Trying to Build LR-308 A4 Classic (Clone)

[kishigo]

Hello,

I'm trying to build an LR-308 A4 Classic upper using the following parts:

DPMS Upper Receiver

Rainier Arms Select 20" rifle length gas system barrel

DPMS Chrome Bolt Carrier

Armalite Clamp On A2 Front Sight

DPMS 308 barrel nut & Delta Pack

Old Colt Sporter Mil Spec 2 Piece Handguards

The handguards appear to about 1/4" too long for this configuration.  From comparing the distance from front sight to receiver with my ar-15, the Rainier Arms barrel does indeed look like it has a rifle length gas system.  The gas tube appears to fit properly in the receiver. 

The only problem I see seems to be that the barrel nut and delta pack assembly are about 1/4" wider than the ar-15.  When DPMS made their A4 Classic, does anyone how they got mil spec standard sized handguards to fit?  Did they use a slightly longer gas system?  Modified handguards?  Any input would be appreciated.

Thank you,

Kevin

[edgecrusher]

ok, one thing at a time.

colt as a manufacturer has slightly different sized handguards for their carbines, so their rifle length may also be different.also if they are ar15 handguards they may not work.

your 20" Rainier barrel is definitely a rifle gas. I think the Armalite rifle tubes may be a little longer.

[kishigo]

Thank you for the information.

Yeah I thought that the Rainier Arms barrel was within spec.  I just need to figure out how DPMS assembled the A4 classic using mil-spec handguards.  If as you suggest, the old Colt handguards are out of spec, then it might be a simple matter of purchasing DPMS handguards.  I saw them at their website, under the LR Platform section.  They have the same model number as the ones under the AR Platform section.  I assume that means they're the same for both platforms.

Kevin

[unforgiven]

Welcome from Indiana brother Kevin.

[kishigo]

@unforgiven

Thank you.  I've been an unregistered lurker here for a while.  It's just now that I'm involved in a build do I realize how much I don't know.  That's why I'm here.

Kevin

[unforgiven]

Your at a good place brother lots of very bright men here. <thumbsup>

[kishigo]

Well, here's an update.  I ordered DPMS 2 piece handguards from Midway USA and they don't fit.  They, like the other handguards, are about 1/4" too long.  Or rather, the gas system is 1/4" too short.  Either the Rainier Arms barrels are not made to DPMS's specs, or DPMS fibbed on their specs for the LR-308 A4 Classic rifles.

If anybody has any input, please let me know.  If anybody has an A4 Classic rifle with the mil-spec 2 piece handguards, perhaps if you could take a picture of your rifle sans handguards, maybe I can figure this out.

Thank you

Kevin

[survivalshop]

Mid length gas system or a variant of it  ?

Call Rainer arms.

[kishigo]

Actually, I'm 99.9999% sure that the barrel is indeed an ar-15 rifle length gas system.  1st of all, that's what it says at their website.  2nd of all, edgecrusher confirmed that the Rainier Arms barrel is rifle length.  And thirdly, I can see the the gas tube protrusion into the receiver is about the same as my rifle length ar-15.

[survivalshop]

Measure the distance between the the Delta ring & hand guard cap of both your 308 & 5.56 ( inside )to see if there is a difference .

It may be nothing more than needing a slight modification to the hand guards for fitment .

It may also have some thing to do with the hand guard cap/ front sight /gas block.

[kishigo]

Well I bit the bullet, so to speak.  I cut the handguards down to fit.  It's not exactly the way I want, but it'll do.  I've been told that the handguards won't stay in with the way I modified them, but they seem fairly stable.  I'm not planning on installing anything on them, so they should be alright.

@survivalshop:  I had previously measured and I recall about a 3/16" to 1/4" difference in the measurements.  As I said before, I believe that the wider (longer?) delta ring and barrel nut on the LR-308 is what causes that difference.  I just don't know, all things being equal,  how DPMS made milspec handguards fit their A4 Classic rifles.

[ghorn]

I am having the same problem with DPMS. I have a DPMS AP4 factory stock rifle and last month decided to replace the smooth free float hand guard with a picatinny style hand guard from Midwest Ind made for the DPMS AP4 308cal.  The hand guard is almost 1/4 inch longer and will not fit on the rifle.  Now how can that be?  Midwest Ind contacted, never heard of this problem.  The gunsmith working on my rifle is making a schematic of my barrel and sending it in to DPMS.  If anyone else is having problems with DPMS AP4 please let me know.  Will keep everyone updated.