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Posted: 2/15/2015 1:32:14 AM EDT
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I've decided that 2015 is the year I build my AR. There are a lot of lowers to choose from, and I noticed that some are marketed as "Multi-caliber".
Is there a significant difference between these and the .223/5.56 lowers? Is there any potential downside to using a multi? Secondary: Regarding finger guards - why are interchangeable finger guards the standard? Seems like it would be simpler to make lowers with an integrated guard, and the interchangeable ones would be the exception! Aside from just needing a more open trigger for gloves, this seems like a primarily cosmetic choice... weird. Tertiary: Is 'co-witness' a real concern? I feel like the correct way to sight in a rifle would be to zero each sighting system independent of the other, whereas 'co-witness' makes it sound like they are all lined up the same to the exact same POA? Maybe I'm over-thinking this... |
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Is there a significant difference between these and the .223/5.56 lowers?
No Is there any potential downside to using a multi? Aesthetics  Usually if I have the money I'll spend the extra coin to get a lower that's marked to match the caliber of my upper. Tactical Machining for one has a pretty good selection of different caliber roll marks. Only common one they're missing is 6.5 Grendel.
Secondary: Regarding finger guards - why are interchangeable finger guards the standard? Seems like it would be simpler to make lowers with an integrated guard, and the interchangeable ones would be the exception! Aside from just needing a more open trigger for gloves, this seems like a primarily cosmetic choice... weird. I guess because that's what the military uses, so when AR's started getting marketed to civilians the finger guard design went with it. You can get lowers with or without integrated finger guards so just get whatever suits you. Like caliber designation on the lower, it's just cosmetic unless you need more room for shooting with gloves on. |
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Good to know, Glockr, thanks!
While I'm thinking aloud, I handled a few forged lowers at my LGS yesterday, and I noticed that the markings on some were set up like a Select-Fire weapon even though it was clearly not compatible with that kind of fire control group. Which means it's totally cosmetic. It strikes me as pretentious. It's annoying to me, even though I acknowledge that looks will be a primary deciding factor in several of the choices I make as I'm building my rifle. |
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Quoted:
Tertiary: Is 'co-witness' a real concern? I feel like the correct way to sight in a rifle would be to zero each sighting system independent of the other, whereas 'co-witness' makes it sound like they are all lined up the same to the exact same POA? Maybe I'm over-thinking this... Assumming the same zero for the optic and iron sight (a good thing), they should have the same point of aim. Their independence should be confirmed by firing actual groups, one using the optic and another using the iron sights. |
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Quoted:
While I'm thinking aloud, I handled a few forged lowers at my LGS yesterday, and I noticed that the markings on some were set up like a Select-Fire weapon even though it was clearly not compatible with that kind of fire control group. Which means it's totally cosmetic. It strikes me as pretentious. It's annoying to me, even though I acknowledge that looks will be a primary deciding factor in several of the choices I make as I'm building my rifle. Plenty of lowers to match your needs. Technically, it would only be pretentious of the manufacturer if the lower was incapable of hosting an auto-sear, itself a registered NFA item. |
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Quoted:
Good to know, Glockr, thanks! While I'm thinking aloud, I handled a few forged lowers at my LGS yesterday, and I noticed that the markings on some were set up like a Select-Fire weapon even though it was clearly not compatible with that kind of fire control group. Which means it's totally cosmetic. It strikes me as pretentious. It's annoying to me, even though I acknowledge that looks will be a primary deciding factor in several of the choices I make as I'm building my rifle. Not so long ago you'd be right, but there are a couple of FCGs out there these days that have a "3rd position" that allows for a more rapid firing without going full rock and roll. Honestly though you can't see those markings from behind the sights, which is the happiest place to be when referencing the view of an AR. |
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Quoted:
I've decided that 2015 is the year I build my AR. There are a lot of lowers to choose from, and I noticed that some are marketed as "Multi-caliber". Is there a significant difference between these and the .223/5.56 lowers? Welcome to the world of the AR! In most cases, there is no different between forged lowers. In fact, they are all made by probably 5-6 different companies who then stamp them according to the final manufacturers spec. As long as you’re not dealing with an odd caliber that requires a differently sized lower, all forged 5.56mm/.223 lowers will be the same. Quoted:
Is there any potential downside to using a multi? No. Quoted:
Secondary: Regarding finger guards - why are interchangeable finger guards the standard? Seems like it would be simpler to make lowers with an integrated guard, and the interchangeable ones would be the exception! Aside from just needing a more open trigger for gloves, this seems like a primarily cosmetic choice... weird. As someone mentioned above, it’s because that’s what the military uses. A lot of things in the AR world can be explained by the fact that this was originally a military-only weapon. If the military specifications called for something, or it got approved that way, that’s the way we civvies get it too. That said, the term “mil-spec” is bandied about far too much. Just remember that just because it’s “mil-spec” does not mean it’s the best, just that it’s been built to a consistent standard and will work with other “mil-spec” parts. Quoted:
Tertiary: Is 'co-witness' a real concern? I feel like the correct way to sight in a rifle would be to zero each sighting system independent of the other, whereas 'co-witness' makes it sound like they are all lined up the same to the exact same POA? Maybe I'm over-thinking this... All non-magnified sighting systems co-witness to some degree. Most people zero each one separately. I have an Aimpoint PRO that is a lower 1/3 co-witness. I zeroed the BUIS first, then put the PRO on and zeroed it. POA is the same, and since they’re both zeroed at the same range, POI is the same as well. That’s assuming I do my part of course! 
Quoted:
While I'm thinking aloud, I handled a few forged lowers at my LGS yesterday, and I noticed that the markings on some were set up like a Select-Fire weapon even though it was clearly not compatible with that kind of fire control group. Which means it's totally cosmetic. It strikes me as pretentious. It's annoying to me, even though I acknowledge that looks will be a primary deciding factor in several of the choices I make as I'm building my rifle. See my comments on “mil-spec” above. The AR-15/M16/M4 platform is originally a full-auto gun, so most of the parts reflect that. Doesn’t bother me. YMMV though. ETA: I should clarify this last point. I mean most non-functioning elements of the full-auto feature are maintained. The sear or whatever that actually makes the gun FA is illegal unless you have the necessary paperwork. But most companies leave the FA marking on the lower. Why? Guess folks think it's cool and it usually doesn't bother anyone. |
The mil-spec (label) says that it is built to "these" standards of tolerances and dimensions. Stay with an Aluminum (Forged or cast) lower and you will be fine. (NO POLYMER)
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Quoted:While I'm thinking aloud, I handled a few forged lowers at my LGS yesterday, and I noticed that the markings on some were set up like a Select-Fire weapon even though it was clearly not compatible with that kind of fire control group. Which means it's totally cosmetic. It strikes me as pretentious. It's annoying to me, even though I acknowledge that looks will be a primary deciding factor in several of the choices I make as I'm building my rifle. It annoys me too. I equate it to someone putting a turbo badge on a non turbo car... you're not fooling anyone... |
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