AR Rifle Upper - Lower Fit & Impact on Accuracy

[Phil3]

I am assembling all the parts for my AR15, and I have two lower receivers I can use. A Noveske N4 forged 7xxx aluminum or a Sundevil billet 6xxx aluminum. The SunDevil has the tension screw to eliminate slop between upper and lower, the Noveske does not.

Many say the slop does not affect accuracy. After all, the scope is tied to the barrel, so wherever the scope is pointing, so goes the bullet. But, could not the barrel/bullet/scope possibly move on firing, relative to what you are holding onto (the lower)? I recognize the upper is supported at the front end by bipod or bag, but the rear can move to side and up and down a bit. If this movement happens and the point of aim changes prior to the bullet exit, it would seem that having a tight fit between upper and lower is desirable.

This rifle is for top accuracy off a bench. Does upper/lower fit really matter and which receiver would you use?

Thank you for your thoughts.

- Phil

 

[cyberpuppy42]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Phil3</div><div class="ubbcode-body">But, could not the barrel/bullet/scope possibly move on firing, relative to what you are holding onto (the lower)? I recognize the upper is supported at the front end by bipod or bag, but the rear can move to side and up and down a bit. If this movement happens and the point of aim changes prior to the bullet exit, it would seem that having a tight fit between upper and lower is desirable.</div></div>

This. My IRA-10D .308 lower has a similar tension pin. In most cases, and for 'regular' tactical shooting this isn't an issue, and makes the rifle easier to maintain. For matches, any slop can become an issue where precision is measured in the tens of MOA. Basically for match shooting you want to get your AR to come as close as possible to a bolt rifle short of actually welding your upper to your lower.

Having said that, I use a simple AccuWedge in my OlyArms PCR-1 and I'm able to get sub 1/4-MOA groups at 100'.

 

[Rovieairto]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

Yes, movement will take place while the bullet is in the bore.
If the movement isn't the same every time then the POI will not be either.
This is way down on the list as far as a practical concern but a good solid recoiling unit SHOULD, under most circumstances, give better accuracy than something that is at the whim of it's position at the point of recoil.
Unless you're going for sub 1/2 moa groups (which it sounds as if you might be) I really wouldn't worry about it.
Personally I feel that a tight fit helps me to control the rifle and break the shot more consistently especially off of a bi-pod.
IMVHO

 

[Stealth-X]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

+1 for the accuwedge

 

[Phil3]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

Yes, I built this rifle to eek out the last bit of accuracy. It sounds then that a tension screw setup might help. - Phil

 

[Chris F]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

I've seen folks apply bolt gun methodology and reasoning to AR's without really rigorously having tested what works and what doesn't. I know someone who has though. Bill Wylde is one of the pioneers in accurizing AR's and has his own 500yd range. He's also shot AR's in sanctioned Bench Rest matches and done well enough to scare the BR folk. He's said that AR's like to shoot with some rattle.

So there's your voice of dissention.

 

[Phil3]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chris F</div><div class="ubbcode-body">I've seen folks apply bolt gun methodology and reasoning to AR's without really rigorously having tested what works and what doesn't. I know someone who has though. Bill Wylde is one of the pioneers in accurizing AR's and has his own 500yd range. He's also shot AR's in sanctioned Bench Rest matches and done well enough to scare the BR folk. He's said that AR's like to shoot with some rattle.

So there's your voice of dissention. </div></div>

I'll of course defer to the experts (Bill Wylde). I'd like to know why the rattle or looseness has no negative effect on accuracy...just for educational purposes.

- Phil

 

[nhm16]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Phil3</div><div class="ubbcode-body">I'll of course defer to the experts (Bill Wylde). I'd like to know why the rattle or looseness has no negative effect on accuracy...just for educational purposes.

- Phil </div></div>

I'd venture to guess that all the action happens in the upper, and specifically in the interface of the bolt and the barrel extension. Any forces on the bolt/barrel extension imparted by the upper/lower interface, and the looseness or tightness thereof, will be insignificant compared the inherent slop of the bolt locking into the barrel extension.

 

[scotharr]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

John Feamster, in his book "Black Magic" performed accuracy tests and determined that rattle does indeed have a small impact on accuracy: small fraction of an MOA. This is too small for XTC competitions where a 1MOA gun is plenty. The more anal folks actually bed their upper to the lower to reduce slop...without introducing undo stress. An overly tight accuwedge or tension screw applying excessive pressure can actually reduce accuracy....so don't go overboard and perform before and after testing to make sure you are getting what you hope for.

I have a Sun Devil lower and use the screw to minimize the slop. But I don't put it so tight that I feel friction on the rear retaining pin when removing it.

 

[oneshot onekill]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cyberpuppy42</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Phil3</div><div class="ubbcode-body">But, could not the barrel/bullet/scope possibly move on firing, relative to what you are holding onto (the lower)? I recognize the upper is supported at the front end by bipod or bag, but the rear can move to side and up and down a bit. If this movement happens and the point of aim changes prior to the bullet exit, it would seem that having a tight fit between upper and lower is desirable.</div></div>

This. My IRA-10D .308 lower has a similar tension pin. In most cases, and for 'regular' tactical shooting this isn't an issue, and makes the rifle easier to maintain. For matches, any slop can become an issue where precision is measured in the tens of MOA. Basically for match shooting you want to get your AR to come as close as possible to a bolt rifle short of actually welding your upper to your lower.

Having said that, I use a simple AccuWedge in my OlyArms PCR-1 and I'm able to get sub 1/4-MOA groups at 100'. </div></div>Uhh... 1/4-MOA? Sorry to hi-jack but I gotta throw up the BS flag on this one!

As far as the question... It makes sense that a tighter fit would improve accuracy.

 

[apexcncshop]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

Nothing wrong with either, (the Sundevil looks great with our Gator grip handguard ). But the Accuwedge is probably a better all around solution.

 

[bigwheeler]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

A foam ear plug works as well, new or used.

 

[BasraBoy]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

I don't much care for a sloppy fit either....I've got Accuwedge on both my AR's,

Before that I used a pencil eraser cut to the appropriate size/shape!

 

[cyberpuppy42]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body">Uhh... 1/4-MOA? Sorry to hi-jack but I gotta throw up the BS flag on this one!
</div></div>

Throw whatever flags you want, it doesn't make it untrue. Handloads (lengthy and structured load development process), 80 VLD bullets fired from a bench in a controlled environment from a PCR-1 with 24" bbl and a set trigger. Best 5-shot group was around .12" at 100 yards. Others on this forum have confirmed this type of accuracy out of the PCR-1. It's possible.

Have a nice day.

EDIT: Link to a thread from just the other day on this topic: http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=1292026&page=1

 

[oneshot onekill]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

OK...OK... But 1/4 MOA?... Damn! Just Damn! I guess all I can really say is: Nice Shootin'!

 

[scotharr]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: oneshot onekill</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cyberpuppy42</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Phil3</div><div class="ubbcode-body">But, could not the barrel/bullet/scope possibly move on firing, relative to what you are holding onto (the lower)? I recognize the upper is supported at the front end by bipod or bag, but the rear can move to side and up and down a bit. If this movement happens and the point of aim changes prior to the bullet exit, it would seem that having a tight fit between upper and lower is desirable.</div></div>

This. My IRA-10D .308 lower has a similar tension pin. In most cases, and for 'regular' tactical shooting this isn't an issue, and makes the rifle easier to maintain. For matches, any slop can become an issue where precision is measured in the tens of MOA. Basically for match shooting you want to get your AR to come as close as possible to a bolt rifle short of actually welding your upper to your lower.

Having said that, I use a simple AccuWedge in my OlyArms PCR-1 and I'm able to get sub 1/4-MOA groups at 100'. </div></div>Uhh... 1/4-MOA? Sorry to hi-jack but I gotta throw up the BS flag on this one!

As far as the question... It makes sense that a tighter fit would improve accuracy. </div></div>

Ya, its funny how I never see 1/4" groups in any of the competitions I go to, but folks seem to get those 1/4" groups all the time elsewhere.

 

[Chris F]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">John Feamster, in his book "Black Magic" performed accuracy tests and determined that rattle does indeed have a small impact on accuracy: small fraction of an MOA</div></div>

There were a couple of methodological problems with Feamster's "test".
1) He fired the groups serially for each condition...stated another way, he didn't alternate tensioned versus loose, introducing the possibility conditions such as wind or mirage etc could have favored one intervention more than the other.

2) The number of groups fired was small (9) especially for discerning the difference in group size that he was observing.

3) Related to #2, John himself will tell himself that his observation did not reach statistical significance, meaning the difference was just as likely due to chance as it was due to the tested intervention (tight versus loose).

He does write in other places of other observations that led to his testing, and they're interesting and worth noting.

That reminds me that I owe Uncle Yoda a call to ask about his 500yd observations and methodological rigor.

 

[AK10mm]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

I use an accuwedge mainly because I find any rattle to be distracting,the three AR's I'm using right now are an ASA side charging upper with RRA lower,little loose,needs Accuwedge.My custom side charge upper,RRA lower is tight with almost no rattle.On my 20" target AR I have Matched Sundevil upper and lower an use the tension screw.Sundevil said they could actually make a set that had to be used as a matched set,but recommended against it.The AR-15 is pretty simple,a good FF barrel,good trigger,a thought out method of mounting your scope for proper eye relief and cheekweld and your AR will do the job.Don't like slop?Use an Accuwedge.

 

[christian77]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

I use the Accuwedge in 7 or 8 of my ARs.

 

[cyberpuppy42]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scooter-PIE</div><div class="ubbcode-body">
Ya, its funny how I never see 1/4" groups in any of the competitions I go to, but folks seem to get those 1/4" groups all the time elsewhere. </div></div>

Maybe it's because not everyone who shoots well enters competitions...

 

[scotharr]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cyberpuppy42</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scooter-PIE</div><div class="ubbcode-body">
Ya, its funny how I never see 1/4" groups in any of the competitions I go to, but folks seem to get those 1/4" groups all the time elsewhere. </div></div>

Maybe it's because not everyone who shoots well enters competitions... </div></div>
Now that is funny. You take the time to tell everyone what a great group you shot on a public forum, but then you say...well....I shot it by myself, so you'll just have to trust me. Please..... If you can't prove your boasts in a real competition...you're a poser. 1/4" group? What for 3 shots? Shoot a 10 or 20 shot group at 300 yards and get back with me.

 

[Former0302]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

Seems counter-intuitive to me that rattle wouldn't have an effect on consistent alignment with the sights. Maybe less of an issue if scoped (assuming paralax is taken out)...but with iron sights seems like it'd matter.

Also, seems counter-intuitive it wouldn't have an impact on consistent follow through.

Regardless, I just hate a rattling AR. The truth is that if psychologically it's bugging me, it's probably having a negative impact on my shooting.

So, for me +1 on the accuwedge.

Man, I wish I could shoot 1/4 MOA with my ARs!

 

[PeteCamp]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If you can't prove your boasts in a real competition...you're a poser. </div></div>

Just curious. What "real" 100-yard competitions do you shoot a scoped heavy barrel AR from the benchrest in? Seems to me that is the only way one could shoot a 1/4" group.

 

[cyberpuppy42]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scooter-PIE</div><div class="ubbcode-body">
Now that is funny. You take the time to tell everyone what a great group you shot on a public forum, but then you say...well....I shot it by myself, so you'll just have to trust me. Please..... If you can't prove your boasts in a real competition...you're a poser. 1/4" group? What for 3 shots? Shoot a 10 or 20 shot group at 300 yards and get back with me. </div></div>

So by your account nothing anyone has ever written on this forum and elsewhere is valid because it wasn't done during competition? Whatever...

I already explained the conditions in which I accomplished that grouping. I don't need to prove myself to anyone but myself, nor am I posting here to boast. I'm simply sharing my personal experience to try and answer questions people have asked. Like I said, others have confirmed similar results to what I achieved, and that should be confirmation enough that what I'm saying is entirely achievable. I can't control what you believe or not - that's on you and doesn't interest me in the least bit, nor does it invalidate my personal experience.

Cheers!

 

[Sterling Shooter]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: cyberpuppy42</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Scooter-PIE</div><div class="ubbcode-body">
Now that is funny. You take the time to tell everyone what a great group you shot on a public forum, but then you say...well....I shot it by myself, so you'll just have to trust me. Please..... If you can't prove your boasts in a real competition...you're a poser. 1/4" group? What for 3 shots? Shoot a 10 or 20 shot group at 300 yards and get back with me. </div></div>

So by your account nothing anyone has ever written on this forum and elsewhere is valid because it wasn't done during competition? Whatever...

I already explained the conditions in which I accomplished that grouping. I don't need to prove myself to anyone but myself, nor am I posting here to boast. I'm simply sharing my personal experience to try and answer questions people have asked. Like I said, others have confirmed similar results to what I achieved, and that should be confirmation enough that what I'm saying is entirely achievable. I can't control what you believe or not - that's on you and doesn't interest me in the least bit, nor does it invalidate my personal experience.

Cheers!</div></div>

I have no doubt, if a shooter is consistent to the molecular level, groups not much bigger than the diameter of the first bullet hole are possible, since, unless the gun is broken, the bullet will always go in the direction the barrel is pointed. My own experience with my iron sight Service Rifle is that 3/4 minute 20-22 round groups at 100 yard reduced course targets are possible under ideal prevailing conditions from the prone sling supported position.

 

[PeteCamp]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">My own experience with my iron sight Service Rifle is that 3/4 minute 20-22 round groups at 100 yard reduced course targets are possible under ideal prevailing conditions from the prone sling supported position.
</div></div>

Charles, I would say that is fine shooting. My service rifle is like a spirited race horse - always wants to go faster than I can stay on.

 

[Chris F]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Ya, its funny how I never see 1/4" groups in any of the competitions I go to, but folks seem to get those 1/4" groups all the time elsewhere.</div></div>
Scooter-Pie,
Take a look at the Feamster book you referenced. Feamster shot a 0.231 5 shot group at 200yds in registered BR competition and writes about it on p19 and shows the pic and the "Precision Shooting Official Screamer" patch that he earned as a result on pages 23 and 135. Oh yeah. Rifle was built by Bill Wylde.

Not 10 or 20 shots, nor 300 yds, but done in an actual match and recorded as such. Still impressive in my book.

 

[scotharr]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chris F</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Ya, its funny how I never see 1/4" groups in any of the competitions I go to, but folks seem to get those 1/4" groups all the time elsewhere.</div></div>
Scooter-Pie,
Take a look at the Feamster book you referenced. Feamster shot a 0.231 5 shot group at 200yds in registered BR competition and writes about it on p19 and shows the pic and the "Precision Shooting Official Screamer" patch that he earned as a result on pages 23 and 135. Oh yeah. Rifle was built by Bill Wylde.

Not 10 or 20 shots, nor 300 yds, but done in an actual match and recorded as such. Still impressive in my book. </div></div>
Yes, that was an impressive recorded group from a reliable source. But,people throw around 1/4" groups like they are easy or common on an AR platform: not. 5-shot .25" groups are getting into benchrest territory and are not common with AR's even match AR's. Or maybe I just suck with my CLE AR. But I did get second place with it in the last 500yard F-class match against the 308s....probably shot 4" groups.

Look at Sterling's post above....3/4MOA under ideal conditions at only a hundred yards. That is the voice of experience.

 

[Explorer]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

"What "real" 100-yard competitions do you shoot a scoped heavy barrel AR from the benchrest in"

I used my 26" heavy AR for a couple matches till I built a benchrest gun. Single loading 80 gr bullets (the 70s were not on the market yet) and the gun would shoot WAY better than I could.
It was easy to tell the difference between a hard/heavy hold and a light hold - the 2 pc receiver is a handicap in that game. but I did well enough to keep a couple folks interested/worried.

That said, it is painfull to acheive such results. The hardware is available, the skills are more challenging. But I do beleive, like fish stories, many just MIGHT be exagerated. But then, is that not part of the constant challenge we pursue?

 

[338LM]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Chris F</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Ya, its funny how I never see 1/4" groups in any of the competitions I go to, but folks seem to get those 1/4" groups all the time elsewhere.</div></div>
Scooter-Pie,
Take a look at the Feamster book you referenced. Feamster shot a 0.231 5 shot group at 200yds in registered BR competition and writes about it on p19 and shows the pic and the "Precision Shooting Official Screamer" patch that he earned as a result on pages 23 and 135. Oh yeah. Rifle was built by Bill Wylde.

Not 10 or 20 shots, nor 300 yds, but done in an actual match and recorded as such. Still impressive in my book. </div></div>

Feamster even admitted there was a lot of luck in that group that he shot and that the odds of him being able to duplicate it again was quite slim. But he did get to enjoy his day of glory that day.

As for the sub 1/4-MOA groups at 100 yards that is the funniest f#^*&%@ thing I have heard in a long time. If you want to brag about something, brag about what size groups the rifle shoots on a consistent basis. Not your flash in the pan best group that you shot on any certain day.

 

[AK10mm]

Re: AR Rifle Upper - Lower Fit & Impact on Accuracy

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: former0302</div><div class="ubbcode-body">Seems counter-intuitive to me that rattle wouldn't have an effect on consistent alignment with the sights. Maybe less of an issue if scoped (assuming paralax is taken out)...but with iron sights seems like it'd matter.

Also, seems counter-intuitive it wouldn't have an impact on consistent follow through.

Regardless, I just hate a rattling AR. The truth is that if psychologically it's bugging me, it's probably having a negative impact on my shooting.

So, for me +1 on the accuwedge.

Man, I wish I could shoot 1/4 MOA with my ARs! </div></div>

As I said in an earlier post,a rattling AR is a distraction to me,as is a rattling POS carbine stock,for collapsible,I use a CTR,they lock up tight,for fixed a PRS or just an A2 with a pnumatic buffer and no spring noise either.Just my 2 cents.