PRI vs. LaRue FF tube for SPR upper

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[ARCHIVED THREAD] - PRI vs. LaRue FF tube for SPR upper (Page 1 of 2)

Posted: 12/14/2005 1:44:20 PM EDT

I am in the process of spec'ing out an SPR upper, and am leaning towards the PRI FF tube over the LaRue. Full length rails aren't particularly needed for the intended application....plinking and potential small game hunting.

Has anybody had any problems with the PRI?

Thanks.

Posted: 12/14/2005 2:49:39 PM EDT

[#1]

Daniel Defense

Posted: 12/14/2005 3:30:45 PM EDT

[#2]

Quoted:
Daniel Defense

Posted: 12/14/2005 4:14:24 PM EDT

[#3]

I have a DD 7.0 on my carbine, and like the heck out of it......maybe this should have been a three way question?

ETA: Ian, that looks alot like where I am heading; thanks for the pic.

Posted: 12/14/2005 4:46:25 PM EDT

[#4]

I have had a PRI tube for maybe 3 years now. More than 2 for sure. I've built several other guns for others with them as well. They are great tubes with a lot to offer. The rails dont extend the full length of the handguard which in many cases is nice, and on top of that, you can remove unwanted or unneeded rails reducing weight and bulk. Being made of carbon fiber, many expect these to be very light. They arent. It's not like they are over weight, but they have a heavy steel barrel nut and a strong and solid locking nut. The rails that are on the tube also require screws to attach. All of this adds weight and makes it as heavy as a lot of rails, and heavier than a few. But it is very solid.

I have one LaRue rail, but have yet to build a gun for myself with one. I have put together several guns for others using LaRue rails though. This is also a very sold rail. The LaRue has a special locking collar that no other rail I know of has. This keeps the rail locked solidly into place. The LaRue is an all rail design, giving you rails from start to end. They are not removable which makes it a little slimmer than the PRI, but it is best to cover the rails with some sort of pannel to both protect the rail, and your hands. Most pannels will add to the bulk of the rail, some more so than others.

The DD rail will be much like the LaRue, but will be welded together instead if being a one piece machined design, will lack the locking collar, and will use a much lighter aluminum barrel nut, making the DD noticably lighter. The DD is thinner side to side than the LaRue, but the LaRue is shorter top to bottom than the taller DD.

In all honesty, you are looking at high end pieces. In many regaurds, one is not better than the other in any real or dramaticly obvious reguard. They are different though. Take a look at the differences, see which ones meet your needs or wants more so than the other, and make your choice. I really dont think you can make a bad choice between any of the three.

edited b/c I cant type!

Posted: 12/14/2005 5:00:57 PM EDT

[#5]

Quoted:
The DD rail will be much like the LaRue, but will be welded together instead if being a on piece machined design, will lack the locking collar, and will use a much lighter aluminum barrel nut, making the DD noticably lighter. The DD is thinner side to side than the LaRue, but the LaRue is shorter top to bottom than the taller LaRue.

Who makes a one piece machined design? I assume you meant one when you wrote on piece?

Posted: 12/14/2005 5:24:14 PM EDT

[#6]

Man, I cant type. The fact that I dont go back to reread what I just typed doesnt help either!

I did mean one peice. I dont know exactly how it works, but the DD rail, like the Knights rail, have big weld marks near the rear of the rials. What these welds are for or what they are welding together I dont know. But I do know the LaRue rail is not welded together like the DD or Knights, which I take to mean, (and am sure have read the same) the LaRue was one peice where the others were two (not including the barrel nut or lock ring).

Posted: 12/14/2005 5:31:04 PM EDT

[#7]

Damn, you are quick with the edit...I was just fixin' to point out that the LT is shorter than the DD [not LT].

Nice post, and thanks...it is indeed all about "feel".

Posted: 12/14/2005 5:31:12 PM EDT

[#8]

Quoted:
which I take to mean, (and am sure have read the same) the LaRue was one peice where the others were two (not including the barrel nut or lock ring).

The PRi and LaRue (both are 2 pieces) are glued together. The DD and KAC are welded.

Posted: 12/14/2005 5:33:39 PM EDT

[#9]

Quoted:
Damn, you are quick with the edit...I was just fixin' to point out that the LT is shorter than the DD [not LT].

Yes, the LaRue is shorter which some may like better, but is also the reason there is currently no "FSP" version of the LaRue rails.

Posted: 12/14/2005 5:35:23 PM EDT

[#10]

Quoted:
The PRi and LaRue are glued together. The DD and KAC are welded.

I stand corrected and apologize. I thought for sure I had read it was one peice, but cant say I know enought about it to feel confident about it. If it is indeed glued, I must say, I would probably rather have one that is welded!

Posted: 12/14/2005 5:48:25 PM EDT

[#11]

How does one "glue" aluminum other than by welding? CF, I understand gluing.

Posted: 12/14/2005 5:50:07 PM EDT

[#12]

There is no way in hell I am saying a thing.

Posted: 12/14/2005 6:13:19 PM EDT

[#13]

Quoted:
There is no way in hell I am saying a thing.

I think we should start a bet on how many pages this will go. Where is Grant?

Epoxy, it's not just for toilette seats anymore.

Posted: 12/14/2005 6:18:32 PM EDT

[#14]

Quoted:
How does one "glue" aluminum other than by welding? CF, I understand gluing.

Epoxy. I trust epoxy. Hell, some of the planes we fly on are epoxied together.

Posted: 12/14/2005 6:58:36 PM EDT

[#15]

Didn't you know ?

Some paper mache, black Krylon, a little Elmers...... and Bamm !

You're good to go

_______________________________________________________

"Plasma rifle in the 40 watt range"

Posted: 12/14/2005 7:04:22 PM EDT

[#16]

Shit here we go.

Posted: 12/14/2005 8:32:40 PM EDT

[#17]

Quoted:
Shit here we go. www.activistsandiego.org/wwwboard/images/smiles/lsvader.gif

Posted: 12/15/2005 6:07:47 AM EDT

[#18]

Larue...Hands down

Posted: 12/15/2005 6:18:39 AM EDT

[#19]

Quoted:
Larue...Hands down

Thanks for the very detailed explanation of why you think so.

Posted: 12/15/2005 6:28:36 AM EDT

[#20]

I like my glued together LT 9.0!

I've got plenty of glue sticks left over from art class in case it breaks, so no worries from me!

Seriously, I don't think you can go wrong with the DD or the LT. The DD is lighter. I don't think the fact that the LT is "glued" and the DD is welded should really even be an issue in deciding which one you buy. They're both plenty strong I'm sure. I haven't personally heard of either breaking (not that they haven't...everything breaks).

Posted: 12/15/2005 6:39:22 AM EDT

[#21]

MM, all your choices are quality ones (PRI, DD & LT). I sell all three and will tell you which one I like and why.

LT Fit and finish is the highest of any of them and believe that they have the capability to follow the dead middle of the M1913 spec better than anyone. They also feature a locking system that none of the other ones offer. This fact alone makes the choice easy for me as barrel nuts DO & CAN come loose.

DD Light weight and quality made. Come with 3 rail covers as well.

PRI GEN III Nice fit and finish and has a more traditional look to it IMHO. Can get them ordered with custom rail lengths. Rails do not follow the M1913 spec so you cannot fit a TD VG on them.

C4

www.GRTactical.com

LT 13.2

Posted: 12/15/2005 6:39:36 AM EDT

[#22]

Can someone point out where the LT rail is glued.
I am looking at a 12.0 and it looks like all one piece.

Posted: 12/15/2005 6:43:33 AM EDT

[#23]

Quoted:
Can someone point out where the LT rail is glued.
I am looking at a 12.0 and it looks like all one piece.

They are refereing to where the threads(Mating the barrel nut) meets the rails on the inside of the tube.

Posted: 12/15/2005 7:32:09 AM EDT

[#24]

Thanks for the objective comparison feedback, Grant. I wasn't aware that the PRI rails weren't M1913 spec. It is probably not that big a deal in this particular case, since I don't use VFG's, but good to know nonetheless.

Decisions, decisions....

At least I know that I will be using LT for the bipod mount, gas block, and scope mount [assuming that the SPR's eventually get off backorder].

BTW, what kind of stock is that on the rifle in your pic?

Thanks.

Posted: 12/15/2005 7:37:21 AM EDT

[#25]

Quoted:
Thanks for the objective comparison feedback, Grant. I wasn't aware that the PRI rails weren't M1913 spec. It is probably not that big a deal in this particular case, since I don't use VFG's, but good to know nonetheless.

Decisions, decisions....

At least I know that I will be using LT for the bipod mount, gas block, and scope mount [assuming that the SPR's eventually get off backorder].

BTW, what kind of stock is that on the rifle in your pic?

Thanks.

That's the new Magpul PRS stock. Sounds pretty sweet from what I've read. There's more info in the industry section in Magpul's forum.

Posted: 12/15/2005 7:50:24 AM EDT

[#26]

Quoted:
Thanks for the objective comparison feedback, Grant. I wasn't aware that the PRI rails weren't M1913 spec. It is probably not that big a deal in this particular case, since I don't use VFG's, but good to know nonetheless.

Decisions, decisions....

At least I know that I will be using LT for the bipod mount, gas block, and scope mount [assuming that the SPR's eventually get off backorder].

BTW, what kind of stock is that on the rifle in your pic?

Thanks.

To be honest, the rails on the PRI do follow (somewhat) the 1913 spec, but they don't have the high "neck" to allow the TD VG to interface. This is most likely not an issue for most people.

As far as Bipods go, the new TD one is about to be out (have one and love it). So you might want to rethink your options.

The stock is the Magpul PRS.

C4

Posted: 12/15/2005 8:40:11 AM EDT

[#27]

Quoted:
... they have the capability to follow the dead middle of the M1913 spec better than anyone.

C4

What exactly is the middle of the M1913 spec? Since the spec does not really specify variation what would the middle be?

Posted: 12/15/2005 9:04:19 AM EDT

[#28]

Quoted:
Quoted:
... they have the capability to follow the dead middle of the M1913 spec better than anyone.

C4

What exactly is the middle of the M1913 spec? Since the spec does not really specify variation what would the middle be?

I asked Jeff C. of TD once what rails he has found that fit with their VG's the best. He said that LT's rails fit the best as they follow the middle of the 1913 spec. So apparently there is somewhat of a "zero" (neither on the - or + side) if you will and they seem to follow it the best from what I am told.

C4

Posted: 12/15/2005 1:26:06 PM EDT

[#29]

Can the rails be moved aroun on the PRI rail? Are the top rails to the correct height for a rail mounted front sight? Does anyone have a pic of the INSIDE of a PRI rail? Carbine hopefully? Need to see how far the rail screws stick in.

Posted: 12/15/2005 1:51:36 PM EDT

[#30]

--------------------------------------------------------------------------------
Quoted:
Larue...Hands down
--------------------------------------------------------------------------------

Thanks for the very detailed explanation of why you think so.
....your welcome......{rolleyes}

Posted: 12/15/2005 3:06:38 PM EDT

[#31]

Quoted:

As far as Bipods go, the new TD one is about to be out (have one and love it). So you might want to rethink your options.

C4

I had been planning on a Harris with a LT mount.

I am not familiar with the TD unit; would you mind sharing any details...advantages/improvements? In particular, does it mount to a QD sling swivel; I try to maintain modularity whenever possible, and a QD swivel mount would allow use on my bolt guns.

Thanks.

Posted: 12/15/2005 4:06:03 PM EDT

[#32]

Quoted:
Quoted:

As far as Bipods go, the new TD one is about to be out (have one and love it). So you might want to rethink your options.

C4

I had been planning on a Harris with a LT mount.

I am not familiar with the TD unit; would you mind sharing any details...advantages/improvements? In particular, does it mount to a QD sling swivel; I try to maintain modularity whenever possible, and a QD swivel mount would allow use on my bolt guns.

Thanks.

Here ya go: www.ar15.com/forums/topic.html?b=3&f=19&t=260308

I really like mine a lot!

C4

Posted: 12/15/2005 4:12:41 PM EDT

[#33]

Quoted:
Quoted:
Quoted:
... they have the capability to follow the dead middle of the M1913 spec better than anyone.

C4

What exactly is the middle of the M1913 spec? Since the spec does not really specify variation what would the middle be?

I asked Jeff C. of TD once what rails he has found that fit with their VG's the best. He said that LT's rails fit the best as they follow the middle of the 1913 spec. So apparently there is somewhat of a "zero" (neither on the - or + side) if you will and they seem to follow it the best from what I am told.

C4

So there is no "middle of the 1913 spec?"

Posted: 12/15/2005 5:30:16 PM EDT

[#34]

Quoted:
Quoted:
Quoted:
Quoted:
... they have the capability to follow the dead middle of the M1913 spec better than anyone.

C4

What exactly is the middle of the M1913 spec? Since the spec does not really specify variation what would the middle be?

I asked Jeff C. of TD once what rails he has found that fit with their VG's the best. He said that LT's rails fit the best as they follow the middle of the 1913 spec. So apparently there is somewhat of a "zero" (neither on the - or + side) if you will and they seem to follow it the best from what I am told.

C4

So there is no "middle of the 1913 spec?"

There probably is a middle ground, but am not a mechanical engineer and don't have a copy of the M1913 spec so I cannot say for certain.

C4

Posted: 12/15/2005 5:58:15 PM EDT

[#35]

That bipod looks pretty nice, but I'll probably just settle for the Harris, since it will fit other weapons without rails equally well.

Thanks for the link.

Posted: 12/15/2005 6:03:12 PM EDT

[#36]

Quoted:
That bipod looks pretty nice, but I'll probably just settle for the Harris, since it will fit other weapons without rails equally well.

Thanks for the link.

Your welcome.

C4

Posted: 12/15/2005 6:22:58 PM EDT

[#37]

Quoted:
Quoted:
Quoted:
Quoted:
Quoted:
... they have the capability to follow the dead middle of the M1913 spec better than anyone.

C4

What exactly is the middle of the M1913 spec? Since the spec does not really specify variation what would the middle be?

I asked Jeff C. of TD once what rails he has found that fit with their VG's the best. He said that LT's rails fit the best as they follow the middle of the 1913 spec. So apparently there is somewhat of a "zero" (neither on the - or + side) if you will and they seem to follow it the best from what I am told.

C4

So there is no "middle of the 1913 spec?"

There probably is a middle ground, but am not a mechanical engineer and don't have a copy of the M1913 spec so I cannot say for certain.

C4

If the spec does not allow for any variation how can there be a "middle ground?"

Here is the spec:

Here is a link to the thread where the spec was posted.

Posted: 12/15/2005 6:31:42 PM EDT

[#38]

I went with DD strictly for the weight savings. So far I haven't had any reasons to not like it. It's solid, fit and finish are excellent. I will try the Larue on my next build, simply because I'm a big Larue fan. Also like the sounds of the locking system.

Posted: 12/15/2005 6:43:50 PM EDT

[#39]

Quoted:
Quoted:
The PRi and LaRue are glued together. The DD and KAC are welded.

I stand corrected and apologize. I thought for sure I had read it was one peice, but cant say I know enought about it to feel confident about it. If it is indeed glued, I must say, I would probably rather have one that is welded!

I was suprised too:

www.ar15.com/forums/topic.html?b=3&f=12&t=258573

But whatever

Posted: 12/15/2005 7:29:38 PM EDT

[#40]

.

Posted: 12/15/2005 8:09:04 PM EDT

[#41]

Just FYI, those protective ceramic tiles on the space shuttle also glued and withstand temperatures as high as 2500-3000 degrees F.

Posted: 12/15/2005 8:18:36 PM EDT

[#42]

LaRue 12.0

The DD will be a bit lighter, but I prefer the LaRue's steel barrel nut and the anti-spin device.
LaRue's customer service is the "best in the business", and DD's is not far behind, if not as good.

Posted: 12/15/2005 9:36:27 PM EDT

[#43]

Went with the PRI over the LaRue for this build as was thinking for off hand was a little nicer (no rails to worry about / smaller diameter than with covers ?). The PRI works well, however, only using with a bipod, so the remaining rails are open at the moment. Additionally this PRI forearm was to have been a FBI mod that has the longer rail on the bottom to allow options on the location of the bipod.

With the existing holes, appears one can pick up extra short or long rails from PRI and add them to an existing forend, however, have not tried yet.

Next build will probably be a full rail system such at the LaRue or KAC FF (no one carries the DD in Indiana) and use the ACOG full time with the Colt A2 barrel (the PRI forend and Leupold scope then gets a semi match barrel for either Mk262 "5.56" or 6.8 SPC is ever end up with cases and realoading supplies).

Also one of these days need to get a photo of the upper with all the parts installed (Troy rear sight, charging handle, bolt, bipod) and on the M16A1 instead of the loaner AR15.

Posted: 12/16/2005 3:53:31 AM EDT

[#44]

If the spec does not allow for any variation how can there be a "middle ground?"

Here is the spec:

www.gunzilla.com/images/picshot.JPG

Here is a link to the thread where the spec was posted.

That is not the only opinion. Here is what EOTech had to say on the subject. So YES there are deviances in the spec:

Please do a search for the MIL-STD-1913 rail Federal Publication from 3 Feb 1995. Near the end of the document are engineering schematics with the "precise" dimensions of the accessory or picatinny rail. You will notice that there is a range of allowable measurement for the thickness of the rail, height, and width. The range for the width of the rail alone allows for a possible difference in inches of over EIGHT TENTHS (0.8). That is not a small allowance when it comes to interfacing products. The height of the rail allows for a variance of .14 inches! The impact this has, is that if you produce something to fit a tight or specific tolerance (one exact measurement), you will only fit on the few rifles that meet that specification (less sales, less profit, less money to be spent on quality control...). Additionally, the amount of scrap that would be produced by rifle manufacturers due to not meeting that specification would make the industry completely not-profitable, and you'd be paying $4,000 for a new M4 as opposed to $900 (as an example).

C4

Posted: 12/16/2005 4:50:08 AM EDT

[#45]

Quoted:
That is not the only opinion. Here is what EOTech had to say on the subject. So YES there are deviances in the spec:

Please do a search for the MIL-STD-1913 rail Federal Publication from 3 Feb 1995. Near the end of the document are engineering schematics with the "precise" dimensions of the accessory or picatinny rail. You will notice that there is a range of allowable measurement for the thickness of the rail, height, and width. The range for the width of the rail alone allows for a possible difference in inches of over EIGHT TENTHS (0.8). That is not a small allowance when it comes to interfacing products. The height of the rail allows for a variance of .14 inches! The impact this has, is that if you produce something to fit a tight or specific tolerance (one exact measurement), you will only fit on the few rifles that meet that specification (less sales, less profit, less money to be spent on quality control...). Additionally, the amount of scrap that would be produced by rifle manufacturers due to not meeting that specification would make the industry completely not-profitable, and you'd be paying $4,000 for a new M4 as opposed to $900 (as an example).

C4

You have got to tell us who at EOTech said this!

Posted: 12/16/2005 5:02:54 AM EDT

[#46]

Quoted:
Quoted:
That is not the only opinion. Here is what EOTech had to say on the subject. So YES there are deviances in the spec:

Please do a search for the MIL-STD-1913 rail Federal Publication from 3 Feb 1995. Near the end of the document are engineering schematics with the "precise" dimensions of the accessory or picatinny rail. You will notice that there is a range of allowable measurement for the thickness of the rail, height, and width. The range for the width of the rail alone allows for a possible difference in inches of over EIGHT TENTHS (0.8). That is not a small allowance when it comes to interfacing products. The height of the rail allows for a variance of .14 inches! The impact this has, is that if you produce something to fit a tight or specific tolerance (one exact measurement), you will only fit on the few rifles that meet that specification (less sales, less profit, less money to be spent on quality control...). Additionally, the amount of scrap that would be produced by rifle manufacturers due to not meeting that specification would make the industry completely not-profitable, and you'd be paying $4,000 for a new M4 as opposed to $900 (as an example).

C4

You have got to tell us who at EOTech said this!

Dennis Fennigan said it here in this thread: ar15.com/forums/topic.html?b=3&f=18&t=259397

Posted: 12/16/2005 5:34:12 AM EDT

[#47]

Quoted:

You have got to tell us who at EOTech said this!

I agree. There are some decimal points and a few zero's misplaced in that "info".

over .8 inches..????? I'd love to see the prints on a machined feature of that size that would allow almost an inch in variation (tolerance) because you wouldn't machine it you'd cut it with a torch or saw. The BASIC width of the rail itself is around .835 and we are supposed to believe that the width can vary as much as .800?

.835 +/- .400 ?
.835/.035 ?
.835 +.800/-.000 ?

Let's use some common sense here guys.

Posted: 12/16/2005 6:26:39 AM EDT

[#48]

As was suspected, it was MORE BAD INFO and has been retracted.

From the above linked thread. Eotech thread

Quoted:
ATTENTION EVERYONE.

My math was wrong, and to additionally show that I don't have an issue correcting or admitting mistakes; my interpretation of the math (and a limited explanation provided me) on the schematic was incorrect. I am not an engineer either, BTW.

The measurements are not .8" but smaller. However, there is still a variance in the possible dimensions which account for the cant issue. The measurement takes into account the use of geometric dimensioning and tolerance. It is more complex than a simple measurement but the variance still exists.

I apologize for posting incorrect numbers, but the point remains the same. Thanks for your patience.

More like 100 times smaller than .800 inches.

Posted: 12/16/2005 7:26:18 AM EDT

[#49]

Quoted:
As was suspected, it was MORE BAD INFO and has been retracted.

From the above linked thread. Eotech thread

Quoted:
ATTENTION EVERYONE.

My math was wrong, and to additionally show that I don't have an issue correcting or admitting mistakes; my interpretation of the math (and a limited explanation provided me) on the schematic was incorrect. I am not an engineer either, BTW.

The measurements are not .8" but smaller. However, there is still a variance in the possible dimensions which account for the cant issue. The measurement takes into account the use of geometric dimensioning and tolerance. It is more complex than a simple measurement but the variance still exists.

I apologize for posting incorrect numbers, but the point remains the same. Thanks for your patience.

More like 100 times smaller than .800 inches.

He made a typo on his comments and corrected the mistake (no one is perfect).

C4

Posted: 12/16/2005 7:39:05 AM EDT

[#50]

Quoted:

If the spec does not allow for any variation how can there be a "middle ground?"

Here is the spec:

www.gunzilla.com/images/picshot.JPG

Here is a link to the thread where the spec was posted.

That is not the only opinion. Here is what EOTech had to say on the subject. So YES there are deviances in the spec:

Please do a search for the MIL-STD-1913 rail Federal Publication from 3 Feb 1995. Near the end of the document are engineering schematics with the "precise" dimensions of the accessory or picatinny rail. You will notice that there is a range of allowable measurement for the thickness of the rail, height, and width. The range for the width of the rail alone allows for a possible difference in inches of over EIGHT TENTHS (0.8). That is not a small allowance when it comes to interfacing products. The height of the rail allows for a variance of .14 inches! The impact this has, is that if you produce something to fit a tight or specific tolerance (one exact measurement), you will only fit on the few rifles that meet that specification (less sales, less profit, less money to be spent on quality control...). Additionally, the amount of scrap that would be produced by rifle manufacturers due to not meeting that specification would make the industry completely not-profitable, and you'd be paying $4,000 for a new M4 as opposed to $900 (as an example).

C4

I didn't know that the 1913 spec was an opinion. Would you please post 1913 spec prints showing differing opinions?

[ARCHIVED THREAD] - PRI vs. LaRue FF tube for SPR upper (Page 1 of 2)

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