Alternatives to side reinforcing rails?

[r.erichsen]

Now that I've received my HKParts "L" rails (about $77 vs. the "T" rails that run $180), I'm a little miffed at how little there really is to the design. Other than length and a fairly simple shape to fit into the rails, nothing special. I wanted to see them before deciding if I would buy another set or try something else on the CETME build. It's still a fairly extensive welding task to get the the L or T rails in and smooth over the welds. As someone with no CNC and access to no appropriate tooling to fabricate a proper L or T shaped reinforcing rail, I'm wondering if the simpler answer is to just fill the "void" of the rail with weld buildup to a suitable degree (probably not all the way to the receiver face, that would be a lot of additional mass) and then just top this with a flat sheet metal cover/cap tack welded in a few spots and smoothed over with grinding. In both cases I'd be using a set of copper pipes of the right diameter as heat sinks, with C-clamps holding it tight and compressed air used every few seconds to keep things to a reasonable temperature during the process. Does this sound reasonable?

R

[holescreek]

Does this sound reasonable?

Not to me, unless all you're going for is the "look". Welding in the slots ought to create some good warpage in the sheet metal over the length. You'd be better off JB welding some flat stock on and calling it a target rifle.

Since I always make my own rails it's amazing to hear that the teardrop shaped L? rails are cheaper than the T rails. The T rails are pretty easy to make with a standard mill whereas the L rails I've seen required a long throat wire EDM to cut out the shapes. Seems kind of backwards.

http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/HSG-1/Rails031211001.jpg

[bladeworks123]

+1 to what Holes says, Do not try to fill weld the rails. T or L makes very little difference. The key is to keep the receiver from flexing just behind the trunnion.

[r.erichsen]

Holes just posts his self-made reinforcement rails to taunt me, I'm sure of it. ;)

[r.erichsen]

+1 to what Holes says, Do not try to fill weld the rails. T or L makes very little difference. The key is to keep the receiver from flexing just behind the trunnion.

Sounds like I'll be buying another set of L rails then. From the shape, I'd agree the T "should" be cheaper to fabricate. Go figure, I haven't a clue why. Teutonic bragging rights would have been my guess, but the rails I've seen are mostly from Michaels Machines and CNC cut, none were made by Gnomes in the Black Forest and spirited away in some workshop raid.

Thanks all.

[holescreek]

If you don't need them right away I'd make you a set of T rails for about what you're paying for the others.

[bladeworks123]

I will ad that the T rails are, IMHO, easier to keep from warping when welding them up. Once they are welded in they both do the same job. And I would take Holes up on his machine work. It is top notch.

[automick]

On the subject of rails...do they realy make a diference.?
Has anyone got before and after acuracy results.
just wondering.
auto.

[holescreek]

On the subject of rails...do they realy make a diference.?
Has anyone got before and after acuracy results.
just wondering.
auto.

That's a great question!! I have no idea what the answer is though. I have them on two rifles but only put them on because "accurate rifles all have them". I just finished my third range trip with the PSG1 clone build this morning and my best two 3 shot groups were about 1/2". Must be the stiffening rails!

http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/HSG-1/target101211001.jpg

http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/HSG-1/target101211002.jpg

[automick]

Nice group holes.
What ammo did you use....and what barrel do you have.
Im realy wondering about the rails.
if i add them to my g3 build...maybe better groups.
I guess i need to justify the $200 bucks.

[holescreek]

$200 for t rails is insane.
I used the cheapest ammo I could find. Tula steel cased 150gr bought from CTD. Barrel is a 25" McGowen (custom) on the PSG1 retro build.

[spectre]

holes, i always get better groups with tula 150 than with winchester or surplus also but not quite as tight as your groups

[holescreek]

Must be the T rails then, I can't shoot for ******** anymore. Those were 6 shots out of 40, I just didn't photograph the ones that looked like a shotgun pattern.:machinegun:

[automick]

The more i read the more i wana do a before and after test with the T rails
and use some of that tula ammo.

[holescreek]

I was just checking online to see if there was anyone selling the Tula with bulk pricing. Didn't have any luck but only searched through ammoengine.

[holescreek]

I haven't tried it yet but I have the GHG1 I built last year with a 20" B5 DM barrel. It already has the rails on the sides though. I think next time out to the range I'll take it and run some Tula through it to see what happens with a different barrel. With the SA and Portugese ammo the best I could ever get out if it was 3-4" groups, same as with this build. If the groups tighten right up with the Tula at least I'll know it isn't just because of the better barrel on the PSG1 retro build. If it still shoots like crap I'll pull the B5 barrel and put in my other McGowen.

[r.erichsen]

If you don't need them right away I'd make you a set of T rails for about what you're paying for the others.

I would very much appreciate that. PM sent.

R

[drine]

$200 for t rails is insane.
Your dang right! (in my best Southern drawl) Back when I first got in to the DRB rifles I really wanted to PSG my CETME but the costs were borderline insane. Granted trigger groups, etc. are rare but the rails really turned me away and I thought even a crudely fashioned t-rail with taper to go in the slot would be easy to make. I left it alone since I don't have the equipment at home to do it.

[holescreek]

I made two sets of rails a week or so ago, meant to post something about them but got hung up on the new 70 degree LP's I'm making. R.erichsen has dibbs on one set (if he still wants them).
http://i2.photobucket.com/albums/y29/Holescreek/Gunstuff/Fluting/chamberfluting007.jpg

[Lalvis]

Do you think the T-rails would make any difference on a stainless receiver?

[holescreek]

I have no experience with stainless receivers.

[rpmfly2]

Stainless receivers are stiff as you can get since they are thicker and the stainless is cast. Try drilling that receiver, it's not easy. My Hk91 build on a stainless shoots better than my 2 CETME and other 2 HK builds done on stamped receivers.
Stainless cast doesn't flex like the softer sheets that are stamped I guess.

[r.erichsen]

I made two sets of rails a week or so ago, meant to post something about them but got hung up on the new 70 degree LP's I'm making. R.erichsen has dibbs on one set (if he still wants them).

Is there any question I still want them? - Why, of course I do! PM sent. :)

Thanks,

R

[r.erichsen]

Stainless receivers are stiff as you can get since they are thicker and the stainless is cast. Try drilling that receiver, it's not easy. My Hk91 build on a stainless shoots better than my 2 CETME and other 2 HK builds done on stamped receivers.
Stainless cast doesn't flex like the softer sheets that are stamped I guess.

I still wonder what aspect of "flex" diminishes accuracy - is it variability in point of aim vs. point of impact as I suspect, or something else? There are theories, but I wonder if anyone has a more definitive reason for the cause an effect.

R

[holescreek]

I don't see how accuracy is effected since the round is already in the chamber, bolt is in place, and all that's left is the trigger pull. Maybe in a course of quick firing/follow-up shots but not in slow fire. Maybe the idea is to disallow minute receiver stretch or trunnion droop. I don't think it would affect us mere mortals but they do look cool.

[bladeworks123]

I was told once by another armorer whose opinion I respected very much, that over time, repeated recoil will eventually cause the receivers to bend to the ejection port side slightly, slowly changing POI. He would always check the line of the bottom of the ejection port to see if it was curved in towards the bolt rather than having a nice straight edge, which he said was a pretty good indicator how much an Hk91 had been shot...not much of an issue on an MP5 or 93. He called it a swaybacked ejection port. Whether that was true or not, or just more of the Hk factory hype about the importance of in spec rifles. (not just an Hk thing, a lot of manufacturers have it) I'm not sure. He had a jig to set a rifle in that checked it for alignment both horizontally and vertically. You can do the same thing with a string line or a straight edge, it's just not as "mechanically accurate". He also had a jig for bending the receivers back into alignment,,,,, basically it was a mandrel that went inside the receiver the cocking tube and the trunnion, with a rod that extended out the back, which was used to check the alignment of the trunnion for whether or not it was square to the bolt carrier during operation. Then there was a cradle which fit the receiver behind the trunnion and supported the very front of the trunnion, and you bent the receiver back in line by pressing and bending the receiver on the opposite side from the direction of the bend, and measuring the rod in the rear to see if it was centered inside the receiver, it was called a symmetry guage. It was really more for correcting receiver to barrel alignment....If the trunnion is not perfectly square to the receiver, the theory is that one roller will set farther inside the trunnion than the other by a few thousandths of an inch, enough in some cases that with no round in the chamber, one roller will be floating and the other in tight contact with the locking piece and the trunnion, making for premature wear on one side over the other because one roller is taking more of the load than the other..... It will also show up as a bright wear spot on one side of the collar at the front of the carriers recoil barrel were it drags a bit inside the cocking tube. But his theory also was that if the receiver was bent so bad from just recoil that the sights/scope wouldn't take care of it, the rifle had enough rounds through it that it didn't make any difference in straightening it anyway.

So, because of all that, I'm not convinced that the rails do much more than just assure there is no flexing to the right or left with changes in the temperature of the receiver, or to just make the rifle more durable in the event that you happened to have somebody lay on it or lean hard on it causing it to bend a little. I think it's more about maintaining accuracy than creating it. And they do look cool....

[r.erichsen]

I was told once by another armorer whose opinion I respected very much, that over time, repeated recoil will eventually cause the receivers to bend to the ejection port side slightly, slowly changing POI. He would always check the line of the bottom of the ejection port to see if it was curved in towards the bolt rather than having a nice straight edge, which he said was a pretty good indicator how much an Hk91 had been shot...not much of an issue on an MP5 or 93. He called it a swaybacked ejection port. Whether that was true or not, or just more of the Hk factory hype about the importance of in spec rifles. (not just an Hk thing, a lot of manufacturers have it) I'm not sure. He had a jig to set a rifle in that checked it for alignment both horizontally and vertically. You can do the same thing with a string line or a straight edge, it's just not as "mechanically accurate". He also had a jig for bending the receivers back into alignment,,,,, basically it was a mandrel that went inside the receiver the cocking tube and the trunnion, with a rod that extended out the back, which was used to check the alignment of the trunnion for whether or not it was square to the bolt carrier during operation. Then there was a cradle which fit the receiver behind the trunnion and supported the very front of the trunnion, and you bent the receiver back in line by pressing and bending the receiver on the opposite side from the direction of the bend, and measuring the rod in the rear to see if it was centered inside the receiver, it was called a symmetry guage. It was really more for correcting receiver to barrel alignment....If the trunnion is not perfectly square to the receiver, the theory is that one roller will set farther inside the trunnion than the other by a few thousandths of an inch, enough in some cases that with no round in the chamber, one roller will be floating and the other in tight contact with the locking piece and the trunnion, making for premature wear on one side over the other because one roller is taking more of the load than the other..... It will also show up as a bright wear spot on one side of the collar at the front of the carriers recoil barrel were it drags a bit inside the cocking tube. But his theory also was that if the receiver was bent so bad from just recoil that the sights/scope wouldn't take care of it, the rifle had enough rounds through it that it didn't make any difference in straightening it anyway.

So, because of all that, I'm not convinced that the rails do much more than just assure there is no flexing to the right or left with changes in the temperature of the receiver, or to just make the rifle more durable in the event that you happened to have somebody lay on it or lean hard on it causing it to bend a little. I think it's more about maintaining accuracy than creating it. And they do look cool....

Now THAT was a wonderful set of detailed explanations Bladeworks. I'll pay attention to the 'squareness' of barrel trunnion to receiver, makes good sense.

R