Are Pre-Ban Colt AR-15 Sporters Mil-Spec?

[Chris]

If this has to go into the "Firearms" category, so be it, but I wanted to hit as wide an audience as I can to answer this...

So, I FINALLY got the adapter pin so that I can mount my Beowulf upper onto my Colt Sporter AR-15 lower.

I assembled it, adjusted the adapter pin to get a nice fit between the receivers, ditched the Accu-Wedge as it isn't needed, and went to pull back the bolt.

And I can't.

So, I opened up the receivers, pulled the bolt out and tried fitting it into the recoil tube. Fits fine.

Only thing I can think of is that the upper does not align the bolt with the recoil tube of the lower.

Has anyone seen this kind of thing with Colt Lowers? I know the pivot pin was different in the Colt lowers, but I thought that was the only difference. Since I've only found ONE posting of someone with a similar problem on the web (his was also a pre-ban Colt) I'm wondering if this is some kind of known issue with swapping uppers on the Colts, or should I start looking for other lowers to do some test fits?

I just hope that the Anvil Arms lower that is coming in Group Buy fits.

 

[Mike-Mike]

If this has to go into the "Firearms" category, so be it, but I wanted to hit as wide an audience as I can to answer this...

So, I FINALLY got the adapter pin so that I can mount my Beowulf upper onto my Colt Sporter AR-15 lower.

I assembled it, adjusted the adapter pin to get a nice fit between the receivers, ditched the Accu-Wedge as it isn't needed, and went to pull back the bolt.

And I can't.

So, I opened up the receivers, pulled the bolt out and tried fitting it into the recoil tube. Fits fine.

Only thing I can think of is that the upper does not align the bolt with the recoil tube of the lower.

Has anyone seen this kind of thing with Colt Lowers? I know the pivot pin was different in the Colt lowers, but I thought that was the only difference. Since I've only found ONE posting of someone with a similar problem on the web (his was also a pre-ban Colt) I'm wondering if this is some kind of known issue with swapping uppers on the Colts, or should I start looking for other lowers to do some test fits?

I just hope that the Anvil Arms lower that is coming in Group Buy fits.

YES! I have a large pin colt lower and a new upper. insert the offset pin from the left side and torque the right side slotted nut.

You should be ok.

 

[economist]

Some preban sporters have a sear block that was installed by Colt to make it extremely difficult / impossible to put full-auto parts into the lower. In addition, the hammer and trigger pins are slightly larger, along with the irritating large hole front takedown "bolt", IIRC.

Your problem may be that the sear block is interfering with the bolt carrier. If you have a sear block (rear of receiver, above selector), it has a little bit of metal that sticks up over the top of the receiver. A notch in the carrier allows the carrier to ride over this block. If your Beowolf upper has a carrier without this notch, you can file or grind down the sear block such that the carrier will travel. Don't try to remove the sear block.

[edited to add: I just looked at my preban colt lower and tried to mount an upper with a milspec carrier. It doesn't work. The sear block interferes with the carrier as I mention above (take out the carrier and try to move it over the lower into the buffer tube to see the interference). This must be your problem. Note how your Colt upper has the back end of the carrier completely removed on the bottom. So, just grind down the sear block until it is flush with the lower. But go slow, the block is steel.]

 

[Chris]

Hmm... I need to do some measuring.

This is the Sear Block (the part marked COLT)

The Beowulf bolt carrier is closed at the rear, but then opens up like the Colt's bolt. It looks like it should miss the Sear Block and since the carrier goes backwards...

 

[economist]

Yes, that is it, and it depends on your carrier whether it will work. I know in my case that a milspec carrier on an ar-15 upper will not work with my preban Colt lower. Good luck, and please post your results if you don't mind; I am interested in what you find.

 

[economist]

I bet the sear block is your problem. I did some searching, and found the following review on the Cabela's website. So another solution appears to be to use your Colt carrier with your Beowulf bolt. I would add that using the lighter Colt carrier might argue for switching to a heaver buffer in your lower when using the Beowulf upper:

"I ordered my Beowulf .50 Entry Kit from Cabela's in October of 2007. Product arrived on time and as advertised.
I was putting the Beowulf on my post ban Colt HBAR Match Target Rifle ar-15. My Colt has the block over the safety and the Beowulf bolt carrier would not move past that point. Not happy about the prospect of having to buy another lower to make the Beowulf function I called Alexander Arms. I spoke to their gunsmith and he told me to use my Colt bolt carrier with the Beowulf bolt. Problem solved. He also assured me that there would be no damage to either platform by interchanging parts. Sixty rounds later, no problems to report.
Off to the range to zero in. Firing 400gr. Alexander Arms soft point bullets I was able to fire a 1.1" cloverleaf at 100 yards. Recoil was way less than I was anticipating, along the lines of a 30-06 firing 180gr. bullets. I don't think it needs the optional muzzle brake, the noise is not worth the minimal recoil reduction.
I took it out hunting in Shenandoah County Virginia over Thanksgiving. Harvested a button buck and a doe. One shot stops with devastating results and accuracy.
I am very pleased with the Beowulf and the versatility it gives my ar-15, it is no longer relegated to just a varmint and small game gun."

 

[icyclefar]

Remove the sear block, and you should be fine.

This might help:

http://www.ar15.com/forums/topic.html?b=3&f=118&t=380384

 

[Chris]

OK..

I could not get a real accurate measurement, but the block was CLOSE.

So, I went out to the garage and used some marking paste that is normally used to align ring and pinion gears in a differential. I placed some on the rear of the sear block, and on the edge of the bolt carrier. I then assembled the rifle and attempted to move the bolt.

On disassembly I could see that the sear block does indeed contact the edge of the bolt carrier (and after cleaning the marking compound off I could see the slight impact marks. I also saw marks on the upper edge of the recoil tube. From the looks, the Sear Block is pushing the bolt carrier up just enough that it can't fit into the recoil tube. This is probably a very good thing as it would be a real PIA to pull the gun apart if I had managed to get the bolt carrier to move rearward off the Sear Block.

I took some pics, but the dark red compound was not easy to see against the black parts unless the light was just right.

Thanks for the help.

Remove the sear block

As tempting as that is, this is an all original Pre-Ban Colt (I've only swapped out the pivot pin with an easy take-down, but I kept the screw) Since it is worth some $$ in MA, I'm going to try to keep this in original condition.

Just means that I'm REALLY EXCITED for the NES lowers to arrive. (^_^)

 

[Jake L]

It sounds like it is the sear block on the Colt is causing the problem. Once you get your Beowulf together check if the bolt goes in and out of the barrel without binding, see if you can chamber and extract a round without firing it. Try this with a random sample of your ammo I had 12 out of 20 that would stick in the chamber and I would have to pry the bolt back to extract them. It turned out not to be the ammo but the barrel.
After talking with Alexander Arms I had to send my Beowulf barrel back to AA because it was chambered to tight.
Where did you find the upper? Right now it seems that if you want one of these you have to order now and wait until Feburary 2009.

 

[Chris]

Thanks for the head's up on the chambering. In playing with just the upper, new rounds seem to chamber and extract without any issues.

I ordered mine in March as soon as the AR lower buy was finalized. I picked it up about two weeks ago but just got the adapter for the Colt Pivot the other day.

Here is the "Beauty Shot" I took once I got the accessories installed:

BEOWULF (shown here modeled by the Colt Lower)

That's the Alexander Arms full floating "Precision" upper. I added the proper size dustcover (standard one doesn't fit the larger ejection port) and the sling stud for the bipod. The EOTECH is model 556 (new side mount buttons with NV)

Now I need to find more ammo. All I have are those 4 boxes of the 400 Grain. Have several cases on order, but still backordered.

 

[Joe R.]

Not trying to be Scrivener but are you planning on selling the Colt lower? These rifles, like any other item, are only worth what money someone is willing to spend on it. If you plan on keeping the rifle, get rid of the block. If you plan on selling it, swap the carriers. Just because something is here in MA as a pre-ban doesn't mean it will be bought... just ask Jolly Roger about his SP-1 that is gathering dust at Northeast Trading!

Joe R.

 

[Chris]

I hear ya.

There are other reasons. I really hate the adapter pin as it isn't nearly as easy to deal with. I like the idea of keeping the Colt as issued for teaching purposes. Having the block in there and being able to say "this prevents anyone from installing the parts to make this a machine gun" has some value.

Little stupid things like that all add up to me not wanting to alter this one. Which is why I need more lowers to build on. (^_^)

 

[vellnueve]

New lowers can be had pretty cheap. Even retail at FS, they're only $130.

 

[Mike-Mike]

Yes, that is it, and it depends on your carrier whether it will work. I know in my case that a milspec carrier on an ar-15 upper will not work with my preban Colt lower. Good luck, and please post your results if you don't mind; I am interested in what you find.

I have used both carriers without a problem and I got a really old sp1 lower.

 

[M1911]

I have used both carriers without a problem and I got a really old sp1 lower.

Does your SP1 have the sear block? IIRC, Colt didn't start putting in the sear block until later.

 

[Mike-Mike]

Does your SP1 have the sear block? IIRC, Colt didn't start putting in the sear block until later.

No block here. Actually the first time I look at one of those bad Larry's was in that pic.

 

[Wildweasel]

Mill a slot in the carrier to clear the block. from what you describe you don't need to go all the way through. just a clearance cut. it is the cheaper part of the two. and replaceable.

I would not alter the lower.

 

[Jake L]

Chris the 50 Beowulf is great. This is mine on a Alaxander Arms 50 Beowulf lower I built.
If fact most of this gun was built by me.

 

[brad3]

colt lower

go ahead and clean off the block and enjoy the rifle,,it wont affect the value and that lower isnt one of the more sought after ones as it has the large pushpin hole. you dont gain much with that lower because it came orig built with a standard stock so you cant install a slider,,you can have some other un important features though. that blosk was mostly meant to prevent people from using drop in auto sears..unless you know how installing the real full auto parts is more involved. just enjoy the rifle and shoot lots of ammo,,,,,,our govermant will be comming for yours and everyones guns,,,we have socialists in power that love lenin and marxist ideas......
our country is in trouble ,,,,,,, enjoy your toys