DMR/Precision AR Reloading

[hhudson]

Hello everyone, new here. I am loading for a Seekins DMR in 6 ARC. I don't have any problems holding around 1 MOA 10 shot groups but I was wondering if there are any resources specifically for precision semi auto reloading. There's a million pages on precision reloading but it's pretty much all for bolt guns.

Mainly wondering if or when there are diminishing returns of accuracy for effort in gas guns, and what has proved to be worth it or not. How far down the rabbit hole is worth going?

 

[mtncwru]

I had similar questions when I started shooting Service Rifle. The answer might be different for you than for me, but something to highlight is your technique on the bench. The AR platform wasn't designed as a bench gun, so you'll want to pay a lot of attention to how you set it on the rest every time. Tilting your gun will ruin groups real fast through no fault of the ammo, for example.

Beyond that, the answer to "When do I hit diminishing returns?" will be "It depends!" Sharing more detail about what you're currently doing might help you get a more meaningful answer. Some questions that leap to my mind include:

1. What distance are those 1 MOA groups at?
2. What are you current reloading practices (e.g., what's your sizing process, are you annealing, are you throwing or weighing each charge)?
3. What does your test setup look like (bipod vs rest vs front bag, any rear support, off a bench or the ground, do you have a bubble level)?
4. What scope do you have on there now (e.g. testing with my 1-4.5x scope is a very different experience than with my T-24)?
5. What patterns are you seeing with your current groups? Are they mostly round? Are they all vertical/horizontal? Something else?

 

[hhudson]

I had similar questions when I started shooting Service Rifle. The answer might be different for you than for me, but something to highlight is your technique on the bench. The AR platform wasn't designed as a bench gun, so you'll want to pay a lot of attention to how you set it on the rest every time. Tilting your gun will ruin groups real fast through no fault of the ammo, for example.

Beyond that, the answer to "When do I hit diminishing returns?" will be "It depends!" Sharing more detail about what you're currently doing might help you get a more meaningful answer. Some questions that leap to my mind include:

1. What distance are those 1 MOA groups at?
2. What are you current reloading practices (e.g., what's your sizing process, are you annealing, are you throwing or weighing each charge)?
3. What does your test setup look like (bipod vs rest vs front bag, any rear support, off a bench or the ground, do you have a bubble level)?
4. What scope do you have on there now (e.g. testing with my 1-4.5x scope is a very different experience than with my T-24)?
5. What patterns are you seeing with your current groups? Are they mostly round? Are they all vertical/horizontal? Something else?

My most accurate load so far and the one I want to use for hunting and plinking is

Sierra Game King HPBT 85gr
26.6gr 8208 XBR
Fed 205MAR primers
Hornady brass, kept in lots
2.050” COAL

My process is to tumble in walnut for 3-4 hours, universal decap, lube with imperial wax, resize in a RCBS Small Base die, chamfer and deburr, clean the primer pocket and brush the necks, prime with a Frankford hand primer tool, scoop a bulk charge and trickle up to 26.6gr, then seat with a Lee micrometer adjust seating die. No crimp.

The last box I loaded the CBTO was extremely consistent within half a thou (even though the calipers aren’t that accurate).

Rifle is a 22” Seekins DMR in 6 ARC with a Vortex Strike Eagle 5-25x56mm on a Seekins one piece cantilever mount. The upper and hand guard are supposed to minimize any bipod pressure shifting groups but who knows to what extent. No muzzle device yet. A suppressor is on my list. AccuTac bipod and an Armageddon Gear squishy rear bag off of a nice solid (but wood) bench. No bubble level.

Haven’t gotten to the point of needing to trim brass yet.

I just started from scratch in October and bought everything at once including the rifle and optic so the wallet is a little tired. I’m just using a Lee Breech Lock Challenger single stage press and don’t have an annealer or chrono yet. Probably makes the most sense to add a chrono first to see velocities and ES/SD but I was waiting on a sale hopefully.

Groups look decent and pretty round, I’m still getting back into shooting and still testing bullet and powder combos so this isn’t 6 of the best groups I can shoot.

Groups were shot quickly late afternoon just before the range closed in about 20 minutes. A few seconds between shots and maybe a couple minutes between groups.

x9 85gr SGK, 28.0gr Accurate 2520
x9 105gr Hrdy, 27.5gr Accurate 2520
x11 85gr SGK, 26.6gr IMR 8208 XBR
x10 85gr SGK, 26.6gr IMR 8208 XBR
x15 90gr Nosler BT, 26.9gr IMR 8208 XBR (bullets were pulled)
x9 90gr Nosler BT, 26.9gr IMR 8208 XBR (bullets were pulled)

I haven’t gotten the 105gr Hornady Match HPBT (group 2) to shoot with anything in this gun after trying 3 powders and different charges. Not sure if it’s the 1:8 twist or if I need to try different seating depths. I’m just loading everything at book recommended length. 2.20” for the 105s. I don’t particularly care if they don’t shoot as I love the SGKs for hunting and they’re cheap enough to shoot paper with but I have another box of the Hornady 105s to play with and it might be a good learning experience to try to improve the group size, or maybe the rifle just doesn’t like them.

Some things I’m considering that might improve accuracy are
Berger Target 90gr (maybe heavier)
SMK 95gr (maybe heavier)
Mandrel expanding dies
Annealer
Chrono
Muzzle device

Not sure where my money is best spent.

I’ve got 50 of the SGK 85gr and 8208 XBR loaded and I can do 5 or 10 shot groups one day this week with time to cool between groups. Unfortunately they were loaded with a different lot of bullets but that’s life I suppose.

 

[GLShooter]

Look up the books buy ZEDIEKER he has one on precision loading for the AR and several others that are very well done.

 

[neckturner]

wondering if or when there are diminishing returns of accuracy for effort in gas guns,

I ran a JP Enterprises AR-15 that would to .4's all day. It depends on, mostly, the barrel. Loading mag length, so Hornady 75gr HPBT - p/n 2279. The modern version of that is the 22791

 

[jelenko]

depends on, mostly, the barrel.

This.
It may also help to 'bed' the barrel extension to the upper receiver with shims or loctite. Or, use a upper receiver that requires a thermal fit.

 

[neckturner]

It may also help to 'bed' the barrel extension to the upper receiver with shims or loctite. Or, use a upper receiver that requires a thermal fit.

JP does both those things (barrel changes are challenging). Also, they provide a bolt that is hand-lapped to the barrel extension. At least that's how my rifle was done.

 

[jelenko]

bolt that is hand-lapped

Does that mean they lap the face of the receiver so it's square to the bore? If so, I do that also. There seems to be some controversy over whether it helps.

 

[Mark611]

I don't have a 6 ARC, but I do have a 6.5 Grendel, I can tell you this, I had a hard time finding the right combo of powder and bullets that my barrels liked, I tried about 9 or 10 different powders and 4 or 5 different bullets, A2520 was one of them, didn't work, first I'll start off how I prep my brass, if new I trim if needed chamfer and debur and uniform the flash holes and anneal the brass then run it through a expander mandrel, I seat my primers -4k under the case head, all this is done after I run my brass through a Sheriden slotted Case gage to make sure all the cases are in spec, once I fire my brass I de-prime them, wet tumble with Dawn and SS pins, dry them, I use a case pad and lube, I resize my cases with a Redding body die hand wipe off the lube, neck size with a LCD, trim, Chamfer and de-burr, Anneal, seat my primers, the best powder I have found for the 6.5GRR is AR Comp, none of the other powders I have tried gives me the velocity or accuracy I was looking for, from my 24'' 1&8 twist barrel I get 3/4'' groups @200m with 27.2gns of AR Comp with a 120gn SMK, @2600fps, all loaded to mag length 2.260, my second bullet is the 123gn Match Monsters, like I said I have tried H4895, H322, A2495, A2460, A2520, SWMR, TAC, and a few others, none of them would shoot over 2450fps without pressure signs, in the brass, I don't have this with AR Comp, to note, other that turning the necks, I prep my brass just I would for my precision bolt guns, YMMV.

 

[Hoser]

My 6 Grendel will routinely shoot 1/2 - 3/4 MOA groups out to 600 yards with Lapua brass and Berger 105 Hybrids. The hard part was getting the shoulders bumped back enough, getting the gas adjusted and finding H4895.

 

[Mark611]

Very good Hoser!

 

[neckturner]

Does that mean they lap the face of the receiver so it's square to the bore?

Yes, that's how they describe it.

 

[lb-ft]

HHudson,
Might add crimp step. Lee FCD is my favorite. I crimp for any autoloader rifle. Bolt action is really fast on your rifle and inertia can cause your cartridge OAL to change if bullet isn’t firmly crimped in place. Bolt flies back, picks up new cartridge, slams it home, cartridge body abruptly stops in chamber but bullet can move out a few thou or maybe more. I say buy the lee FCD, watch a few videos and start crimping.

If $ are really tight right now you can test sufficency of your neck tension in battery by loading a mag, pull the charging handle back, let the bolt fly and chamber the round, rinse & repeat for the mag and then measure to see if any have grown in length.

 

[GetReal]

I get 0.35 moa from my 6 ARC using the same reloading techniques as I used for my bolt guns.