Longevity, Accuracy Tips for the AR15

[Klem]

I agree with Futz', with an AR and all the martial connotation and expectation that goes with it having a muzzle device is 'de rigeur'. A military assault rifle without a muzzle device is akin to being naked! But, when you think about the SR25 and how it is often shot without a can, 308 recoil as well, it is not much of a leap to consider nothing on the end to interfere with exiting gasses and pressures.

A case in point is the Lilja M4 'Navy' .223 Wylde drop-in. With a can on the end it gets filthy extemely quickly, caking a layer of ceramic burnt powder where ordinarily the crown would be clean with only tiny black spider lines coinciding with the lands and groves. I heard from more than one old-timer one way to check the efficacy of your crown (apart from the obvious groups) is to fire a few rounds and look at the pattern of carbon on the crown, is it exactly even?

[NugginFutz]

I heard from more than one old-timer one way to check the efficacy of your crown (apart from the obvious groups) is to fire a few rounds and look at the pattern of carbon on the crown, is it exactly even?

Interesting that you would mention this, because my non-threaded 24" BBL 5.56 consistently paints a very symmetrical "star" on the crown. Quite striking, as it is a stainless steel barrel. It also happens to be one of my more accurate AR's. I'll be sure to look for this, if/when I cut the 22" Grendel down.

[NugginFutz]

You do have to be mindful of what greases you choose when assembling the upper, as some chemical elements may react with the aluminum. There is the account of the Ranger School student whose barrel fell off in Florida Phase, but they were doing a lot of waterborne patrols and something fishy was particular about his M4.

That must have been embarrassing for the student or the armorer responsible for the weapon.

Regarding your comment on assembly grease: consider me now mindful. Since you mentioned it, what are some of your recommendations? Bear in mind that my AR family lives in the high desert, where salt and humidity are a dirty lie told by vengeful builders.

[LRRPF52]

I had this discussion with Bill A. about grease on the threads, and he mentioned the benefits of cosmoline over white lithium grease, which rots and smells.

I have done some where I tried thin Remoil over my Cerakote finishes. Every receiver I mess with now is Cerakoted, so I don't have a steel on aluminum fit anyway. The Cerakote galls when dry, so it's best to have oil on the threads. Other than that, I'm not sure how big a deal it is.

Here's the picture of the M4 that appears to have the threads stripped on the upper too:

[montana]

Do not use a torch on a heat-treated aluminum or steel part on the AR15 would be my advice. I have been able to do all the heating necessary with a hot air gun, which is used to loosen up Loc-tite and things of that nature. 7075 aluminum is about as hard as you want for a receiver.

I have used a small butane torch for many years with out any problems. Just keep the flame moving till the desired heat is applied evenly and you wont have any problems.

[dave102269]

Thanks for the heating and lapping comments. I'm waiting on a barrel from PF. Once assembled I'll report back on what it took to get it together.

[customcutter]

I had this discussion with Bill A. about grease on the threads, and he mentioned the benefits of cosmoline over white lithium grease, which rots and smells.

I have done some where I tried thin Remoil over my Cerakote finishes. Every receiver I mess with now is Cerakoted, so I don't have a steel on aluminum fit anyway. The Cerakote galls when dry, so it's best to have oil on the threads. Other than that, I'm not sure how big a deal it is.

Here's the picture of the M4 that appears to have the threads stripped on the upper too:

Interesting, improper heat treat, too much heat transfer due to rapid fire, possibly heated with a torch to remove stuck barrel extension from upper? If I had to guess I'd guess the later. Maybe even the barrel nut was over torqued and damaged the threads.

[waveslayer]

Is this the one?


$27 (with discount) at Brownells
http://www.brownells.com/gunsmith-to...prod20220.aspx

What's the discount?

[explorecaves]

To give you a better idea what you will be truing up on the receiver face. This is from a milling operation that is performing the same operation (fixing a receiver that is way out of spec) as the Brownells tool with lapping compound.

[Klem]

What's the discount?

$34.95, but if you have a discount account $26.95.

[explorecaves]

$34.95, but if you have a discount account $26.95.

Midway $21.49 http://www.midwayusa.com/product/810...ing-tool-ar-15

Edit: This one comes with 220 grit lapping compound but has a flex shaft (not sure if that is a pro or con?) http://www.midwayusa.com/product/821...vc=subv1810457

[aclark]

Thanks for that picture explorecaves. I thought the lapping was being done on the inside of the threads, to smooth out the inner surface. Makes a lot more sense now that you posted that picture. I feel much more confident that I can go ahead and do this now. I guess I was a bit confused before.

[65man]

What's the discount?

101213 - $10 for $100
201213 - $20 for $200
301213 - $30 for $300
int50 - $5 for $50

[NugginFutz]

101213 - $10 for $100
201213 - $20 for $200
301213 - $30 for $300
int50 - $5 for $50

Those are the current MidwayUSA discounts - not the Brownells discount.

[aclark]

Do you guys use just 1 grit of lapping compound, or do you go through different steps when you lap the receiver? I'm thinking it should be ok just using 1 (ie 320) to square it off. I don't see needing to make it super smooth, just square. Correct?