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Old 05-15-2013, 08:53 PM   #1
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Default Useful General AR15 information. Now with Pictures and Hyperlinks!

Posting up some links, charts and pictures to commonly asked questions. Hopefully you will all find this as a good reference to help you understand and visualize the concepts better.





Written and produce by Dieselpower@calguns.net
This is chart that shows the ideal twist rate for different types of projectiles for the .223 remington/5.56x45 NATO. This is just a generalization. Its makes the assumption that all projectiles are of solid lead core construction. Twist rates in reality are directly correlated to bullet length not weight. So bullet's of lesser density, like hollow points or lead free hunting bullets will be longer/bigger than bullets of the same weight but higher density materials (like lead). So please use this this chart just as a general guidline.

One more thing, please do not make the assumption that if the twist rate is ideal for the bullets you are using that you can automatically expect sub moa accuracy. Conversely, do not assume that if your twist rate is less than ideal for the bullets you are using, that you can only expect 8 moa accuracy. Twist rates are just one factor of many that must be considered when trying to predict overall accuracy.





Written and produce by Dieselpower@calguns.net
Here is a diagram detailing the differences in how an absolute (100%) cowitness and lower 1/3 cowitness looks. Please not the right hand column: when your back up iron sights are folded down and out of the way, they look identical. The biggest difference is when you have a fixed front sight, the lower 1/3 will give you a larger sight picture as the front sight sits lower and out of the way.

Pay special attention to the two diagrams on the right. See how they look exactly same. This is the way your sight picture will look 99.9% or the time with either method.







Started by Rob_S, and recommended by Quentin, this is chart detailing specs on various AR15. Please note, this was started by Rob_S, he no longer maintains it, it is not up to date, and I do not know if it is the most recent update.

Just use it as a reference guide. One guiding principle you must understand is that "milspec" is just a certain specification that the military has deemed to be important to them. It doesn't necessarily mean that it is the best, nor does it mean its the worst. I recommend using mil spec as a minimum standard. In other words, get at least mil spec, or get better than mil spec if at all possible.

Another way to look at this list, is to see how and why some ARs are cheaper or more expensive than others, and why some brands are considered higher quality. There is a direct correlation in the amount of time and expense invested in testing to the overall quality of the unit produced. Less testing should always mean the unit can be produced faster and cheaper.

Batch testing- while better than no testing, is often considered just barely better than no testing. Simply because if batch testing turns up a defect, you really don't know what the manufacturer's standards and procedures are to fix that mistake. You also don't know if they batch test 1 out or 10 units, or 1 out of 10,000. If a defect is found do they go back and retest the whole batch for defects or just keep on trucking along. If only manufacturers would be more forth coming with testing procedures......

MPI bolt - Magnetic particle Inspection for internal flaws and defects.
HPT bolt - High Pressure Tested Bolt and over pressure round is fired then the bolt is MPI tested to make sure there no defects.
Extractor spring insert -The insert (o ring) is design to help the extractor do its job. There is a lot of debate whether its really needed, but imho every little bit helps.
Properly Staked Gas Key - added insurance to prevent your gas key from coming loose and creating a stoppage. With the proper tools, it would take a manufacturer seconds to do this.
Bolt Carrier Style. M16 Full Auto carriers are heavier, and have a protective shroud which protects the firing pin as the BCG cycles out of battery and resets the hammer. AR15 semi auto style is light and usually does not have the protective shroud, tho some hybrid carriers do have it. For all intents and purposes a civilian semi auto AR15 will do fine with either type of carrier, tho many people prefer M16 FA for the aforementioned attributes. Use of the M16 FA carrier, cannot and will not make your AR full auto.





Barrel Length and Velocities for 5.56 Nato M193 and M855
A great chart showing the different velocities from different barrel length and types of Nato ammunition. Use it as a general guide, some variables not taken into account are environmental factors (ie altitude and temp etc), mechanical factors (button rifling vs polygonal, semi auto with a gas port, bolt action no gas port) and finally differences in ammo manufacturing.





Basic trajectory curve--Ballistics of the 5.56x45 NATO
This link shows the ballistics of M193 55gr FMJ and M855 62gr FMJ and goes into depth the differences between 25, 36, 50, and 100 yard zeros. It is very well written and objective, and has lots of pretty charts and graphs. This link sends you to M4carbine.net and was written by Molon dated 9/30/10. Please bear in mind that the charts do not take into account for different barrel lengths, ie 14.5, 16, 18 or 20 inches, as the added velocities of the longer barrel lengths will change ballistics and zero distances. This is a heavy read, but very indepth and chock full of valuable information.





Aftermarket Trigger Review #1
A great read, with lots of great information about the people behind all the aftermarket triggers, and the differences between the models. Truly a read for the gun geeks in most of us.





Aftermarket Trigger Review #2
Very nice and objective review of some of the lighter aftermarket triggers available. There a review of a milspec LWRC coated trigger. Most reviewed are 2-4# target/competition type triggers. Pretty pictures, objective review, hard numbers. Very well useful imho.





Tactical Yellow Visor's Rob_S' *Handguard charts
Not complete or comprehensive but a very nice chart to reference different dimensions, weights and prices of various FF handguards. *Lots of work and research went into it!

AR15 various weights
Great thread with various configs and weights.



If anyone else has some suggestions or would like to add stuff to this post, please do so. Or if a mod would like to add this info to my other thread, Please do so at you discretion (I can no longer modify my AR15 primer thread since its been so long.)

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Old 05-15-2013, 09:36 PM   #2
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This shows where you zero at and what distance it crosses back over at , I prefer a 35 yard zero this crosses back over at 200 and is only -6.5" low at 300

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Old 05-15-2013, 09:50 PM   #3
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My Hera Arms 15th Dynamic is 1/7 twist. Gun is wicked accurate with 55 grain Bellot and Sellier in both hard and soft tip (hunting). The rifle is designed for the competition circuit, and really shines with heavier rounds.

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Old 05-15-2013, 10:10 PM   #4
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They are packaged as Sellier & Bellot over here.

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Old 05-15-2013, 10:30 PM   #5
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Great info so far. Thanks.

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Old 05-15-2013, 10:35 PM   #6
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Oh where oh where did I put my copy of The Chart!

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Old 05-15-2013, 10:43 PM   #7
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Thanks Tikki! Great information!

I would also like to add as Jagermeister made mention! Guns are like people! I always state they have personalities!
This due to slight variations in metallurgy, parts and the individual manufacture of that particular rifle.
I have had two RRA 20" Varmint Rifles that both have shot 1/4 MOA 5 Shot Groups with 55 Grain Bullets in a 1:8 Twist. And a friend of mine shoots 40 grain ultra varmint loads in his 1:8 twist and it is extremely accurate? So although the charts are excellent and very informative and are the general rule there are exceptions! Also to shoot the 80 grain bullets and heavier they must be loaded one at a time since they are too long to function in the standard AR Magazine. I can not remember who manufactures them but there is a solid mag that you can load one at a time. It is solid and has no spring or moving follower. The general rule the heavier the projectile (Grain) the faster the twist for maximum performance!

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Old 05-15-2013, 11:33 PM   #8
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Yes, IIRC Purehavoc had 2 1x7 barrels, both from PSA, I think both were CHF (FN made) that he bought within weeks of one another. One liked 55gr, and the other didn't. Hope he chimes in.........

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Old 05-16-2013, 12:05 AM   #9
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Quote:
Originally Posted by AgentTikki View Post
Yes, IIRC Purehavoc had 2 1x7 barrels, both from PSA, I think both were CHF (FN made) that he bought within weeks of one another. One liked 55gr, and the other didn't. Hope he chimes in.........
Pretty close both were FN made barrels one was dead nutz with 55 gr 1moa or less the other was 3moa+ with 55 gr , put 62 gr fmjs in and its back to 1moa. Crazy I know and it had me stumped until I got a couple boxes of 62 gr figured it out . My 1:9 savage bolt gun shoots 1/2 moa with cheap remington umcs my buddy built me some of his prescription hand loads and it will clover leaf multi rounds all day long. You just have to find what works best in your gun because a identical guns may not even be close to the same liking
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Old 05-16-2013, 12:11 AM   #10
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My buddy got ahold of a non cl dpms barrel 1:9 @ 50 yards " max range at his place " I can repeat hole in hole or close to it shots with cheap wolf . I would like to have his barrel I was pretty impressed with its accuracy for being a dpms and crap ammo ,which I believe are wilson made barrels

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