that the bolt rotates 22.5 degrees and unlocks, if it does this the cam pin should never contact the wall. Careful mapping and modeling of the cam path revealed the problem; the cam path had been drawn incorrectly right from the start, allowing the bolt to unlock at 20.7 degrees and so strike the upper receiver wall.
By correctly redrafting the cam path, we were able to have the bolt open at 22.5 degrees when the cam pin is top dead center, as originally intended, and thus avoid the interference with the receiver wall. An itch had been scratched.
We ran ten pre-production bolt carriers and the first was test fired on May 24th 2019. The rifle functioned flawlessly and it was an emotional experience for all closely involved; witnessing an AR15 operating as originally intended for the first time in 62 years. Subjectively, the gun felt smoother locking and unlocking, which was the initial impression of everybody firing it. We decided to extensively test the pre-production run prior to making the decision to offer the product commercially.
By delaying opening for almost, two degrees, we’ve allowed chamber pressures to drop slightly, and additionally, a little extra time for the cartridge case to contract from the chamber wall easing extraction. While it’s not for everyone, and certainly we have encountered market resistance from those denying there was an issue to start with, we feel that there are enough potential customers who understand what we are trying to do to make a production run worthwhile.
This is a drop in part and will work with all existing bolt carrier group components currently available. Why not have the gun function as intended.