A3 vs A4 upper

[spryan]

Please excuse my ignorance, but what are the differences between A3 and A4 uppers.

spryan

 

[sparrow]

Please excuse my ignorance, but what are the differences between A3 and A4 uppers.

spryan

Both are flat top, most A3 upper do not have the M4 feed ramp cuts, also there is a deck height difference on the flattop that requires the use of different FSB. For instance the 6920 series is A4 with a F marked FSB, if you take the carry handle from a Colt and apply it to a A3 Bushmaster you will have difficulty in obtaining a zero, there is a different post you can use that is taller. The are other technical specifications but those are the only ones that matter to most of us.

 

[spryan]

OK, thanks for the input, so If I wanted to change my A2 upper on a Colt HBAR AR-15 A2, to a flat top for mounting a Elcan, I should use a A3 or A4, or does it matter?

spryan

 

[sparrow]

OK, thanks for the input, so If I wanted to change my A2 upper on a Colt HBAR AR-15 A2, to a flat top for mounting a Elcan, I should use a A3 or A4, or does it matter?

spryan

You HBAR uses an A2 FSB, for most intensive purposes it will not matter what you go with as there will be a quick remedy if you use a carry handle, but I would use a A3 to make life easier.

Ray

 

[spryan]

Thanks, thats what I really needed to know, I understand I need a large to small adapter pin as well.

regards,

spryan

 

[sparrow]

Thanks, thats what I really needed to know, I understand I need a large to small adapter pin as well.

regards,

spryan

The adapter pin is a $10.00 part, or you could just get a Daniel Defence flattop upper from Wolverine which has a large front pivot hole so you could just use the factory two screw method.

 

[RifleDude]

Please excuse my ignorance, but what are the differences between A3 and A4 uppers.

spryan

I'm no expert on this, but isn't it an A3 or M4 upper? The main difference being that the A3 has the older feed ramps and the M4 has the modified feed ramps. All else being the same for the upper receiver. If this is not so, please set me straight

 

[BattleRife]

Both are flat top, most A3 upper do not have the M4 feed ramp cuts, also there is a deck height difference on the flattop that requires the use of different FSB. For instance the 6920 series is A4 with a F marked FSB, if you take the carry handle from a Colt and apply it to a A3 Bushmaster you will have difficulty in obtaining a zero, there is a different post you can use that is taller. The are other technical specifications but those are the only ones that matter to most of us.

???WTFAYTA???

There is no difference between A3 and A4 uppers. They are the same thing with different names.

The problem comes about because the last AR-15 to use a fixed-handle upper was the AR-15A2, but the last US rifle to use a fixed-handle upper was the M16A3.

When the flat top uppers came along, some manufacturers chose to use A3, because that was the next number in the AR-15 series, while others chose the A4 designation because it jived with what the US military was calling their flat tops.

Whether or not the upper has RAS markings, M4 feed cuts or what have you has much more to do with who made it and when than it does with what they are calling it. Best to clarify all these details explicity rather than interpreting them based on a meaningless name.