All the lot #4 of CFEBLK I can stuff in the case and still seat the bullet to proper OAL. You can't get enough powder in the case to even reach 55k psi with this bullet. SOCOM is a more practical choice, but you can't reach 2735fps at a safe pressure, more like 2650fps out of a 16". The current lot #5 that's available is too bulky to reach top velocity with the 110gr

I'd love to hear everyone's thoughts on the new Hornady 6mm ARC. From what I've read, it was designed to maximize the potential of the AR-15 platform. But I don't really see this as competition with the .300 HAM'R, but more of an optimized long range focused cousin. In essence both of these new calibers focused on squeezing more out of an AR-15. But whereas the 300 HAM'R has a larger and heavier bullet for increased penetration potential on tough game over shorter distances, the 6mm ARC, in contrast, optimizes longer range with a lighter bullet and different cartridge geometry.

I'm no ballistics expert, but I would love to hear from those who are about the trade offs. Of course, Bill, the HAM'R is your baby, but I see that Wilson Combat will also be producing 6 mm ARC components/rifles. So you would be the most versed as to how these two cartridges compare.

I love my two 300 HAM'Rs, but I'm wondering if I need to make space for a 6mm ARC in the collection.

I've spent most of a day for the past 4 days on the range doing 6mm ARC testing and load development. So far my observations are that this cartridge isn't anything special (basically a 6mm BR which has been around for a long time) and I was actually disappointed in how little velocity I was able to get out of the MAXIMUM charge weight loads Hornady provided me. The top velocity load with TAC pushed a 103gr ELD-X to 2521fps with so so accuracy, my most accurate load (consistent sub .8") with Benchmark only gives 2507fps. Considering I can get 2735fps from a 16" bbl (and stay under 57k psi) out of the Hornady 110gr SP in the HAM'R this didn't excite me much. However it made me want to do a head to head trajectory comparison, which ended up showing that out to any range where either cartridge still has much power their isn't much difference at all in how flat they shoot.

On the positive the test rifle ran 100% with all loads tested, has very mild recoil and is pretty quiet with a Quell suppressor. It just doesn't fit any need I personally have......kinda like the .224 Valkyrie a nice range toy.

Some personal testing with the 8-inch pistol using Wilson Combat Flat Wire Extra Power Spring and H1 buffer: holding it one-handed loosely the bolt will lock back on an empty mag all day long with 130 HHC. Same loose one hand hold with 150 gr HB-bolt will not lock on empty mag but rounds will feed. Same loose one hand hold with 150 gr SST-bolt will not lock on empty mag but rounds will feed.

Everything same as above with carbine buffer in lieu of H1: no difference in mag lock results above. With the pistol gas I prefer a heavier buffer to save my extractors. Next time I'm at the range I'll see if an H2 has any negative effects on full bolt travel.

I am chomping at the bit for the 135 HAM'R Bonded round and think this will be my single solution for this caliber (although my experience has been there is very little POI change between the 130 gr and 150 gr bullets within 100 yards, a testament to the accuracy of the caliber). I've tired of my schizophrenic gun collection and ammunition selection and am now paring down to just a few favorite calibers with one or two "go to" rounds. For 556, I use XM193 exclusively for range and stockpile ammo, and Black Hills 77 TMK's for "carry" ammo, although those AR's have been mostly collecting dust since HAM'R came along. Since I don't reload, I'm hoping some cheaper practice ammo will become available as the popularity of this caliber sky-rockets.

I really think the Army should abandoned their new plans for a proprietary 6.8 and just swap all their M-4's to HAM'R. This is a selfish wish since I would love a milspec HAM'R round with crimped and sealed primers and sealed case mouths (Bill is already using cannelures). I experienced first hand what a blown primer can do in the FBI HRT Bus Assault school when it lodged between the front of the lower receiver and hammer. AR dead in the water with no available remedial action to correct except transitioning to handgun.

Regarding the 11.3" barrel, the gas port seems a bit undersized. I'm running that gun with a carbine buffer and standard power flat wire spring. Same results above with one hand loose hold.

I should add performing the same test above with a loosely shouldered 8 and 11.3 inch, results in full bolt travel and empty mag lock with 125 TNT, 130 HHC, 150 HB and 150 SST's. Just depends on how OCD you want to be with full feeding reliability for worst case scenario vs. a slightly softer recoiling rifle. It seems counter-intuitive that the heavier bullets would have less bolt thrust but that is exactly what my testing proves out.

Your observations are all correct, the 125gr-135gr loads cycle the guns more positive than the 110gr or 150gr loads. Our 110gr loads are loaded with SOCOM due to the smaller powder charge required and the 150gr loads as commented have a smaller powder charge than the 125gr-135gr loads. We test for bolt stop operation with both the 110gr and 150gr loads for this reason. We've found that some BCGs aren't getting full gas flow and often a BCG change will make a non functioning gun function fine leading us to believe this is the largest variable in the system.