There are getting to be a large family of SIR systems. I don’t pretend to have knowledge of all of them. I will list the ones that I am aware of, what guns they fit, and what makes them different from one another. I’m not really going to go into the advantages of a SIR or similar system, nor the differences between SIR systems and other Free Float rail systems. There is ample discussion about that elsewhere on the board.

Brief SIR family line up;
ARMS #45m and #45c:
Fits standard carbine length flat top uppers. Uninterrupted top rail. Forward section of top rail is removable/reversible and includes a built in PEQ 2 mount

#46c (no M model is available that I know of):
Fits standard carbine length flat top uppers. Slim line design with uninterrupted top rail. Forward section of top rail is removable/reversible and includes a built in PEQ 2 mount. Different from #45 only in that it is slimmer and slightly lighter.

#50m and #50c:
Fits standard carbine length flat top uppers. Slim line design with bi-level top rail. Forward section of top rail is slightly lower to accomidate cowitnessing of optics such as Trijicon Reflex and EoTechs. A separate rail is available to create an uninterrupted top rail similar to a #45 or #46 SIR.

#51c (no M model is available that I know of):
Fits A1/A2 carbine length carry handle uppers. Slim line design with a rail on top of carry handle and see thru channel to maintain use of iron sights. Forward section of top rail is slightly lower to accomidate cowitnessing of optics such as Trijicon Reflex and EoTechs.

#58m (only M model is available that I know of):
Fits mid-length flat top uppers like Armalite carbines. Slim line design with bi-level top rail. Forward section of top rail is slightly lower to accomidate cowitnessing of optics such as Trijicon Reflex and EoTechs. A separate rail is available to create an uninterrupted top rail similar to a #45 or #46 SIR.

#58mod (only M model is available that I know of):
Fits standard carbine length flat top uppers or mid-length flat top uppers like Armalite carbines. Slim line design with bi-level top rail. Forward section of top rail is slightly lower to accomidate cowitnessing of optics such as Trijicon Reflex and EoTechs. A separate rail is available to create an uninterrupted top rail similar to a #45 or #46 SIR.

#59m (only M model is available that I know of):
Fits full gas systems as on a standard 20” barreled gun. With a low enough gas block like a Bushmaste shaved front sight or a Knights Armament low profile gas block, you can put a #59mon a carbine or mid length gas system gun. Slim line design with bi-level top rail. Forward section of top rail is slightly lower to accomidate cowitnessing of optics such as Trijicon Reflex and EoTechs. A separate rail is available to create an uninterrupted top rail similar to a #45 or #46 SIR.

Now that is out of the way, I will concentrate on the newest of the SIR systems, the #58mod. I was fortunate enough to get a hold of one of these new ARMS #58mod systems. When I first got it, I put it on a spare upper I had. I took one look at it and immediately took it off. I didn’t like it, at all…. Sitting on a spare upper that is! I thought to myself, there is no way I am wasting this thing on a spare upper. I immediately went about putting it on my favorite gun. My favorite gun gets all of my favorite gear. And after all, this is, as of now, my favorite SIR system.

Why? Well, you just get a little more. Close to two years ago, I got one of the very first SIR systems to come out (a #45m) and it has been on my favorite gun since then. Mine is so old, it only has one screw on either side of the barrel yolk. All current SIRs have two screws each, and have for some time. Anyway, at the time, I went out and got the M verison. I thought it would mount more securely than the C version. As it turns out, I was mistaken. Both the C and the M mount equally as sturdy.

More than a year later, when the slim line SIRs came out, I sort of scoffed at them at first. I didn’t know what the big deal was and figured I would not care for them any more than the #45 I had already. Then I saw one.  I wanted one bad. I liked the idea of a slimmer, lighter system. I especially liked the bi-level, slim line #50. While I believe the fatter #45 has superior cooling capabilities due to larger area between the barrel and inside of the system, I believe the reduced weight and width of the slim lines in a greater advantage for me and my non-full auto needs than the slightly better air flow you get with the fatter #45s. It would appear as though ARMS agrees. To my knowledge, every single SIR they have made after the #45 has been slimline. Of the SIR systems I am aware of, only the original #45 is not slim line.

However, all the slim line SIR systems were only available in the C model. The rifle I wanted a slim-line SIR for has a 14.5" barrel with a permanently attached Vortex. Taking the Vortex off to re-install the delta ring assembly I removed to install the M model did not appeal to me. So I just left everything alone and made due with the #45.

Enter the #58mod. When I saw that it was an M model, I was stoked. Finally, a slim-line, bi-level SIR that I can drop on my delta ringless rifle. And that’s just what I did. The one problem I ran into was needing to remove the handgaurd cap. The #58mod will not fit over the handgaurd cap and will require removal. All I did to take mine off was get a dremel tool and grind into it until I could peel the piece off. It was easy and took me about 10 minutes. The handgaurd cap is actually quite thin and can probably be ripped off with a set of tin snips.

As previously stated, the #58mod will fit on either a carbine length or mid-length gas systems. When installed on a mid length gas system, the #58mod will extend all the way out to the front sight/gas block. When installed on a standard carbine length ghas system, the #58mod will surround the front sight/gas block, leaving a space at the top for the front sight to poke up. For those mounting to a standard carbine legth system, the extra rail length on coverage of the front sight is the only difference between a #58mod and something like a #50. But this seemingly small difference is what actually makes all the difference and makes it my favorite SIR to date.

The extra rail space on the bottom leaves sufficient room to mount both a forward grip and a Surefire light to the bottom of the gun. Especially 3 cell Surefire lights which are longer and stronger and, IMHO, better matched for the capabilities of the rifle. Other rail systems like #45, 46, 50 SIRs, RAS II and others do not leave what I consider to be sufficient room to mount something like a Dieter grip and a Surefire 3 cell light. I have tried and it is just too crowded under there. The #58mod gives you the space you need to accomplish such a set up. The added bottom rail is also ideal for adding a bi-od, especially with the ARMS throw lever bi-pod attachment. Wes of [url=www.mstn.biz]MSTN[/url] pointed out another benefit of shrouding the front sight while briefly discussing the #58mod. The shroud will protect your legs, especially if wearing shorts, from a hot barrel/front sight/gas block when transitioning from rifle to pistol with a tac sling.

Some folks have compared the #58mod to a Knights Armament MRE. While I do not own a Knights MRE, I believe I am familiar enough with the system to feel confident saying the systems share some similarities, but are distinctly different and unique. The MRE offers [b]M[/b]ore [b]R[/b]eal [b]E[/b]state (more rails) on all sides than the #58mod. Personally I think the MRE looks cooler [;)]. I also like the fact that the MRE does not use the upper receivers flat top rails for installation, and therefore does not raise the height of the mounting surface on your flat top. But the MRE requires the removal of the front sight/gas block for installation. This is the only thing that has kept me from getting one. The rifle I wanted to put one on has a permanently attached Phantom flash suppressor, and the ordeal it would require me to remove the flash suppressor does not seem worth while.

The #58mod does not require the removal of anything except the delta ring and handgaurd cap. Both of which are very inexpensive parts to replace, and can be removed with a dremel tool with minimal skill, in a matter of minutes. Believe me, if I can do it, any one can. The #58mod can also be used on both carbine and mid length gas tube systems unlike the Knights MRE which can only fit on carbine length systems. Despite the fact that the SIR raises the mounting platform of the flat top uppers, they remain my favorite Free Float handgaurd system for a variety of small reasons. While I say this with confidence, I also say it hoping people understand that this is merely my opinion and is in fact, largely an opinion based on personal biases and preferences. If someone were to post a thread saying why they like the FF RAS, RAS II or MRE, I would not argue with them. I like all of those systems as well, own one of them, and plan to buy another.

As always, everything is a compromise and nothing can ever be absolutely perfect (although I think the TA31 ACOG comes damn close!). Having said that, what don’t I like about the #58mod? There are a couple things I would like to see changed or at least available. I would like to see it available in a C model. While in this specific instance, it happened to work out in my favor that the #58mod is an M, I tend to recommend the C model these days. While I think the M models look a little sleeker when installed, and actually reduce the weight of the rifle when fully installed (due to the removal of the delta ring, weld spring and snap cap), installation of the M models require more or less semi-permanent modification to your rifle. As easy as it is to take a delta ring off, it is not as easy to get back on. While weighing ever so slightly more when installed (maybe an ounce), C models are easy drop on and take off items allowing for more modularity and configuration possibilities. I would like to see all SIRs available in both M and C models. While I presume there must be a reason, I freely admit to not knowing the ins and outs of why some systems are only C and some are only M.

I also think the #58mod will look sort of dumb on a mid length gas system gun. There will be a gap between where the top rail ends and where the front sight would be. This gap would leave the gas tube exposed and I think it would just be awkward. What I would like to see is a top rail, similar to those available for the bi-level #50, except made specifically for the #58mod. This optional rail could attach to the rear handgaurd section and then at the front cross pin, except instead of ending at the front cross pin, extend out to the front sight of a mid-length gas systems front sight. I think that would really make the #58mod more useful to a mid-length carbine system owner. As it stands, and unless such a rail is already available, I don’t foresee many mid-length system owners buying the #58mod over the #58.

Folks, I will post pictures later... I am way too tired right now!

Excellent review.  Exstensive.  As I would have expected from NewARGuy.  I second NewARGuy's endorsement of te new #58MOD, like the other SIR systems available.  Awesome FAQ too.

S2

Thanks for the info, Neil.  Great job.

Great review and lot of good info!

I wonder if ARMS will make a front end adapter that will give the SIR 50 a 58-Mod extension?  It doens't look like it would be difficult to do...oh well, just dreaming again.[:D]

Great Review!

and where can I find the review for other system like RASII?

I edited the first post to correct part of the SIR line-up. ARMS recently released a #50 SIR M model. I was told that eventually, all SIR systems would be available in both C and M models.

I did a review of the RAS II back when I first got one. But my search function does not go back that far. I triedto look it up but found nothing. Sorry?

new-arguy,

Thanks anyway!! :)

Alright you just wait until ARMS release SIR 58mod-C! [:D]

I installed the 58M on this Armalite SOF and am very inpressed with it!
[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=18056&iGalleryUnq=1168&iImageUnq=19733[/img]
[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=18056&iGalleryUnq=1168&iImageUnq=19735[/img]
[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=18056&iGalleryUnq=1168&iImageUnq=19739[/img]
[img]http://photos.ar15.com/WS_Content/ImageGallery/Attachments/DownloadAttach.asp?sAccountUnq=18056&iGalleryUnq=1168&iImageUnq=19736[/img]
[img]

Hey Green18,

I'm kinda new and was wondering what model of Sure-Fire that is on this weapon? and who's vertical grip?

Brian

That would be a Surefire M962SU and a Dieter CQD vertical grip.  The Surefire came from Eagle firearms and the CQD grip from the good folks at MSTN  
  I love both of them and the ARMS 58M is a definite keeper!

Thanks,

I gotta get them


Brian

You won't regret it!

^

The 58mod is way cool.  I like the MRE too.  But the one I would really like to see a review of is the Daniels Defense models, like the 9.5FSB or the 12.0FSB.  Anyone with knowledge of this type?  I think a review/roundup of all the beyond-the-front-sight forearms would be of interest to many.  

I think Wes had some pics recently, but so far I am red-exed on those.

link to DD pics:
[url]http://www.danieldefense.com/store/cart.asp?catid=3[/url]

TJ

BTT  Methinks this should be tacked.