What the heck is a .220 Thunderbolt?? Good question. In short, it's .22-250 performance packed into a more efficient cartridge designed for the AR-15 chassis.
It's design origin came from the now largely popular 6mm Hagar in its infancy stage back in 2003. One of the designers of the Hagar introduced me to his new cartridge in which I had an immediate interest in due to its then obvious potential. I built a Hagar and was instantly impressed with the reliable function capability of the .30 Rem based cartridge in the AR-15 chassis and the overall performance. At that particular time, I was on a military competition rifle shooting team which allowed me access to an untold quantity and variety of .22 cal. bullets that were predominantly used in the .223 AR-15 service rifle.
Having experience with this new cartridge and access to a variety of .22 cal. projectile weights, my next thought was... you guessed it, to combine the Hagar performance potential with my own interest and experience of the .22 cal projectiles in the hopes of developing a super .223 target rifle or ultra varmint rifle with .22-250 like performance while still retaining the benefits of an AR-15 semi-automatic and ergonomic platform. I was particularly interested in driving the JLK or Berger 90 grain bullet for long range competition use for a substantial velocity gain than the .223 Rem was limited to since I had experienced such good results the year prior, winning the 1000 yard Porter Trophy at the National Rifle Matches at Camp Perry, OH. Although I had a good performance that year, it took a back seat to Chris Hatcher 's of the Army Marksmanship Unit, shooting the first ever 200 (perfect score) with a service rifle at 1000 yds with the same 90 grain bullet at the annual Interservice Rifle Matches held at Quantico, VA just 2 weeks prior to my own accomplishment. Needless to say, I had big plans in mind for the 90 gr bullet.
After getting the project off the ground, the Thunderbolt results were staggering to say the least, displaying fantastic accuracy at 600 yards. My biggest mistake was the original choice of barrel twist rate of 1:6.5". Although perfect for the .223/90 gr. combination, a 6.5" barrel twist teamed up with the beefier Thunderbolt powder capacity pushed the bullets too far past the stability threshold for the increased velocity of the brawny Thunderbolt case. This choice forced me to keep the 77 gr bullets limited to about 3200 fps and not even consider trying lighter bullets for fear of inevitable bullet explosion from over rotation. Through successful experimentation, I determined that a 1:7" twist was just right for the 90 gr bullet in this powerhouse cartridge.
Hiatus & Resurrection:
Unfortunately, due to the lack of Hagar brass production at the time, I was limited to forming soft .30 Remington brass which was not designed to withstand modern day pressures that today's high power rifle cartridges produce. I soon grew tired of shelling out money to continually buy brass and go through all of the work that it took to make the Thunderbolt a reality only to find out that the brass just could not go the distance.
Thanks to the guys at H&K Associates together with Hornady, the brass is not only a reality, it is very high quality brass that was designed for modern day cartridge performance. Today, the brass contract has been continued with Creedmoor Sports via Hornady. The only thing that must be done prior to loading the Thunderbolt brass is run it through the .220 Thunderbolt sizing die in order to reduce the neck diameter by .019" and that's it. The shoulder angle and all other body dimensions are the same as a 6mm Hagar alleviating the need for any type of additional die or fire forming. Please see the tab to the left of this page "6mm Hagar" to see more information on the Hagar brass which is used for this cartridge.
I felt very fortunate for several months in the summer of 2013 that I have 2 gentlemen, who claimed to be willing to put the cartridge to the test, however their promises never panned out even though they received free barrels in order to test and evaluate. This was a brief disappointment, however, in the mean time, I have sold several .220 Thunderbolt uppers to varmint hunters and target shooters around the US. I am proud to say that they have been very pleased with the results that they have been experiencing with this cartridge using various bullet weights.
I have now been shooting competitively exclusively with this cartridge from 200-600 yards, off and on since 2004 and steadily since May of 2013 with nothing less than stellar results. One customer in Georgia commented that "the .220 Thunderbolt is everything that the .223 Remington could have been".