Ensuring absolute concentricity of muzzle devices

[76Too]

will be installing a Smith Enterprises 'Good-Iron' Coast Guard style brake on a Bula XM21 barreled receiver at some point soon and i'm wondering how you guys ensure the proper alignment of muzzle devices. I realize that once threaded on, any device worth its salt should automatically align, but I'm thinking better safe than sorry in this case. I was thinking a piece of bar stock brass or another soft(ish) metal to go 6 or so inches into the barrel and then out the business end and check for clearance around the edges of the bar stock?

 

[W.E.C]

View attachment 198780 Just hand load one of these for the first shot. Jk. Don't really.

 

[milktree]

What problem are you trying to solve? Do you think the bullet might hit the muzzle device?

 

[76Too]

View attachment 198780 Just hand load one of these for the first shot. Jk. Don't really.

Hmmm...I can't seem to find any load data, so i think I'll just fill the case with the hottest pistol powder to the top and compress the load...I'll back it up with a magnum primer and lube my barrel with ghost pepper hot sauce...ought to do the trick.

 

[Another_David]

just open the chamber and look down the barrel.

the chamber end should be in the center of the muzzle opening.

 

[76Too]

What problem are you trying to solve? Do you think the bullet might hit the muzzle device?

Also, from what I understand of physics (which is to say, not much) that achieving absolute concentricity will allow for gasses to surround the projectile and escape the ports evenly, so as to not effect the yaw as it leaves the barrel. Some might say 'so bring it to a gunsmith', but there's basically zero fun in that.

 

[76Too]

just open the chamber and look down the barrel.

the chamber end should be in the center of the muzzle opening.

That's where the purpose of my question comes in...an XM21 is an M14 Variant...no way for me to see line of sight down the barrel, as it's already installed on the receiver. It's not like an AR where I can just pop out the bolt and see straight down. I'm not even sure I'd get a good picture from a boroscope either (and I don't have a boroscope to begin with)...if any of you feel differently, please chime in.

 

[Another_David]

Also, from what I understand of physics (which is to say, not much) that achieving absolute concentricity will allow for gasses to surround the projectile and escape the ports evenly, so as to not effect the yaw as it leaves the barrel. Some might say 'so bring it to a gunsmith', but there's basically zero fun in that.

that's all fine and dandy but presumably the threads are already on the barrel and he's just going to screw it on then needs to check that it's not going to cause a major malfunction before letting his buddy make the first shot with it. then it is what it is.

if he was going to thread it himself (doubtful) then the real question would be how to align the threads and for that the answer is go to a smith

 

[Another_David]

That's where the purpose of my question comes in...an XM21 is an M14 Variant...no way for me to see line of sight down the barrel, as it's already installed on the receiver. It's not like an AR where I can just pop out the bolt and see straight down. I'm not even sure I'd get a good picture from a boroscope either (and I don't have a boroscope to begin with)...if any of you feel differently, please chime in.

right but what I was saying is you (obviously unload first then) open the camber and lay the rifle flat on a table. then you do what you're never supposed to do and go stand in front of the muzzle (where the bullets come out real fast) and from just the right distance you should see the light in the chamber in the center of the end of the muzzle device. takes just the right lighting.

for extra credit do it at your gun range during a cease fire just to give everyone a good chuckle (okay maybe not)

am searching for a photo but can't find one.

 

[76Too]

Hmmm...interesting. I'll look more into this option. I thought you were saying to look from the chamber end. I have a super bright borelight I can try. If you find the picture, let me know please...so I can see basically what I'll be looking for.

 

[Another_David]

Hmmm...interesting. I'll look more into this option. I thought you were saying to look from the chamber end. I have a super bright borelight I can try. If you find the picture, let me know please...so I can see basically what I'll be looking for.

yeah you don't really want the bore light in the bore but in the chamber. then the end of the chamber should be like a white moon in the center of the muzzle at a distance.

it's no different than looking from the chamber end, it's just recommended to look from the chamber to the muzzle for safety.

 

[vicorjh]

Interesting question. I'm curious myself as I had this exact problem with a factory installed muzzle brake on a Ruger RPR. I figured the muzzle brake would be relatively concentric with the barrel crown for bore-sighting purposes. I was very mistaken. Had to take the muzzle brake off.

Otherwise, same reason as Dakar notes, reduce uneven pressure around the projectile.

So, if anything, you might be able to use my mistake. In this case, I have a site-lite green laser that is installed into the crown end of the barrel. The laser has a shaft with specifically sized o-rings (for the caliber) that centers the shaft in the bore. The laser shaft, on the far end, has a bevel that is then pressed against the crown making the assembly fairly well centered and parallel to the bore. It's not perfect but gets zeroing within a couple of minutes or so.

With the muzzle brake off, install the laser and sight it to some distance target through a scope. Install the brake and do the same. Repeat a couple of time. If the two ports, the bore and the muzzle, are concentric the laser dot should remain in relatively the same location. If they are not concentric, you'll see significant offset. Offset could be from poor tolerances on the machining of the brake, poor machining of the barrel threads, something else?, etc. There is a some margin of error due to the way the site-lite centers the laser but it should be small relative to non-concentricity between the two ports.

Also, the shaft on the site-lite is not very long, so the brake can't be very long using this laser. The brake you have might be too long for this particular tool.

This, of course, doesn't fix any problems but may provide some insight to tinker around with.

 

[76Too]

That is a fantastic idea! I have an awesome laser boresighter that fits muzzle end that should work very well to try this method. Like you stated, it won't be perfect, but will give me a better idea than most anything else aside from a brass rod machined to the exact dimensions of my bore perhaps.

 

[milktree]

Also, from what I understand of physics (which is to say, not much) that achieving absolute concentricity will allow for gasses to surround the projectile and escape the ports evenly, so as to not effect the yaw as it leaves the barrel. Some might say 'so bring it to a gunsmith', but there's basically zero fun in that.

The bullet is going supersonic, so it should be way ahead of the gases that follow it (since there should be *zero* preceding it if the bullet is sized correctly and you don't have gas blow-by)

Interesting question. I'm curious myself as I had this exact problem with a factory installed muzzle brake on a Ruger RPR. I figured the muzzle would be relatively concentric with the barrel crown for bore-sighting purposes. I was very mistaken. Had to take the muzzle off.

What were the symptoms you saw with shooting? Was it just problems with the bore sighter?

 

[Glockster30]

It's a little pricey, but you could also use a bore alignment rod similar to your idea in your OP. Surefire has them for $79 for a suppressors, but should also work for a muzzle brake (there are other makers too). I can't imagine that it would cost that much for a gun smith to do the same thing though.





http://www.surefire.com/sf-bore-alignment-rod.html

 

[icyclefar]

The bullet is going supersonic, so it should be way ahead of the gases that follow it (since there should be *zero* preceding it if the bullet is sized correctly and you don't have gas blow-by)

Exactly this.

Short of a muzzle device strike, the device should have zero influence on accuracy of the shot in an of itself.

But if you really want to over think it, a muzzle device can change the barrels harmonics causing accuracy issues in short timed multi shot strings.

Concentricity is nice and it begins at the chamber. There are multiple ways to screw it up along the way, too many for me to be able to actually measure, and accuracy needs a lot more than just concentricity.

Buying the best quality components that you can afford usually negates any concern.

 

[76Too]

Exactly this.

Short of a muzzle device strike, the device should have zero influence on accuracy of the shot in an of itself.

But if you really want to over think it, a muzzle device can change the barrels harmonics causing accuracy issues in short timed multi shot strings.

Concentricity is nice and it begins at the chamber. There are multiple ways to screw it up along the way, too many for me to be able to actually measure, and accuracy needs a lot more than just concentricity.

Buying the best quality components that you can afford usually negates any concern.

well, I guess I did right by getting Smith Enterprises then...they are known as a 'holy grail' of M14 parts. Even the purists seem to allow for the use of their parts.

 

[mac1911]

That's where the purpose of my question comes in...an XM21 is an M14 Variant...no way for me to see line of sight down the barrel, as it's already installed on the receiver. It's not like an AR where I can just pop out the bolt and see straight down. I'm not even sure I'd get a good picture from a boroscope either (and I don't have a boroscope to begin with)...if any of you feel differently, please chime in.

I will chime in.......... way over thinking this. mount the device. You will most likely see a problem if there is one. Your other option is to find a machinist who has the proper gauges to measure these kinds of thing

 

[76Too]

I will chime in.......... way over thinking this. mount the device. You will most likely see a problem if there is one. Your other option is to find a machinist who has the proper gauges to measure these kinds of thing

noted...posted...lol. not sure if you noticed, but over thinking things is kind of my thing. i has the dumb so basically any thinking is over thinking.

 

[Another_David]

noted...posted...lol. not sure if you noticed, but over thinking things is kind of my thing. i has the dumb so basically any thinking is over thinking.

in the overthinking dept., you can also use a level if the barrel and muzzle device are not tapered. put rifle in vice (or rest on sandbags, rags, or your wife's favorite down comforter) and use the level to position the barrel perfectly level. then put the level on the muzzle and it should be equally level.

but you still want to look down the barrel. there was an epic thread here a while back whereby someone had their muzzle device "professionally" pinned and welded and before shooting they had the foresight to look down the barrel only to find the pin was protruding into the barrel causing an obstruction that surely would have lead to a catastrophic failure.

 

[icyclefar]

in the overthinking dept., you can also use a level if the barrel and muzzle device are not tapered. put rifle in vice (or rest on sandbags, rags, or your wife's favorite down comforter) and use the level to position the barrel perfectly level. then put the level on the muzzle and it should be equally level.

The problem here is that everything can be level and your muzzle device still not concentric to your bore.

 

[Another_David]

The problem here is that everything can be level and your muzzle device still not concentric to your bore.

and being concentric to your bore doesn't mean the device won't obstruct the bullet (because it could be undersized, e.g. the wrong caliber)

there is always another what if.

if you want to go nuts measure the device with some calipers both for caliber and centrality to itself.

 

[vicorjh]

What were the symptoms you saw with shooting? Was it just problems with the bore sighter?

Just a problem bore-sighting with a laser and zeroing from that (brake in-line). Zero was offset significantly. Not concentric or otherwise. Was resolved by temporarily removing the brake during the bore sight in...

 

[mac1911]

The problem here is that everything can be level and your muzzle device still not concentric to your bore.

This is very true

- - - Updated - - -

I say get the gun up and running with out those silly things on it... then after you get it shooting well try it.

 

[josh2600]

Exactly this.

Short of a muzzle device strike, the device should have zero influence on accuracy of the shot in an of itself.

It can. Ever have a muzzle brake loosen up on you w/o knowing about it? It will open your group way up, BUT you would know something was wrong quick and it's still not a device strike (not dangerous).

- - - Updated - - -

If it's a new muzzle brake, take five shots with it on and five with it off, your group will move but if it stays just as tight, you're g2g.

 

[drgrant]

will be installing a Smith Enterprises 'Good-Iron' Coast Guard style brake on a Bula XM21 barreled receiver at some point soon and i'm wondering how you guys ensure the proper alignment of muzzle devices. I realize that once threaded on, any device worth its salt should automatically align, but I'm thinking better safe than sorry in this case. I was thinking a piece of bar stock brass or another soft(ish) metal to go 6 or so inches into the barrel and then out the business end and check for clearance around the edges of the bar stock?

If you're not buying a barrel or a device from a shit manufacturer this is overkill.

-Mike

 

[Squire]

Shoot it. Check the brake. If you see copper or lead, it's not aligned.

 

[JRLB]

You could get a gauge pin to fit inside the barrel. McMaster has them in all sorts of sizes.

 

[hminsky]

Hmmm...interesting. I'll look more into this option. I thought you were saying to look from the chamber end. I have a super bright borelight I can try. If you find the picture, let me know please...so I can see basically what I'll be looking for.

You can hold a slip of white paper in the back of the chamber, it reflects a lot more light down the barrel..

 

[Sweeney]

There are alignment gauges for the M14 to check the concentricity of the bore to the muzzle devise. If cutting threads on a barrel the use of a 4 jaw independent chuck and pin gauges to index the barrel in a lathe is the way to go. You center the bore and not the outside of the barrel to cut the major diameter then, ideally, single point cut the threads.