After doing a little research on some other forums, I think I've actually slightly changed the direction I'm thinking about going. I'm still set on the Grendel for caliber. But after reading some threads on the 6.5 forum, I think I'm looking at 12.5", 16, or 18" as my barrel choices.
As for the 12.5" option, this surprised me, but there seems to be a lot of guys saying that you're getting around 2400fps from the muzzle. That's pretty impressive for a 12.5" barrel. What I liked about this option was three-fold. One is that I already have a dedicated SBR lower in 300BLK that I've never even shot so I could add a 12.5" Grendel upper to my SBR lower and be all ready to go. Second is that I could afford to go with some higher quality components if I'm only building an upper as opposed to a complete gun. And three is that my state has a separate deer season for pistols, so I could throw on an SB Tactical brace (which I already have) and have an AR pistol that I could use as a legal means to hunt in a separate deer season that I wouldn't normally be able to hunt in. I really like this option because I seems to have the most versatility to me.
Then the second choice is between the 16" and 18" rifle. I feel like if I built the 18" rifle, I would want some higher magnification optics. I'm wondering if I can build an 18" rifle the way I want it and still keep the weight reasonable. I know I could do it on a 16" rifle build.
I had a 12.5” 6.5 Grendel for a while, and it was a very productive little rifle. I built it too light, so it balanced like a bowling ball in the field, but the concept is sound. I built a 10.5” 6.8 SPC for my suppressed short range deer hunting pursuits, which I’d say is largely analogous. I’d be a coin flip even today between that and a 12.5” Grendel - both will work. If you take the Han Solo approach to rounding in your favor, then 2400 from a 12.5 cut rifled barrel might be a thing. Mid to upper 2300’s were more common for me with book loads in a 12.5” Grendel. Splitting hairs, but fair warning to not excite yourself for mid to high 2400’s. Poly tipped bullets will open, typically, at slower speeds than cup and core pills like the Prohunter. Reiterating over the washout - a polygonal rifled barrel could help you keep a little extra speed in an SBR length barrel.
Quick reminder: Be sure your can is rated for a 12.5” Grendel. My Omega is NOT rated for 10.5” SPC, so technically, damages to the internals are my problem to manage if I had an issue and were mindless enough to state the conditions upon repair request. I don’t do a lot of mag dumps or high volume shooting with that upper, just hunting, so I don’t bother much about the letter of policy, but it’s something to keep in mind in your decision making.
If you do end up punting to a Title 1 length, then - again, reiterating over the washout - we’re talking about ~45-50fps difference between a 16” and 18” - and again, you’re largely talking about a bit less than a half pound of weight difference between a 16” carbine and an 18” middy. The more tangible difference will be the much more (stable) forward balance in the 18”. Lots of guys like 16” pencil barrel AR’s because they carry well, and “you carry it a lot more than you shoot it.” Personally, I only carry it so I CAN shoot it, so I build my stuff to be shot, and carry weight is always secondary. Considering your specific desires expressed, my first choice would be an 12.5” carbine, second choice 18” middy, third choice a 16” middy suppressed only.
Similarly, I buy my scopes with the intention of shooting, with aesthetic scale to the rifle secondary (or tertiary, or not even considered). For hunting, I REALLY like 4-16x44 scale and zoom. The Bushnell LRHSi 4.5-18x44 is a nice optic in the class, and I have a pair of Sig Tango4 4-16x’s I like a lot as well. For an SFP, I really like the Bushnell Elite 6500 2.5-16x and 4.5-30x, but they’re 50mm objectives and a little big. But I do like ~4-16x44 on any hunting rifle - even on a 10.5” SBR. If you really want something smaller, the Vortex Strike Eagle 1-8x is good for the money (especially pro-deal priced), and has JUST enough magnification for me to tolerate it for 300-400yrd occasional use - and considering a 250yrd limitation, it could work well for you. I’m not sure I can even remember the last time I shot a deer below 9x, regardless of range, and only used 9x because that was the top of my 3-9x (2011, 253 yards across wheat with a 45-70 sporting a 3-9x Bushnell Elite 3200, replaced since with a 4.5-14x40 Nikon). So for ME - I’d be looking at a something in a 4-16x44mm ballpark, but I’d get it if a guy dropped a 3-9x40mm or 1-8x32mm on top.
