Gunsmithing The Kiss of Death

[zenbiker]

Got my Armalite M15 A4 back from a gunsmith to have a thread adapter and SureFire 556 QD mount attached. Sent it off because the headstock on my lathe is too long to for a 20" barrel and I detest turning between centers because I can't indicate an erratic bore. Job looked good, set up a 3 foot by 3 foot target, reattached the scope with the QD mount that has brought me back to at least 1 moa if not better every other time I remove/reinstall it. Bore sight with the eyeball (as if you can see the tolerances being dealt with here) and everything appears good. Send one round downrange; cant see a hit. Send one more, same thing. Walk downrange, and there is nothing on the target. Nothing. Get a sinking feeling in my stomach and hobble back to the firring point and take off the can, and....nothing. No baffle strikes, no end cap strikes. Check to see that Federal did indeed put powder, primer, and bullets in the cases - yep, they did. Stop and go home.

Can't use boresighter because the QD is glued on with RockSett (I guess, because I can't get it off). Start looking at the muzzle brake/suppressor mount, and here is what I see:

The exit bore of the brake is .250". Considering opening to .275 at least. Opinions?

ADD: I gave the suppressor another good hard look. I can see a couple of baffles that look like the carbon buildup was brushed by the bullets. The most I can tell until I figure out a better way to see inside. Nothing on the endcap.

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[RonA]

Someone needs to design a brake /suppressor combo that has a bunch of baffles with needle bearing apertures that will force the bullet to follow the path of suppressor bore instead of the barrel. Think of the money it would save gunsmiths if they didn't have to have good chucks, indicators, or talent.

 

[Chucky]

Have you dropped a bore alignment rod down the barrel to see how bad it is? The reason being is even if you open up the brake the threads seem to already be not even close to concentric to the bore and if the rounds are hitting the brake a few inches in front of the barrel when you put on the suppressor with that brake opened up you are almost going to guarantee a baffle strike if not now later down the road. If you compound the problem with a hot barrel or a round that just doesn't stabilize quite right then once again most likely baffle strike.

If it is Rocksett that he used soak it in a bucket of hot tap water for a few hours and it should just spin off. If it doesn't let it soak for up to 24 hours to break down the adhesive.

 

[zenbiker]

Have you dropped a bore alignment rod down the barrel to see how bad it is? The reason being is even if you open up the brake the threads seem to already be not even close to concentric to the bore and if the rounds are hitting the brake a few inches in front of the barrel when you put on the suppressor with that brake opened up you are almost going to guarantee a baffle strike if not now later down the road. If you compound the problem with a hot barrel or a round that just doesn't stabilize quite right then once again most likely baffle strike.

If it is Rocksett that he used soak it in a bucket of hot tap water for a few hours and it should just spin off. If it doesn't let it soak for up to 24 hours to break down the adhesive.

Good idea with the range rod, I'l give it a ry tomorrow. I'm a it perplexed because I used a reputable 'smith who I assumed would be able to indicate the bore properly, i.e. through the lathe headstock with twi dial indicators in a range rod i a 4 or six jaw chuck. My lathe is too big to do that and still have enough barrel sticking past the chuck to work on.

Another thing: why do manufacturers run the tolerances so tight on their brakes? A brake is one thing; a suppressor is a whole different animal. This suppressor mount leaves and end cap leaves a whopping 0.0125" per side on a bullet traveling 3250 fps; is .0250 or (gasp) .050" going to make that much difference in recoil or sound reduction? And when you're dealing with barrels that notoriously can be drilled less than straight, wouldn't a little extra clearance be a good thing? Oh, and thanks for the Rocksett info. Going to give the 'smith a call tomorrow to see how he did this job.


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[zenbiker]

Someone needs to design a brake /suppressor combo that has a bunch of baffles with needle bearing apertures that will force the bullet to follow the path of suppressor bore instead of the barrel. Think of the money it would save gunsmiths if they didn't have to have good chucks, indicators, or talent.

I'd just be happy if the manufacturers used barrels with straight freakin' bores.


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[Chucky]

I'd just be happy if the manufacturers used barrels with straight freakin' bores.


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This is the exact reason I have the Geiselle bore rods. I have seen more than one barrel that was way off.

 

[GH41]

Hopefully installed with shims and not a crush washer. How does it group without the can? How far down range is this 3x3 target? GH

 

[zenbiker]

Hopefully installed with shims and not a crush washer. How does it group without the can? How far down range is this 3x3 target? GH

I spece'd NO SHIMS. This smith is capable of timing the installation so that none are needed. I refuse to have shims on any of my guns. As far as targeting goes, I need to get to a range where noise won't bother my neighbors.


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[GH41]

Take a look at the Accu-Washer system. It might change the way you look at shims. Accu-Washer Muzzle Device Alignment System - Precision Armament
GH

 

[zenbiker]

Take a look at the Accu-Washer system. It might change the way you look at shims. Accu-Washer Muzzle Device Alignment System - Precision Armament
GH

If I'm reading the propaganda right, these are simply crush washers that give a screw-on muzzle device a shoulder to torque up against in the event, that for whatever reason, the shoulder that was machined during the barrel threading process is not perfectly perpendicular to the bore line. This results from either turning a barrel between centers, or holding the barrel through the headstock of the lathe ( the right method), but only using one dial indicator on the range rod, or worse, trying to dial the bore in off the lands and grooves. The only way that has ever been demonstrated to me to get the bore indicated properly every time is to run the barrel thru the headstock, holding the rear with a spider on the bore spindle and putting the muzzle in a live center on the tailstock. the rear of the barrel is dialed in using whatever means is appropriate: if its a chambered barrel, I use a piloted reamer inserted (but not rotated) in the chamber, and indicate the shank of the reamer. You have to pay constant attention to make sure the spider holds the barrel firmly enough to keep it tight against the live center. When the chamber end is dialed in as close as you can get it, at least .001 or better, gently tighten the chuck ( 4 or 6 jaw) against the barrel, pull the tailstock and live center away from the muzzle and insert a range rod. Set up two indicators as far apart on the range rod as you can get them. Take a sharpie and number each chuck jaw and spider leg. Rotate the chuck to jaw one and zero the dial indicators. Now, the fun starts.

You probably know that a lot of barrels do not have straight bores. You need to determine the path the bullet is going to take as determined by about the last two inches of the bore as it exits the barrel. You'll get a good idea of how straight your bore is when you put the lathe in neutral and by hand rotate the chuck, If the dials on the indicators do not move in sync, runout not considered yet, your bore is crooked relative to the outside of the barrel. Barrels are better these days in that regard than they used to be, and you may get away with just one indicator, but you better check it by moving the carriage down the range rod and see if the needle moves and how concentric it is or isn't in different areas. Chances are, the bore will be off enough to cause bullet strikes on your brakes and suppressors. If that is the case, you need to learn how to use the spider legs and the chuck jaws until both muzzle indicators give you runout of .0005" or less. Understand, when you get the muzzle bore dialed in, the chamber end may have visible runout as you rotate the chuck. That is a testament to the difficulty of drilling a 20-some-odd-deep or deeper hole in rod of steel and keep it straight. If you do get a straight one, it's by the grace of God, because those steel blanks aren't homogeneous. There are hard and soft area that deflect the deep hole drill. EDM and possibly lasers are the only technologiesii that stand a chance of drilling straight, deep, barrel holes, and last I knew, these technologies are beyond the means of most barrel makers, so they keep giving us barrels with some degree of crookedness to them, an they work fine - if the gunsmith knows how to deal with it. Crush washers should be called Crutch Washers, because they are just that - a crutch to keep from spending the time and acquiring the expertise necessary to deal with either crooked bores or its-not-my-gun attitudes in gunsmithing.

So, respectfully, while they are a really nice set of crutch washers, they don't change my mind about how I feel about them on MY guns.

Your results may vary; Objects in Mirror are closer than they appear.


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[GH41]

If I'm reading the propaganda right, these are simply crush washers that give a screw-on muzzle device a shoulder to torque up against in the event, that for whatever reason, the shoulder that was machined during the barrel threading process is not perfectly perpendicular to the bore line. This results from either turning a barrel between centers, or holding the barrel through the headstock of the lathe ( the right method), but only using one dial indicator on the range rod, or worse, trying to dial the bore in off the lands and grooves. The only way that has ever been demonstrated to me to get the bore indicated properly every time is to run the barrel thru the headstock, holding the rear with a spider on the bore spindle and putting the muzzle in a live center on the tailstock. the rear of the barrel is dialed in using whatever means is appropriate: if its a chambered barrel, I use a piloted reamer inserted (but not rotated) in the chamber, and indicate the shank of the reamer. You have to pay constant attention to make sure the spider holds the barrel firmly enough to keep it tight against the live center. When the chamber end is dialed in as close as you can get it, at least .001 or better, gently tighten the chuck ( 4 or 6 jaw) against the barrel, pull the tailstock and live center away from the muzzle and insert a range rod. Set up two indicators as far apart on the range rod as you can get them. Take a sharpie and number each chuck jaw and spider leg. Rotate the chuck to jaw one and zero the dial indicators. Now, the fun starts.

You probably know that a lot of barrels do not have straight bores. You need to determine the path the bullet is going to take as determined by about the last two inches of the bore as it exits the barrel. You'll get a good idea of how straight your bore is when you put the lathe in neutral and by hand rotate the chuck, If the dials on the indicators do not move in sync, runout not considered yet, your bore is crooked relative to the outside of the barrel. Barrels are better these days in that regard than they used to be, and you may get away with just one indicator, but you better check it by moving the carriage down the range rod and see if the needle moves and how concentric it is or isn't in different areas. Chances are, the bore will be off enough to cause bullet strikes on your brakes and suppressors. If that is the case, you need to learn how to use the spider legs and the chuck jaws until both muzzle indicators give you runout of .0005" or less. Understand, when you get the muzzle bore dialed in, the chamber end may have visible runout as you rotate the chuck. That is a testament to the difficulty of drilling a 20-some-odd-deep or deeper hole in rod of steel and keep it straight. If you do get a straight one, it's by the grace of God, because those steel blanks aren't homogeneous. There are hard and soft area that deflect the deep hole drill. EDM and possibly lasers are the only technologiesii that stand a chance of drilling straight, deep, barrel holes, and last I knew, these technologies are beyond the means of most barrel makers, so they keep giving us barrels with some degree of crookedness to them, an they work fine - if the gunsmith knows how to deal with it. Crush washers should be called Crutch Washers, because they are just that - a crutch to keep from spending the time and acquiring the expertise necessary to deal with either crooked bores or its-not-my-gun attitudes in gunsmithing.

So, respectfully, while they are a really nice set of crutch washers, they don't change my mind about how I feel about them on MY guns.

Your results may vary; Objects in Mirror are closer than they appear.


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Obviously you did not look at the link I sent if you think they are crush washers. GH

 

[zenbiker]

could be... let me look again....


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[zenbiker]

OK- are these beveled washers? I'm trying to figure out from the description.


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[GH41]

They are ground hardened steel washers. 18 thicknesses. One for every 20 degrees of rotation. Each one is marked. I'll put the instructions up tomorrow. A monkey can do it. GH

 

[GH41]

It was easier to find than I thought. If you have problems because of the attachment size pm me. GH

 

[zenbiker]

So, these washers solve a different problem altogether - rotational alignment, not bore alignment. Have I got it right now?


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[zenbiker]

They are ground hardened steel washers. 18 thicknesses. One for every 20 degrees of rotation. Each one is marked. I'll put the instructions up tomorrow. A monkey can do it. GH

Oh, so these are meant to correct rotational alignment?


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[LRI]

A washer, be it shim, crush, peel, etc is a means of easily adapting a timed brake/suppressor mount to a threaded muzzle. You fiddle till you get the clock position right so that the device orients correctly.

that's all they do.

alignment issues resulting in bullets making contact with brakes/cans are a deeper issue that almost certainly involves machine work to correct.

c.

 

[VJJPunisher]

tis why i prefer the barrel contour two point attachment type

 

[alpine44]

<snip>

That is a testament to the difficulty of drilling a 20-some-odd-deep or deeper hole in rod of steel and keep it straight. If you do get a straight one, it's by the grace of God, because those steel blanks aren't homogeneous. There are hard and soft area that deflect the deep hole drill. EDM and possibly lasers are the only technologiesii that stand a chance of drilling straight, deep, barrel holes, and last I knew, these technologies are beyond the means of most barrel makers, so they keep giving us barrels with some degree of crookedness to them, an they work fine - if the gunsmith knows how to deal with it. <snip>

Stupid question: Why doesn't the barrel maker drill the bore, straighten the blank with respect to the bore, and then turn between centers?

 

[zenbiker]

Stupid question: Why doesn't the barrel maker drill the bore, straighten the blank with respect to the bore, and then turn between centers?

My guess: the time it would take. Besides, if a hole can 't be drilled on precision machinery, how do you straighten it after? I can"t think of a method to straighten the drilled blank relative to the bore unless it might be hydrauilic. I think the real answer wouod be to use a different method, again, such as wire EDM or lasers to cut the initial bore.

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[zenbiker]

A washer, be it shim, crush, peel, etc is a means of easily adapting a timed brake/suppressor mount to a threaded muzzle. You fiddle till you get the clock position right so that the device orients correctly.

that's all they do.

alignment issues resulting in bullets making contact with brakes/cans are a deeper issue that almost certainly involves machine work to correct.

c.

That is about the size of it, especially when it is a relatively easy job to machine the shoulder to the proper rotational timing w/o "guesswork"


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[NXS338]

Good idea with the range rod, I'l give it a ry tomorrow. I'm a it perplexed because I used a reputable 'smith who I assumed would be able to indicate the bore properly, i.e. through the lathe headstock with twi dial indicators in a range rod i a 4 or six jaw chuck. My lathe is too big to do that and still have enough barrel sticking past the chuck to work on.

Could it possibly be the brake is not made exactly straight? You seem to be blaming the smith here and assuming that the brake is exact in all specs.

 

[GH41]

A washer, be it shim, crush, peel, etc is a means of easily adapting a timed brake/suppressor mount to a threaded muzzle. You fiddle till you get the clock position right so that the device orients correctly.

that's all they do.

alignment issues resulting in bullets making contact with brakes/cans are a deeper issue that almost certainly involves machine work to correct.

c.

You can't lump crush washers in with shims and peel washers. Crush washers are known to crush inconsistently. Most can and tight comp manufacturers warn against using them for that reason. GH

 

[GH41]

Zen, did you ever move the target closer and shoot the rifle? You had the barrel off, scope off and added the weight of the can. Your POI could be off 6-8" or more at 100 yds. Move the target up to 25 yds and get the thing on paper before pulling your hair out chasing problems that may not exist. GH

 

[PCR]

Stupid question: Why doesn't the barrel maker drill the bore, straighten the blank with respect to the bore, and then turn between centers?

They do! Well they drill the hole and then turn between centers. But you still end up with a barrel contoured between centers with a bend in the bore. The idea is to indicate the end of the barrel you are working on, in line for the first 3 inches. Gimble the working end in a 4-jaw and indicate the first 3 inches or so and let the other end go where it wants to without any stress while holding it in the outboard spider.

This is how you eliminate baffle strikes. The bullet follows the bore straight on through the brake.

 

[zenbiker]

Zen, did you ever move the target closer and shoot the rifle? You had the barrel off, scope off and added the weight of the can. Your POI could be off 6-8" or more at 100 yds. Move the target up to 25 yds and get the thing on paper before pulling your hair out chasing problems that may not exist. GH

Going to try it this weekend. I've had the scope off and on before and it always comes back within 1 moa; not perfect. but never this much. You're right, the can and the muzzle work may very well be moving it more than expected. I'll take some phone pics and post them; it was stupid of me to shoot the rifle with the can on right out of the box; It was likely only the Grace of God that I didn't totally frag the suppressor.


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[zenbiker]

You can't lump crush washers in with shims and peel washers. Crush washers are known to crush inconsistently. Most can and tight comp manufacturers warn against using them for that reason. GH

In my mind, there is only one place for shim washers, and that is to temporarily correct rotational timing issues when changing between muzzle devices; say, you had a muzzle brake installed that had holes all around and changed to a model that only had holes on the top and sides, and the new brake won't align properly with the shoulder setback for the original brake; shims can get you by until you can get to a gunsmith to properly set the shoulder back Or, they could be used by a machinist who doesn't know any how to set up the the installation for proper timing. Getting the right rotational timing on an initial installation is basic machining.


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[zenbiker]

Could it possibly be the brake is not made exactly straight? You seem to be blaming the smith here and assuming that the brake is exact in all specs.

I'm inclined to at least partially agree. I think the brake/suppressor mount may be partially responsible since it was made to only allow 0.0125" bullet clearance per side. Even George Vais allowed .020" per side depending on the caliber. Here is a question I can't answer, but isn't it better to open up the bore to .020" or .030" per side and be all but certain the bullet doesn't hit anything on the way out? Does it make that much of difference in recoil or noise reduction to risk damage to your suppressor or cause a frustrating sight in session, wasting ammo because the bullet is hitting the brake?

BTW, I have this same model brake/suppressor mount on a .17 HMR, one AR rifle (this problem child), and a bolt action rifle. All of them have the same 0.250" exit bore, but this is the only one that has had this problem. The mount in question is CNC machined, a great way to make a lot of exactly the same object, but not foolproof.

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[GH41]

In my mind, there is only one place for shim washers, and that is to temporarily correct rotational timing issues when changing between muzzle devices; say, you had a muzzle brake installed that had holes all around and changed to a model that only had holes on the top and sides, and the new brake won't align properly with the shoulder setback for the original brake; shims can get you by until you can get to a gunsmith to properly set the shoulder back Or, they could be used by a machinist who doesn't know any how to set up the the installation for proper timing. Getting the right rotational timing on an initial installation is basic machining.


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I agree with you 100% when your statement is applied to work outside of the AR15 world. Some guys (Me included) change muzzle devices every time the wind changes directions. Indexing a new device with the Accu-Washer system takes all of 10 minutes and the mechanical result is no different than facing the shoulder of the barrel. GH

 

[NXS338]

I'm inclined to at least partially agree. I think the brake/suppressor mount may be partially responsible since it was made to only allow 0.0125" bullet clearance per side. Even George Vais allowed .020" per side depending on the caliber. Here is a question I can't answer, but isn't it better to open up the bore to .020" or .030" per side and be all but certain the bullet doesn't hit anything on the way out? Does it make that much of difference in recoil or noise reduction to risk damage to your suppressor or cause a frustrating sight in session, wasting ammo because the bullet is hitting the brake?

BTW, I have this same model brake/suppressor mount on a .17 HMR, one AR rifle (this problem child), and a bolt action rifle. All of them have the same 0.250" exit bore, but this is the only one that has had this problem. The mount in question is CNC machined, a great way to make a lot of exactly the same object, but not foolproof.

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I am still learning about fitting muzzle brakes and have only done a few and I'm sure there are alot of guys here who have done more than they can count. What I have had a good amount of experience with is the fitting of compensators to competition pistols and here is what I have found. First the use of rocksett is outdated and is a pain to work with as well as a pain to remove, there are locktite formulas that work way better and are easier to work with. But here is the important part, when we get a compensator that is new we fit it to the barrel just as you would with a brake, they usually have finer and closer fit threads than most rifles and you would assume they would fit and be straight upon installation. They are not, we have gotten them that were made on CNC, or EDM and even few manually machined. We usually get them with .005 clearance for the bore which is tight, but after install and the locktite sets we ream them in line with the bore to a minimum of .030 clearance. This is done after it is set and locked down to make sure everything is straight with the bore to avoid bullet strikes with only having .015 clearance around bullets. If this is going to just be a screw on job with no fitting the comp would have .030 clearance all around so the comp maker gauranttee's no bullet strike. If this has to be done this way for a short pistol barrel that is easier to make all straight then why would you not do same for a rifle brake on a long barrel that we know isn't necessarily a perfectly straight bore. Simply my thinking on this....could be way off not sure here.

 

[alpine44]

They do! Well they drill the hole and then turn between centers. But you still end up with a barrel contoured between centers with a bend in the bore. The idea is to indicate the end of the barrel you are working on, in line for the first 3 inches. Gimble the working end in a 4-jaw and indicate the first 3 inches or so and let the other end go where it wants to without any stress while holding it in the outboard spider.

This is how you eliminate baffle strikes. The bullet follows the bore straight on through the brake.

My question was geared towards the practices of barrel making. Shouldn't the customer expect a straight bore in high end barrel ?

Since it seems that we have to deal on the lathe with "banana" bores not just in the cheapest factory barrels, what do you use to gimbal a barrel stress free in a 4 jaw chuck? ( I am familiar with a 2 spider setup) Did you cut back the bearing surface of a dedicated jaws set ?

 

[PCR]

My question was geared towards the practices of barrel making. Shouldn't the customer expect a straight bore in high end barrel ?

Since it seems that we have to deal on the lathe with "banana" bores not just in the cheapest factory barrels, what do you use to gimbal a barrel stress free in a 4 jaw chuck? ( I am familiar with a 2 spider setup) Did you cut back the bearing surface of a dedicated jaws set ?

You can hold the working end with large diameter copper wire wrapped around so it will pivot as you indicate the first few inches with your rod or long stem DTI.

 

[alpine44]

You can hold the working end with large diameter copper wire wrapped around so it will pivot as you indicate the first few inches with your rod or long stem DTI.

Great idea. Thanks.

 

[zenbiker]

In the end, the problem ends up being the most common problem in gunsmithing - a loose nut behind the stock.

After further testing, it turns out the mount is fine and properly installed, Upon inspecting the rifle at the range next trip out, I discovered the left front corner of the scope base was barely contacting the handguard nut - I'm guessing I reinstalled the base one slot too far forward on the Pic rail. I reinstalled the quick mount one slot further back, the rifle immediately went back to pre-gunmithing zero (!) and standard 1/2 moa with Federal Premium 55 gr NBT ammo. The color on the brake/suppressor must have been red anodizing scraped of my Boresighter during attempts to fit it to the brake, which was not possible due to the construction of the brake. So all is well, and in the end it was anxiety and my own errors that caused the problem, nobody elses.


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