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Posted: 11/22/2010 10:24:25 PM EDT
| I remember reading somewhere that 9mm barrels are not measured the same as 5.56 barrels.....is this true? Example of what I mean is a 7.5" barrel in 5.56 mounted in an upper is shorter (or longer) then a 7.5" 9mm barrel mounted in an upper. I'm trying to figure out if I want a 7" or 9" handguard/rail. If I got a 5" 9mm barrel from spikes and mounted this in an upper...how long would the barrel be sticking out of the upper? |
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A 7" barrel in 5.56 will be the same length as a 7" barrel in 9mm.
The difference that you will notice is that the barrel extensions for 9mm and 5.56 are very different. The barrel is measured from the chamber to the muzzle, therefore the longer case length of the 5.56 will have the 5.56 barrel "stick out" longer than a 9mm barrel. I hope that answers your questions. I'm sure someone who hasn't been awake since Sunday morning could answer it better... 
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| A 7.5" 9mm barrel will extend 0.5" past a 7" handguard. If you get a 5" barrel it will be 2" inside the 7" rail, but does look good if you have a suppressor attached. I like the look of a 5" 9mm barrel with suppressor and 7" handguard a lot. If you plan on shooting without a suppressor then go ahead and get a pistol 5" handguard to go with a 5" 9mm barrel so they are flush. |
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Quoted: I remember reading somewhere that 9mm barrels are not measured the same as 5.56 barrels.....is this true? Example of what I mean is a 7.5" barrel in 5.56 mounted in an upper is shorter (or longer) then a 7.5" 9mm barrel mounted in an upper. I'm trying to figure out if I want a 7" or 9" handguard/rail. If I got a 5" 9mm barrel from spikes and mounted this in an upper...how long would the barrel be sticking out of the upper? How the BATFE measures rifle barrel length: -remove any non-permanent muzzle attachment -close the breach(bolt forward) with the firing pin NOT protruding -insert a dowel down the barrel, touching the bolt face -mark the dowel at the muzzle -measure the dowel to the mark |
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Quoted:
A 7.5" 9mm barrel will extend 0.5" past a 7" handguard. If you get a 5" barrel it will be 2" inside the 7" rail, but does look good if you have a suppressor attached. I like the look of a 5" 9mm barrel with suppressor and 7" handguard a lot. If you plan on shooting without a suppressor then go ahead and get a pistol 5" handguard to go with a 5" 9mm barrel so they are flush. this was what I was looking for. Thanks. |
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Quoted:
A 7.5" 9mm barrel will extend 0.5" past a 7" handguard. If you get a 5" barrel it will be 2" inside the 7" rail, but does look good if you have a suppressor attached. I like the look of a 5" 9mm barrel with suppressor and 7" handguard a lot. If you plan on shooting without a suppressor then go ahead and get a pistol 5" handguard to go with a 5" 9mm barrel so they are flush. so, what is the actual length of the 7.5" 9mm barrel if it sticks out .5" out of the 7" HG....8"? the bolt face of the 9mm and 5.56 are in different spots, with the 9mm being 1/2" or so farther to the rear....which would mean that a true 7.5" 9mm barrel would be flush with the front of the 7" HG. i have seen 9mm barrels advertised both ways....most often as the 5.56 equivalent length, but also as the true 9mm length. Do you guys know which ways each company lists them. thanks, advntrjnky |
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For example:
A 16" 9mm barrel assemby (barrel plus barrel extension) measures 16.0" A 16" 5.56mm barrel assembly measures OVER 16", I am not sure of the exact ammount at the moment but let's say 16.375". Just depends on where the bolt face is, which extablishes your datum point, or zero point. On the 9mm barrel, the bolt face is flush with the left most extremity of the barrel asembly. On a 5.56 mm barrel, the bolt face is somewhere inside the barrel extension, hence the added length to the barrel assembly. ...actually...due to the fact that the bolt face is actually slightly counter-bored, a 16" 9mm barrel assembly will technically measure slightly UNDER 16" It's very easy to measure. In both calibers, close the bolt on an EMPTY chamber. Bottom-out a cleaning rod on the bolt face, sticking it in from the muzzle. Put a piece of tape around the rod at the muzzle or the perm. attached muzzle device carefully and accurately. Remove the rod and measure the distance between the business end of th cleaning rod and the beginning of the tape. ***NOTE*** 16 inches dead-on-the-line is NO GOOD. You do NOT want to have the ATF measure your shit and find out that either your tape measure was slightly "long" or theirs was slightly "short". You want a SOLID, undisputable 16.125" if not 16.25" to be safe. edit: obviously the last couple sentences only apply if you do not have SBR paperwork. |
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The 9mm bolt face (on Colt style setups) is not "flush" with the barrel - it is actually recessed into the bolt. I don't believe the 9mm bolt face is flush with the barrel on a Oly setup either.
My 7.5" 9mm Colt style barrel does not extend out past my 7" YHM railed handguard - it is actually just a hair short of the end of the handguard and I added a Spikes SD-1 fake can/barrel shroud so it would extend just past the end of the handguard. |
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Quoted: The 9mm bolt face (on Colt style setups) is not "flush" with the barrel - it is actually recessed into the bolt. I don't believe the 9mm bolt face is flush with the barrel on a Oly setup either. My 7.5" 9mm Colt style barrel does not extend out past my 7" YHM railed handguard - it is actually just a hair short of the end of the handguard and I added a Spikes SD-1 fake can/barrel shroud so it would extend just past the end of the handguard. My Oly pistol-cal is 1/4" longer than stated. My 16"bbl is actually 16.25" when measured with a dowel/ |
| Well...i thought I was clear but this has just been more confusing. I went ahead and ordered a 6" barrel from Spikes. Thought this would be the best length. I had to switch it to a 5" because I ordered the longer mount for my MM suppressor and did not want it being to long for a 7" rail. I just hope it isnt too short now. I wanted a barrel that would be 2x longer then a hand gun barrel. I guess I'll just have to wait and see. |
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Quoted:
OK, I'll jump in, I have a Tros 5" barrel with a triple lug. I also have a Spike's 7" BAR floating handguard. The end of the barrel is about 2 7/8" to the end of the handguard. http://i974.photobucket.com/albums/ae221/jfcisme/my%20AR/Depthofbarrel.jpg Out of ignorance, what is the point of having the barrel shy of the end of the hand-guard? |
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Quoted:
Quoted:
OK, I'll jump in, I have a Tros 5" barrel with a triple lug. I also have a Spike's 7" BAR floating handguard. The end of the barrel is about 2 7/8" to the end of the handguard. http://i974.photobucket.com/albums/ae221/jfcisme/my%20AR/Depthofbarrel.jpg Out of ignorance, what is the point of having the barrel shy of the end of the hand-guard? Most people do it with the intent of using the upper with a suppressor. The suppressor fits down inside the rails. I looked at doing a 9mm upper three times now. Dropped the idea due to cost the first time. Then wanted one for a SBR. Again dropped due to cost and already had a few SBR uppers. Now..third time the charm..I'm building a SBR 9mm upper with the sole reason to have a AR upper I can mount my MM suppressor to. If it was not for my MM then I would not even be thinking about a 9mm upper again. And this time its getting built as the only thing I have left to buy now is a receiver and bolt. |
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Quoted:
Quoted:
Quoted:
OK, I'll jump in, I have a Tros 5" barrel with a triple lug. I also have a Spike's 7" BAR floating handguard. The end of the barrel is about 2 7/8" to the end of the handguard. http://i974.photobucket.com/albums/ae221/jfcisme/my%20AR/Depthofbarrel.jpg Out of ignorance, what is the point of having the barrel shy of the end of the hand-guard? Most people do it with the intent of using the upper with a suppressor. The suppressor fits down inside the rails. I looked at doing a 9mm upper three times now. Dropped the idea due to cost the first time. Then wanted one for a SBR. Again dropped due to cost and already had a few SBR uppers. Now..third time the charm..I'm building a SBR 9mm upper with the sole reason to have a AR upper I can mount my MM suppressor to. If it was not for my MM then I would not even be thinking about a 9mm upper again. And this time its getting built as the only thing I have left to buy now is a receiver and bolt. How do your spent cases look? Do they look the same as when fired from a 9mm handgun or are they extremely dirty? I feel that with my upper, the bolt opens way too soon, while the hot gasses are still venting from the case. I did a post dedicated to the subject. |
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I have a 5" barrel so that my rounds stay subsonic. I have a 7" handguard for the iron sights to have a decent sight radius. I have a triple lug so that the suppressor stays ON and will not get loose. It is also for when I take it off the thread adapter won't unscrew requiring me to take off the hand guard to get it off.
I took some video when I was first firing this rifle because I was concerned that the bolt may be pulling back before all the combustion was finished. My pistol brass looks the same as my SBR brass. But there is some back pressure from the suppressor causes some debris to blow back. You may not need hearing protection, but you should always have the safety glasses on! 
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Quoted: I have a 5" barrel so that my rounds stay subsonic. I have a 7" handguard for the iron sights to have a decent sight radius. I have a triple lug so that the suppressor stays ON and will not get loose. It is also for when I take it off the thread adapter won't unscrew requiring me to take off the hand guard to get it off. I took some video when I was first firing this rifle because I was concerned that the bolt may be pulling back before all the combustion was finished. My pistol brass looks the same as my SBR brass. But there is some back pressure from the suppressor causes some debris to blow back. You may not need hearing protection, but you should always have the safety glasses on! http://i974.photobucket.com/albums/ae221/jfcisme/my%20AR/NewToy.jpg Are your sights backward on purpose? Your upper is almost exactly what I'm going to do, too. I'm working toward a 9" handguard with a 5 or 6" barrel. While I wait on the money for a can, I intend to put a 5 1/2" flash hider on it (bored out to 9mm diameter) so the carbon, etc won't be blowing around in the handguard.  |
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OP, here are some pictures of an upper in the EE that will add visual confirmation to the explanations of barrel length in relation to the handguard length. http://www.ar15.com/forums/topic.html?b=7&f=22&t=813881 |
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Are your sights backward on purpose?
Yes, they are. This is a little experiment. There is a knob that sticks out on the side of the rear sight that was reducing the space for my gloved finger to grab the charging handle. I switched the front sight to match the rear. Data is still coming in––it's winter time. Snow flurries at the range today! Good luck with your build––mine took 11 months to finish. |
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