jelenko
Gold $$ Contributor
Well, fabulous. I've got a bunch of 220 and 243.
I'll just crank up the rounds down range to use them up
Any AR builders/tuners — Lapping Q?
- Thread starter Rsadams
- Start date
I'll just crank up the rounds down range to use them up
skeeljc
Gold $$ Contributor
I do not remember, but not much.
Have you taken apart an upper receiver and barrel that had been assembled using 620? If so, was it difficult?
LVLAaron
Gold $$ Contributor
I have. It's not pretty but it's not impossible to clean up. Those little wire wheels for your dremel tool are the ticket.
When I get a new barrel, I will shoot it a bit before doing any bedding. If it's a shooter.. I'll take it apart, and glue it in permanently. AR barrels last forever and uppers are cheap... Cost of doing business.
When I get a new barrel, I will shoot it a bit before doing any bedding. If it's a shooter.. I'll take it apart, and glue it in permanently. AR barrels last forever and uppers are cheap... Cost of doing business.
VA_XTC_Shooter
Silver $$ Contributor
Those are thread lockers, not retaining compound. They are specifically designed for different purposes.
It says right there in the link I provided.
Retaining Compound vs. Threadlockers
In most cases, manufacturers asking whether they should choose retaining compound vs. thread lockers must identify their specific application and substrate. Retaining compounds are higher strength and designed specifically for bonding components. This stands in opposition to threadlockers that are usually designed to prevent leakage, loosening, and corrosion of threaded fasteners. Choosing the correct type of adhesive is crucial within automotive and heavy machinery applications and, when high strength bonding is required, retaining compounds are generally the right choice.VA_XTC_Shooter
Silver $$ Contributor
Depends on your purpose. Typically pull mine between 3-5K rounds as they lose accuracy at distance.
Hey thank you very much I have been pretty down on this one but I went to my heart doctor today and got a lot better news than I was expecting... He's told me he thought it was completely different problem which I can definitely deal with... I thought my time might be limited but as it turns out I am not perfect but ok... After surviving two Widowmaker heart attacks in the last three years I think we have things settled down... unfortunately this time I retreated into a dark place and if I wasn't asleep I threw myself into working on this rifle to stay busy and to try and keep my mind busy... The worst part was watching my wife worry...
Once again thanks for your post it means a lot to me.... I really learned who my friends were during this mess.. That alone upset me alot...
I think originally people used Permetex blue, it's a medium strength thread locker.
I use the Loctite 242, which is the equivalent to Permetex blue, to make handsaws. I also use 5 minute epoxy for that purpose. I know they have purple and green, but my understanding is those are not as strong as 242. I could be wrong, if so please correct me. Epoxy also loosens with heat. The 620 is for high heat, whatever that means.
I posted I wanted to be able to remove the barrel and I am glad we got into this discussion and bedding the barrel because I didn't even think of the amount of heat these guns can get to in a situation.... I have this thing about not getting barrels hot but here in Texas they do get hot in a few shots I could only imagine if you were really hard on it in a bad situation..... once again thanks everyone for posting I am learning a lot in the way I was thinking about something as easy as an AR barrel swap.... like I said I may have opened a can of worms...lol
VA_XTC_Shooter
Silver $$ Contributor
Re heat - the retaining compounds are heat rated to indicate the heat range before they break down, stop doing their job. The thread locker, like 242 loses 50% of it's strength 200*, the retaining compounds are rated to 300-400* before they break down.
I face the receiver, sometimes lap the ID and use stainless shim stock. Heat and cool as necessary for slip fit assembly. Once cooled off you can't pull them apart w/o reheating the receiver.
Locktites are nothing more than bondo like fillers and the only strength they provide is in shear.
Locktites are nothing more than bondo like fillers and the only strength they provide is in shear.
jelenko
Gold $$ Contributor
And, that's ok, yes? The barrel nut and index pin are keeping the barrel stationary, yes?
@jelenko
The barrel nut pulls the extension up against the receiver. With shorter barrels that's probably enough to hold the barrel steady. With long heavy barrels, you may need the support of a better fit inside the receiver.
I've heard folks say they slide the extension in and had to tap the last 1/4" or so.
That tells me they have no idea of the fit inside, just that the last little bit of the threaded nose is stabilizing the barrel. Deep inside, it could be loose.
I use a heavy walled upper. A thermal fit, or shims, can give a tighter fit over the entire length of the extension, not just the weaker nose. Might mean making some measurements (receiver I.D. and extension O.D. to know what you are putting together.
This extra effort is not needed for most AR's, just when you are trying to get the best you can at longer ranges.
This barrel/receiver combo won't slip in all the way. But, it is NOT a thermal fit.
Warming it up some it would likely go all the way in without tapping with a 2X4.
How loose is it inside the receiver?
What part of the receiver actually holds a long heavy barrel stable?
The barrel nut pulls the extension up against the receiver. With shorter barrels that's probably enough to hold the barrel steady. With long heavy barrels, you may need the support of a better fit inside the receiver.
I've heard folks say they slide the extension in and had to tap the last 1/4" or so.
That tells me they have no idea of the fit inside, just that the last little bit of the threaded nose is stabilizing the barrel. Deep inside, it could be loose.
I use a heavy walled upper. A thermal fit, or shims, can give a tighter fit over the entire length of the extension, not just the weaker nose. Might mean making some measurements (receiver I.D. and extension O.D. to know what you are putting together.
This extra effort is not needed for most AR's, just when you are trying to get the best you can at longer ranges.
This barrel/receiver combo won't slip in all the way. But, it is NOT a thermal fit.
Warming it up some it would likely go all the way in without tapping with a 2X4.
How loose is it inside the receiver?
What part of the receiver actually holds a long heavy barrel stable?
I have .002" SS material, actually heat treating "foil" which I use as a shim. I cut a piece the full width of the barrel extension and nearly a full wrap all the way around. Then I do the thermal fit, upper heated in an oven. Makes for a very tight fit.
For taking back apart I use some tooling and a hydraulic press to push the barrel out of the receiver, with some heat gun application for good measure.
I've never tried the loc-tite method. I did put a gas block on one time with the 620 sleeve retainer (and set screws lightened gently). Then wouldn't you know it, some time late I had to get that gas block off again. That was a chore.
For taking back apart I use some tooling and a hydraulic press to push the barrel out of the receiver, with some heat gun application for good measure.
I've never tried the loc-tite method. I did put a gas block on one time with the 620 sleeve retainer (and set screws lightened gently). Then wouldn't you know it, some time late I had to get that gas block off again. That was a chore.
It is during these times that you do truly learn who cares about you, sometimes in a good way, sometimes not so much. Praying for your recovery and continued health!
LVLAaron
Gold $$ Contributor
If you can fit 4 thou of shim in there... something is out of spec.
It IS a very solid fit.
I've done several like this. I don't quite recall measurements, and I didn't make any notes. I want to say extensions typically .998" plus a few tenths and receiver bore right about 1 inch. IIRC. These are nothing-special parts, just generic run of the mill stuff.
Oven temperature is about 400 degrees F. No cooling or freezing of the barrel/extension. Fast work and it does usually require cranking the barrel nut with a wrench to draw the barrel in. Not a lot of torque but you're not going to seat the extension by hand. I never used locktite or put one together dry, I always put a light coat of grease in the outside of the shim material mostly for disassembly reasons.
Few years ago I did buy one of the uppers that's said t be a thermal fit and IIRC the interference was about .001" not super-duper tight.
Truthfully the most accurate, or precise if you prefer, upper assembly I have I just put together without any regard to fit at all. The barrel and receiver went together with even a little wiggle between the two. Tightened the nut and that sucker shoots great.
I've done several like this. I don't quite recall measurements, and I didn't make any notes. I want to say extensions typically .998" plus a few tenths and receiver bore right about 1 inch. IIRC. These are nothing-special parts, just generic run of the mill stuff.
Oven temperature is about 400 degrees F. No cooling or freezing of the barrel/extension. Fast work and it does usually require cranking the barrel nut with a wrench to draw the barrel in. Not a lot of torque but you're not going to seat the extension by hand. I never used locktite or put one together dry, I always put a light coat of grease in the outside of the shim material mostly for disassembly reasons.
Few years ago I did buy one of the uppers that's said t be a thermal fit and IIRC the interference was about .001" not super-duper tight.
Truthfully the most accurate, or precise if you prefer, upper assembly I have I just put together without any regard to fit at all. The barrel and receiver went together with even a little wiggle between the two. Tightened the nut and that sucker shoots great.
I'm known for buying cheap parts on sale! After lunch I'll get out some uppers and extensions and measure them.
I'm all for cheap parts
Many of mine use the $99 BCA upper/BCG
Many of mine use the $99 BCA upper/BCG
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.