This is my review of the MFI diopter sight/rail for the Sig 556.
Disclosure: MFI gives a small cash payment for posting a review on a major forum, in this case $25. This did not influence my impression at all, and I intended to post a review before I found this out. I admit to a previous bias towards liking this product, as I was obsessed with my Sig 556 and was on MFI's original mailing list before this product even went into production, way back in 2008.
That being said, why did I wait until 2023 to buy it? I eventually became disillusioned with Sig USA's repeated blunders and poor quality control, and fell out of love with my 556 for a number of years. I have one of the earlier models that came with the fishgill handguards and the terrible flip-up "nail file" rear sight that's begging to get accidentally broken off. Too many questionable design decisions made me become resentful of how much I'd have to continue spending to make it look like a 550-series instead of a bastardized AR that they tried to make in a failed attempt to appeal to the burgeoning AR market. Then Sig USA gave up on their own 556 line altogether, and so did I for awhile.
My rifle has always been very reliable, never misfeeding any ammo I've tried in it. But it sat in the safe for years. I finally took it out to the range a few months ago with the intention of making a final decision: spend some money to make it what I wanted it to be, or just sell it off. I decided it deserved to be what it should have been, and I didn't want to give up a now out-of-production 550-series rifle that takes AR mags AND still has the ability to take any AR stock if I so choose in the future.
I had long ago put classic-style handguards on it. So I bought an AGP 556 folding stock that looks close enough to the 550-series stock, and I ordered the MFI diopter with fiber-optic inserts. The MFI hooded front sight will be ordered as soon as it's back in stock.
This product did not disappoint. At all. It's beautifully crafted. The care and attention to detail that went into its design is obvious. It gave new life to a rifle I was considering getting rid of, and it truly looks like it was supposed to be there all along.
I've corresponded with Michael Frost of MFI a few times over the years. Despite being obviously busy, he's quick to reply and customer service is a top priority.
Installation is a drop-in replacement and takes only a few minutes, a driver, and a few dabs of blue loctite on the threads. It took more time to ensure I didn't lose any pieces from the OEM sight while taking it apart than it did to install the upgrade. The rail itself is obviously better machined than my OEM rail, and the color looks better than the sloppy paint job Sig USA did. The diopter turns easily and the detents click satisfyingly into place. The optional fiber-optic inserts pick up light nicely. You could even drill the holes out and insert tritium if you wanted to go to the trouble.
Cons:
May interfere with some optics (much more so if you get the hooded vs non-hooded front sight)
Price is really the only significant downside here.
That being said, it is not overpriced for what you get. At the time of this writing in 2023, the full set of diopter rail and front hooded sight (both with fiber-optic inserts) is listed at $245. When first offered, it was quite a bit higher than that due to lower-volume production. AR guys are accustomed to seeing a set of good back-up iron sights costing between $100-$200, and those don't include the cost of a rail. The fact that I had to spend that much to make my rifle what Sig USA should have made it in the first place irks me greatly, but I do not regret the purchase.
Pros:
High build quality
Looks amazing
Faithful to the 550-series aesthetic
Disclosure: MFI gives a small cash payment for posting a review on a major forum, in this case $25. This did not influence my impression at all, and I intended to post a review before I found this out. I admit to a previous bias towards liking this product, as I was obsessed with my Sig 556 and was on MFI's original mailing list before this product even went into production, way back in 2008.
That being said, why did I wait until 2023 to buy it? I eventually became disillusioned with Sig USA's repeated blunders and poor quality control, and fell out of love with my 556 for a number of years. I have one of the earlier models that came with the fishgill handguards and the terrible flip-up "nail file" rear sight that's begging to get accidentally broken off. Too many questionable design decisions made me become resentful of how much I'd have to continue spending to make it look like a 550-series instead of a bastardized AR that they tried to make in a failed attempt to appeal to the burgeoning AR market. Then Sig USA gave up on their own 556 line altogether, and so did I for awhile.
My rifle has always been very reliable, never misfeeding any ammo I've tried in it. But it sat in the safe for years. I finally took it out to the range a few months ago with the intention of making a final decision: spend some money to make it what I wanted it to be, or just sell it off. I decided it deserved to be what it should have been, and I didn't want to give up a now out-of-production 550-series rifle that takes AR mags AND still has the ability to take any AR stock if I so choose in the future.
I had long ago put classic-style handguards on it. So I bought an AGP 556 folding stock that looks close enough to the 550-series stock, and I ordered the MFI diopter with fiber-optic inserts. The MFI hooded front sight will be ordered as soon as it's back in stock.
This product did not disappoint. At all. It's beautifully crafted. The care and attention to detail that went into its design is obvious. It gave new life to a rifle I was considering getting rid of, and it truly looks like it was supposed to be there all along.
I've corresponded with Michael Frost of MFI a few times over the years. Despite being obviously busy, he's quick to reply and customer service is a top priority.
Installation is a drop-in replacement and takes only a few minutes, a driver, and a few dabs of blue loctite on the threads. It took more time to ensure I didn't lose any pieces from the OEM sight while taking it apart than it did to install the upgrade. The rail itself is obviously better machined than my OEM rail, and the color looks better than the sloppy paint job Sig USA did. The diopter turns easily and the detents click satisfyingly into place. The optional fiber-optic inserts pick up light nicely. You could even drill the holes out and insert tritium if you wanted to go to the trouble.
Cons:
May interfere with some optics (much more so if you get the hooded vs non-hooded front sight)
Price is really the only significant downside here.
That being said, it is not overpriced for what you get. At the time of this writing in 2023, the full set of diopter rail and front hooded sight (both with fiber-optic inserts) is listed at $245. When first offered, it was quite a bit higher than that due to lower-volume production. AR guys are accustomed to seeing a set of good back-up iron sights costing between $100-$200, and those don't include the cost of a rail. The fact that I had to spend that much to make my rifle what Sig USA should have made it in the first place irks me greatly, but I do not regret the purchase.
Pros:
High build quality
Looks amazing
Faithful to the 550-series aesthetic
