txrider15 Wrote:Hi all,

I'm hoping maybe someone can give me some insight on a precision issue I've been dealing with since I got my first AR and 6.5G about a year ago. The problem: from one range trip to the next and sometimes on the same day I experience a wild inconsistency in my group sizes. They'll go from ~0.8in one day or group to ~1.25in to the next with no changes in the load etc. It's pretty much done this from day one at first I blamed the factory ammo Hornday Black 123 ELDs for the inconsistency. So I started hand loading and every time I thought I'd found a load where I was achieving ~0.75in groups, I'd load more go shoot to end up with 1.25in groups yet again. The best potential so far was 123 SMK with CFE I'd often get one tight clover leaf of 3 and 2 fliers that almost always landed in the same hole. Frustrated, I took the upper apart found the barrel was bedded (yes purchased assembled), removed it any ways and lapped the receiver face and reinstalled bedding with loctite 620. I took it back to the range. Factory ELD Black, 1.2in, 123 SMKs with 2520 ~1.3in, 123 SMKs with CFE one group 0.8 with 4 in <0.5in and then the 2nd group 1.3in only difference about 30 min later in the day. Exact same load within 0.04gr powder wise, within .001 CBTO, Hornady cases, chronograph says the average of each group was within 9fps of the other. Clean barrel with only ~15 rounds before the CFE groups. (Pic of CFE groups attached, 1.3in group was single fed, 0.8in group was mag fed at 3 and then 2 in the mag) (As an aside feeding from the mag use to really effect accuracy, this seems to be less prevalent since remounting the barrel. I also found the receiver bore was misaligned with the carrier bore and had to lap the carrier bore open to allow my face lapping tool to enter the receiver.)

Barrel is a 18in TBox, 1-7.5 twist

Additionally, I've replace the scope and mounts during all this with zero effect on the results. Running Vortex scope mount with Vortex Diamond Back Tactical.

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I'm not sure what to do with the gun at this point. I really just want it to shoot sub-moa but, consistently. Depending on the responses I get here if there's anything else to try before I give up on it, I'm thinking about selling and building from scratch or putting on a new barrel, like a proof research SS, Shilen, Douglas, or maybe trying Criterion or Wilson Combat? (Looking at 18in or 20in)

Sorry for the long post, trying to get the info out there up front. Thanks!

Cloverleaf Wrote:What do you shoot off of bag, bipod, or rest with rear bag? I have no experience with Tbox barrels. But if it is a good free floated barrel and we take shooter error out of this equation i would lean towards neck tension. When you say "within .001 cbto" did you have to adjust your die multiple times to get all of bullets to seat within that range? How many times have you fired the cases you're using?

Lemonaid Wrote:Get a better trigger, even if you don't get better groups you will be happy with the upgrade. The Larue MBT is an excellent value. https://www.larue.com/category/parts-accessories/lower-parts/triggers/
There is a lot of jiggle going on in an AR platform compared to a bolt gun, upper to lower, bolt and carrier moving back and forth, flex in the whole system. For me it takes nearly double the effort to shoot well with a Grendel than a bolt gun. The amount of stock to shoulder pressure, downward pressure from the pistol grip, cheek weld pressure, a round forearm and trying to keep them consistent is hard.

grayfox Wrote:After reading all of this, and if shooter is ruled out ('55 has great points), then your trigger and/or firing base would be where I'd look. Besides the fact that I would say get a Lilja or similar, you've already paid for it Lol. Great barrels are not finicky.

I use timney's or clones with nice 2-2.5# pulls, single stage, crisp, uniform. With me, the shooter is definitely the limiting factor.

For an AR unless you're a competition level shooter <1.25 MOA all day is probably where you'll be. The AR is not like a bolt gun.
Even at my limited skill level, I have (all bolt) a 6 Creed and 243 and 6.5 CM that are each subMoa all day. (I'm not, all day, however.) For my hunting, if I can get my rifle mechanical system reliably <1"/100 on the bench then I'm confident I can stay <1.5" in the field for that 1 or 2 shots I'll get.

txrider15 Wrote:LR1955: Thanks, I would normally tend to agree, especially if I wasn't having any luck with my 308 (bolt gun). However, here's my 308 load development groups (attached). I did shoot off a front and rear bag for these, though I've shot from the bipod/rear bag and had equal results. All were from the same day as the initial group. I will say the trigger on the AR is very inconsistent, I've checked 4.5 to 6lbs it's an RA140 which is supposed to be 3.5 but it's not close nor consistent. The 308 has a TriggerTech now. I've also included a group from before I messed with the rifle two very distinct POIs in my opinion. This and being effected by rounds in the mag are more of what lead be to believe 1. inconsistent bolt lock up due to whatever, 2. barrel 3. Other?

I'd be amiss if I said I never have a flier or didn't shoot "poorly" on somedays. I'd like to think that I have enough data points indicating there's something outside of shooter error contributing to what I'm seeing... maybe not though, maybe I'm not very good a driving an AR, yet. If it is a shooter issue, any recommendations?

FYI: 308 is a Rem SPS Varmint, I dropped into a Stocky's Stock with aluminum bedding black, and a TriggerTech special set to ~2.8lbs

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LR1955 Wrote:TXR:

So far you have not mentioned your calls so I suspect most of the problem is you.

You trust your .308 so are shooting it fine. You do not trust your Grendel so aren't shooting it fine.

Do buy a top end barrel and get your trigger to break at a consistent level, even if it is heavier than you would like. Even though I suspect most of the problem is you, you will never go wrong with a good barrel or trigger.

BTW -- aside from shooting groups at 100 yards, do you do anything with the Grendel like compete or hunt with it?

LR55

txrider15 Wrote:I'd say I'm 50/50 on my calls as far as if I was at fault. I know that I have lots room to improve, I agree it still could be me and to your points I'm a large part of the entire equation, regardless I know I have lots of room to improve. I do plan to hunt with it the next time I go but I don't know when that might be, whitetail/hogs, most of it would be short range <200. I've taken the Grendel out to ring steel at distance but so far that's all I've done besides groups at 100. I'm very interested and planning on doing much more longer range steel ringing. I am thinking about giving a competition a try weather with it or the 308.

Trigger is on the way.
Any recommendations on the barrel?

I appreciate yours and everyone's input/feedback so far, thanks!

txrider15 Wrote:I'd say I'm 50/50 on my calls as far as if I was at fault. I know that I have lots room to improve, I agree it still could be me and to your points I'm a large part of the entire equation, regardless I know I have lots of room to improve. I do plan to hunt with it the next time I go but I don't know when that might be, whitetail/hogs, most of it would be short range <200. I've taken the Grendel out to ring steel at distance but so far that's all I've done besides groups at 100. I'm very interested and planning on doing much more longer range steel ringing. I am thinking about giving a competition a try weather with it or the 308.

Trigger is on the way.
Any recommendations on the barrel?

I appreciate yours and everyone's input/feedback so far, thanks!