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tg4360

Colfax lower safety boss clearance

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Greetings to the .308 brethren.

I was on the wait list for the new Colfax 80% lower and have had it for a bit while myself and a friend studied it carefully (He just got an actual bridge port mill) before we started making chips.

It's done and I just installed a DPMS lower parts kit and stock set.

I'm very please with how everything went together with only two small concerns.

I'm looking for options on how to treat the raw aluminum in the pocket and pin holes.  My friend said Colfax responded to a query stating that it's never been a problem.  I think I'd still like to have some type of finish for long term wear prevention.  As for now I've just CLP'd it.

The second problem is that the boss on the forging around the rear take down pin hole is keeping the safety from going fully horizontal to the safe position.  I know that on military receivers and others I've seen, that boss is machined after forging to a flat bottom that the selector will hit to prevent over travel.  I am toying with the idea of giving that boss one pass with the mill to make it flat.  The other option is to releave the safety just enough to have it  swing all the way.  The first option will require at least a refinish of the receiver at that spot.

Just wanted to put this out there should anyone else be building on a Colfax receiver. 

TG

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Awesome,  and welcome. Personally I think I'd hit the receiver, reason being is if you change safeties at any point you'll run into the same issue, and the possibility of the safety disengaging by accident, no matter how rare the chance, is enough for me.

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The second problem is that the boss on the forging around the rear take down pin hole is keeping the safety from going fully horizontal to the safe position.  I know that on military receivers and others I've seen, that boss is machined after forging to a flat bottom that the selector will hit to prevent over travel.  I am toying with the idea of giving that boss one pass with the mill to make it flat.  The other option is to releave the safety just enough to have it  swing all the way.  The first option will require at least a refinish of the receiver at that spot.

I ran into a similar issue with my SI-Defense when I installed a BAD Inc Short Throw Ambi Selector Switch. I put the lever to a rotary tool and took off the corner. It works just fine now!

If you don't do something about it, it will make a divot on the lower receiver and eventually go through the finish.

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Thanks Edge. 

I hear you about future safeties but at least I know about it now.

Robo, you are correct.  There is already a little bright spot on the boss where the safety is hitting it.

Ordered the upper from Midway today (DPMS Oracal) and it should be here Monday or Tuesday.  I told myself that I'd not go crazy with customizing but I already have a Magpul hand guard on the way.

The whole reason for the new hand guard is that I want to have a sling swivel near the receiver so that the two attach points are at the front and rear of the action and the Magpul has a slick sling ring that attaches to the hand guard.

After that, the only thing I see wanting is some type of glass.

More pictures next week unless I get work busy.

TG

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I told myself that I'd not go crazy with customizing but I already have a Magpul hand guard on the way.

You'll have to mod that handguard slightly, in order to get it to fit the .308 AR.  I'll dig for some pics of what needs to be done - it's very minor.  Basically, you're cutting the internal heatshield, and bending it out of the way, so it'll clear the barrel nut.  <thumbsup>

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So the upper arrived from Midway today and I have to say that for the most part I'm pleased with what I received. 

So far the only hitch is the bolt release.  I remember reading here about someone having trouble with the bolt hold open and stating that "It will not lock back because the carrier is beveled..."  That struck me as odd at the time because the bolt hold open is supposed to catch on the bolt and not the carrier.  I now know why that person thought that and what the problem is/was.

It turns out that the DPMS supplied bolt release needs to be releaved a bit to clear the upper so that it will rise in front of the bolt.  As it is now, it comes up just enough to hit the carrier slightly. 

This is the only thing I need to do to have the weapon 100% functional on the bench.

I just installed Troy flip up sights (which, true to what I've read are hell for stout) and am only awaiting a new hand guard and sling attachments and it'll be range time.

The Colfax lower meets up very nicely with the upper.  The rear pin boss is a very tight fit and I have to smack the receiver extension still to get it open but that is better than to loose.  It has already moderated a bit and I'm sure will wear in nicely.

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Already got it fixed.

A little judicious cutting with a file safety'd with some tape and it's working fine.

Hand guards and sling mounts tomorrow and then it's to the range for testing.

After that, I may take a file to the trigger guard to round it off a little.  It has a very sharp edge that digs into my middle finger the way I carry it when my trigger finger is along the receiver.

Then it'll be some type of refinish of the lower and done except for looking for a scope but that's just gravy.

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Finished.

Well, except for some glass, rounding off the trigger guard and I'm toying with the idea of a dazzle camo paint job.

It was mentioned that the MOE hand guard would need to be modded but it would actually fit and very well with no mods at all were it not for the Troy HK style gas block front sight.  The sight has a round sling attachment point on either side that was just preventing the upper hand guard from going fully home.  Again, a few careful swipes of a file and they all fit together well.

Next stop test fire.

Am I the only guy who's got a Colfax lower project done?

TG

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Ok, took it to the range today and fired about 40 rounds through it.  ZERO problems.

The gun did great.  I sucked.  In mitigation, the firing positions as you can see by the pictures are set up for bipods/rests etc.  This is just a sighting in range at one of our wildlife management areas.  The firing positions don't lend themselves to no sling, no bipod, no rest shooting.

That and I've learned my lesson....  The folding stock that works for a 5.56 does NOT do you any favors when shooting 7.62.  Recoil is not objectionable by any means but you don't want to be wearing nothing but a very thin summer shirt unless there's a recoil pad of some sort.

So I set up at the 25yd line as I'm only working with the troy backup sights and really I'm just function testing/breaking in.

I prepared at the firing point with the weapon, two Pmags and several boxes of Federal gold match.  I also had with me some of my hand loads but I wanted to start with the factory stuff.

My procedure with any semi auto that I've either worked on or in this case is new to me is to load one round and fire it.  The bolt should lock back on an empty mag. 

I fired one round and the bolt locked back. Check.

In this case, since we are in the "break in" period, I cleared the weapon and ran the bore snake wet down with CLP through one time.

I then loaded two rounds and fired one.  Weapon should cycle and be ready for another shot with a proper trigger reset. 

For those who don't know, the disconnector on a semi auto does just that.  As soon as you release the hammer from the trigger sear, you are no longer in control of the process.  In the AR type weapons, the hammer strikes the firing pin which initiates the primer firing the round.  The gas system cycles the action.  During this time, the bolt carrier cocks the hammer but it is captured by the disconnector and not the trigger IF you are using a proper trigger follow through and keeping the trigger held to the rear.  once the action closes on a fresh round, you then release the trigger.  The disconnector releases the hammer which then gets captured by the trigger sear ready to be released again by your trigger manipulation.  This you can feel and hear with the typcial AR "thunk" as the trigger resets.

Thus the reason for the two round test is to check feeding and trigger disconnect.  If the hammer were to not be captured by the disconnector, it would follow the bolt carrier home and possibly fire the cartridge thus (as we only loaded two) doubling.

Rifle didn't double.  Check.

I ejected the live round from the chamber and ran the bore snake through again.

I then loaded up five rounds and fired for effect on the head portion of the target.

Yes the groups stink.  Yes I was dealing with a sub optimal firing position and yes my 49 year old eyes could only make out a very fuzzy front sight and yes, the yet to be broken in DPMS gravally takeup trigger possibly contributed.

I'm still pleased.  PARTS of the groups indicate that the weapon is already way under minute of bad guy/zombie which is it's main purpose.

More shooting will happen at a better range and next paycheck some glass will be ordered.

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It's the Amelia Wildlife Management Area.

I suspect they have a common design they are using all over the state now.

If you look at it in google maps/earth you can see that they used to do the concrete tube thing.

TG

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Great point, about the common design - seeing your photos, that's exactly what they're doing.  I'll dig up some of my pics from Phelps and get them in here.

The chickenwire and clothes pins for hanging targets - brilliant.  The shooting positions are great.  One thing I noticed about your pics - I was wondering when they put the swing-down doors and stop signs up at Phelps...  <laughs>  That wasn't there (at Phelps) when I moved outta VA state in late 2010.  That's another good idea, considering how the places are run (come and go, no dedicated range safety).  <thumbsup>

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It's a pretty slick setup.

Once you all agree to a cease fire, you slide the stop sign in front of the firing port and ALL of them are ganged together so there's no way for someone to not know what's going on.

Every point was in use that day and everyone was very cooperative so it was a non issue but I can see how smart that is just in case there's someone wool gathering or some such.

TG

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