I am wanting to purchase a custom barrell and Have a gunsmith install it on a AR15 I am considering buliding. The gunsmith has chambered several rifles for me but he has never drilled the gas port hole in a barrel and is apprehensive about doing this. Could someone please explain what the procedure is and what steps have to be taken to deburr the inside of the barrel. We do not have access to a Boroscope. Thanks
Drilling gas Port AR15
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Don Nielson
New member
The best way is to EDM the final little bit before you break thru. I drilled almost to the hole and then had my EDM guy finish it. For a standard .223 I would recommend a .104 hole. Don
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rcw3
Guest
Don't go crazy trying to invent a problem that's not there - cue the barrel up in a milling machine and drill the port. You can get obsessive/compulsive about dirlling a port into a barrel and worrying about a burr on the inside (i.e. a burr does shoot off but it is best to make it minimum). There is no real easy way to put a port in and not have some burr, it's just a part of doing AR work. Now if you do it right there will be next to nothing of a burr and that's less of a worry than drilling a port that's too big. The reality is new and sharp high speed steel drill bits work the best for us (the operative aspect is that the bits are sharp and they cut well - if you don't have that get new and sharp ones - don't just pull out the old drill bit and try it out or you may wind up with a heck of a burr inside). The key is using an RPM and feed rate that allows the bits to cut without having to put a lot of pressure on it as you come through the inside but don't go so slow you work harden the metal you are trying to drill. Start with a smaller bit first and step up to final diameter. If you do it right that's about as good as you can get.
My suggestion is to experiment with a barrel end cutoff piece or an old shot out barrel to get your technique down (that only takes a couple minutes) then do it.
BTW, .104" is pretty big of a port for a standard AR-15 (i.e. .093" is standard).
Robert Whitley
http://www.6mmAR.com
My suggestion is to experiment with a barrel end cutoff piece or an old shot out barrel to get your technique down (that only takes a couple minutes) then do it.
BTW, .104" is pretty big of a port for a standard AR-15 (i.e. .093" is standard).
Robert Whitley
http://www.6mmAR.com
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mike in co
Guest
thanks you francis.....but its one thing i have not done yet. i have taken exisiting ar bbls and rechambered them, but timed to the original gas port. i have done some work on the br bbls...but they have no gas port.
the ideal situtation is to time the hole to a groove.
(do a search on this forum..it has been asked before)
mike in co
Spot Drill with a Center Drill first. Use a smaller diameter than desired drill bit for the first hole, make sure it's sharp. Use chucking reamers in progressivly larger diameters until you get to the desired diameter. This will minimize the burr and give you a round hole. Use two or three chucking reamers in the process, sharp reamers at that.
You can only do so much to prevent the burr.
You can only do so much to prevent the burr.
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rcw3
Guest
With no disrespect, I absolutely disagree with that and there is no evidence to support that, in fact, the evidence is to the contrary. After making literally hundreds of AR-15 uppers and after inspecting literally hundreds of AR-15 barrels (with a bore scope), including ones that have hundreds to thousands of rounds through them, it is my opinion based on the evidence I have seen through these inspections that in the groove is about the worst place for the port to be, and if you can stay away from doing that you are generally better for it!
People keep repeating that "in the groove" theory (and it is only a theory at best) as if it is scientific fact, and it is not.
If anyone is game for where it is best and why, make a follow up post and I will explain where it is best and why it is best elsewhere, but I am not going to take the time to explain it if no one cares and just wants to follow supposed conventional wisdom (even if it is unsubstantiated).
Robert Whitley
www.6mmAR.com
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mike in co
Guest
robert...speak up.
my info had been that less pressure in the groove.....
less fouling.
but i am an open minded guy...
so let me hear
mike in co
my info had been that less pressure in the groove.....
less fouling.
but i am an open minded guy...
so let me hear
mike in co
R
rcw3
Guest
Mike
I have inspected the port (with a borescope) on every AR barrel that we have built up in the past couple years, and have inspected the ports again on a number of these barrels after they later came back for a rebarreling after being shot out, and by far the barrels showing the most disruption and deformation of the barrel metal forward of the port inside the bore (i.e. it's always all on the muzzle side of the port) are those where the port is in the groove. The ones that show the least amount (in many cases next to no disruption or deformation of barrel metal) are where the port bisected the land and groove.
When I inspect the barrels where the port is in the groove I typically see a very significant area forward of the gas port (toward the muzzle) where the barrel metal has been repeatedly slammed with bullet jacket, so much so that this rips, tears, wears and deforms a large triangular shaped portion of the bore forward of the port. Many times you can see hunks of torn off copper bullet jacket embedded into this area. Plain and simple, I just don't see this situation so much where the port is in some other locations in the bore and the best looking bores and ports appear to be where the port bisects the groove and a land (i.e. half into a land and half into a groove).
What I see indicates (to me) that bullets are still flexible and plastic even when they pass the gas port. It seems there's still enough pressure in the bore and plasticity in the bullet that it will start to squeeze into an "in the groove" port as it goes by it, and that squeezed in portion of the bullet then slams in to the other side of the port on the muzzle side and either a bit of jacket gets torn off or that portion of the bullet gets swaged back fully into the bore again (or a little of both).
There is consistently less copper seen and evidence of barrel disruption with the 50/50 ports or those that are half in the land and half in the groove (keep in mind the bullet jacket, after engraving into the lands, has adopted a shape with two almost right angles at the location where it is going to go over the 50/50 port and it seems those angles add rigidity to the bullet so that the jacket does not seem as predisposed to squeeze into the port). For an example, angle iron is a lot stiffer than flat iron and so is that portion of the bullet with two right angles in the jacket.
The "in the groove" port is like a big pothole sitting right in the middle of where your car tire will center up and hit it square and hard at high speed and it makes a situation you sometimes see on an asphalt road that started out like a small hole or depression in the road where cars and trucks at high speed keep slamming into it busting it up further along as they keep hitting it and deforming the asphalt a bit beyond that.
The irony of this whole thing is, when we first started building uppers we tried as best we could to hit the groove with ports and I used to have fits when I saw ports half in and half out of the groove, worrying about if a customer would have a fit about that as well. Now I have gone full circle and hope I hit the junction of the land and groove.
Robert Whitley
www.6mmAR.com
I have inspected the port (with a borescope) on every AR barrel that we have built up in the past couple years, and have inspected the ports again on a number of these barrels after they later came back for a rebarreling after being shot out, and by far the barrels showing the most disruption and deformation of the barrel metal forward of the port inside the bore (i.e. it's always all on the muzzle side of the port) are those where the port is in the groove. The ones that show the least amount (in many cases next to no disruption or deformation of barrel metal) are where the port bisected the land and groove.
When I inspect the barrels where the port is in the groove I typically see a very significant area forward of the gas port (toward the muzzle) where the barrel metal has been repeatedly slammed with bullet jacket, so much so that this rips, tears, wears and deforms a large triangular shaped portion of the bore forward of the port. Many times you can see hunks of torn off copper bullet jacket embedded into this area. Plain and simple, I just don't see this situation so much where the port is in some other locations in the bore and the best looking bores and ports appear to be where the port bisects the groove and a land (i.e. half into a land and half into a groove).
What I see indicates (to me) that bullets are still flexible and plastic even when they pass the gas port. It seems there's still enough pressure in the bore and plasticity in the bullet that it will start to squeeze into an "in the groove" port as it goes by it, and that squeezed in portion of the bullet then slams in to the other side of the port on the muzzle side and either a bit of jacket gets torn off or that portion of the bullet gets swaged back fully into the bore again (or a little of both).
There is consistently less copper seen and evidence of barrel disruption with the 50/50 ports or those that are half in the land and half in the groove (keep in mind the bullet jacket, after engraving into the lands, has adopted a shape with two almost right angles at the location where it is going to go over the 50/50 port and it seems those angles add rigidity to the bullet so that the jacket does not seem as predisposed to squeeze into the port). For an example, angle iron is a lot stiffer than flat iron and so is that portion of the bullet with two right angles in the jacket.
The "in the groove" port is like a big pothole sitting right in the middle of where your car tire will center up and hit it square and hard at high speed and it makes a situation you sometimes see on an asphalt road that started out like a small hole or depression in the road where cars and trucks at high speed keep slamming into it busting it up further along as they keep hitting it and deforming the asphalt a bit beyond that.
The irony of this whole thing is, when we first started building uppers we tried as best we could to hit the groove with ports and I used to have fits when I saw ports half in and half out of the groove, worrying about if a customer would have a fit about that as well. Now I have gone full circle and hope I hit the junction of the land and groove.
Robert Whitley
www.6mmAR.com
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NesikaChad
Guest
A barrel maker friend of mine who's been fiddling with AR's since the 70's offered this to me one day a long time ago:
"I've built quite a few of these over the years. I used to just drill the hole and be done with it. Over time guns started coming back to have new barrels hung on them ( talking service rifle shooters) and out of curiosity I began cutting up the old barrels just to see what the hole looked like inside. What I noticed is that the rifles that shot exceptionally well had the hole between the lands. This was purely coincidental as I'd never taken the time to mess with it before.
I began to make the extra effort to time the hole between after that."
Mind you this isn't a direct quote from the conversation as it was almost ten years ago when we had it, but it is accurate in every other way. There's been a lot of funk on the webz lately about how valid this practice is. I personally don't know as I don't have the 30+ years of practical experience with AR-15's that this guy does. I do know that in the ten years I've known him everything he has ever offered to me has been sound advice and his character is beyond reproach. So, I'm going to take him at his word.
I also know that the last couple times I shot a service rifle match it was at the Denver range and up in Bailey, CO and I shot the 3" spotter off the target six times when back at the 600 (all 10's
) and I won the 600 yard line with a 197/13X. That's a 197 with a seven by the way, but that's another interesting/funny story. Point is that ol AR had one of Mark Chanlynn's barrels in it that he had fitted and it performed exceptionally well for me.
One additional item about this is he tilts the barrel 2* off axis when he drills the hole. The idea behind this is to minimize the trailing edge from behaving like a cheese grater and peeling jacket material from the bullet as it passes.
Regarding the burr, break through, and poor edge around the hole/bore from the drill. A centerfire high velocity cartridge can flash to over several thousand degrees in the chamber. 20" out from the chamber the temps are going to be significantly less, but it is still a pretty violent and hot environment to exist in. I doubt a little burr is going to last very long in these conditions. Using a sinker EDM to minimize this is certainly a viable process that delivers a nearly perfect hole no doubt, but unless a guy has easy access to one I personally would not invest any money having it done this way. Just use good quality tooling in a good machine and follow fundemental machine shop practices and you'll be fine.
If your going to be using light bullets you may find you need to open the hole up a bit. .093" is the "std" for a rifle shooting ball ammo. It also works well for the heavier stuff typically used in service rifle competition. On an AR-10 I helped a guy build once we just started small and kept slowly increasing the size of the hole until the bolt would reliably lock to the rear after the last round. That rifle produced a 12X clean at the 1000 yard Tubb range in Raton NM (whittington center) the first time it was taken out to stretch it's legs. Shane Harless was the owner and he is a very, very accomplished long distance competitive shooter.
Hope this helps.
Chad
"I've built quite a few of these over the years. I used to just drill the hole and be done with it. Over time guns started coming back to have new barrels hung on them ( talking service rifle shooters) and out of curiosity I began cutting up the old barrels just to see what the hole looked like inside. What I noticed is that the rifles that shot exceptionally well had the hole between the lands. This was purely coincidental as I'd never taken the time to mess with it before.
I began to make the extra effort to time the hole between after that."
Mind you this isn't a direct quote from the conversation as it was almost ten years ago when we had it, but it is accurate in every other way. There's been a lot of funk on the webz lately about how valid this practice is. I personally don't know as I don't have the 30+ years of practical experience with AR-15's that this guy does. I do know that in the ten years I've known him everything he has ever offered to me has been sound advice and his character is beyond reproach. So, I'm going to take him at his word.
I also know that the last couple times I shot a service rifle match it was at the Denver range and up in Bailey, CO and I shot the 3" spotter off the target six times when back at the 600 (all 10's
) and I won the 600 yard line with a 197/13X. That's a 197 with a seven by the way, but that's another interesting/funny story. Point is that ol AR had one of Mark Chanlynn's barrels in it that he had fitted and it performed exceptionally well for me.One additional item about this is he tilts the barrel 2* off axis when he drills the hole. The idea behind this is to minimize the trailing edge from behaving like a cheese grater and peeling jacket material from the bullet as it passes.
Regarding the burr, break through, and poor edge around the hole/bore from the drill. A centerfire high velocity cartridge can flash to over several thousand degrees in the chamber. 20" out from the chamber the temps are going to be significantly less, but it is still a pretty violent and hot environment to exist in. I doubt a little burr is going to last very long in these conditions. Using a sinker EDM to minimize this is certainly a viable process that delivers a nearly perfect hole no doubt, but unless a guy has easy access to one I personally would not invest any money having it done this way. Just use good quality tooling in a good machine and follow fundemental machine shop practices and you'll be fine.
If your going to be using light bullets you may find you need to open the hole up a bit. .093" is the "std" for a rifle shooting ball ammo. It also works well for the heavier stuff typically used in service rifle competition. On an AR-10 I helped a guy build once we just started small and kept slowly increasing the size of the hole until the bolt would reliably lock to the rear after the last round. That rifle produced a 12X clean at the 1000 yard Tubb range in Raton NM (whittington center) the first time it was taken out to stretch it's legs. Shane Harless was the owner and he is a very, very accomplished long distance competitive shooter.
Hope this helps.
Chad
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Robert,
Have you seen any difference in the condtion around the port between cut and button rifled barrels? The general concensous is that cut rifled barrels typically last longer than button rifled barrels. Not always, but usually. I'm curious if the damage/erosion after the port in a groove may be associated with the fact that the material in the groove has been forced into that configuration by the button. The material in the groove would have more residual stress than that that makes up the land and perhaps it is more prone to failure when it is bisected by a sharp edged hole? I would aslo bet that the worse the surface finish of the hole at the bore, the more likely it is to erode. I'm not a metalurgist (am an engineer) and I haven't slept in a Holiday Inn Express in years.
Greg
Have you seen any difference in the condtion around the port between cut and button rifled barrels? The general concensous is that cut rifled barrels typically last longer than button rifled barrels. Not always, but usually. I'm curious if the damage/erosion after the port in a groove may be associated with the fact that the material in the groove has been forced into that configuration by the button. The material in the groove would have more residual stress than that that makes up the land and perhaps it is more prone to failure when it is bisected by a sharp edged hole? I would aslo bet that the worse the surface finish of the hole at the bore, the more likely it is to erode. I'm not a metalurgist (am an engineer) and I haven't slept in a Holiday Inn Express in years.
Greg
It seems to me that 'shooting off the burr' would be a very poor way of proceeding. Wouldn't that be like lapping the bbl with bbl steel ? The burr isn't going to disappear, it's going to be dragged down the bore with great pressure and violence. Maybe it would embedd into the jacket and not gouge the bore but it would be sheer luck.
At the very least I would want to try to minimize the burr by passing a bronze brush past the hole and then cleaning it off outside the muzzle after every pass.
At the very least I would want to try to minimize the burr by passing a bronze brush past the hole and then cleaning it off outside the muzzle after every pass.
I've done my own barrel work on AR's for the last couple years, probably doing 35 of them or so. I use a jig made from an actual picatinney (sp?) gas block of the proper diameter. If you look at most of those gas blocks, that bottom hole for the rear set screw is in-line with the gas port hole in the block, it's the only way to manufacture them. I made two drill bushings out of set screws (1" long) that I use in that rear hole. After installing the barrel, it's a very simple matter to level the upper receiver on a parallel and the 'top' of the picatinney rail of the gas block (turned upside-down). You can tighten the forward set screw to lock it in place and install the drill guide set screw in the rear hole. It makes locating and drilling that hole an absolute snap (make sure the gas port location on the block is the same as the one you're going to install on the barrel, most times they will use a 10-32 screw and you can use the actual block you're going to install on the gun for the jig). Use the smaller drill guide first, I use a .078 or so, then swap out the set screw with the larger one, and drill out with correct size, .092 is about right for the 20-24" barrels. If building a 17 Remington or 204 Ruger, test fire at the smaller size to see if you get proper function. Easiest way to tell is if after the last round is fired, does the carrier engage the bolt latch...if not, there's not enough gas. I made a few 17 Remingtons with 18" barrels and the mid-length tubes, and if I remember right, they functioned great with a substantially smaller hole, somewhere in the mid-low .08's I think.
I also timed my barrels when chambering to end up in a groove, then pretty much said to hell with it as it didn't seem to make a hoot of difference on how well they shot. Most would go 1/2 MOA regardless of where it was. If you want to time to the groove, get a borescope and run it into depth of where the port will be located, then mark the outside of the barrel shank at each groove location. When threading and fitting the barrel extension it is a simple matter to see if you have the extension indexed to a groove, allow about 1/8" or a hair more for torquing to the spot.
I also timed my barrels when chambering to end up in a groove, then pretty much said to hell with it as it didn't seem to make a hoot of difference on how well they shot. Most would go 1/2 MOA regardless of where it was. If you want to time to the groove, get a borescope and run it into depth of where the port will be located, then mark the outside of the barrel shank at each groove location. When threading and fitting the barrel extension it is a simple matter to see if you have the extension indexed to a groove, allow about 1/8" or a hair more for torquing to the spot.
M
mike in co
Guest
msalm...
great idea!
thanks for passing it on
thanks robert for the info
mike in co
great idea!
thanks for passing it on
thanks robert for the info
mike in co
Gas Port
Thank you all for taking the time to offer your advice to my question, Im sure this topic has been on here before but I couldent find it. I am going to send a link of this thread to the gunsmith who does the work for me I really don't think he would take any advice I would give him to hart because I have never done anything like this. I am one of those who repeated the theroy of drilling between the lands without any evidence to prove it one way or another.
Thank you all for taking the time to offer your advice to my question, Im sure this topic has been on here before but I couldent find it. I am going to send a link of this thread to the gunsmith who does the work for me I really don't think he would take any advice I would give him to hart because I have never done anything like this. I am one of those who repeated the theroy of drilling between the lands without any evidence to prove it one way or another.
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jlmurphy
Guest
I used Cerro Safe to form a plug in the barrel at the point of the gas port, used a smaller pilot drill bit and followed with the finish drill bit, there was no burr, just like drilling in wood with a backup board.
J
J. Pendergraft
Guest
You can also turn an aluminum slug to groove diameter and drive it into the bore to the point the hole will be drilled. When the slug is removed any slight burr seems to be removed as well.
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rossneder
Guest
I have not done this yet but I had anticipated using a very small carbide ball end burr and feeding it through the hole and then along the edge of the hole removing any sharp edge in the bore. I have several that dentists use to open the inside of teeth.
So, is there a problem with this idea that I don't see?
Ross
So, is there a problem with this idea that I don't see?
Ross
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gasgunner
Guest
I locate them in the groove because doing so takes less time than answering the phone call from the customer who is upset that his is not. It makes no difference. But then I've only made about 50 AR barrels........yesterday, and the day before, and the day before, and, well, you get the idea. Once the barrel has about 500-1000 rounds down it the port forms a ramp of sorts on the downstream side from the bullet impacting it as Robert described. I personally think they shoot best once this little ramp is formed. This is one reason I like to head for the nationals with about 700-1200 rounds on my barrel. Drill about .010 undersize and take it up in two steps with a chucking reamer. I like spiral fluted ones.
John
John