Accurizing the AR15 on the cheap: How to shim a barrel extension for a tight fit.
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- Опубликовано: 26 июл 2024
- This is a brief video explaining how to shim a barrel extension to eliminate sloppy fitment, and accurize your AR15.
I'm not a gunsmith, machinist, or expert. I'm just a guy with a webcam and too much time on his hands. This video is provided for informational purposes only. I'm not responsible for anybody who follows this advice.
That being said, I've tested shimmed vs. unshimmed barrels and have found that in receivers that have sloppy fits, this can improve accuracy noticeably.
This will not make a bad barrel good. It just eliminates one small variable in the quest for accuracy.
As soon as you shoot 5 shots in a row, the barrel will swell up to an interference fit in the receiver. So I'm not sure how much this helps. I guess if you have one that is particularly loose it makes sense; but most of the kits I've built, the barrel was already tight enough to where I had to tap it in just a bit.. The main thing I have found that helps with consistency is: When you tighten down your barrel nut-- back it off and tighten it again 3 different times; and make sure the threads are lubed. A lot of issues with stringing can be explained simply by your threads getting a little bound up when tightening it down and causing the torque wrench to give a false reading... causing your nut to be too loose, and you don't realize it. I had this exact issue with a D-ring nut, where you have to line up the hole for the gas tube to go through; and it was already over 40lbs, so I knew there was no way I could get to the next hole----- So I ran it like that for a few months, and had some random stringing after it would heat up. After seeing a few videos explaining to tighten and loosen the nut a few times (with lubed threads) -- I took it apart and tried it, and sure enough- I was able to tighten the barrel nut over to the next gas tube hole, and it was much better after that. So DRY aluminum barrel nut threads is a major cause of issues. Make sure you lube your threads
just leave the gap where the ends dont meet at the alignment pin. no extra cutting needed
Yep, that’s what I did.
I do the same thing.
Like a glove!!!
I cut the mating corners that meet at the pin so they come together to form a notch around the pin
I use stainless feeler gauges and apply a bit of grease to all the surfaces to make the install a bit easier. I've seen varied degrees of improvement, but it's never made a barrel less accurate.
Much better than adding goop that releases from getting too hot after a few mag dumps!
This is great info. I'm gonna try this on my next SPR build..
Thank you. I shimmed mine and it turned my 5inch at 100 Meters group wanting me to throw it away, into a dead center hit on a gong at 400 Meters. ( I Used a feeler gauge to get a shim that worked and used that )
Thanks for that. Seems easier than thermofitting, especially for a beginner such as myself.
I learned this trick years ago from an armourer named Joe Carlos. It’s the first thing I do when building an upper. I bought a roll of stainless steel and it’ll probably last me 10 lifetimes. There was so much wobble even after torquing down the barrel nut. Carlos was an armourer for the US service rifle shooting team. Watch the videos. Search 90 grain .223. He didn’t make a “how to” video but he talked about the identified problem. I usually have to tap it in and haven’t had to pull any because they’re all shooters. Everyone should do this.
Thanks for sharing this information!
I used a dremel with a stone tip and very quicly ground a channel. It also cleaned up the sheared edges quite nicely. Thanks for the video!
Maybe put the barrel in the freezer and/or heat up the upper receiver threads or both? Wouldn't that allow a thicker shim and tighter fit? Anyone try that?
I like the rubber band trick.
There’s not much content out there on this subject. Thanks for posting!
If it’s too tight you can also heat your upper up a bit with a butane or propane torch, causing it to expand and making it easier to fully seat the barrel extension. In fact, I know of a few high end AR manufacturers like JP & Mega Arms/Zev that undersize their uppers a thou or two from the factory and absolutely require “thermo-fitting” of your barrel. (Assuming the barrel is within spec, of course). It makes for a VERY tight fit and a much more accurate rifle assuming all other variables remain constant.
Yup. I've subsequently decided it's generally better to just spend a few extra bucks and buy tighter tolerance uppers to begin with.
Great video, thanks!
I did an Oden Works SS barrel and a VLTOR MUR upper receiver. I had to tap it in the whole way, I guess I got lucky. Both items were pretty expensive so that probably had something to do with it.
Did you write a glowing review for mur upper on optics planet? User reported using the same combo
@@rmblwgn I don't know I would have to look. If you want to know if it's mine just look at if the review says that I used a Daniel defense 14.5 mid length barrel. Or if it's a 20 inch Odin works Grendel with a G2S Geislee trigger with a Luth AR stock If it says that then it's most likely mine. I've done two builds with that receiver
Dry fit first and count on remaking your shim because it will get deformed, then make sure to have a torch and rubber mallet on hand, as you "persuade" the barrel into the receiver, try not to heat the receiver up beyond 300f or so otherwise you may weaken it, make sure the barrel alignment pin is aligned with the slot on the receiver, if not the receiver will cool from contact with the barrel, end up misaligned, and you will have a bad time. Last second add some green loctite to make sure there is no play, keep it off the threads. Have a helper and a plan, some people (me) jumped into this thinking it would be really easy, then end up with the barrel stuck in the wrong position because everything has cooled. Don't freeze your barrel to shrink it, I think it does more harm than good given the difference in the thermal expansion of steel and aluminum, once they touch that aluminum receiver sucks the cold out of the barrel and shrinks fast.
Ever since I have seen your video I have wanted to do this to my barrels. You're video really pointed out an awesome point when installing a barrel to an upper reciever. But I have tried looking for this type of shim stock at every hardware store/Amazon but I can't seem to find it anywhere. Do you know where I could find some? I'd really appreciate any help or advice you can give, Awesome video! Thanks for showing this method of barrel installation!
www.amazon.com/dp/B003CNJB48/ref=cm_sw_r_cp_apa_fabc_Z0JA22Q7479K8YWQNJ2P
Alternatively, you could probably call a machine shop and buy a foot of it for a few dollars, which would be more than enough.
Quick question...did you use a feeler gauge to determine what thickness to order? I see in the comments you used .002, just curious because I’m definitely ordering some. Great video...I have 2 guns with a slight wobble and this is the answer to how I can fix it myself at home! Thx
I just played it by ear.
I have a few thicknesses on hand. .002 is generally a good compromise for all jobs.
If it's a bit tight, just heat up the receiver extension for about 15 seconds and it will thermal fit.
@@inexpensivearms6952 Thanks for the reply...just ordered a lifetime supply for $18 😂 6”x60”
@@bullfrog1807 You'd think that, but I'm already on my second can... LOL.
What thickness of stainless steel did you use and how many times have you done this and noticed an increase in accuracy?
What is your opinion of this method vs Loctite bedding of a barrel? I have a PSA upper apart to get Cerakoted and the barrel fits pretty loose. I checked it in another upper from Aeroprecision and it fit the same. I have seen Loctite 609, 620, 640 or 680 all recommended as a solution for bedding a barrel. It seems like a easier process and installation as I dont have to buy sheet stock in .001 .015 .002 or .003 to determine what will fit?
It's probably easier, to use Loctite. I hate the idea of using compounds though.
If you decide to use shim stock, I'd just buy .002 and call it good. .001 and .0015 will likely be too fragile and slightly loose, and .003 is going to be TIGHT.
I've seen a writeup before about a guy who tested both methods and found the shim method works SLIGHTLY better. it's pretty close. though. You could always do both if you really wanted to hedge your bets...
@@inexpensivearms6952 Thanks. I found this:
www.amazon.com/gp/product/B00065UX42/ref=ox_sc_act_title_1?smid=ATVPDKIKX0DER&psc=1
I am going to use the shim method. I have a SS barrel, alum receiver so it shouldn't matter that the shim material is carbon steel? I may still use 609 on it too. Thanks for the knowledge I found a few of your videos helpful.
I was wanting to try stainless tape on an old A2 upper.
Was wondering if to use copper tape or stainless tape for shimming the barrel.
Definitely stainless.
You might want to consider galvanic corrosion “Corrosion develops when two dissimilar materials are combined in a corrosive electrolyte. This can occur when certain materials (such as aluminum) are in contact with stainless steel.”
If that were a concern, then it would be a concern with any steel barrel extension.
You gave me a great idea. Thanx. What about having not protection from galvanic action?
I guess I've never had an issue with it.
FWIW, the shim is stainless, not uncoated metal. The barrel is nitride treated, and pretty corrosion resistant.
@@inexpensivearms6952 and barrel extension is frequently steel, and reveiver is aluminum... if galvanic corrosion was a problem, you'd already see it
Helpful video, thanks... how much stock do you put in receiver lapping (or truing with a lathe). I have an aero upper set aside for a 20" heavy build but habe no way to check for runout... the shops i spoke with said it will take .003-.005" off the face to make true. I have concerns about barrel extension feed ramp overhang once barrel is installed into receiver. Positive opinions on lapping all over the internet but enough counter opinions to make me scratch my head.
I do it on all my builds, although I'm not so high tech as to have a lathe. I just have a squaring tool with some valve grinding compound.
It helps a bit, in my opinion, especially if you happen to have a dirt cheap upper receiver. I'm partial to 30 dollar uppers that I square and shim, but they tend to have looser tolerances to start with, or more uneven anodizing.
It's really nice when you mount a scope for the first time and the windage is nearly dead on though...
@@inexpensivearms6952 thanks... no concerns about removing the anodizing?
@@Captain_Spaulding_01 No. Personally I consider the upper receiver to be kind of a "replacement" part anyway since they're only 30-50 bucks.
The "exposed" aluminum isn't actually exposed to the elements though, as it's tightly compressed against the barrel extension flange, and there's a greased barrel nut covering it. It will outlast your lifetime, even if you abuse the crap out of it.
@@inexpensivearms6952 thanks for your time. I guess I'm gonna have to pick up one of these tools. Likely from brownells.
@@Captain_Spaulding_01 No worries. I wouldn't even bother chucking the tool up in your drill. Just rotate it by hand and it will be fine.
nice, but if it is Ok for the shim to have nice size gap between the ends, why not just cut it to wrap around to each side of the extension pin, rather than go to all of the trouble to make the little cut out for the pin???
I think ideally there will be only the smallest of gaps, but ultimately, the goal is just to eliminate wobble before torquing the barrel nut to final spec. I think your idea could probably work, but what I've noticed is that the slot on the receiver that the extension pin slides into also happens to be the one area that likes to "grab" the shim and distort it or tear it up as you tap your barrel into place. YMMV. There's more than one way to skin a cat.
I have to assume this would only be worth doing for a barrel 16" or longer? On an SBR or ar pistol you lose some accuracy to begin with. However I suppose if you're building one why not. I'm at the point I already torqued the barrel and muzzle device on and am questioning the value of taking it apart for an 11.5in barrel. There WAS a tiny bit of play at the receiver.
My personal experience is that a loose fit vs tight fit can be up to a 0.5 MOA difference in accuracy, when squaring the face of the receiver and shimming are both done.
Realistically, for the distances you'll likely shoot a 11.5" barrel at (
@@inexpensivearms6952 I think I am in agreement. I will continue with the build and if I feel I am not getting the accuracy I think I should at say 100 yards I will look into shimming. Shouldn't take much, just muzzle device, gas block, hand guard and barrel nut. Thanks for weighing in, I appreciate it.
Bed it with green loctite, grease your barrel nut threads, and torque to spec. Let it set up and your good to go. All my ars have shot sub moa with good ammo, and none are "high end" most expensive barrel was a faxon gunner 18" around $180.
You couldn't pay me to use green loctite. People are obsessed with bedding and green loctite. There are a lot of videos out there confirming that this is a myth. Brownell's does a good one. I want to eventually be able to disassemble the barrel from the receiver, so I only use the loctite moly past on the barrel extension and threads. Done.
@@dickjohnson7845 I've never put it on the threads only the receiver and barrel extension. I don't know if it benefits accuracy and I don't know how permanent it actually would be. I do know with bolt actions it's highly recommended to bed the action for accuracy. I don't understand why it would actually help as your scope is mounted to the receiver which has the barrel mechanically attached with threads, but it's been proven to tighten groups.
@@jcows12 Green loctite 620 is not designed for threads, it's a bonding agent, designed for cylindrical applications like automotive bearings etc. It prevents loosening and leakage, so it's going to make the barrel that much harder to get apart if you already have a tight fit.
I'm gonna try just the shim without squaring off the receiver threads or using compounds, I jumped the gun and just used a feeler gauge I had lying around and didn't wait for the lapping tool.
".0015 fit pretty tight and requires some tapping of the mallet. I'll post my result here for research purposes. The rifle shoots about 2 moa with Hornady frontier and pmc xtac ball now.
you can tighten that up and would suggest taking that back off for a lapped receiver, also use a thing of Tubbs bore lapping bullet system 2moa is not that great at a 1k that is a 20" spread 😬😬😬 what if you are hunting and your animal is 3-400yards out 6"-8" spread is big enough to miss the kill box only injuring or prolonging it's suffering, but whats worse is that leaves room to loose your kill entirely, because it keeps running making harder to track, it's fine if you are just punching paper, or home protection.. but that leaves out a lot of room for shot placement when hunting
@@haylspa no lapping, it's sub moa just on shims. Why fix what's not broke.
Do I need to use grease in the barrel extension and upper receiver when I shim it? Or just use loctite 620?
No grease. If you can't get the barrel extension seated with the shim on it, heat the upper receiver with a heat gun or propane torch for 10-20 seconds near the threaded end and your shimmed extension will drop right in. When the upper cools, it will contract and the barrel will be locked in TIGHT.
If you shim you don't need locktite.
While i do believe this can help, once you tighten your barrel nut, it will not move as much as when you just insert it into the upper receiver. Also, no shim allows for some heat expansion with heavy firing.
My understanding is that the Aluminum is always going to expand more than the steel anyway due to different thermal properties.
Doing this helps the barrel harmonics
@@inexpensivearms6952 Aluminum has a linear expansion coefficient a tad more than twice that of steel.
This is why i like the BCM M4 upper receivers. They require a thermal fit. Just heat up the receiver and slide the barrel extension in. When it cools it makes for a nice tight fit.
Any chance you have links to the foil you used? I’ve searched amazon and not having a lot of luck? Thanks!
www.amazon.com/dp/B003CNJB48/ref=cm_sw_r_cp_apa_fabc_Z0JA22Q7479K8YWQNJ2P
That's enough to last you a lifetime.
@@inexpensivearms6952 thanks. I was able to find .0015, .002 & .003.
Don't cut the notch in the middle, nip off the two corners that will be adjacent when it is wrapped around.
0:40 it's not hard at all just take a propane torch and heat up the area and it should pop out quite easily. Even a high temp loctite can be heated enough to break free without even coming close to a temperature that will change the hardness of the barrel.
Yup. I started thermo fitting and it's way easier to get it on
A solution to a non existent problem.
A similar comment...
May be some sleeve retainer on the inside of the shim.
Can you post the group you got with this way?
Thanks for the video. I was looking for how to do this shim. Can you post a link to the material you used?
www.amazon.com/Stainless-Unpolished-Finish-Temper-Thickness/dp/B000SKV46Q/ref=sr_1_1?keywords=stainless+steel+shim+stock+.002&qid=1571686228&sr=8-1
This is a link for .002 thickness stock. Generally, that's a pretty good middle of the road shim to use. In my experience, only the loosest fits require .003, and .001-.0015 thickness tends to be harder to work with due to it being more fragile.
@@J-Portraits NP. Just be prepared to have more leftover shim stock than you could ever use in ten lifetimes.
@@J-Portraits Correct. If you use Loctite, make sure it's loctite 6xx series. I'm not a fan of that though.
You MAY need to thermal fit your barrel to the extension receiver with shim stock. If .002 is too thick to seat your barrel, then throw the barrel in the freezer for a few hours, and right before you take it out, heat up your upper receiver with a heat gun. It will slide in easily, and lock TIGHT.
@@inexpensivearms6952 do you think it would be ok to use a strip.of aluminim instead of stainless?
@@rememberussliberty1822 Should be ok. The main thing is getting rid of play between the two mating surfaces, not the material itself.
I've literally never seen a barrel fit into the upper without using heat. 😮😮😮😮
"Tell me you've never installed a 50 dollar barrel into a 30 dollar upper without telling me you've never installed a 50 dollar barrel into a 30 dollar upper...."😆
Put the barrel in freezer, heat up the upper, then no hammering involved
That's the AKM way.
Does it have to be stainless shim stock ? Can I use carbon steel shim stock
You could use carbon steel shim stock. The reason I didn't was because of potential for galvanic corrosion. Since the upper receiver is anodized, this shouldn't ever be an issue... I'm just paranoid.
Can I buy some of that extra shim stock off you? Definitely dont need a whole roll
Buy a barrel that comes with a NiB coated Barrel Extension. Easier to clean, smooth feed ramps, the NiB coating makes for a very tight fit into the receiver & longer life. Ballistic Advantage Hanson Profile barrels are amazing & way cheaper than top shelve barrels
What upper receivers are people buying where the barrel isn't a very tight fit 🤣
Shoot son, you never bought a $25 upper on a lark and paired it with a 40 dollar barrel?
you could thermal fit the upper
Not when it's a loose fit only if it's to tight. N yes that is the best situation
if you want to sort through a stack of receivers and find one that is too tight.
You can also over shim and then thermo, which is the most realistic route in my experience. Gives indistinguishable results in my experience, though I would think not having to shim is "better".
@@SCQT that’s what I’m doing as I type this. Barrel is in the deep freeze, getting ready to heat up the upper.
Still selling variety packs?
Nah, but I think I have a few extra pieces if you want me to mail them out. Post an email address I can contact you at and I'll give you a few pieces gratis.
@@inexpensivearms6952 Stuff is expensive when you only need an inch or so lol
Can you use tin foil or Aluminum foil????
Probably. It would probably tear getting it on.
I've heard one guy just cut a soda can into strips and used that. Whatever spray on interior liner would burn off after a bit, and he claimed it worked ok.
@@inexpensivearms6952 I was reading and I read someone using a feeler gauge. And I went get mine and I found one that’s 0.0015 and I put it on and it had a tight fit so imma stick with that because shim stock cost too damn much rn
So, is this method pointless if the barrel is too tight to fit by hand? I'm a newbie here.
Yup. If you have a very tight fit without adding anything, leave it be.
If you REALLY want to, you could bed with green locktite, but you're really chasing diminishing returns at that point.
Did yoy notice any actual increase of accuracy?
Yup. I've tested on barrels before this one and generally found it can shave up to .5 MOA off group sizes, especially once the barrel heats up.
@@inexpensivearms6952 ive been trying to fix my rifle with this trick. Im not if the fitment too tight could also cause inaccuracy. .001 was really loose still with a bit wobble. .002 shim needs to be mallet in but they both didnt seem to increase much accuracy.
@@seek3n It's not going to magically turn a bad barrel good. In my experience, it tightens up groups by about 0.5 MOA for the barrels I've measured it on.
What barrel do you have right now?
What kind of accuracy are you getting?
What kind of ammo are you testing it with?
@@inexpensivearms6952 im trying to tune the rifle to the 5.56 55g frontier ammo. Ive also tried with federal gold match. Black and vermint. They all have 2 to 3 inch groups at 100 yrd. Some have random circle pattern some vertically up and down. Im using a 223 wylde 18 inch 1/8 twist by ceiterion. I have a bench vise and 1.5 lb timney trigger. I do notice my upper receiver flange diametwr is a .0015 larger than the flange on the barrel extension. Upper receiver by aero precision. BCG by cryptic, go and no go tested. Im wondering if is the receiver extension portion is out of specs.
@@seek3n I doubt that's the problem. Honestly, given the quality of the components that went into your build, I'd probably call Criterion.
I've never shot any of their barrels, but everything I've seen says your rifle should easily be capable of sub-MOA accuracy with match ammo.
They'll probably recommend a bolt matched to your barrel.
Things you can eliminate yourself:
- Remove your handguards and barrel nut. Retorque your barrel nut. Barrel nut should be torqued to 30-80 lb/ft if using a steel barrel nut, and somewhere around 40-45 lb/ft if using an aluminum barrel nut.
- Check if your gas key is hitting the gas tube oddly. I've seen guys that claim a bad fit between the two can hurt accuracy because it causes pretensioning.
- Look up "Carrier Tilt" and make sure there's no weird marks on your buffer or buffer tube.
- Remove your muzzle device and take some shots with a bare muzzle. An overly tight crush washer can make your barrel shoot really inconsistently, especially when it's hot. If your rifle shoots fine with a bare muzzle, use peel washers or pre-crushed crush washers that lock down after hand tight+ 1/8th of a turn or less.
- I assume that your barrel is free-floating, but check to make sure the gas block, gas tube or barrel isn't touching anywhere inside the barrel.
- The last thing I'd try is to test a few match loads that are 69 grain or less.
1:8 should be able to stabilize up to 77 grain loads just fine, but my experience with 1:8 barrels has been that they tend to like loads under 70 grains more than heavier bullets.
Lastly, I'm not a gun guru. I'm just a guy who stumbled into assembling ARs on the cheap, and likes to test cheap barrels and get them to shoot well as possible. I generally do pretty well, but there's no substitute for the old guys who cut their teeth on the platform since Stoner invented it. There's probably a few guys on the ARF boards that can help you quite a bit more.
cut a v notch
Or just buy quality parts and you won't have to shim or lap anything. BCM and others make their receivers thermal fit. And Loctite doesn't get better accuracy, it's unnecessary. Permatex anti seize.
Sure, but where's the fun in that?
HEAT THE THREADS ON THE UPPER CHILL THE BARREL TO SHRINK IT......................
Exactly, this is what I mentioned and asked about in a prev post. Since then I have built over a dozen AR's and ea time I Shim it till it's too tight to pound in and Thermofit. I really think it is the best way to go and don't like using the Loctite compound at all.
Thermal fitting is great if the upper and barrel are already a tight fit now if they are loose shim the barrel then Thermo fit
What about a coke can
You can try. Keep in mind those cans have a lining on the inside. I think they'll be too fragile to get tight enough to bed.
Budweiser is the only way to go
Hey guy. I see your receiver, it looks to be a reg. mil spec forge. you can buy a decent forge stripped receiver fron Andersen, which is decent forges for less than the money you spent and no work. just trash the upper receiver. and put that decent barrel on a new receiver, seriously you can get decent receivers for way less than you think. just go ahead and use high temp lock tight. loose fit means that you should just stop. get another receiver. just stop. all that work for maybe a 79.00 upper receiver? actually just buy a good receiver like bullet. still this hack is the last thing you want to do guy..IMHO
That was a 28 dollar receiver. and a $50.00 barrel. I absolutely agree that if you're actually doing any kind of build, you should just bite the bullet and pay a bit more for the parts.
I was out when he said. Tap the barrel 🤣 clown