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Posted: 1/24/2012 6:54:16 AM EDT
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Hey all this is my first post,I think this site is awsome!
I have been looking at building a ar15 pistol and noticed some lowers are marked multi caliber,is this the way to go and will the mags fit tight on the sides no matter what caliber is used or will there be a slight built in "over size" or possible air gap on the sides of the mags. or any other built in over size anywhere for the larger caliber rounds? Also when useing iron sites and installing a red dot site to" site in the red dot",,",cant you just look thru the irons and see the red dot sitting atop the front site post"? Will i save much money by building myself?Any brands you recommend? |
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I am new here as well but I can answer the sight question. In a perfect world yes you could. That set up would be Absolute Co-witness. There is so much controversy about what the terms "co-witness", "absolute co-witness" and every variation of the two. Here is how I see it.
Absolute Co-witness is when your iron sights (BUIS) and your red dot are aligned together and at POA/POI. This is possible depending on how you set up your optics. Some optic set ups will not work and you are looking at your BUIS being in the lower 1/3 of your optic picture. That can be called Lower 1/3 co-witness. Co-witness is when you can utilize your BUIS in your optic picture, but they are not necessarily at thesame exact point. Many people do not have "absolute" ability so they say "my iron sights are where they are, and my red dot is where it is." Confused, sorry. Every answer wil probably be different, but that is my take on it. Hope it helps. On the multical, I assume that as long as you are using a standard AR Mag that is modified to accept a different caliber it should "seat" just as designed. I am a 5.56 guy so I an not even sure how they set up mags for the different calibers. |
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The CAL-MULTI are the same dimensionally as any other AR15 lower. The AR10/AR308 is what gets the bigger mag well. They are just stamped that way in case you want to do a 300BLK, 6.8, etc, etc. The actual caliber marking in these cases is usually on the barrel.
Most people do a lower 1/3 cowitness, so the dot isn't obstructed by the front post. It puts the irons 1/3 the way up from the bottom. What you can do, assuming the irons are sighted is put a piece of painters tape on the wall, and prop the gun on a table. Line up the tape dot with your irons, then without moving the gun adjust the red-dot so it is also centered on the tape dot. This will get you pretty close, but you will probably still need a little fine tuning at the range for a real sight-in. You might save a couple of bucks building yourself, assuming you have all the punches, vices, etc you need. I always recommend receiver and barrel blocks so you can clamp it into a vise, and a set of headspace gauges, to make sure it is safe to shoot. Buying the tools might actually make it more expensive. If you have a set of punches, and basic tools, I usually recommend people build their lower and buy a complete upper for their first rifle. You don't need all of the specialty tools that way, and you know the upper is safe and reliable. The upper is where safety, gassing issues (under/over) and proper alignment of the gas tube are an issue. Check out Palmetto State Armory. They sell individual parts, complete uppers, stripped lowers, lower parts kits, lower build kits, and even full gun build kits. Would give you many options to choose from. |
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Quoted: I'm not following your explanation of co-witness, absolute, and lower 1/3, but it seems like your answer is wrong or maybe your just not explaining it right.I am new here as well but I can answer the sight question. In a perfect world yes you could. That set up would be Absolute Co-witness. There is so much controversy about what the terms "co-witness", "absolute co-witness" and every variation of the two. Here is how I see it. Absolute Co-witness is when your iron sights (BUIS) and your red dot are aligned together and at POA/POI. This is possible depending on how you set up your optics. Some optic set ups will not work and you are looking at your BUIS being in the lower 1/3 of your optic picture. That can be called Lower 1/3 co-witness. Co-witness is when you can utilize your BUIS in your optic picture, but they are not necessarily at thesame exact point. Many people do not have "absolute" ability so they say "my iron sights are where they are, and my red dot is where it is." Confused, sorry. Every answer wil probably be different, but that is my take on it. Hope it helps. On the multical, I assume that as long as you are using a standard AR Mag that is modified to accept a different caliber it should "seat" just as designed. I am a 5.56 guy so I an not even sure how they set up mags for the different calibers. Co-witnessing is the act of sighting through both your optic and iron sights. When both sights are zeroed the same then the dot, in the case of a RDS, will sit right on top of your front post. Absolute co-witness is when you are looking through your iron sights and the sight picture is centered in the optic. Again if the two sights are zeroed to the same distance, the dot will sit on top on the front post. Lower 1/3 co-witness is when you are looking through your iron sights and the sight picture is in the lower 1/3 of the optic. As in the above cases, the dot will sit on the top on the front post. The good thing about this setup is when your not co-witnessing, the field of view in the optic window is clutter free. The thing to remember is there is no reason to co-witness at all with a red dot. That's the whole point of the dot. nothing to line up, no cheek weld to worry about, hell you don't even need to be directly behind the firearm. As long as you can see the dot and the target, simply place the dot on your target and bang. If the dot fails then go to the irons, hence the name BUIS, Back Up Iron Sight Edit to answer the OP's question. Yes, as long as your iron sights are zeroed you can pop a RDS on and adjust the dot to sit on top of the post while your looking through your irons. This will get it very close, you should still make final zeroing at the range using just the dot. The only reason I co-witness is to verify that my optic is still zeroed when I take it out of the bag, or after rough handling or accidental banging, dropping, throwing down a driveway.....(you'll understand this after spending some time here on ARFCOM) As far as multi cal, don't worry about it. There is probably in the area of 85 or so calibers that are capable of utilizing the AR lower. Some people don't like their lower saying .223 or 5.56 on their .50 or .300 or .270 or 9mm or .45 or....... |
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I am sticking to my story.
Co-witness: Just being able to use your BUIS through your optics. Abs Co-witness: Red dot and BUIS are aligned to the same point in the optics. (my red dot is never anywhere but the center of my optics so yes they will both be in the center) Lower 1/3: Your BUIS is in the lower 1/3 of your optics due to a riser or higher mount for your optics. I have a firend whose Buis are slightly to the left of center and lower so you could say he has: lower 1/3 left quadrant co-witness, but that is ridiculous it is just co-witness. Like I said, you look at ten different websites you will get 10 different answers. |
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Quoted: You can stick to your story all you want as long as you keep it to yourself, this is a tech forum and not a place to spread mis-information.I am sticking to my story. Co-witness: Just being able to use your BUIS through your optics. Abs Co-witness: Red dot and BUIS are aligned to the same point in the optics. (my red dot is never anywhere but the center of my optics so yes they will both be in the center) Lower 1/3: Your BUIS is in the lower 1/3 of your optics due to a riser or higher mount for your optics. I have a firend whose Buis are slightly to the left of center and lower so you could say he has: lower 1/3 left quadrant co-witness, but that is ridiculous it is just co-witness. Like I said, you look at ten different websites you will get 10 different answers. Regardless of "absolute" or lower 1/3, when properly sighted in the dot will sit on top of the front post. |
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Quoted:
I am sticking to my story. Co-witness: Just being able to use your BUIS through your optics. Abs Co-witness: Red dot and BUIS are aligned to the same point in the optics. (my red dot is never anywhere but the center of my optics so yes they will both be in the center) Lower 1/3: Your BUIS is in the lower 1/3 of your optics due to a riser or higher mount for your optics. I have a firend whose Buis are slightly to the left of center and lower so you could say he has: lower 1/3 left quadrant co-witness, but that is ridiculous it is just co-witness. Like I said, you look at ten different websites you will get 10 different answers. Except that 9 of those answers will be wrong, because in this case the correct answer has been posted already. |
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Perhaps this will help you better understand.
http://www.weaponevolution.com/forum/showthread.php?2497-UNDERSTANDING-CO-WITNESS |
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The "multi" caliber lowers have nothing to do with what magazines will fit as they are all dimensionally the same. The only true 'multi-caliber' lowers are the Hydra models made by MGI as the magazine wells are interchangeable within the limited range of the calibers they offer. Federal regulations require that the 'firearm' has to be engraved with the manufacturer's identification, a serial number, and the caliber. "Multi" has met that requirement for some time. People making short-barreled rifles were able to list that on their Forms 1 for a long time, but the ATF NFA Branch has now ruled that invalid; you have to pick a caliber. Since AR uppers are largely interchangeable, I think the use of that marking was a marketing thing, much like the use of "pistol" on some lowers. You could put any caliber upper on the lower that you wanted and that is what you would shoot. But for matters of records and transfers, something had to be there.
I have a couple of the "multi" marked lowers, but my .50 Beowulf pistol is built on one marked 5.56mm. Makes no difference. |
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