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Determining The Round Count On A Used AR15 (not 56k friendly)

Discussion in 'Rifle Country' started by Bartholomew Roberts, Jul 27, 2006.

  1. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    I like to play with AR15s quite a bit and when I see one for sale used, I usually ask about it. Often (especially at gunshows) I get the comment "I've probably fired less than 100 rounds through her" or something similar. Because I log the number of rounds fired on all of my firearms and already own a few AR15s, I am usually able to estimate the number of rounds on an AR15 by examining it.

    However, for those of you who aren't as fortunate, I thought I would put together this guide to show what different parts of the AR15 look like at different round counts. Hopefully this information will help you estimate the amount of wear and tear left in a used rifle.

    First some important caveats:

    The AR15 is a very modular system. You can replace virtually any part in it with a brand new part very easily. As a result, just because one part is brand new doesn't necessarily mean the rest of the rifle is in the same condition.

    This guide concentrates on the bolt carrier group. This is for two reasons - one is that the bolt carrier group is a part that is critical to the function of any AR15, two is that the bolt carrier group is like the rings on a tree - it is one of the best ways to figure out the wear on an AR15.

    This is not an exact science. Using different lubrication, different amounts of lubrication or shooting under different conditions may cause you to have similar wear but with significantly less/more round count than the pictures here. However one thing that does remain constant is these pictures give you a good idea of wear on these parts over time and a rough idea of how much use remains in the part.

    How to determine the round count on an AR15:

    We will start from the outside of the bolt carrier group and work inwards. Key parts to examine on the bolt carrier group are the bearing rails (particularly the front and rear of the rails), the underside of the bolt where the hammer drags, and the front edge of the base of the gas key. These are areas where wear will show first. The shinier these areas are and the further the wear extends towards the center of the bolt carrier, the more rounds have been fired with that bolt carrier. One nice thing about the bearing rails of the BCG is that they serve as a rough guide from 0 rounds to 10,000 rounds. At 10,000+ rounds, much of the finish will be gone from these rails and they will be shiny and polished.

    [​IMG] [​IMG]
    Bolt carrier group w/ 276 rounds vs. Bolt carrier group w/1,849 rounds
    Note how the 276 bolt carrier has just a tiny spot of wear on the front of the rail and at the top corner of the base of the gas key. Also head of the 276 cam pin has just a few scratches in the finish; but still has a lot of finish. In contrast the 1,849 bolt carrier group is missing most of the park from the front section of the rail, has more finish wear at the base of the gas key and more finish wear on the head of the cam pin.
    Examples (Hi-Res): Bolt Carrier Group with 276 rounds, Bolt Carrier Group with 315 rounds, Bolt Carrier Group with 1,849 rounds

    While it is less reliable, you can also look at hammer wear on the underside of the bolt in order to get a rough guess of the round count. However, bolt carrier groups will typically not show substantial wear from the hammer until after the 2k mark.

    This picture shows (from front to back) 1,849 rounds, 276 rounds, and 315 rounds:

    Even better than examining the bolt carrier, is examining the bolt itself and the cam pin. The shinier the cam pin and the more obvious the "groove" in the pin, the more rounds that cam pin has seen. On the bolt, you are looking at three areas - the ring right behind the extractor cut, the tail of bolt behind the gas ring, and the bolt face.

    The ring behind the extractor cut bears on the inside of the bolt carrier and is one of the first places to show wear. The less parkerizing you see here, the more rounds through the gun. Likewise, the tail of the bolt behind the gas rings gives two signs of wear - first the parkerizing wears off the tail from hot gases flowing around it. Second, over time carbon that is very difficult to remove begins to build up even with dedicated cleaning efforts. The carbon buildup can be a misleading indicator though since it depends on the cleaning habits of the shooter, type of firing done, and once it reaches a certain point it becomes self-limiting and a bolt with 12k rounds will look much like a bolt with 6k rounds. However, when a seller is claiming less than 1,000 rounds and you notice significant carbon build-up, that is a good sign of bad maintenance habits or more shooting than claimed. Let's look at some examples:

    Here is what a brand new, never fired bolt looks like (Hi-Res) for comparison (keep in mind that a bolt in this condition may also indicate a potential problem - the gun has never been fired with this bolt):

    Bolt with 276 rounds Hi-Res:
    Note that this bolt has just a tiny bit of wear on around the leading edge of the ring, almost no wear on the tail and just a tiny bit of carbon buildup from lax cleaning :)o ). The cam pin shows wear at the bottom, on the edges of the top of the pin and around the groove.

    Bolt with 295 rounds Hi-Res:
    Very similar to the previous example; but with a bit more wear on the tail and less even wear on the ring.

    Bolt with 315 rounds Hi-Res:
    Wear on the cam pin is not much different; but there is noticeably more wear on both the ring and the tail of the bolt as well as more carbon build-up. This bolt was run fairly dry and you can see the difference in the wear.

    Bolt with 1,849 rounds Hi-Res:
    By comparison, even though this bolt has five times as many rounds on it, it has been kept drenched in Slip 2000 gun lube and is in better shape than the 315 bolt. With one major difference being that although this picture doesn't show it well, there is significantly more carbon built up on the tail of the bolt.


    As you can tell, even with a significant difference in the round count, it can be tricky business trying to guess the difference between a well-maintained bolt with 1,500 rounds on it and a poorly maintained bolt with 300 rounds on it; but what about that bolt face business? Well, the bolt face is probably the single best place to see small differences in round counts on low round count guns, however as round counts increase, it becomes less useful.

    Let's take a look at a new, never fired bolt face Hi-Res:
    As you can see, the bolt face itself is black as night. There is no wear on the ejector pin and no wear at all on the face of the lugs. No powder residue, no sealant, no brass marks - completely new.

    Bolt face w/ 276 rounds Hi-Res:
    Still pretty good here - all of the parkerizing is still on the face of the bolt; but we have a little leftover primer sealant and powder residue on the face as well. Also, the ejector and the face of the bolt lugs are missing some parkerizing; but all in all, pretty good condition.

    Bolt face w/ 295 rounds Hi-Res:
    Pretty much the same, with a little less wear on the face of the lugs and a different pattern of wear on the ejector. Also more sealant and powder residue around the bolt. You can also see a small ring starting to form around the firing pin hole. This ring will start to form around 300 rounds and becomes more pronounced over time.

    Bolt face w/315 rounds Hi-Res:
    Once again, similar to the other examples except we begin to see some wear on the actual bolt face and the ring around the firing pin hole is more clear.

    Bolt face w/1,849 rounds Hi-Res:
    Remember how it was more difficult to tell the 1,849 bolt from the 315 bolt? Not so difficult now is it? The 1,849 bolt is missing most of the park from the bolt face and has an even, shiny pattern of wear on the lugs and ejector. Further the ring is fully formed now and probably won't look much different at twice this round count.


    As you can see, estimating the round count on an AR15 involves knowing what parts to check. For a low round count gun that hasn't had time to develop wear on the bigger parts, the bolt and bolt face will be critical in determining the round count. As the gun starts to get a higher round count, there will be less difference between a bolt with 7k rounds and a bolt with 5k rounds. At that point, you will want to start examining the bolt carrier group more, looking particularly at the areas we covered. The less finish you see in those areas, the higher the round count. No finish at all and a bright shiny polished surface means quite a few rounds.

    Hopefully this guide was helpful to you in evaluating your used AR purchase. For those of you who have an accurate round count on your weapons, please feel free to share your own pics of the bolt, bolt face, cam pin and bolt carrier group. Hopefully, this will make a better resource for all of us.
  2. 1 old 0311

    1 old 0311 member

    Thanks! THAT is a neet idea. I also find EVERY used firearm has "only 100 or so rounds through it."
  3. blackhawk2000

    blackhawk2000 member

    Great post!
  4. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    Glad y'all found it useful.

    On a related note, here is the Powerpoint presentation for the SOPMOD Block II program presented at the 2006 NDIA Small Arms Conference.

    On pages 43-52, this presentation notes that bolts in the M4 carbines subjected to harsh firing schedules show initial cracking at either the cam pin hole or the bolt lugs between 3,000 and 6,000 rounds. They go on to state that even with a milder schedule of firing, nearly all M4 bolts will show initial cracking between 6,000 and 10,000 rounds. They go on to state that once initial cracking starts, bolts can fail immediately or continue on for thousands of rounds. Lots of good pictures explaining what to look for as well.

    I would guess that what the SOPMOD program considers a mild program is probably a lot worse than most civilian M4geries will see; but a bolt with more than 6k on it needs to be checked and a bolt with 10k on it may be nearing the end of its usefulness.

    It is also important to remember that pressures on the bolt are a lot higher in the carbine gas systems and that a bolt in a midlength or rifle length gas system may see longer life.
  5. johnmcl

    johnmcl Well-Known Member

    Really Nice Work


    First let me thank you for the hours you invested in that post. Now *this* is why I hang around THR, not for the Glock bashing, nor the 5.56 vs 308 'debates', nor the government conspiracy theories, nor all the other things that repeat themselves here on a weekly basis.

    It is for experts like you taking time out of your busy lives to impart your expertise to any that'll take the time to read. I'm an engineer and just love these functional decomposition exercises such as you just completed. You take complex problems and decompose them to a simple, understandable segments. I immediately pulled my A2 bolt and simply understood.

    I'm sure I'm going to read this post many times.

    Thanks again,

  6. Kaylee

    Kaylee Moderator

    EXCELLENT post sir. THANK YOU for contributing to the knowledge base like this!!

  7. Chipperman

    Chipperman Well-Known Member

  8. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    I'm glad you enjoyed it and found it useful; but even in the relatively small pond that is THR I am far from an expert. I read THR for the same reasons you do, there are lots of people to learn from. This post was just written in the spirit of TFL/THRs "Share what you know, learn what you don't know" motto.
  9. DMK

    DMK Well-Known Member

    Great post! :) This ranks right up there with Jim March's used revolver checkout back in the TFL days. Thanks B.R. <we need a hoist a beer smilie>

    Another nice thing about these pics is they show the important places to lube.
  10. taliv

    taliv Moderator

    if you want some cheap entertainment, i'll post pics of a few of my bolts and let you guess how many rounds went through

    i just completed my 5000 rnd "break-in" period on one last week :evil:
  11. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    That would be a pretty good experiment actually if you have a good round count on the bolts. It isn't the same as examining them firsthand; but it would give people a chance to put their newfound skills to work.

    The extra pictures and information will be useful in any case.
  12. taliv

    taliv Moderator

    Bolt-carrier group specimen A

    I'll post three sets of pics here, one set from each of three guns. all pics will be attachments, since they're all about 300-400KB.

    I will post the round count in each post, but will change the text color to white on white, so you'll have to highlight the text (with your mouse) to view the answer.

    This came out of a RRA with 16" barrel, midlength gas system, standard trigger.
    This is a mall-ninja gun, and it is often shot rapidly. I use very little oil or grease on this rifle as it's extremely tight and suppressed and blows fumes up my nose when i overlube it :cuss:

    Highlight this area to see round count: 2431

    Attached Files:

    Last edited: Jul 30, 2006
  13. taliv

    taliv Moderator

    Specimin B

    This bolt/carrier came from a RRA National Match that I use for High Power.
    I don't use grease on this gun, but squirt it full of LSA while shooting. (and I mean full :) )
    This gun has a jewel trigger

    Highlight here for Round Count:
    I have 1263 rnds in matches and practice in my log.
    I have an estimated 1500 rnds of slow-fire bench from before i started keeping logs.

    Attached Files:

  14. taliv

    taliv Moderator

    Specimen C

    Finally, this is from an Essential Arms pre-ban. 1980s era 11.5" barrel with the perm attached FS. It's my blaster / making noise gun and it primarily gets shot as fast as i can pull the trigger, which is a standard ar15 trigger.

    I use red grease on the rails and varying amounts of LSA in the bolt itself.

    highlight here for round count:
    I don't keep a log for this gun and I bought it used (it looked VERY used when i bought it) so I have no idea how many rounds have been through this gun. I've put many thousand (at least 7000, possibly >10,000) through it myself, based on how many empty 8lb jugs of 2230c i have sitting here :)

    Attached Files:

    Last edited: Jul 30, 2006
  15. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    Hmmm... choice A looks about like my Bushmaster BCG that had 10k on it; but you mentioned it has been run pretty dry, so I am going to guess about 7-8k on A.

    Choice B looks like about 5k to me.

    Choice C is the worst looking bolt I've ever seen. I thought it might be chromed at first with carbon on it. However the BCG doesn't seem to match it. I would guess about 4-5k based on the BCG; but the bolt looks like it has seen 15k easy. That one puzzles me. Even on the BCG, the wear on the gas key and hammer wear are more typical of an older BCG than the wear on the rails would indicate. I'd consider the bolt on the 11.5" at the end of its useful life and probably replace it unless it looks better in person than it does in that picture.
  16. Thin Black Line

    Thin Black Line Well-Known Member

    Nice pics. Good thing for touch up pens and new cam pins......JK.....

    Do you have some pics of the inside of the upper receivers so we can
    compare the low vs high milage in those?
  17. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    I didn't do upper recivers because they wear in only a few spots and the wear is difficult to distinguish. To use one example, I have one upper with 8k rounds on it. It looks pretty much like the upper with 1k rounds on it.
  18. taliv

    taliv Moderator

    i don't think i could take a pic of the inside of an upper. it would be challenging for me. probably require some pointers from oleg.

    in the case of example A above, it would be somewhat different because i also have just shy of 2000 rnds of 22LR shot through the upper via a ceiner 22LR conversion (which replaces the BCG). i suspect the extra dirt from the 22LR might be accumulating in the upper and contributing to the extra wear of the 223 BCG.

    Bartholomew, as for the bolt on C, yeah, it's pretty scary in person, but i was planning to run it until it fails just to say i'd worn one out. In person, the bolt face actually looks like a nickel plating. But I keep a spare handy. Your guess there on round count was pretty close to mine, since i don't know how many the previous owner put through it. But I wanted to ask you about those cracks you were talking about. Can you see them in my pics? I can't see any cracks. What should I look for?

    Interestingly, the carrier for C doesn't look like it has a lot of wear, (despite a 5-digit round count) but the bottom, where the bolt drags, is as rough as it looks in the picture.

    Another point of interest is that the jewel trigger's hammer is more narrow and wears a different spot.
  19. Thin Black Line

    Thin Black Line Well-Known Member

    Must be once a couple of small wear points are made in an upper, they
    don't change that much.
  20. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    Well, it looks like I was way off on the first two. The first one obviously shows more wear from being run dry. I wouldn't have guessed it was that low though - it is almost a twin for my older BCG as I remember. On the second one, I think the appearance of hammer wear and wear on the gas key through me. Also wear on the outside of the bolt lugs (not just the face) usually indicates a higher round count. So the shiny high spots on the top of the lugs made me guess more rounds.

    The NDIA briefing (see the link above) talks about micro cracking and that the cracks are very small. They usually start on either side of the cam pin hole or at the right angle where the base of the lugs meet with the bolt. The NDIA Powerpoint (start at page 43) also has some pictures showing some examples of the cracks. Considering that is an 11.5" barrel and the condition of the bolt, I would bet it has cracks somewhere in it already. It is just a question of how far they have propagated. See any pitting anywhere on the bolt? Usually the base of the lugs and the bolt face are where it will show first...

    As far as running it to failure, an AR15 can run even with a few sheared bolt lugs. The major problem is when the sheared lugs end up in some awkward place inside the rifle and another shot is fired. Then you can start doing damage. I've also seen bolts let go at the cam pin hole without doing any additional damage; but it does put metal into odd places and it will stop the rifle cold.

    Thanks for the contributions!

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