ar-10 accuracy, what is to be expected from a factory upper?

[MarkCO]

what should one watch for as far as gas-block adjustment ?

stagpanther probably answered as best as can be done without one actually being their looking at the rifle, knowing the load, etc.

Almost all Large frame ARs are significantly overgassed. The shorter the gas system in relation to barrel length, the worse it is.

Checking brass rims and even case bodies for extraction issues is first. How far the cases get thrown is next, but that is as much the ejector as the bolt carrier velocity.

 

[jetinteriorguy]

Jet, is it a custom or factory build? What is you barrel length and weight? Asking for a friend who might want to have a 10 in 6.5 CM.

It’s a stainless heavy profile barrel with an adjustable gas block from PSA. I bought it as a full built rifle other than adding a Geissele two stage trigger and a muzzles brake, been a few years and I can’t remember what brand muzzle brake it is.

 

[georgehwbush]

update.

i ran a ladder test today, got 0.930" 5 shot group with only three holes in the paper, out of 43grs. of reloader-19 : but was starting to see preasure signs. so i'll back that down just a little. not bad speed either, avg. 2928 with sd 24. yes the sd is a little high but i'm not done either.


anyway, just wanted to update the post, and say thanks again.

 

[Shadow9mm]

i ran a ladder test today, got 0.930" 5 shot group with only three holes in the paper, out of 43grs. of reloader-19 : but was starting to see preasure signs. so i'll back that down just a little. not bad speed either, avg. 2928 with sd 24. yes the sd is a little high but i'm not done either.


anyway, just wanted to update the post, and say thanks again.

Don't forget to keep things in perspective. In all honesty a SD of 24 is pretty good and will beat most factory ammo and some match ammo. Last testing I did was with 6mm arc and Hornady match ammo, SD of 22, ES of 83. While you may want, and even be able to get, better SD numbers, 24 is nothing to scoff at.

 

[stagpanther]

You should both try single-feed hand loading into the chamber --you'll see those numbers drop and better accuracy more than likely. But no autofeed.

 

[MarkCO]

Almost every semi-auto throws the first, or the last round, sometimes both, a little out of the group.

Shooting 10mm dots on 3x5 cards at 100 yards, most guys at that match would toss the first round on steel (allowed) and unchamber the last round to resuse as a first. The guys who did that almost always had clean cards. The guys who did not never won.

 

[tangolima]

Almost every semi-auto throws the first, or the last round, sometimes both, a little out of the group.

Shooting 10mm dots on 3x5 cards at 100 yards, most guys at that match would toss the first round on steel (allowed) and unchamber the last round to resuse as a first. The guys who did that almost always had clean cards. The guys who did not never won.

Are the 1st and last shifts consistent (predictable)? Are there theories explaining the shifts? Thanks.

-TL

Sent from my SM-N960U using Tapatalk

 

[georgehwbush]

stagpanther; i was hand feeding that ammo...

 

[georgehwbush]

Don't forget to keep things in perspective. In all honesty a SD of 24 is pretty good and will beat most factory ammo and some match ammo....

if i couldn't beat most factory ammo, i'd quit reloading... and i'm no expert. but i can normally get sd's down to around 15, sometimes with powders like 414 even as low as 10 or lower on a few occasions. "very few" but yes youi are right, if i were only going to shoot out to 600 that would be great. but past 1k it's not acceptable. but i will work on it and see if i can make it acceptable

 

[MarkCO]

Are the 1st and last shifts consistent (predictable)? Are there theories explaining the shifts? Thanks.

-TL

Sent from my SM-N960U using Tapatalk

Usually yes. The first is not as common, but it is due to the rifle chambering a little different from bolt release than from firing. The last is because the bolt locks open eliminating the full set of recoil impulses. The shorter the barrel or the higher the MV, they less the affect on the last.

They can be worked on, to some degree by tuning of the gas system and or load. On my match .223, there is no measurable difference between 1st, middle and last round. The slower the bullet, the more the bullet weighs, the more pronounced. My .450Corvette, with 300+ grain slugs was very precise, but the first round was a good 5/8" out of the group while the last was almost one inch out of the group when shooting at 200 yards and printing the main group right at 1 inch. I could draw a 2" line with 3 rounds. But 5, 7, 10 rounds, it was boringly consistent. 1st high, last low.

 

[tangolima]

If they are consistent, one can adjust the hold to compensate. One of my rifles has cold bore shift, and having different holds for 1st 6 rounds is what I have been trying to do. Sometimes it works better than the others, meaning the consistency is so so.

I can understand the mechanism for the 1st round, when chambering happens while no recoil is in effect. But for the last round, I have hard time to wrap my head around. By the time the action unlocks, let alone bolt locking back, the bullet is long gone. It may sound and recoil differently, it shouldn't alter the bullet's trajectory.

-TL

Sent from my SM-N960U using Tapatalk

 

[101combatvet]

just bought my first at-10 and was wondering if i could expect anywhere close to the same accuracy from this gas gun as i get from a factory bolt gun of like caliber.

i have been shooting a savage 243win for several years now. just sold it and bought a new ar-10 in 243win, havent had time to work up a load yet. but was hoping that it would be somewhere close to the same. is that just wishful thinking ?

I've never reloaded for that caliber; however, if you use a suitable powder and bullet combination for accuracy, you should be able to get at least one MOA at 100 meters. What it does beyond that range will depend on other factors.

 

[USAF Ret]

It’s a stainless heavy profile barrel with an adjustable gas block from PSA. I bought it as a full built rifle other than adding a Geissele two stage trigger and a muzzles brake, been a few years and I can’t remember what brand muzzle brake it is.

PSA stock. I have seen some good results and owned a PSA 308. It was a good shooter but heavy as all getout. I sold and got a Ruger SFAR. Love the weight, but still have not nailed down a load that will get me sub MOA. Closest I have gotten is 150 grain Speer Gold Dot over 44.5 grains of Varget with an average velocity of 2653.

I am just really liking my 6.5 CM rifles. Not sure about adding a 6.5 CM to the stable yet, but PSA has been running some crazy deals. Have not seen a 6.5 upper on that list yet.

 

[MarkCO]

But for the last round, I have hard time to wrap my head around. By the time the action unlocks, let alone bolt locking back, the bullet is long gone. It may sound and recoil differently, it shouldn't alter the bullet's trajectory.

One of the things I do with new LR shooters is, after dialed in and they can shoot a good 100 yard group, is put them on the 330 yard plate (bolt gun). We adjust hold and let them prove to themselves that one hold sends the bullet over the plate and one sends it under the plate. Alter the spine angle to the bore, and you can push left and right of the plate. It's truly amazing once you figure it out. The plume of ejected gases affects the bullet flight for more than just the length of the barrel.

The difference in the cycling of a gas gun absolutely affects the POI. One of the many reasons folks still think they are not as accurate as bolt guns. They are, if you know.

 

[tangolima]

Deleted


Sent from my SM-N960U using Tapatalk

 

[jetinteriorguy]

PSA stock. I have seen some good results and owned a PSA 308. It was a good shooter but heavy as all getout. I sold and got a Ruger SFAR. Love the weight, but still have not nailed down a load that will get me sub MOA. Closest I have gotten is 150 grain Speer Gold Dot over 44.5 grains of Varget with an average velocity of 2653.

I am just really liking my 6.5 CM rifles. Not sure about adding a 6.5 CM to the stable yet, but PSA has been running some crazy deals. Have not seen a 6.5 upper on that list yet.

Funny thing on the weight, my heavy barrel 18” from Aero Precision is almost as heavy as my AR10, and it has a lighter scope on it. The scope on my AR10 is a fixed 16X SWFA and it’s a bit of a tank but works real well and I’ll never carry it for hunting anyway. In the hand the AR10 actually feels better balanced than my AR15, just a perception thing on my part. One thing in both cases, these SS barrels seem to shoot better after around 500 rounds, just breaking in good I guess or maybe just me getting used to them. The PSA AR10 was putting some pretty good scratches on the brass at first and upon inspection I could see machining marks in the chamber. PSA sent me a return label and a couple weeks later I got it back. They hadn’t replaced the barrel but polished out most of the machining marks instead. I was a bit disappointed at first, but after shooting it was more than satisfied. The brass was no longer getting scratches and being the same barrel was still the same consistent accuracy so no big deal.

 

[zeke]

While my experience is a tad dated, have gotten excellent accuracy from all the free floated Rock River rifles and uppers owned. Have 2 of their older 308's and both are .5 moa capable. Heavy as rocks, Fal mags and slightly overgassed, but extremely accurate.

 

[georgehwbush]

"The last is because the bolt locks open eliminating the full set of recoil impulses" <<< MarkCO

strange. i was under the impression that the projectile was out of the pipe before the bolt reached the backstop. isn't that why in slow motion film we see the muzzel flash before the shell ejects? and you are probably right about first round shooting high because of the way it's chambered, i have a 223 that does that very thing.

 

[MarkCO]

"The last is because the bolt locks open eliminating the full set of recoil impulses" <<< MarkCO

strange. i was under the impression that the projectile was out of the pipe before the bolt reached the backstop. isn't that why in slow motion film we see the muzzel flash before the shell ejects? and you are probably right about first round shooting high because of the way it's chambered, i have a 223 that does that very thing.

The bullet does leave the barrel before the bolt locks back. But there is still vectoring of the gas plume.

 

[tangolima]

The bullet does leave the barrel before the bolt locks back. But there is still vectoring of the gas plume.

Gas plume is the exiting gas at the muzzle? How is it different for the last round? The gun doesn't know it is the last round till the bolt returns and stopped. The bullet must be tens of yards away from the muzzle if not more.

-TL

Sent from my SM-N960U using Tapatalk