Tuning an AR....

Discussion in 'Rifle Country' started by BigBore44, Mar 6, 2019.

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  1. BigBore44

    BigBore44 Member

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    As stated in another thread I want to tune my AR’s (assuming I need to). So I have a few questions.

    1. What advantage will tuning give me?

    2. How do I know if my AR (AR-10 and AR-47’s) need to be tuned?

    3. How do I know (diagnose) if it’s a gas problem or a recoil problem?

    Assume all rounds are factory, or if handloaded, are safe and under max loads. I don’t want to beat up a gun unnecessarily.
    Thanks to all who reply. And please, provide reasoning for your suggestions. I don’t mind an argument. But I’d like you to be able to provide actual support for your arguments.
     
  2. Sistema1927

    Sistema1927 Member

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    What, if any, problems are you experiencing?
     
  3. BigBore44

    BigBore44 Member

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    Reference question #2 in my post. I don’t even know what to look for. If there are symptoms of over/under gassing, or problems with the recoil system.

    If we can get good info, I’m hoping this may become a sticky for current (myself) or future members to learn.
     
  4. jonnyc

    jonnyc Member

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    If it ain't broke........
    You start "tuning" a perfectly functioning firearm, you know what you get? A big bill from your friendly neighborhood gunsmith.
    It's an AR, you're really over-thinking it. Shoot happily and fix it when/if something doesn't work right.
     
  5. LoonWulf
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    LoonWulf Contributing Member

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    Depends on what "tuning" means to you, what parts you have, and your specific usages. And again, this is just MY opinion.

    Your unlikely to really run into a functional issue with most builds. Deviating from the norm may require modifications, and tuning, otherwise it's all personal preference.

    My favorite build, and the only one I currently own is a an ultralight.
    With it's reduced mass carrier, 3oz buffer, and reduced power buffer spring, it needs significantly less gas to actuate than a more traditional build.
    To "tune" that one I used a mid length gas system on a 16" barrel, and installed an adjustable gas block.

    With the gas system set to lock back + 1/4 turn (odd that's how I tuned my autocockers also) the gun runs smoothly with the recoil and action impulse not being as jerky as my other builds.

    That's how I prefer my semis to run, and I've "tuned" my mini, and sks to operate similarly.

    This also theoretically means they are more likely to choke in poor condition, but for my uses that doesn't matter, and I've never had any malfunction.

    I do think having an adjustable gas block is worth the slight extra cost, at least on a gun that's used for recreation.

    There are other forms of tuning, but the gas systems all I really mess with.
     
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  6. Matt.Cross

    Matt.Cross Member

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    In a general sense, it will make your gun more pleasant to shoot, which in turn could increase your proficiency and overall satisfaction with the gun. Optimally, it would also increase the longevity of the gun and the likelihood that someone else would be happy to buy it or receive it as a gift.

    If they function correctly but some aspect of their performance isn't satisfactory, ie too much recoil, damaged brass, awkward trigger mechanics, etc... Tuning is a good way to address those issues.

    Process of elimination. Problems tend to have common manifestations and common solutions. Focus on a minimal number of components when making changes. If you can't define your problem, you probably don't have one.

    If you want to know the symptoms of some basic issues look for: weak/erratic ejection, erratic feeding issues, fail to feed/eject, failure to strip rounds from the mag reliably, and so on....
     
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  7. BigBore44

    BigBore44 Member

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    So if my AR is throwing brass into next week?

    What if it’s barely getting the brass out of the way, or not, causing the gun to jam?

    If my spent brass is dented on the case mouth?

    If I’m not reliably getting the rounds to cycle out of the magazine but I know they are the correct mags and are seated correctly.

    Without having fired a properly tuned AR, how do I know if I have too much rearward bolt thrust causing unnecessary harm?
     
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  8. Hokie_PhD

    Hokie_PhD Member

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    Most ARs are over gassed to be reliable. As others have mentioned it’s done to ensure they work under almost all conditions.

    So as long as the gun is firing, ejecting, cycling and firing again and the bolt holds open on the last round everything is probably right on a mil spec gun.

    Now when you get into custom parts, then tuning may be an issue. As mentioned by others, adjustable gas blocks and different buffers and springs are the tools to adjust it with.

    Now, if this is your only AR the advise would be to leave it alone if it’s working. Keep it reliable and go out and shoot it, then. clean it regularly.

    If it’s a competition gun, or one you want to mess around with then start with an adjustable gas block and adjust until the bolt won’t stay open. Then add 1/4 turn or so.

    The beauty and curse of the AR is that you have a zillion things you can do to it. So you’ll have to decide what to do.

    In my own case I have a PSA bare bones mil spec AR that’s my “reliable gun”. I don’t mess with it. It’s nothing special but it goes bang and is accurate. It’s not as nice to shoot as my first AR that I had to sell but it’s a reliable gun.

    I also have one I built for 3 gun. It’s much nicer in that it has a better stock, longer barrel with longer gas tube, better trigger, a muzzle brake instead of flash hider, etc. it shoots shorter and has less muzzle flip. As a gun for competition I’m ok with messing with it and getting it “perfect” for playing run and gun games.

    The thing is that the AR is a soft shooting gun with low recoil and littlemuzzle rise. And trying to get less isn’t hard but it takes a little time and thought. And it’s a bunch of decisions to decide if the small gains are worth the time and expense. In a competition gun, the answer is going to usually be yes. In a range duty gun, probably not, and in a range toy a solid maybe.

    So if you go down this route get a good notebook, and think about what you’re doing and why. Ask lots of questions here and do lots of google searches. And of course make it fun, or you’ll go insane and get frustrated.
     
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  9. imashooter

    imashooter Member

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    Advice will be more forthcoming and helpful if, instead of "what ifs", you provide exactly what is occurring with the firearm regarding a safe and fully functional weapon, perceived recoil, accuracy, all that stuff. Some if not all might be only a guessing game over the internet but should be more accurate rather than answering multiple, "what if" questions. Or if you want, google all your "what if" questions, post and provide a minimum of 3 answers (including links) here, and then they can be scrubbed as being realistic or bs.
     
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  10. BigBore44

    BigBore44 Member

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    Well this thread was more about potential problems and fixes. Even problems other members have had and fixes that members have figured out. Like tips and tricks.

    And seeing as how I’m a big bore guy (44Mag, 444, 45-70, 375 H&H all with heavy handloads) I’m not sure I have any idea of what recoil “should feel like”.

    I’m not actually experiencing any issues that I know of with the AR-47’s. Accuracy is pretty good. Not quite 1 MOA, at least not consistently. They both throw the cases into pretty good groups about 12-14’ from the gun. Occasionally I have dented case mouths.

    The AR-10 shoots well. But if I had to guess with the limited knowledge I have of AR’s, it seems like the bolt thrust is excessive. It definitely whacks the back of the receiver. But it hasn’t failed to feed or extract. It’s an Aero Precision 18” stainless upper.
     
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  11. Skylerbone

    Skylerbone Member

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    The real eye opener for me was the day I got to compare my (then) only AR, a midlength gas, to a carbine and a rifle length system. Each had a distinct impulse with the same loads.

    If you don’t know already, it may be useful to try a few for perspective. Once you’ve found what you like you can tune for reliability if necessary using an adjustable gas block. Assuming the AR is semi-auto, if it feeds, shoots, and extracts with the ammo you use...leave it alone.
     
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  12. Chuck R.

    Chuck R. Member

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    I have 1 AR (out of 5) that I consider "tuned" and it's my 3Gun rig.

    For this purpose the combination of: adjustable gas block (AGB), low mass BCG, compensator, light buffer and short reset trigger make this gun easy to shoot quickly due to the decreased recoil and muzzle rise.

    Compare it to a stock carbine like my Colt LE6920 and it literally is night and day.

    An added benefit to the AGB is that it bleeds off the unneeded gas thereby keeping the action cleaner and reducing some wear. My gun probably has about 4000 rds through it without a hitch. Average match is about 100-120 rds and I've run it through a couple carbine classes at 500+ rds a day without an issue.
     
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  13. Matt.Cross

    Matt.Cross Member

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    That's a great starting point! That's a recoil issue. So now the idea would be to look at the components of your recoil system and see what you have in order to see what changes could/should be made.

    Is this an off the shelf rifle or a personal build?
     
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  14. MistWolf

    MistWolf Member

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    As far as 5.56 ARs for duty go, the buffer & spring is already figured out. If using a carbine RE, use a standard carbine spring or a Sprinco blue spring. The buffer should be either an H buffer or an H2 buffer. CAR buffers are just too light and if an H3 buffer is desired, it's more efficient to switch to an A5 RE with an A5H2 buffer or a rifle re with a rifle buffer. With the A5 or rifle buffer, use a standard rifle spring or a Sprinco green spring. Then use the correct gas port. For example, the correct gas port for a carbine gas in either a 14.5 or 16 inch barrel, is .0625 unsuppressed. This gas port gives the greatest span of operation for reliable function with a variety of ammo and conditions without excessively sharp recoil, especially with an H2, A5H2 or rifle buffer.

    If the gas port is too large, use a BRT micro port or an SLR adjustable gas port. Both are reliable and both are backed by excellent customer service.

    Other variations can work, but after experimenting with the above in various ARs, the combination has worked for me every time.

    I don't recall exact weights and I don't have my noted before me, but the H3, A5H2 and rifle buffers are about the same in weight. The H2 and carbine buffer works very well but for some reason, the H3 doesn't work as well. When using a buffer that heavy, I find the A5H2 or rifle buffer is smoother.

    Again, this info is for 5.56 general purpose ARs only. I haven't had a chance to explore other calibers yet, or to tune one to the ragged edge for competition.
     
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  15. jonnyc

    jonnyc Member

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    "Well this thread was more about potential problems and fixes."

    If you clean and inspect your rifle regularly, your potential problems will usually narrow down to ammo or mags. For anything else, I just keep a couple of sets of lower and BCG parts around. The two sentences above will probably cover about 95% of your potential issues. Anything else would be filed under "Personal Preferences".
     
  16. IndianaBoy

    IndianaBoy Member

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    A topic that is near and dear to my heart.

    I have utilized adjustable gas blocks, muzzle brakes, low mass carriers and buffers, etc.


    Muzzle brakes work, and work well. The question is if they are worth the increased noise and muzzle blast. Some are better or worse than others. Some that are really obnoxious are not very effective.


    Adjustable gas blocks work and work well.


    Low mass components, etc are not as big of a difference maker.



    Most ARs are overgassed to ensure reliability. Shooting a properly tuned AR is a thing of beauty. Here is an example of yours truly calling my hits through my scope, before the bullet hits, because I was able to see exactly where my crosshairs were when the shot broke.

     
  17. IndianaBoy

    IndianaBoy Member

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    You could add mass or a stronger spring, or throttle back the gas.

    I really like the 2 piece click detent adjustable gas blocks from JP rifles.
     
  18. RecoilRob

    RecoilRob Member

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    It's a machine, and all machines are a compromise of many components to arrive at a desired end. You must have a goal for your tuning.....reduce recoil? Increase reliability? Increase accuracy? The old engineering adage of 'there's no free lunch' comes into play and often times something else must be compromised to increase whatever it is you're trying to improve. Pushing anything to it's maximum will decrease others perhaps below their minimum so a clear understanding of what you are trying to achieve is needed before any modification is begun. Within reason you can make the gun do anything you please but are always bound by the other compromises of operation for a fully useful firearm.
     
  19. Varminterror

    Varminterror Member

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    Why do you think the carrier velocity is excessive? (Bolt thrust is a very different thing). The buffer does have a rubberized bumper for a reason. Are you getting any other signs of excessive carrier speed other than feeling like the reciprocating mass is whacking the end of the receiver extension (like it’s supposed to)?
     
  20. silicosys4

    silicosys4 Member

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    Varminterror,
    The problem as I understand it, is the .308 if overgassed sends the BCG moving backwards with more force and velocity than is necessary to fully compress the recoil system. Couple this with the fact that the .308 BCG is much heavier than the 5.56 BCG, and you get more compression of that buffer bumper than you would in a 5.56. The rebound from this excess compression plus the excess initial velocity causes the BCG to return to battery before the ejected brass has the chance to clear the ejection port, can be compounded by too much extractor tension which either causes FTE issues in which the fired case is holding the bolt open, or the bolt physically impacts the brass on its way out, causing the 1:00 ejection pattern that so many people complain about.
    This is my understanding of the issue.

    Edit: here is a video that shows what I mean. It looks like there could be an extractor/ejector issue as well, but from what i'm understanding, carrier velocity also contributes to these symptoms.

     
    Last edited: Mar 9, 2019
  21. Varminterror

    Varminterror Member

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    @silicosys4 - are you describing the issue @BigBore44 is having with his rifle, in his stead? Or just pontificating on basic principles of AR operation?
     
  22. silicosys4

    silicosys4 Member

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    It seems pretty clear to me that I'm correlating the two.



    Am I mistaken in my understanding of the issues with excessive carrier velocity in an AR 308 and the issues it causes, and if so, how?
    Am I wrong in suspecting that the questions BigBore asked in the quote above can be explained as such? If so, how?
     
    Last edited: Mar 9, 2019
  23. Varminterror

    Varminterror Member

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    Your bolded statement is non-sequitur. The compressive force to which the buffer is exposed is not uniquely dependent upon the carrier weight, and the rest of the “symptoms” he’s speculating either aren’t caused by excessive carrier speed at all, or aren’t ONLY caused by said.

    Example: Dented brass on the case mouth has next to nothing to do with carrier speed - AR’s do not have a fixed ejector, it’s a spring ejector - so increasing carrier speed does not increase the ejection force. Dented case mouths are over strength ejectors pressing the case mouth against the extension during extraction. If that over strength ejector is over powering the extractor too early during the bolt stroke, it can fall limp in the action before it clears the port, causing a double feed or overbolt jam (really raunchy double feed), or it might cause a stovepipe if it does clear the port and leave the case head in the way of the closing bolt. But equally - an overstrength extractor can cause stovepipes as well, as the extractor doesn’t release the round readily to clear the bolt travel.

    What you might be confusing here - dents in the case body below be shoulder where the round is bouncing off of the brass deflector (as it is designed to do) are typically an example of excessive carrier speed. The ejector is doing its job, as in flicking the case out of the port, but the carrier is pulling the case rearward so quickly, it cartwheels around and smashes its shoulder into the deflector. The faster the carrier, the faster the case is moving rearward, the faster it’s moving, the harder it hits the deflector. That’s a different symptom than dented mouths, squished by an overpowered ejector spring.

    Not getting “rounds to cycle out of the magazine” might describe symptom of a multitude of operating issues; an undergassed or over sprung AR which is short stroking may not cycle rounds out of the magazine because it doesn’t open far enough to pick up the next round - leaving either an empty chamber, or a bolt-over jam. An overgassed or undermassed AR might outrun the mag and also leave the chamber empty or cause a bolt-over, but it also might just be an out of spec mag catch or out of spec mag leaving rounds too low in the receiver for pick up... Could be under powered ammo causing a short stroke, or a gas system leak, or excessive drag on the carrier, or over length buffer spring, or a plugged RE vent... or the OP may have said “it won’t feed from the mag,” generically, describing what is really a double feeding issue, described above, which has its own systemic solution.

    So instead of speculating based on any particular source of a mechanical failure, I asked the OP to better define the symptoms, specifically why he thought he had a “bolt thrust” issue, other than feeling like the buffer was bouncing off of the RE (like it’s supposed to).

    If his particular combination of symptoms are real, then a systematic troubleshooting of these symptoms will generally yield the singular solution.

    But I rather expect this is nothing more than a thought experiment kind of akin to a hypochondriac perusing WebMD and determining they have EVERYTHING disease... AR’s with multiple concurrent/coincidental, independent failures do happen, but more often, it’s just one issue, and the troubleshooting path is short and sweet.
     
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  24. Varminterror

    Varminterror Member

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    In simple terms - I define a well tuned AR to have sufficient but not excessive gas flow to fully cycle the reciprocating mass against the recoil spring reliably for the intended ammunition, without excessive reciprocating mass to dampen the carrier speed, and with sufficient but not excessive spring pressure to strip and feed the rounds from mag to chamber reliably without bolt bounce or failures to close into battery.

    With as many threads we see online about these, a guy would think we were curing cancer while playing the French horn, but AR’s are remarkably simple machines - forgetting that fact can lead to a path of darkness and despair.
     
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  25. Skylerbone

    Skylerbone Member

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    In regards to his AR-10 this is the entirety of the OP’s “symptoms” in conjunction with his statement “But if I had to guess with the limited knowledge I have of AR’s, it seems like the bolt thrust is excessive.” I would agree with @Varminterror that barring physical damage to the rifle or unusual damage to brass that the rifle is operating normally and that fueling further speculation may induce real problems.
     
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