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  • Originally posted by davisac View Post
    just a thought but jwise you should probably add NJ to your list of states in your sig line. we definitely "deserve" it.
    Good point...
    J. Wise

    AR-15 - AK-47 - NFA Trusts - My Pick - Carry Guns - 1911s

    "Some say you can tell how the world stands by the prices of AK-47s...." Chit2001

    Any comments contained herein regarding the legality of firearms, or the application of law, are strictly applicable to Texas. If you live in CA, NY, IL, MA, D.C., etc., the above comments will probably shock you, and should be read for educational purposes only. Most likely nothing I write will apply to you.

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    • Fragmentation of the heavier rounds for the AR-15 ?

      Sticking within the 5.56/.233 family of rounds, please point out any errors in the logic below.

      A slower but heavier bullet (like the oft-reccomended 75 or 77 grain options) should be less affected by the wind and maintain its energy at long distances better than a faster but lighter round (like our old friend, 55 gr.). These are obviously good things. Feel free to chime in with other advantages to the heavier rounds (Given the same bullet, material, shape and caliber, I don't know what the speed/weight trade off means in terms of penetration.).

      Many people claim that the effectiveness of a 5.56 bullet in stopping a threat is tied to impacting the target with a velocity high enough to cause fragmentation of the bullet upon penetration. At least for the military-style bullets associated with the M193 and M855 rounds, it is usually claimed that penetrating the target at a minimum of 2700 fps is necessary to ensure fragmentation.

      With the selection of a 16" (or even shorter) barrel, we take a substanitial reduction in the velocity at which any given weight bullet will leave the barrel (as compared to the same round through a longer barrel). When we couple this with selecting heavier (and correspondingly slower) bullets, we get a further reduction in velocity that looks like you start out below the 2700 fps threshold or drop below it at a relatively short range.

      Do these slower, heavier rounds incorporate some feature that allows RELIABLE fragmentation at a lower speed or do they get their effectiveness through a RELIABLE mechanism other than fragmentation? Otherwise, it would seem that we are migrating to a round that can be more accurately delivered at a longer distance, but doesn't do much when it gets there (and may be so slow, that it doesn't reach its full potential even up close).

      In other words, if high velocity is needed to get this relatively small round to be effective, why are we choosing a slow round?

      Comment


      • Originally posted by chris falk View Post

        Many people claim that the effectiveness of a 5.56 bullet in stopping a threat is tied to impacting the target with a velocity high enough to cause fragmentation of the bullet upon penetration. At least for the military-style bullets associated with the M193 and M855 rounds, it is usually claimed that penetrating the target at a minimum of 2700 fps is necessary to ensure fragmentation.
        This is not a claim. It IS the way a FMJ 5.56mm round is supposed to work. High velocity causes the bullet to yaw and fragment upon impact..

        With the selection of a 16" (or even shorter) barrel, we take a substanitial reduction in the velocity at which any given weight bullet will leave the barrel (as compared to the same round through a longer barrel). When we couple this with selecting heavier (and correspondingly slower) bullets, we get a further reduction in velocity that looks like you start out below the 2700 fps threshold or drop below it at a relatively short range.
        The reduction of velocity is correct. However, a 14.5 barrel will retain sufficient velocity for a 55gr FMJ round (M193) out to about 100 yards. M855 will fragment at about 50 yards. Even a 10.5" barrel will maintain sufficient velocity with M193 to about 40 yards.

        Do these slower, heavier rounds incorporate some feature that allows RELIABLE fragmentation at a lower speed or do they get their effectiveness through a RELIABLE mechanism other than fragmentation? Otherwise, it would seem that we are migrating to a round that can be more accurately delivered at a longer distance, but doesn't do much when it gets there (and may be so slow, that it doesn't reach its full potential even up close).

        In other words, if high velocity is needed to get this relatively small round to be effective, why are we choosing a slow round?
        The heavier rounds rely on their relatively high velocity, bullet weight, and expansion. Hence the hollow point and ballistic tip designs that are prevalent among the 75-77gr projectiles.

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        • OK I have a friend who's trying talk me out buying a Colt 6920. I usually don't listen to him but today he told me Colt chrome lined barrels are only good for 15,000 rounds.

          I know nothing about barrel life and would be surprised if I ever shoot 15,000 rounds.

          So what can I expect for barrel life if I only shoot semi-auto and not abuse a barrel?
          Last edited by NavyDavy; 11-10-2009, 04:30 PM.
          "You won't rise to the occasion - you'll default to your level of training." Barrett Tillman

          "Success is not Final, Failure is not Fatal, it is the Courage to Continue that Counts" Sir Winston Churchill


          Speed is fine, accuracy is final.

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          • Originally posted by NavyDavy View Post
            OK I have a friend who's trying talk me out buying a Colt 6920. I usually don't listen to him but today he told me Colt chrome lined barrels are only good for 15,000 rounds.

            I know nothing about barrel life and would be surprised if I ever shoot 15,000 rounds.

            So what can I expect for barrel life if I only shoot semi-auto and not abuse a barrel?
            Depends on what you define "barrel life". First sign of accuracy degradation? Throat erosion? 15K to 20K is a "good" replacement time.

            Comment


            • Thank you for your response. It's good to see I wasn't making any very basic errors in my thinking or getting bad information. If I could impose just a bit more...

              Originally posted by beavo451 View Post
              The heavier rounds rely on their relatively high velocity, bullet weight, and expansion. Hence the hollow point and ballistic tip designs that are prevalent among the 75-77gr projectiles.
              I wasn't sure about whether expansion would be significant because I had read (perhaps wrongly) that the "open tip" designation of the OTM ammo was not a hollowpoint for expansion purposes per se but was more of a byproduct of the design and manufacture of the match grade projectile.

              I guess I'm left wondering:

              1. Assuming adequate velocity, is the expansion of these heavy bullets very reliable or more of a crap shoot affected by other factors, like layer of clothing?

              2. After starting from a 16" barrel, at VERY ROUGHLY what range does the loss of velocity begin to reduce the reliability of the expansion of these 70+ grain bullets? In other words, are we ditching a light projectile that was limited to 150 yards with enough velocity to get fragmentation because we can count on expansion out of this heavier projectile to 250 yards?

              3. Assuming they either would take place, is there a concensus on whether fragmentation or expansion is considered a more effective stopper?

              What I'm trying to work out is why the move to the heavier (and consequently slower) projectiles and what the downside is (penetration, reliable effectiveness, cost per round). If it was all upside, it would seem like there would have been a migration to the heavy side sooner.

              Comment


              • I don't know the exact answers, but given that LE ammo and military snipers are migrating towards 75gr and 77gr rounds, I would assume that these designs are proven and favored over fragmentation of FMJ rounds.

                Comment


                • Originally posted by NavyDavy View Post
                  OK I have a friend who's trying talk me out buying a Colt 6920. I usually don't listen to him but today he told me Colt chrome lined barrels are only good for 15,000 rounds.

                  I know nothing about barrel life and would be surprised if I ever shoot 15,000 rounds.

                  So what can I expect for barrel life if I only shoot semi-auto and not abuse a barrel?
                  Colt like any manufacturer will give relatively conservative barrel life estimates under generally more extreme use. Therefore 15K rounds is very very relative. If you don't do a lot of select fire and / or rapid fire where you frequently heat up a barrel and if you are good about cleaning and maintenance, than a barrel can go far beyond that factory number. Most average paper punchers or even Officers who may only shoot at qualification times, will more than likely not have an issue.

                  Since there are variables that influence life span of a barrel, the number is not arbitrary but should be looked at as more of a reference. When judging the life left in a barrel, you should be looked more closely as to when accuracy starts to drop beyond an acceptable standard.

                  I will also say that Colt uses very good quality steel, 4150 steel with the mil spec standard B-11595E. ALL of their barrels are MPI/HPT and the chrome lining is also a big plus.
                  The comments made herein are those solely of author and in no way reflect the opinions of any other person, agency or other entity.

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                  • Originally posted by chris falk View Post
                    A slower but heavier bullet (like the oft-reccomended 75 or 77 grain options) should be less affected by the wind and maintain its energy at long distances better than a faster but lighter round (like our old friend, 55 gr.). These are obviously good things. Feel free to chime in with other advantages to the heavier rounds (Given the same bullet, material, shape and caliber, I don't know what the speed/weight trade off means in terms of penetration.).
                    You are correct in your estimation of wind vs weight, also the design / Ballistic Coefficient is a big factor. I also highlighted penetration, as this is a key factor which I will get into below.

                    Originally posted by chris falk View Post
                    Many people claim that the effectiveness of a 5.56 bullet in stopping a threat is tied to impacting the target with a velocity high enough to cause fragmentation of the bullet upon penetration. At least for the military-style bullets associated with the M193 and M855 rounds, it is usually claimed that penetrating the target at a minimum of 2700 fps is necessary to ensure fragmentation.
                    To expand a bit on what Beavo mentioned, there is definitely a line between velocity and the weight of the bullet and at what velocity that it will reliably fragment (bonded rounds aside). We also need to consider that fragmentation is not the only advantage that the round has, but we also need to consider "yaw" and the bullet keyhole and possible tumbling action of the round causing damage, not just the bullet fragmenting into a shotgun effect. The lightweight round at high velocity can also cause the bullet to take some crazy paths of travel through tissue and bone. However we need to back up a moment to address what you mention earlier in penetration. First and foremost penetration is key, not fragmentation. Penetration is always placed before permanent wound cavity. You first need the round to be able to penetrate a sufficient depth to disrupt or destroy the major blood bearing organs / arteries.

                    Originally posted by chris falk View Post
                    With the selection of a 16" (or even shorter) barrel, we take a substanitial reduction in the velocity at which any given weight bullet will leave the barrel (as compared to the same round through a longer barrel). When we couple this with selecting heavier (and correspondingly slower) bullets, we get a further reduction in velocity that looks like you start out below the 2700 fps threshold or drop below it at a relatively short range.
                    Your estimation is not necessarily true here. Much is dependent upon the load used and not necessarily the bullet. I will however say that there does not seem to be a SIGNIFICANT difference in many factory match or LE loads of ammo between a 16" and 20" barrel. Now when you start talking shorter SBR's there is a more of a significant difference.

                    Originally posted by chris falk View Post
                    Do these slower, heavier rounds incorporate some feature that allows RELIABLE fragmentation at a lower speed or do they get their effectiveness through a RELIABLE mechanism other than fragmentation? Otherwise, it would seem that we are migrating to a round that can be more accurately delivered at a longer distance, but doesn't do much when it gets there (and may be so slow, that it doesn't reach its full potential even up close).

                    In other words, if high velocity is needed to get this relatively small round to be effective, why are we choosing a slow round?
                    You are thinking too much along the lines of the bullets ability to fragment. A bullet will also benefit from similar properties no matter what, and penetration will always remain King. A .22 cal bullet through the heart is better than a .308 through a lung. So now you need to consider accuracy and distance into the equation. Also keep in mind that a bullet from 55 to 75 or 77 gr will have relatively similar distances at which fragmentation occours, however relatively long distance effectiveness for accuracy is much different between the rounds. While a .223 may not fragment at 600 yards no matter its weight, the accuracy and terminal effects are much more benefitted from the heavier grain bullet. Of course we need to consider the weapon firing the bullet or more importantly the barrel and twist rate. It is better to over spin a bullet as opposed to under spinning it.

                    So in other words, if you are getting similar benefits or properties out to a certain distance (all beyond CQB distances) say 100 yards as an arbitrary number for fragmentation no matter the weight, why not incorporate a heavier bullet when perhaps its ability to perform at distance is much better. We have not even touched on intermediate barrier performance.
                    The comments made herein are those solely of author and in no way reflect the opinions of any other person, agency or other entity.

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                    • Originally posted by chris falk View Post
                      I guess I'm left wondering:

                      1. Assuming adequate velocity, is the expansion of these heavy bullets very reliable or more of a crap shoot affected by other factors, like layer of clothing?
                      It is hard to discount "outside factors". And because there are so many possible variables or scenarios that can play out, making any kind of accurate estimations or assumptions as to a bullet expansion or fragmentation type of performance, once striking any type of object or intermediate barrier, would be difficult.

                      Originally posted by chris falk View Post
                      2. After starting from a 16" barrel, at VERY ROUGHLY what range does the loss of velocity begin to reduce the reliability of the expansion of these 70+ grain bullets? In other words, are we ditching a light projectile that was limited to 150 yards with enough velocity to get fragmentation because we can count on expansion out of this heavier projectile to 250 yards?
                      Again you need to consider the load of the bullet. As an example in a 75 grain Hornady round you have a few different loads. 2 good LE choices have been the 75gr Hornady TAP FPD and 75gr Hornady TAP T2. While they are both 75gr one produces a muzzle velocity of around 2640 and the other of 2820. Their range for fragmentation out of a 16" barrel would put them at 100y and 165 yards respectively.

                      Originally posted by chris falk View Post
                      3. Assuming they either would take place, is there a concensus on whether fragmentation or expansion is considered a more effective stopper?

                      What I'm trying to work out is why the move to the heavier (and consequently slower) projectiles and what the downside is (penetration, reliable effectiveness, cost per round). If it was all upside, it would seem like there would have been a migration to the heavy side sooner.
                      Penetration comes first, permanent wound cavity comes second. Fragmentation or expansion of any bullet is ideal or a bonus provided that its penetration is in the 12" depth range. You also need to consider at what ranges you anticipate your engagements and what are the rifle set ups that you are running. Then you also need to factor in potential for intermediate barrier penetration (car window glass, car doors etc) and if your goal is a long range precision application or CQB. If precision, you may also want to consider selection of an additional "barrier round" or bonded type of round that can be loaded as needed.
                      The comments made herein are those solely of author and in no way reflect the opinions of any other person, agency or other entity.

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                      • Go read this: http://ammo.ar15.com/project/Self_De...index.htm#.223

                        Then this: http://www.ar15.com/content/page.html?id=185
                        J. Wise

                        AR-15 - AK-47 - NFA Trusts - My Pick - Carry Guns - 1911s

                        "Some say you can tell how the world stands by the prices of AK-47s...." Chit2001

                        Any comments contained herein regarding the legality of firearms, or the application of law, are strictly applicable to Texas. If you live in CA, NY, IL, MA, D.C., etc., the above comments will probably shock you, and should be read for educational purposes only. Most likely nothing I write will apply to you.

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                        Comment


                        • AR guru's, I have a department issued Colt M16A1. As posted above, I was asking about the Colt AR15A3. A team leader from one of our larger SWAT teams here in Indiana suggested that I keep the M16A1, with these modifications, see what you think....

                          Since the A1 is already a registered machine gun, I can mod it however I need to without ATF approval. Since this is a primary entry weapon, he suggested I look at 10.5" to 12.5" barrelled upper receiver. I can reuse the bolt/carrier, however, will need to change the extractor spring and insert to match the now shorter barrel, otherwise I'll get malfunctions.

                          Suggestions for the uppers - 10.5" LMT ($455), or a Bravo Company Manu. upper from Bravo Company USA.

                          Then look at a mil-spec receiver extension and any number of collapsible stocks on the market. After this, I'll need to get an "H" buffer and spring to go with the new stock and barrel.

                          After looking at his suggestions, I'm looking at somewhere in the range of $650 (more for a rear sight system and optics of course). Basically, taken my fully auto Colt A1, put a short barrel on it and have a hell of an entry rifle.

                          What say you one and all????
                          Why are there so many babies on O.com? Creole, you and your buddy JPSO Recruit help me out on this one....

                          * "Preach always, if necessary, use words!" St Francis of Assisi

                          * Luke Chapter 6, Verses 27-36

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                          • Are you going to use it more as a patrol rifle or as an entry?

                            I would stay with a longer barrel to maintain velocity at longer range shots if its a patrol rifle.

                            Thats common knowledge stuff there so I'll let the experts here go deeper.
                            Due to the Juvenile bickering and annoying trolling committed by members of this forum I have started an igore list. If your name is listed below I can't see you.

                            CityCopDC, Fire Moose, Carbonfiberfoot, Damiansolomon

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                            • OK, we earlier talked about "The Chart" and where the Daniel Defense rifles stack up in comparison to others listed. Well here is the latest version of "The Chart". If anyone needs confirmation from a spread sheet in order to confirm what the manufacturer already lists on their site, or what can be seen from visual inspection of the rifle, just look under the "specs" tab at the bottom.

                              "THE CHART"
                              The comments made herein are those solely of author and in no way reflect the opinions of any other person, agency or other entity.

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                              • Originally posted by towncop View Post
                                AR guru's, I have a department issued Colt M16A1. As posted above, I was asking about the Colt AR15A3. A team leader from one of our larger SWAT teams here in Indiana suggested that I keep the M16A1, with these modifications, see what you think....

                                Since the A1 is already a registered machine gun, I can mod it however I need to without ATF approval. Since this is a primary entry weapon, he suggested I look at 10.5" to 12.5" barrelled upper receiver. I can reuse the bolt/carrier, however, will need to change the extractor spring and insert to match the now shorter barrel, otherwise I'll get malfunctions.

                                Suggestions for the uppers - 10.5" LMT ($455), or a Bravo Company Manu. upper from Bravo Company USA.

                                Then look at a mil-spec receiver extension and any number of collapsible stocks on the market. After this, I'll need to get an "H" buffer and spring to go with the new stock and barrel.

                                After looking at his suggestions, I'm looking at somewhere in the range of $650 (more for a rear sight system and optics of course). Basically, taken my fully auto Colt A1, put a short barrel on it and have a hell of an entry rifle.

                                What say you one and all????
                                If it is to be primarily an entry weapon then IMO anything 16" and under is good to go. There is much to be said for even shorter SBR's especially for entry work, but just be aware that as length lessens, weapons manners decrease. Not that it is a huge issue, just be aware an SBR will behave differently than the M16.

                                As for pure conversion and not getting into any dept policy etc on SBR or modifications, yes you can use the M16 bolt carrier group and go with a black insert and spring. As for off the shelf uppers, the LMT and Bravo Company are GTG and will generally have the dust cover and forward assist installed. You could also re-use the charging handle, just depends on what you want to do.

                                As you mention, for the lower if you want a collapsible stock, you will need to do a new buffer tube (receiver extension), buffer and spring. Might want to do a spring change on the lower parts while your at it.

                                $650 sounds reasonable for the bare bones, but as you mention, red dot, BUIS, rail, light, VFG, sling / mounts, grip, stock etc...things start adding up quickly. Because we all know, once you start down the "path", nothing is cheap.
                                The comments made herein are those solely of author and in no way reflect the opinions of any other person, agency or other entity.

                                Surfs Up on youtube!

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