Barrel Fitment

[mustachexpress]

Hey y'all first time poster here.I did a quick search to see if I could find an answer to my question, but did not notice anything. I have been in the process of assembling my first ar-10. I have assembled an ar-15 prior to this. I purchased a Wilson Combat receiver set and have already noticed some issues. First the pivot and takedown pins (CMMG) were too large in diameter and will not fit, Wilson Combat says "buy from us". Now I have run into an issue with the barrel. I purchased a Faxon Match series heavy fluted 18". The barrel will not seat into the Wilson Combat receiver. Using a set of calipers it seems there is a 0.65mm difference in diameter. I have tried to check for compatibility before I purchase and ensure that everything I have is DPMS styled and have even seen posts of Faxon barrels with Wilson Combat receivers. Did I purchase a Wilson Combat lemon? Or does Wilson Combat manufacture their receivers to only be compatible with their parts? I appreciate any help/advice y'all can provide, thanks.

[jtallen83]

1 hour ago, mustachexpress said:

First the pivot and takedown pins (CMMG) were too large in diameter and will not fit,

More who not to buy from than who to buy from lesson here.

Sounds like you have a nice tight fit, excellent for accuracy. Try some heat;

 

[DustBuster]

I have the exact same barrel and just like jTallen says, HEAT.  I did it different than the video, I haven’t watched it yet.  I put my receiver in oven on some bricks at about 300?degrees after I put my Barrel in the freezer the previous night.  Then after about 20 minutes in the oven, I quickly  smeared some barrel grease on it and the two slid right together.  I gentle tap with a board and a hammer on the back of the receiver made it seat completely the last 1/8 inch.  Sweet thermal fit.  Eye ball the feed ramps and make sure you like that alignment before it all gets normal temp again. My receiver was also smaller inner diameter than the barrel extension outer diameter.  Faxon seems to do it that way.

[98Z5V]

10 hours ago, mustachexpress said:

Hey y'all first time poster here.I did a quick search to see if I could find an answer to my question, but did not notice anything. I have been in the process of assembling my first ar-10. I have assembled an ar-15 prior to this. I purchased a Wilson Combat receiver set and have already noticed some issues. First the pivot and takedown pins (CMMG) were too large in diameter and will not fit, Wilson Combat says "buy from us". Now I have run into an issue with the barrel. I purchased a Faxon Match series heavy fluted 18". The barrel will not seat into the Wilson Combat receiver. Using a set of calipers it seems there is a 0.65mm difference in diameter. I have tried to check for compatibility before I purchase and ensure that everything I have is DPMS styled and have even seen posts of Faxon barrels with Wilson Combat receivers. Did I purchase a Wilson Combat lemon? Or does Wilson Combat manufacture their receivers to only be compatible with their parts? I appreciate any help/advice y'all can provide, thanks.

This is tough.  Hear me out.  When you're dealing with precision parts, dimensions matter.  So...

#1.  You're dealing with TWO very reputable companies.

#2.  Your stated measurement was 0.65mm.  Weird measurement, but that's exactly 0.025" - 25-thou. 

#3.  In precision measurement, and fitment of parts, 0.001" difference is usally called a "press-fit".  You know the parts are different, and they're gonna require some external force to make those parts mate together.  Wheel bearings in a hub are a perfect example.  When you get to a 0.002" difference is often called an "interference fit."  There's a reason those parts need to be held together. with that much press-force, and never come apart under "intended use." 

#4.  With press-fit force, you can accomplish this with no additional actions, besides making these things go together, press, hammer, whatever.  With an interference-fit, you need additional steps.  You either heat parts, or freeze parts, or a combination of the two - in order to get those parts to mate. 

#5.  You are stating that the difference is 0.025".   That's a pretty serious interference-fit, right there.  In order to mate this barrel to this upper, you'll HAVE to do two things, and it'll go RIGHT together.    You have to heat the bare upper receiver in an oven to 300* for one hour.  You have to freeze the barrel in your freezer overnight.  Period.  That's it (wear an oven mitt...).  Pull the upper out of the oven (oven mitt), and pull the barrel out of the freezer, and slide them together.  Might take some pressure, at 0.025" fitment, but it shouldn't be much.

This isn't my first rodeo with interference-fit parts.  They're in engines everywhere, and I've built alot of engines.  And guns.

That's my $0.02 on this whole affair... 

[98Z5V]

My final comment is - you always verify your measuring equipment FIRST, when a number that is normal, comes out different.  Verify your measuring equipment.  True it up before you measure something important.  Calipers come with verified dimensional slugs, just for this purpose.

[mustachexpress]

Hey all, just wanted to say thanks for the advice. The heat treatment worked like a charm, cold barrel slid right in to the hot receiver. Great community we got here!

[DNP]

I love it when a plan works out. Thanks for taking the time to come back and confirm it worked. This thread will help a lot of people out there who won’t ever wind up posting. Getting to hear that it worked for you will seal the deal and provide them with the confidence to give it a shot. 

[98Z5V]

50 minutes ago, mustachexpress said:

Hey all, just wanted to say thanks for the advice. The heat treatment worked like a charm, cold barrel slid right in to the hot receiver. Great community we got here!

That's epic news, man, and I'm happy that it went together - not much force, putting those two together after that process?

When I have to do bearings in a motorcycle engine case, or a separate transmission, and I'm dealing with the removal of all those press-fit bearings - I bake the cases at 300* for an hour.  I pull them out of the oven, and SLAM that case half down on the workbench...   and all the bearing fall out, onto the bench.  The new bearings were already frozen - like yesterday - and I drop them right into that hot engine case, right then.  Biggity-BAM!  Done deal, let it cool, and move on to engine assembly.

I'm VERY glad that work for you, and VERY glad that you provided numbers beforehand.  Maybe now, some of these other fuckers will start listening to me, and stop thinking I'm craaaaazy...  

[Matt.Cross]

On 9/19/2021 at 1:30 AM, 98Z5V said:

I'm VERY glad that work for you, and VERY glad that you provided numbers beforehand.  Maybe now, some of these other fuckers will start listening to me, and stop thinking I'm craaaaazy...  

You ARE crazy. It just happens that all your other qualities are redeeming.... 

[98Z5V]

Just now, Matt.Cross said:

You ARE crazy. It just happens that all your other qualities are redeeming.... 

I resemble that remark.  That doesn't mean that I accept it, though...  

[DustBuster]

Congrats Mustache.  Before I baked my 6066-T6 aluminum upper, and froze my 416R steel barrel, I tried to do the math on the thermal expansion/contraction of those materials.  I think you find the thermal expansion Coefficient, multiply it with the Change in Temp, and multiply that with the number of interest( diameter).

I believe Most of the help in mating the two is due to the growing of the aluminum, with a teanie, Tiny, bit of help of shrinkage of the steel (almost negligible).

 It’s a friggen sick feeling to try and put the ol Faxon Barrel into the hole, before Temperature Therapy,  and it only goes in a painfully tight 1/16” of an inch, rubbing off the Teflon.  I’m sure you felt the same shock.  Happy results.  When your all done @mustachexpress let us know how that Barrel and you shoot. 

[DNP]

A side track, but made me think of it. Back when we used to use steel tapes on the regular for surveying, you had to apply a coefficient to adjust for expansion of steel above a certain temp. Those tapes would be pulled to a specific tension and you would multiply by .000001 or something in that ballpark times every degree of temp over 74 times your measurement and add that to your total. It’s funny how metal works.  It’s also funny that we wasted our time with that crap when there are so many other sources of error. 

[Lane]

4 minutes ago, DNP said:

you would multiply by .000001 or something in that ballpark times every degree of temp over 74 times your measurement and add that to your total. It’s funny how metal works

There is also a twist factor; which had to be factored into that length. Any "round" tube will twist a tiny amount with temperature. A long steel measuring tape has both length and twist to contend with. Sometimes the decimal place matters; other times. I wish I didn't care at all. 

Twist is a pretty big one though. Is that really a millionth of an inch?

[DNP]

Of a foot. And we use tenths and hundredths of feet…no inches.  Tapes were flat steel and 200’ long. 

[DNP]

I had to go look it up. I was way off. .000645. 

[jtallen83]

14 hours ago, DNP said:

 It’s also funny that we wasted our time with that crap when there are so many other sources of error.

I've got an old compensating ruler for 100 ft steel tapes and railroad track, I would need a magnifying glass to see the the smaller increments. 

[Tack14]

haha, glad this worked out. 

With my KAK LR-308 upper and BA barrel for first 308 AR upper build,  it was kind of a loose fit, easy to rotate etc. and i was a bit disappointed.  Although the barrel nut is holding it fine

[98Z5V]

8 hours ago, Tack14 said:

haha, glad this worked out. 

With my KAK LR-308 upper and BA barrel for first 308 AR upper build,  it was kind of a loose fit, easy to rotate etc. and i was a bit disappointed.  Although the barrel nut is holding it fine

Bed that barrel extension with some Loc-Tite 609, in that instance right there ^^^, and your accuracy will improve.  For real.  

[Tack14]

45 minutes ago, 98Z5V said:

Bed that barrel extension with some Loc-Tite 609, in that instance right there ^^^, and your accuracy will improve.  For real.  

wow thanks @98Z5V - will look into that. I still consider this one "in progress" lol.