AR10 Acceptable Accuracy (10 Shot Groups)

[rlsmith1]

So I was shooting an AR10 in 308 yesterday (prone, bipod and rear bag) and I'm just trying to figure out what load it likes (eventually try to replicate that load with handloads).

I shot some cheap stuff and got cheap accuracy (2-3 MOA) so I pulled out some 175gr FGMM. My group was about 2 MOA but the first shot was the one that opened the group up. The last 4 were all more like 0.75 MOA. Happy with that but I have no idea why that first shot was significantly higher than the rest (barrel was already warm). So I load up 5 more, hold same POA and proceed to put 4/5 into a 1 MOA group (including 4 from the first group).

At the end of the day, I ended up with a 2.5 MOA 10-shot group. But if I exclude the 1 flyer, I had an 9-shot group closer to 1-1.4 MOA with 5 of them stacked into 0.45 MOA. Very happy with that.

My question is, those of you who use 10 shot groups, do you also use a hit %? I never paid much attention to hit % until this experience. Basically, 100% of the time I will hit a 2.5 MOA target, but 80% of the time I would hit a 1 MOA target and 50% of the time I would hit a 0.5 MOA target. What's the best way to determine what the capability of your system is?

I guess just as an observation, a "lucky" 5-shot group would have lead me to believe I had a 0.5 MOA gun and stopped shooting. I'm sure I could grab the other 10 rounds of the FGMM and they would probably all end up in a 1.75 MOA group.

 

[Ape_Factory]

It could be as simple as the factory load ammo, that first cartridge, being a different "spec" than the rest. I've experienced this with several factory loads including Federal Premium Gold Medal Sierra Match King 168 grain. Could also be a change in the shooting conditions depending on where you live.

I am not an experienced reloader (yet) but according to my mentor, you can basically get anything to shoot fairly tight groups consistently with precise hand loading once you figure out what works best with what (bullet, brass, powder, etc...). What your rifle likes with factory loads may or may not translate to the hand loads. But I did the same, shot a bunch of different loads just to see (AR10, bipod).

It can just vary widely with factory ammo. I was zinging cheap PMC Bronze FMJBT at 100 yards for a bit and then had one mag which was all over the place. Factory loads. Always leaves me second guessing either my rifle or my abilities!

 

[Odysseus1911]

Your spread is vertical as well as horizontal so it isn't environmental. That leaves :
-Variance in factory ammo
-Your equipment
-Your technique

Can you consistently shoot sub moa groups with other rifles? If so, have you consistently shot sub moa groups with a gas gun?

Tell us about the gun, scope, scope mount, and bipod.

 

[Romeo458]

Were you using the same magazine for all of the strings?

 

[8up]

It shoots well, the human factor is causing the group spread and limitations. Practice with the large frame, and at distance, you will be more consistent and be able to extend those ranges out more.

 

[rlsmith1]

Thanks guys, lots of great info / suggestions here. I've been shooting forever and I can shoot sub MOA with my RPR in 6 Creed (much better trigger). I'd say it probably isn't me but I do know my form isn't perfect. I think I'm consistent if nothing else at least (archery background as well). My 20" RRA shoots sub MOA consistently with multiple ammo types.

16" BA barrel on an Aero receiver set that I traded a guy for who wanted a bolt gun. He said it liked the heavier bullets but made no comments on accuracy. I've got a MK5 3.6-18 in an ADM mount with the same PMag for each group. Harris bipod up front with a bag in the rear. UBR stock (not precision oriented but I felt steady). RRA 2 stage trigger that breaks at approx 4.5 lbs. Dead Air brake WAITING on a Sandman S...

I'd give my equipment a 7 or 8 out of 10 with the only improvement that could be had would be in the barrel and maybe bipod. I'm happy with an honest 1.5 MOA gas gun so i'm not overly disappointed but am open to thoughts / suggestions.

One question I've always had with AR's is do you want your handguard snugged up against the receiver or just a small gap between the handguard and receiver? I've heard contacting the handguard with anything but the barrel nut can take away from some of the advantages of a free floating handguard.

 

[rlsmith1]

Also, the group up and to the right is a group of Federal 150 SP

 

[mercervillerental]

One question I've always had with AR's is do you want your handguard snugged up against the receiver or just a small gap between the handguard and receiver? I've heard contacting the handguard with anything but the barrel nut can take away from some of the advantages of a free floating handguard.

Having just built my first upper (WOA kit) I had the same thought when the instructions stated to allow "no less than 0.25"" between the hand guard and receiver. I assume that's why they suggest that?

 

[hlfazn]

It almost looks to me like the first shot spent more time in the chamber before you fired it. If you're using a different routine than you use on a bolt gun it's possible you havent considered the difference in dwell time in a warm or hot chamber for each shot.

Peronally, I've never had issues with the first shot being off like that one, just the last shot in a magazine. If you don't think it's a you problem then it might've been a bad factory load, it happens.

 

[knuckleballz]

This is my acceptable accuracy 10 shot group, prone, bipod, rear bag....at 1000 yards.... from my ar10.

 

[Odysseus1911]

16" BA barrel on an . . .

 

[rlsmith1]

That's why I'm not expecting this to be a sub MOA gun. Add to that I have zero clue what the guy before me may have done to "care" for it....

After using the search button, I'm thinking a Criterion, Lilja, Krieger or similar would do well for me. I just don't think it's worth the $350+ to squeeze some more out of it. Is there anything in the sub $300 range worth shooting? Want to stick with 16" so I'm not waving a flag pole once I suppress it.

 

[rlsmith1]

It almost looks to me like the first shot spent more time in the chamber before you fired it. If you're using a different routine than you use on a bolt gun it's possible you havent considered the difference in dwell time in a warm or hot chamber for each shot.

Peronally, I've never had issues with the first shot being off like that one, just the last shot in a magazine. If you don't think it's a you problem then it might've been a bad factory load, it happens.

That would be possible, but I left the bolt open while I walked 100 yds to check the first group so I don't think it was that. My bet is it was a fluke in the ammo or my routine. I'll work on the shooter being more consistent!

kuckleballz, that's better than acceptable at 1000 in my book! What's your setup?

 

[knuckleballz]

Its an older factory jplrp07 with 22inch rifle length gas barrel. Shooting factory Prime 130 grain 6.5 Creedmoor.

 

[rlsmith1]

Its an older factory jplrp07 with 22inch rifle length gas barrel. Shooting factory Prime 130 grain 6.5 Creedmoor.

22", Creedmoor, JP, makes sense...

 

[LR308guy]

Nice shooting "knuckleballz"

I am not saying it cant be done with a AR-10 in .308, because a lot of people already do, but, it does seem a small touch easier with a nice 6.5 Creedmore at 1,000 yards, especially with something as nice as a JPLR07.

I am still in the breaking in phase on my AR10. So I don't know what I have yet when it comes to accuracy.

 

[theLBC]

Its an older factory jplrp07 with 22inch rifle length gas barrel. Shooting factory Prime 130 grain 6.5 Creedmoor.

what's with #3?

 

[bfoosh006]

@
rlsmith1

IMHO... you may have just witnessed why you should "season the bore" to a different ammo.
Over the years.. I have witnessed many times a different load "settle in" after shooting a prior different reload / factory load.

Enough so that I tend to throw away the first 5ish rounds ( of a different load than just used ) when testing for precision of the next specific round.

CMP had /has a list of what powders not to shoot after another, mainly because your group size will be altered, until the bore seasoning settles in.

I have no scientific proof... I do have many, many different factory rounds fired from the same barrels when chronograph testing at a 9hr day at the range... that is where I first noticed the trend.
I saw my 10 rd groups slowly tighten up, repeatedly, when changing to the next factory round to chrono. ( hope that makes sense.. so 10 rds one brand ammo , next, different brand ammo 10rd groups would tighten up .. kinda doing what you described....... repeat, repeat, repeat... )

It happened so often, I believe in it. Hence the throw away those first 5 seasoning rounds group.

Are there a ton of other possible variables that factor in ... sure... but it just kept happening.

Anyway... next time try shooting and throwing away 5ish rounds to season the bore... then shoot for precision.
Or do your 10rd groups, and see if they slowly tighten up.... maybe, you will see what I saw.

 

[bfoosh006]

FWIW... here is my thread looking for the subject from CMP... and here is the list.
It is older.. but...

https://forums.thecmp.org/showthread.php?t=247798

http://forums.thecmp.org/showthread.php?t=194007&highlight=powder+compatibility

And ultimately... this is a great read... and well worth joining the linked forum just to read it.
http://www.usrifleteams.com/forums/index.php?/topic/14581-mixing-loads-during-a-match/&_fromLogin=1

 

[eastexsteve]

So I was shooting an AR10 in 308 yesterday (prone, bipod and rear bag) and I'm just trying to figure out what load it likes (eventually try to replicate that load with handloads).

I shot some cheap stuff and got cheap accuracy (2-3 MOA) so I pulled out some 175gr FGMM.

I guess just as an observation, a "lucky" 5-shot group would have lead me to believe I had a 0.5 MOA gun and stopped shooting. I'm sure I could grab the other 10 rounds of the FGMM and they would probably all end up in a 1.75 MOA group.

If it's a 1-10" twist barrel, the 175 GMM should perform better than the 150s. Barrel manufacturing and ammo has greatly improved over the last 10 years. Unless there is something wrong with the barrel, ammo, or mechanically with the gun in general, almost everything will shoot sub-MOA out of a vise. It's only going to be a "sub-MOA" gun in your hands if you can shoot it that way.

 

[rlsmith1]

Unless there is something wrong with the barrel, ammo, or mechanically with the gun in general, almost everything will shoot sub-MOA out of a vise. It's only going to be a "sub-MOA" gun in your hands if you can shoot it that way.

I've looked around and haven't seen much on shooting a large frame AR consistently. Is there a thread I should read or does anyone have a few quick tips on shooting a large frame consistently? I'm thinking I will just go with a bag up front and bag in the rear. Swapping the trigger to a lighter 2 stage as well.

 

[theLBC]

I've looked around and haven't seen much on shooting a large frame AR consistently. Is there a thread I should read or does anyone have a few quick tips on shooting a large frame consistently? I'm thinking I will just go with a bag up front and bag in the rear. Swapping the trigger to a lighter 2 stage as well.

i'm not sure if there is a thread specific to this. the most important tip i have heard is "follow through". maybe that can help your search.

 

[1500varmint]

It almost looks to me like the first shot spent more time in the chamber before you fired it. If you're using a different routine than you use on a bolt gun it's possible you havent considered the difference in dwell time in a warm or hot chamber for each shot.

Could you explain this a little more? I'm relatively new to gas guns (building AR15 and AR10 lowers now for rainy day builds) and I thought dwell time was a fixed thing/distance. How would dwell time change based on temperature?

Thanks.

 

[Powder_Burns]

If it's a 1-10" twist barrel, the 175 GMM should perform better than the 150s. Barrel manufacturing and ammo has greatly improved over the last 10 years. Unless there is something wrong with the barrel, ammo, or mechanically with the gun in general, almost everything will shoot sub-MOA out of a vise. It's only going to be a "sub-MOA" gun in your hands if you can shoot it that way.

Couldn’t agree more. I did some ladder tests last week with 175 smk’s, just working up to find pressure signs, and still clustered them at 100 with all holes touching. My 155gr ladder test had shots as far as 5” away from point of aim.

 

[knuckleballz]

I've looked around and haven't seen much on shooting a large frame AR consistently. Is there a thread I should read or does anyone have a few quick tips on shooting a large frame consistently? I'm thinking I will just go with a bag up front and bag in the rear. Swapping the trigger to a lighter 2 stage as well.

You are in luck! Look at the Snipers Hide Training offered on this website! That Training is what enabled me to shoot that 10 shot group I posted above. You will find the knowledge you seek! It is incredibly inexpensive to be able to access the online training videos compared to the time and money wasted going to the range and getting frustrated without the knowledge needed for drastic improvement

 

[rlsmith1]

Thanks! I will check them out for sure! Amazing what education is out there for so cheap. Thanks for pointing me in the right direction

 

[hlfazn]

Could you explain this a little more? I'm relatively new to gas guns (building AR15 and AR10 lowers now for rainy day builds) and I thought dwell time was a fixed thing/distance. How would dwell time change based on temperature?

When you pull the trigger on a bolt gun, the gun fires and you have time to watch your shot, line up your next shot, get off the rifle, change position, record in your book, etc while the next round sits in the magazine unless you immediately cycle the bolt to re-chamber a cartridge. This way, as the barrel warms you can adjust your shooting mechanics to ensure a round spends a consistent amount of time in a hot chamber before firing. In a gas gun, if I warm up a barrel, I have to make sure that I spend the exact same amount of time between each trigger pull from chambering to get consistent temperature effects since the action will cycle and push the next round into the chamber automatically and any amount of time it dwells in the chamber it starts to affect pressure to varying degrees based on your powder. In a cold barrel this won't matter since the barrel can still be assumed to be ambient temperature and thus doesn't heat up the round but over the course of shooting for the session as the barrel gets hotter, the amount of time the round spends heating up in the chamber is the equivalent of experiencing a drastic change in ambient temperature during the day.

This can be tested in a semi-scientific manner. Shoot a barrel enough to make it "hot." Run a chrono on ammo from one lot with 5 seconds between shots, then 15 seconds between shots for two 10 shot groups. In my experience the the 15 second dwell time will have higher velocity and the average POI will also shift. If you were to combine the two groups it would look more sloppy and have a higher "MOA."

 

[theLBC]

^ good point.
i always try for a constant rate of fire, and only load the mag with the number of shots i intend to shoot.

 

[mheimer_45]

I’ll be honest I didn’t read the whole thread but did the first 5-6 post. Did you release the mag catch on the first round? I may be ocd but I’ve recently started shooting 7 rd groups. If I hit the bolt release that round is usually off. Also the very last round is usually off. Different recoil pulse. So first shot I shoot cheap lake city ammo along with the last at a different group. So basically I’m shooting rounds 2-6 for a group size.

 

[eastexsteve]

I’ll be honest I didn’t read the whole thread but did the first 5-6 post. Did you release the mag catch on the first round? I may be ocd but I’ve recently started shooting 7 rd groups. If I hit the bolt release that round is usually off. Also the very last round is usually off. Different recoil pulse. So first shot I shoot cheap lake city ammo along with the last at a different group. So basically I’m shooting rounds 2-6 for a group size.

I've never noticed any such thing in any semi-auto rifle I've ever owned. If you're getting flyers on the first and last round, I'd be looking elsewhere for the cause. As long as the bullet has a smooth feed from the mag up the ramp, there should be no problems.

 

[nick338]

Something pertaining to short barrel .308 accuracy has always bothered me. Can't tell you how many times Iv'e heard someone recommend a 1-10 twist for an 18" or shorter barrel.

So help me understand the logic in this. Using a 175 Sierra Matchking as a baseline and a ridiculously low mv of 2000 fps, in the absolute worst environmental condition I get a stability factor of 1.61

Stay with me now

Yet a 1-8 twist is almost a given in a 6.5 whatever and a sample Creedmoor running a Berger 140 hybrid at 2700 also in the worst environmental conditions gives a stability factor of 1.39

So anyone care to explain what I'm missing here?

 

[Ledzep]

I once started a thread where I was trying to point out that mean radius and SD on mean radius was drastically more informative than outside to outside "group size", but it quickly devolved into me trying to defend the fact that you can't cheat statistics with small sample sizes...

So whatever. I can't shoot as good as you. You should omit and ignore bad groups and fliers, and no matter how many shots you shoot, only 2 of them are worth measuring. That's how we've always done it.

 

[Ledzep]

I’ll be honest I didn’t read the whole thread but did the first 5-6 post. Did you release the mag catch on the first round? I may be ocd but I’ve recently started shooting 7 rd groups. If I hit the bolt release that round is usually off. Also the very last round is usually off. Different recoil pulse. So first shot I shoot cheap lake city ammo along with the last at a different group. So basically I’m shooting rounds 2-6 for a group size.

Everything up to and a little bit after the bullet exiting the barrel is identical as far as recoil goes. Should not affect POI. The only difference *can be* upward pressure on the BCG from follower vs. cartridges.

I agree with the above post that you might look elsewhere for the solution.

 

[FCS]

I've never noticed any such thing in any semi-auto rifle I've ever owned. If you're getting flyers on the first and last round, I'd be looking elsewhere for the cause. As long as the bullet has a smooth feed from the mag up the ramp, there should be no problems.

Pretty well defined and established phenomenon.
First rd chambers differently than subsequent rds.
Last round has no pressure on bottom of BCG and different mechanical movement.
More pronounced in some rifles than others.
Name of the game is “the same”, first and last rounds are definitely not the same on how sent up feed ramp or pressure on bottom of BCG.
Isn’t like first or last is 2-3 MOA out, pretty common for it to be 0.25”-0.625” out of core group @
100.

IF you have never seen this, couple possible reasons:
You’ve only had exceptional rifles.
You’ve seen this but don’t recognize it as outlier shot(s) are within your normal group size.

 

[eastexsteve]

Pretty well defined and established phenomenon.
First rd chambers differently than subsequent rds.
Last round has no pressure on bottom of BCG and different mechanical movement.
More pronounced in some rifles than others.
Name of the game is “the same”, first and last rounds are definitely not the same on how sent up feed ramp or pressure on bottom of BCG.
Isn’t like first or last is 2-3 MOA out, pretty common for it to be 0.25”-0.625” out of core group @
100.

If this is the case, then the groups would be constantly changing as the spring pressure from the mag is constantly changing on the BCG. It makes no sense that only the first and last rounds would be different. I can think of other things that would have much greater effect than spring tension in the magazine.

IF you have never seen this, couple possible reasons:
You’ve only had exceptional rifles.
You’ve seen this but don’t recognize it as outlier shot(s) are within your normal group size.

I don't think my guns are any more exceptional than anyone elses. But, whenever I've had a grouping problem, I've always sought to resolve it. When I did resolve it, it was never magazine spring tension on the BCG. That's definitely a new one on me.

 

[Powder_Burns]

Something pertaining to short barrel .308 accuracy has always bothered me. Can't tell you how many times Iv'e heard someone recommend a 1-10 twist for an 18" or shorter barrel.

So help me understand the logic in this. Using a 175 Sierra Matchking as a baseline and a ridiculously low mv of 2000 fps, in the absolute worst environmental condition I get a stability factor of 1.61

Stay with me now

Yet a 1-8 twist is almost a given in a 6.5 whatever and a sample Creedmoor running a Berger 140 hybrid at 2700 also in the worst environmental conditions gives a stability factor of 1.39

So anyone care to explain what I'm missing here?

Bullet dimensions, ie caliber, how many calibers long the bullet is, how much mass, muzzle velocity etc. have an impact on calculating a twist rate that will stabilize a projectile in flight. Short fat bullets generally require less twist to stabilize versus long skinny bullets.

 

[sea2summit]

View attachment 7376170This is my acceptable accuracy 10 shot group, prone, bipod, rear bag....at 1000 yards.... from my ar10.

.308?

Nevermind, I kept reading.

 

[Rancid Coolaid]

How many total rounds have you put through the gun? If your whole outing is on that posted target, you are at the first date part and already asking if you should marry the girl.

If you put 100 rounds through ol' girl and still see stuff like this, then it might be worth a conversation.

I see lots of guys chasing bullet holes on rifles they don't yet know.

Saying you can punch paper with a 223 or an RPR bolt gun doesn't mean that will directly translate here.

Then again, I'm just a dumb ol Marine that eats crayons and licks windows, so...carry on.

 

[nick338]

Bullet dimensions, ie caliber, how many calibers long the bullet is, how much mass, muzzle velocity etc. have an impact on calculating a twist rate that will stabilize a projectile in flight. Short fat bullets generally require less twist to stabilize versus long skinny bullets.

I understand that but the sg numbers on Berger's twist rate calculator are what they are. My question is not why a 6.5 bullet is twisted faster than a .308 bullet. It's why gunsmiths recommend a 1-10 twist in a short barreled .308 over a 1-11 when the sg with the 1-11 is still better than what everyone seems to run in 6.5.

If people were using a long bullet like a Barnes 168 TTSX or 185 gr or heavier than I get it but this is specifically related to semi auto AR-10 style or M1A style rifles and restricted to magazine length .308 so really neither would apply.

 

[Greg Langelius *]

Where bullets disperse to and why first rounds are off has been a subject of conjecture here since this site began.

There's a number of things going in inside the barrel, and a lot going on outside it; and they all bear on the question.

The first to mind is that the bore condition left by the preceding shot has left a deposit of copper fouling and powder fouling that is different from the new batch of ammunition. This affects bore lubricity, and with it, pressure and velocity. This dictates that barrel fouling will be in transition at least for the first shot of the new ammo. This changes bore transit time. That, in sequence, changes the recoil. Longer recoil duration, higher impact, and vice-versa.

Next in line is the cold shooter phenomenon. Reloading draws the shooter out of the position they're been residing in for the previous string, requiring the shooter to load and then set back up. Odds are high that something is not the same, usually the shoulder and cheek pressure, that won't settle down until after that first recoil pulse of the new string.

Something as simple as a softer hold can alter bore transit time. It's not by much, but it doesn't need to be by much.

When one considered the difference between a 100yd zero and 1000yd zero is about 30MOA, we are talking about a ten foot drop at 1000yd being sight compensated by about, or less than, 1/2 of one degree. I.e. if the bore axis shifts upward 1/2 a degree, it changes the POI from 100yd to 1000yd. Not much, but plenty still.

I often wonder at how precisely our rifles actually shoot, and how well disciplined a shooter must be in order to achieve good scores at longer distances.

Looking at your 100yd target; that group at 1000yd, if centered properly, would all be within the 7 ring, and nearly all within the 8 ring. From a 308 AR I'd be working on form and execution, and not equipment and/or ammunition. This comment completely disregards wind. If you can shoot 1 MOA at 1000yd, you can shoot a perfect score. If you can shoot 1/2MOA at 1000yd, you're shooting all X's.

Nearly no shooters can do either; and unless I'm behind the times, none at all can do both.

Greg

 

[FCS]

If this is the case, then the groups would be constantly changing as the spring pressure from the mag is constantly changing on the BCG. It makes no sense that only the first and last rounds would be different. I can think of other things that would have much greater effect than spring tension in the magazine.



I don't think my guns are any more exceptional than anyone elses. But, whenever I've had a grouping problem, I've always sought to resolve it. When I did resolve it, it was never magazine spring tension on the BCG. That's definitely a new one on me.

You are missing the main points. I’m not sure if you are deliberately misrepresenting or really struggling to grasp the differences.

First rd chambers differently as BCG from pull CH rearward & release or trip bolt stop from locked back isn’t same as when bolt cycles from gas cycling the BCG.
Last rd has no pressure on bottom of carrier.
Not saying anything about mag spring tension affecting first or last rd.

Usually, over gassed guns have shown more first round variability as BCG cycles more violently.
More dialed in the rifle is for just right amount of gas, less of an issue I’ve seen. Could all be between my ears though.

 

[flyright]

I've seen the first round "flyer" issue with several new SA rifles. I was told to shoulder the rifle prior to bolt release, slingshot with the charging handle and other techniques. The first did seem to help a little. Ultimately, I found the problem disappeared after getting about 100 rounds or so through the rifles. Maybe I just got better with first round control but I believe it's a matter of the bolt wearing in for more consistent lock up. Now, the last round of a beautiful 3/8" five round group I can always seem to F up.

Edit: Cool, I can now use the follower tension thing as an excuse on that fifth round flyer...

 

[Powder_Burns]

I understand that but the sg numbers on Berger's twist rate calculator are what they are. My question is not why a 6.5 bullet is twisted faster than a .308 bullet. It's why gunsmiths recommend a 1-10 twist in a short barreled .308 over a 1-11 when the sg with the 1-11 is still better than what everyone seems to run in 6.5.

If people were using a long bullet like a Barnes 168 TTSX or 185 gr or heavier than I get it but this is specifically related to semi auto AR-10 style or M1A style rifles and restricted to magazine length .308 so really neither would apply.

I think that aspect has to do with the number of full twists in the barrel, ie a 22-24” bbl for a 5.56 was 1/12, 16” was 1/9, and the m4 14.5” bbls and shorter were 1/7..granted the bullet selection differs from a 55gr m193 to a 69gr m855 or a 77gr smk etc, and twist rates are optimized for a given projectile, but the trend seems to be a faster twist for a shorter barrel. So a .308 barrel under 20” would get close to two full twists, over 22” a 1/11 would get the same two full twists. Same ratio seems to apply to those 5.56 barrels, a 24” 1/12 gets two twists, a 1/9 at 18” gets two, a 1/7 at 14.5” gets two.

 

[rlsmith1]

How many total rounds have you put through the gun? If your whole outing is on that posted target, you are at the first date part and already asking if you should marry the girl.

If you put 100 rounds through ol' girl and still see stuff like this, then it might be worth a conversation.

I see lots of guys chasing bullet holes on rifles they don't yet know.

Saying you can punch paper with a 223 or an RPR bolt gun doesn't mean that will directly translate here.

Then again, I'm just a dumb ol Marine that eats crayons and licks windows, so...carry on.

I'd say I've got 75 rounds through it and bought it used, but I'm not sure how used it really was. I'll definitely keep shooting and work on my end of the equation. I'd just like to make sure I'm not missing anything and wasting $1 every time I pull the trigger.

Who knows, maybe it's the crayons and window licking that would make me shoot better??

 

[nick338]

I think that aspect has to do with the number of full twists in the barrel, ie a 22-24” bbl for a 5.56 was 1/12, 16” was 1/9, and the m4 14.5” bbls and shorter were 1/7..granted the bullet selection differs from a 55gr m193 to a 69gr m855 or a 77gr smk etc, and twist rates are optimized for a given projectile, but the trend seems to be a faster twist for a shorter barrel. So a .308 barrel under 20” would get close to two full twists, over 22” a 1/11 would get the same two full twists. Same ratio seems to apply to those 5.56 barrels, a 24” 1/12 gets two twists, a 1/9 at 18” gets two, a 1/7 at 14.5” gets two.

Actually the most accurate M1A barrel I've owned was a 22" 1-12 Krieger and I believe the SR-25 20" barrel was 1-11.25. I think it's just a conspiracy to try and confuse me.

 

[Rancid Coolaid]

As an FYI: I run a Sig716 with 16" barrel and mine, shooting 168gr TAP will do right around an MOA if I do my part. If I get a poor natural point of aim, if I anticipate the trigger break, if I dick around with a round in a hot chamber, if I clean the barrel and don't foul it before the needed shot, things opens up, sometimes a lot.
Over-gassed is indeed a large AR issue, that warrants some looking at. And sometimes a rifle just don't like a certain ammo that you want it to.

Lastly, I'd call my 716 a 500 yard gun, beyond that, wrong tool.

 

[eastexsteve]

Last rd has no pressure on bottom of carrier.
Not saying anything about mag spring tension affecting first or last rd.

Then, what's causing the pressure on the bottom of the BCG? Are you not speaking of the next round being pushed upward from the magazine by the mag spring? If true, that pressure is constantly changing as you fire the gun. And, as you stated above, it reduces to zero on the last round.

Usually, over gassed guns have shown more first round variability as BCG cycles more violently.
More dialed in the rifle is for just right amount of gas, less of an issue I’ve seen. Could all be between my ears though.

OK, in this case, what is causing this second round to be different? The BCG only has so much travel. In loading the second round, is it moving the bullet forward in the case neck when it comes to a stop against the chamber? If so, that can easily be checked. And, why isn't it doing it on the first round when you pull the charging handle all the way back, and let if go? The reason I mention these things is because I've checked all this on guns that had cycling issues, and perhaps subsequent accuracy problems. But, the only time I saw this on a gun was due to insufficient neck tension on reloaded ammo, and it was happening sporadically. If a gun is cycling smoothly and properly gassed, whatever accuracy issue it was having turned out to be something else.

Out of all the guns I have, I own five 7.62 gas guns. Two of them are AR10 clones. I'm fortunate enough to own enough property that I have my own range out to 600 yards. Consequently, I shoot a lot. Of all the accuracy issues (and I've had my share) I've had to deal with, "recoil pulse" isn't one of them. And, in an AR10 gun, there are PLENTY of things that can cause an accuracy issue. I'm definitely going to jot that one down in my notes. Every now and then, I always try a few shots in my guns by just dropping a round in the chamber and putting in an empty magazine to see if the cycling has any effect on accuracy. Nothing seems to change. If it did, I would be carefully examining loaded rounds to see if they were being beat up in any way while cycling. To me, this would be a cycling problem.

 

[bfoosh006]

How many total rounds have you put through the gun? If your whole outing is on that posted target, you are at the first date part and already asking if you should marry the girl.

Excellent viewpoint. ... If you don't mind, I am going to use that analogy frequently.

 

[FCS]

Then, what's causing the pressure on the bottom of the BCG? Are you not speaking of the next round being pushed upward from the magazine by the mag spring? If true, that pressure is constantly changing as you fire the gun. And, as you stated above, it reduces to zero on the last round.



OK, in this case, what is causing this second round to be different? The BCG only has so much travel. In loading the second round, is it moving the bullet forward in the case neck when it comes to a stop against the chamber? If so, that can easily be checked. And, why isn't it doing it on the first round when you pull the charging handle all the way back, and let if go? The reason I mention these things is because I've checked all this on guns that had cycling issues, and perhaps subsequent accuracy problems. But, the only time I saw this on a gun was due to insufficient neck tension on reloaded ammo, and it was happening sporadically. If a gun is cycling smoothly and properly gassed, whatever accuracy issue it was having turned out to be something else.

Out of all the guns I have, I own five 7.62 gas guns. Two of them are AR10 clones. I'm fortunate enough to own enough property that I have my own range out to 600 yards. Consequently, I shoot a lot. Of all the accuracy issues (and I've had my share) I've had to deal with, "recoil pulse" isn't one of them. And, in an AR10 gun, there are PLENTY of things that can cause an accuracy issue. I'm definitely going to jot that one down in my notes. Every now and then, I always try a few shots in my guns by just dropping a round in the chamber and putting in an empty magazine to see if the cycling has any effect on accuracy. Nothing seems to change. If it did, I would be carefully examining loaded rounds to see if they were being beat up in any way while cycling. To me, this would be a cycling problem.

Are you saying bolt speed is fixed regardless of how much gas is used to cycle bolt?

 

[Pappasniper]

I didn't read this entire tread so this may have already been covered. However, I will often pop the 500 yard target first shot because the way the AR10 pulls the next round can be different from how you load the first round. And that can effect how its chambered and delivered.

PB