Is the bottom rail of the #58 Mod 2 levels or just one? How about the top? Is it bi-level like the #50? Thanks.

bottom 1 top 2 like the 50.

The auxillery top rail from the #50 also interchanges with the #58MOD, if you want to make either one a straight rail.
Good shootin, Jack

I think I found about the answer to my own question. below is a link to another thread that showed a close up of the #58 Mod. The bottom rails are bi level, or at least, that's what it looks like in the pic :)

http://www.ar15.com/forums/topic.html?b=3&f=12&t=176082

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19737[/img]
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19735[/img]
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19739[/img]

green18, thanks for the pics. That's the SIR #50 , right? Can the bottom rails of the SIrs be adjusted back and forth? I think I saw some on the internet with the bottom rails starting further back.

The bottom rails, side rails are put where ever you want them. Gree18 is showing a pic of a 58MOD.
Jack

...SIR #58...

I think I'm missing something here. Isn't the #58 Mod supposed to have a cut in the front part of the top rail to accomodate the front sight? The first pic is the top view, right? The second is the bottom view which still shows the handguard cap which I've read should be removed when installing the #58Mod. If I understand correctly, the first 2 pics is the #50 SIR. What I cannot understand is the third pic which shows that it is an M version which the #50 SIR is not. Please tell me what I am missing. I still new and want to learn especially that I am hoping to get a SIR also. Thanks :)

Yes, both std. front sights and PRI FUFS will fit well.



Yes, top view, but of a #58, not #58MOD.


Correct.



No, its the #58 for midlenth systems, the extra aluminum at the front sight is the giveaway, the #50C orM has just the Polymer/synthetic lower handguard.



The #50 is now available in an M version.



A pleasure.



The bottom of the #58 mid length, and the #58MOD are bilevel top and bottom.  The bottom rail, on the aluminum extension is 1 level, the removable/re-positionable 1913 rail attaches to the synthetic lower handguard, and/or the aluminum extension.  Maknig 2 heights possible, hope it helps.

/S2

Thank you for explaining and helping me out. Playing catch up is a hard thing to do :) I know now that it is the #58 M version. I still don't understand the "extra aluminum at the front sight" though.

By the way, if I do not install the removable/re-positionable 1913 rail, can I still use the whole lenght of the bottom rail? This may sound like a joke but I still haven't actually seen a SIR. Just pics :)

Lastly, I have an M4 and I'm trying to determine what is the best SIR for me. I thought about the #58 Mod but I don't like the fact that I have to remove the delta ring and the handguard cap. Even if a C version will eventually come out, I still don't like the idea of removing the handguard cap. This leaves me with only 3 C version choices: #45, #46 and #50. I have an Aimpoint with 22M68 mount right now. My dream machine is to add the OTAL and the Surefire M900. Can you suggest what SIR I should get? Sorry for the long post but I would really appreciate your input. Thanks.

dgo7,

By looking at the gear you will be mounting and seeing that you don't want to mess with the delta ring or the handguard cap and I would go with the SIR 50c.

In your case you can mount the Aimpoint with the 22M68 at the end of the high rail right before the step down, your OTAL(IIRC, the OTAL has a built in Picatinny Rail mount.)can be mounted on the lower 12 o'clock rail and your M900a will be mounted on the 6 o'clock rail.

As mentioned above, the 50 can also be fitted with a add-on rail to bring the stepped down foward rail to the same level as the high rail in essense turning it into a SIR 46.  You will be saving a bit of weight with the #50 compared to the #46 if you don't need this rail.

IMHO, there's no reason to go with the #45 now that the slimline #46 is available.  The only reason I would go with the #46 would be if you will be mounting a AN/PEQ style aiming device mand need a built in 12 o'clock mount such as the #46 has.

Hope this helps![8D]

Agreed, 100%. Yojimbo's #50C:

[img]http://www.hunt101.com/img/083199-big.JPG[/img]



Again I'd agree, but would add, that the #45, gets a slight nod over the #46 in a slight increase in the ability to dissipate heat better, but that would only be a significant advantage in a FA settup.  Having said that, I'd go w/ a #46, even on a FA settup as multiple mag dumps aren't a concern, and if it ever was, just getting through it alive would be the main concern.

The lowest aluminum rail on the extra aluminum spacer at the front of the #58 and #58 MOD is lower than the ht. of the 1913 add on rail on the synthetic, so w/o the add on rail, you would only have a 2" portion of 1913 rail, on that aluminum spacer forward of the synthetic handguard.  The add on can go on the AL spacer and the synthetic and will mount at the same height 1 level, or on just the synthetic bi-level. But, w/o it, at all, you have only a 2" section of rail on the Al. spacer.  That's one reason I like the #58 and #58MOD, you can use the 2" lowere rail for lights and still have a std. CAR length forearm to use, or use a short add on rail for a Fwd. PG.

The original SIRs were std. CAR gas system length (see the #50C above).  Due to requests for a mid-length gas system SIR ARMS developed the #58 (pic'd below).  And used a 2" aluminum extension in front of the std. CAR forearm to bridge the gap created by the longer distance between the front of the receiver and the ffront sight assy./gas block.  Later at a gov't trial they had a #58 cut to fit around the front sight assembly of the AR/M16, to create a MRE type settup.  It occured to them what a unique settup they had, but needed to re-work the #58 as they needed the front rail pivot pin assy, moved rearward instead of cut-off and needed to enlarge the opening on the experimental one to facilitate the use of the PRI FUFS.  So the #58MOD was born.

Green18's mid length/#58M from a different angle:
[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19738[/img]

The 2" aluminum extension is visible below just in front of the synthetic (drker) handguard.

And a #58MOD on a Std. CAR length gas sysytem upper.
You can see the bi-level nature of the lower rail on the #58MOD
And the front rail in the lower pic. is the same one used to level the #50C/M bi-level or forward rail. It works on #s 58MOD and #50.

[url="http://www.hunt101.com/?p=72430&c=500&z=1"][img]http://www.hunt101.com/img/072430.jpg[/img][/url]

On the MOD model, the front rail pivot pin was re-machined farther back, just behind the front sight assembly/gasblock, and the opening was enlarged for the PRI FUFS.

[img]http://photos.ar15.com/ImageGallery/Attachments/DownloadAttach.asp?iImageUnq=19905[/img]
Treetop's pic, thanks Tree...

/S2

Sulaco2,

I was wondering how much different the 58-Mod feels from the 50?  I know the 58-Mod is a bit longer and heavier how does this change the handling characteristics compared to the 50?

I can comment on what I liked more on the 58MOD than my #50, is the little bit more room for my large hand away from the selective rails. Both are comfortable, one has more length in the hand guard area, but that's what all mid lengths do and now on a carbine weapon.
Jack

Jimbo,

The are virtually identical in feel and swing, when on the same weapon and w/ the same accessories of course. I can tell absolutely no difference between the 2 in weight.  The weight difference is negligible in use.  On paper I can't imagine it being more than a few ounces of difference.  If you're worried about feeling much of a difference between your #50C and the #58MOD, I don't think you'll notice much of a difference in wt.  Now I like the added real estate a lot, it's assuring to know that you don't run out of room for the support hand even w/ lights mounted.

Thanks Jack and S2!

Thank you very much to all for your inputs and assistance and most especially, for your patience in explaining. I joined this forum to learn and I learned more than I expected. I posted in different areas of the forum and always gets very informative replys and for a newbie like myself, this is greatly appreciated. Happy New Year to all fellow forum members. May the New Year bring more joy and happiness and most importantly, more accurate shooting :)

Sorry I mixed up the #58 and #8MOD since I was looking ate everything but the top, other than that they look identical. The bottom foward portion hand guard gives the perfect low profile built in rail to put a bi-pod onto.
Good shootin, Jack