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Bench techniques for AR's - Dr. Lee - 12-29-2021
I have a PF built 16" Krieger barreled upper that I am having trouble getting consistent groups with. I managed to get one 3/4" group, but the others are all about an 1.5"-2". This is with PF assembled ammo with 123gr Lapua Scenars and Lapua brass. Thinking about the variables, such as scope and mount, which I may switch out, I had to look at my bench setup. I made a 3" wide front bag runner to fit in a standard 3" wide benchrest bag and made a 1" diameter Delrin bag runner for the rear bag. It all feels solid and slides very smooth on the bags. It does however like to bounce some on the front. My rest is a Caldwell Fire Control rest with the joystick. After every shot the reticle does not come back to the center of the target. I have to readjust the rest after each shot. I really don't know I managed to shoot a group with 4 shots touching and one outside making the 3/4" group. How are you guys shooting your AR off a bench to test ammo and get consistent groups ?
Thanks,
Dr.[ATTACH=CONFIG]18531[/ATTACH]
Bench techniques for AR's - lazyengineer - 12-29-2021
I would say this is not as easy as people act, and the 6.5 Grendel is not as forgiving as .223. I also personally feel like Grendel barrels can be highly variable on how well they will decide to group, much moreso than .223 - is just my opinion. Don't just assume that Krieger BBL is necessarily a sub MOA barrel, just because it's that brand. I went through 3 barrels on my 20", before I found one that would shoot at the MOA level.
One of the first things to check, is your cartridge OAL. I have learned the hard way that "fits in the magazine length", does not automatically mean "not jammed deep into the rifling lands" with Grendel. And many barrels are very short throated. In my experience, that will never shoot well, if that's the case.
regarding accuracy and staying on target, I don't run one of those sleds, so am not a good hand at telling you how to get best results with it. I tend to run either a bipod or sandbags.
And finally while Lapua does have excellent reputation, I haven't found Scenars to automatically be 1/2 MOA bullets. Not saying they can't be, but I've gotten some surprisingly large groups with them too.
My advise for trying to get best performance you can, out of you the shooter at least, is to test your rig with dry fire. When you "shoot", are the cross hairs still on target? are they close to target? Are they easily 3 MOA off target now?
Bench techniques for AR's - Dr. Lee - 12-29-2021
I can say that I have not dry fired this rifle in this rest, but I'm confident in my trigger squeezing abilities. The puzzle is that one 3/4" group. Sure it could be luck, but that's hard to say.
I also fired ammo with Nosler 120gr. BT's. Same results. Thanks for the reply.
Dr.
Bench techniques for AR's - grayfox - 12-29-2021
Like LE says, not always an easy thing.
Some really experienced shooters will of course do better than a more average guy like me.
But couple of things to ponder:
1. I would use a plain front rest with bag (like the caldwell rock jr, or similar I mean), without that white-slidey-whatever-it-is thing you show there. And a plain rear bag, frankly I like a more solid rear stock like the luthar mba-3 (carbine style). I don't favor those triangle-design butt stocks. There are rear bags with a slope to them so that you can always get a good rest-purchase without hanging up on it during the shot.
2. ARs, IMO, need a decent amount of downward force applied to the front handguard, think like allowing your off-trigger hand (mine is left as I am right handed) to be an 8-10 lb "weight" pulling down, you don't need force just the free-weight of the arm. Let the rifle slide straight back during the shot; it does have to move, we are not 1000 lb cannon mounts (even though I should lose some weight lol!).
3. Setup: the rifle needs to be freely set up to align right on target, you can't be using muscle to pull it right or left onto the zero. If it is not there, re-adjust so it is. And since I have some back issues (mostly age) I adjust my seat so I am able to line up the rifle without bowing my back much, it's easier on my back if it can stay straight pretty much. For prone shooting, need to ask somebody else b/c I don't do prone any more. Find a setup and rifle position that you can repeat easily, consistency is the goal.
4. So I pull the AR back into the shoulder with my right (trigger) hand on the hand grip, allowing the trigger finger to be free to shoot, and down with the left hand on the HG. The upward recoil kick will be about 6-7 lbs worth (or so) which the downward arm-weight on the HG should balance it out, allowing the rifle to slide straight back. Rifle and shooter should be a one-piece blend/machine that moves as a single unit.
I will freely confess that there are much more expert shooters on here, and they will chime in I'm sure, but these are some things I have put into my setup and they do seem to help me.
Bench techniques for AR's - grayfox - 12-29-2021
Reason you want just a bag-surface in front, is that a hard surface tends to magnify the upward recoil force of the muzzle, A bag tends to absorb some of that impulse.
Bench techniques for AR's - SCJim - 12-29-2021
Dr. Lee Wrote:How are you guys shooting your AR off a bench to test ammo and get consistent groups ?
As far as I am concerned the AR is not suitable to shoot well off a benchrest regardless of what front bag you use. The handguard is much too narrow. I much prefer a good bipod, preferably a F class bipod with "ski" feet such as a Sinclair. I felt like mine had a bit of wobble induced by the cant mechanism so I epoxied it to where the cant is non adjustable which is fine since I either use it on a concrete shooting pad prone or sitting at a concrete bench,. I use a thin doormat under the skids to all it to slide.
https://www.brownells.com/shooting-accessories/bipods-monopods-amp-accessories/bipods/f-class-bipod-sling-swivel-mount-non-elevation-knob-prod87342.aspx
On the rear I prefer a squeeze bag
Bench techniques for AR's - LRRPF52 - 12-29-2021
How did you attach your barrel to the upper and did you ensure the upper receiver face is square?
Are you free-recoiling the rifle?
When I shoot lightweight AR-15s chambered in 6.5 Grendel, or AR-10s, I apply a lot of rear pressure into my chest with a very solid cheek-to-stock weld.
When I get on a bolt gun, it feels like cheating because I dont have to work anywhere near as hard to get tight groups.
Once I get down to 100gr or 90gr in the Grendel, then I dont have to apply as much rearward force and can shoot more like a .223 Rem.
Start with a square upper receiver face and a bedded barrel into the upper, or a really tight-fit barrel extension-to-upper fit.
Use less torque on a lightweight AR-15 barrel when tightening the nut closer to that 35-45ft-lbs range, and more torque on a heavier barrel going between 60-80ft-lbs.
Make sure the torque is equal/balanced on your optic mount cross bolts and ring fasteners.
Ive seen the best results with lightweight carbines when I shoot them bipod-folded on a softer bag with a rear soft bag that I can squeeze to get ideal POA, followed by bipod extended on a solid surface with rear bag.
Im talking about shooting multiple 16 and 18 lighter Grendels over the years, measured against multiple 20, 22, 24, and 28 Grendels from varying positions.
Sometimes, Ive just hit barrel/torque/rifle set-up combos that just hummed out of the gate.
Other times, they would shoot 1.5 MOA 5rd groups and send me head-scratching, but those were either lower price barrels or not-bedded barrels.
After bedding, the 1.5 guns would drop to no greater than .85 guns, no other variables.
PFs Krieger, Bartlein, Lilja, and Criterion pipes have been some of the most accurate barrels Ive ever shot, even compared to all the bolt guns Ive shot over the years.
I used to do final QC for a local rifle manufacturer taking a truck full of rifles to the range to accuracy-test each one, all of them being high-end bolt guns.
Ive seen a lot of different barrels and how they perform. Those rifles were either Krieger or LW from the 2009-2010 timeframe.
Krieger performance was night-and-day difference to the LW pipes. They almost always would shoot 3/4 to 1/2 MOA out of the gate. LWs, not so much.
Ive also independently tested complete uppers that PF sent out that customers said wouldnt shoot. I offered to buy one of them after printing 8+ round bug hole groups using PF 123gr SMK loads in Lapua brass. I couldnt believe how accurate they were. I had to look back at the ammo box to see how many rounds I fired. It was so unbelievable I wont even say how many, other than 8+.
I fully documented the test groups with witnesses and sent the photos and test targets back.
Another thing Ive noticed is that depending on the range gradient from shooting position to the targets, you will see tighter groups either in the top, middle, or bottom set of bulls on paper.
Some nuances to fundamentals with light guns:
This is determined by how your position is oriented to the target, and how naturally you settle into the position relative to how high each row of bulls are.
If youre too cramped or neck cranked while shooting the upper or bottom row, the groups will be larger.
Once you have the more ideal position, the groups will tighten-up. For me, thats often the 1st top row of bulls.
Once I depress the muzzle, I need more rear bag support, so if I dont build up that bag support to present the same tension, the groups will open.
This is most-true with the lighter weight guns, not as much of a problem with the heavier guns. Heavy rifles like to just settle into position well and are somewhat immune to these little quirks.
I like lightweight guns, so I try to get them to shoot as close to the heavier barrel rifles as possible.
Bench techniques for AR's - Dr. Lee - 12-29-2021
This is an upper completely built by PF. I have to think it's as good as it could be, build wise. When it comes to shooting the rifle (Geissele SSA-E trigger BTW), I do have the butt lightly against my shoulder, so it's pretty much free recoiling. The barrel is a medium weight Krieger. I am not using any pressure to speak of; with the rest and front bag runner I have it is basically free recoiling. I believe my bench setup as far as the rest and bags are concerned, needs to change. It is nowhere near the kind of support you guys are talking about. I believe the rest/bags are too hard, not at all soft enough to nestle the gun in.
Bench techniques for AR's - LR1955 - 12-29-2021
Dr. Lee Wrote:This is an upper completely built by PF. I have to think it's as good as it could be, build wise. When it comes to shooting the rifle (Geissele SSA-E trigger BTW), I do have the butt lightly against my shoulder, so it's pretty much free recoiling. The barrel is a medium weight Krieger. I am not using any pressure to speak of; with the rest and front bag runner I have it is basically free recoiling. I believe my bench setup as far as the rest and bags are concerned, needs to change. It is nowhere near the kind of support you guys are talking about. I believe the rest/bags are too hard, not at all soft enough to nestle the gun in.
DL:
Ditch the sliding stuff under the blaster. Solid position, solid hold, rapid fire string of five. No looking at holes until you shot your string. Ought to take you at most ten seconds for five. Focus your attention on sight picture and you will shoot the shot when you see a good one.
LR-55
Bench techniques for AR's - Dr. Lee - 12-30-2021
LR1955 Wrote:DL:
Ditch the sliding stuff under the blaster. Solid position, solid hold, rapid fire string of five. No looking at holes until you shot your string. Ought to take you at most ten seconds for five. Focus your attention on sight picture and you will shoot the shot when you see a good one.
LR-55
This is what I will do. It all makes sense now. Thanks to everyone for your replies. They all are helpful and I will make the changes offered and get back to you.
Happy New Year to all.
Dr.
Bench techniques for AR's - Mesa1978 - 12-30-2021
My Lilja barreled PF built upper in Grendel is usually a 3/4" shooter with handloads, occasionally 1/2" with 5 shot groups. This is from a Caldwell front rest and a Protector rear bag. Free recoil works well on my bolt guns, with an AR I have to really hold it firmly through the shot and bolt cycle to get decent groups. With factory ammo it was usually a 1" shooter, AA Lapua was the best factory ammo across 4 Grendels. My experience has been that bolt guns offer the most accuracy across 4 calibers when compared to AR guns.
Bench techniques for AR's - BowChamp - 12-30-2021
The advice given is spot on for what I have experienced. I have ar grendels that shoot 1/2" to 5/8" groups. If I try to free recoil them they got to 1 1/2 rifles real fast.
Like the OP...I would get the occasional good group and just scratch my head wondering what was going on. Finally started figuring it out by trial and error.
Bench techniques for AR's - Bill2336 - 12-30-2021
I regularly get sub MOA five shot groups out of my hand loads using Hornady 120, 123, and 130 ELDM bullets along with Speer 90 Gr TNT HPs. The rifle is a Seekins upper and lower paired with a no name 20 barrel from classic firearms, a Larue MBT-2S, and a Magpul PRS Gen 3. I use a Magpul bipod and a Cole-Tac rear bag. I havent gotten anything below .6 MOA so far but Ive definitely had more success loading for my 6.5 Grendel than I have my 5.56 precision AR.
Bench techniques for AR's - Dt219 - 12-30-2021
Id gladly send you a upper and all the powder, primers, pills you can stand to make it shoot LR