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Posted: 3/10/2010 6:37:03 PM EDT
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hello everyone, I could really use help with your expertise on an issue that I just realized existed.
Problem: I cannot figure out how to mount the Front Sight to the M4 Cut barrel. Background: Before I get started I would like to tell you all that I have built an A2 before but this is my first attempt at an M4. I ordered a Daniel Defense Stripped Barrel from Bravo Company USA This Exact Part Notice that this barrel is smooth and unlike the a2 and heavy barrels it does not have grooves for taper pins, other than the gas port its smooth, not even a dimple which worries me because now looking at the barrel description is says theres a "dimple under the gas port". I bought the barrel months ago when ar parts were really hard to find. The a2 tower gas block I ordered was a standard post-ban, it is the correct diameter but have run into a problem. The block very smoothly slides on and off the barrel, there is alot less friction than there was with the Heavy a2 I built in the past.(is that going to be a problem ?) Second and most importantly The gas block does not have any holes in it for tape pins either, so it matches the barrel and seems to be appropriate for the barrel. The gas block does have a single hole milled on the underside where the sling attachment mounts. It is roughly the same size as the gas port and lines up with it perfectly with the gas port. So my question is, Whats the deal? Scouring the internet I have found quite a few examples of m4 cut barrels having standard a2 gas block NOT held together with taper pins (the bushmaster m4 carbine on their site is an example) so that leads me to believe that there is a way to mount these two pieces together, but if so, what am I missing? How does this gas block mount on this barrel? Are they compatible ? if not please let me know so I can return the gas block. or is the barrel missing a feature, that dimple? Would a barrel like this require a clamp on gas block ? if so, how do I ensure that the tower and gas ports align properly?? Im starting to really regret getting a barrel without the grooves milled into it. Please help a fellow rookie ar gear head out. I am not familiar with this gas block configuration. thanks |
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A standard A2 front sight base/ gas block is drilled for taper pins together with the barrel.
The holes are then tapered for the pins. This is a pretty precise and involved step when setting up a virgin barrel. That barrel has the dimple so that you have the option of using a set screw type gas block. You could send it out to have the one you have mated, or you could use another type of sight/ gas block. There are ones out there that have 2 halves that screw together as well. Hope this helps. It is how I am understanding this 
Edit for clarity |
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I have the same problem with two 'green' A2 barrels. My barrels at the blow hole are 0.625".
I bought a YHM-9394-H bolt on front sight, but its too big(0.7+). I'll call YHM to see if they have one for a smaller A2 barrel. I also have decided to cut pin slots in one of the barrels to be able to put the stock sights on it. Jerry |
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Ok, I ill try to clarify as best as possible. I am familiar the standard tapered pin design of standard barrels. However there are many gas blocks on the market that have niether tapered pins or screws to clamp to the barrel. Here are some examples of similar designs. Example one , Example Two , Anyway there is an A2 tower that apparently mounts in a similar manner since it does not have places for taper pins.
If you go to bushmaster.com and click on the enlarge photo for any of their m4 carbines, the photo shows an a2 gas block ithout taper pins. So I guess the question is how are these none clamp or pinned gas blocks held on? in either case is the clamp on block sturdy enough compared to the tapered pins? |
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Quoted:
Ok, I ill try to clarify as best as possible. I am familiar the standard tapered pin design of standard barrels. However there are many gas blocks on the market that have niether tapered pins or screws to clamp to the barrel. Here are some examples of similar designs. Example one , Example Two , Anyway there is an A2 tower that apparently mounts in a similar manner since it does not have places for taper pins. If you go to bushmaster.com and click on the enlarge photo for any of their m4 carbines, the photo shows an a2 gas block ithout taper pins. So I guess the question is how are these none clamp or pinned gas blocks held on? in either case is the clamp on block sturdy enough compared to the tapered pins? example 1 (yhm-9383) uses set screws. look up YHM-9384 it uses clamp screws i found a pic for you 
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Thank you, ok so it looks the gas block that I have mounts ith set screws which means that im going to need to have a gunsmith tap the barrel for the set screws unless I get a clamp on block like those made by YHM or JP. Has anyone used the clamp on gas blocks before? do they hold zero with any kind of abuse? Of the three designs, Tapered pins, set screws and clamp on, which is the most durable and reliable? Any recommendations? Thanks again everyone 
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Just got a 16in. hbar from DZ arms on GB came with an A2 FSB with set screws in all five holes. I had to remove it to mill off the bayo lug when I reinstalled it (I had the barrel in the upper so I could line it up). I then used the Set screw under the sling portion of the FSB to hold it while I drilled in the four side scew hole (Careful it wants to draw down into the threads go slow ) The center 8-32 set held the FSB tight. Even if it slides on easy the forces of tightening the scews will force the FSB tight against the gas port. The lower 4 set screws were 6-32 . If you really want to be sure it all lines up tighten the center then the sides and go shoot it If its good go ahead and dimple the sides a bit. Remember loctite and tighten lowers evenly little a time and should be good. Hope this helps
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