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Posted: 4/18/2010 6:05:35 AM EDT
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I am having trouble with my Ar-15 short stroking and I just want to make sure that I have done everything I personally can do to make sure that the gas block and the gas port are aligned properly. Other that Eyeballing it or marking the ports position around the diameter and length of the barrel and also on the gas block and matching up the markings or using a level to insure that the rail on the clamp on block is on a level axis with the rail of the upper assembly what more can be done? How precise does the alignment have to be? What is the allowable tolerance that an ar15 will accept and still function reliably?
what tips and tricks do you all have? |
| When you remove the gas block you should be able to see the round "burn" pattern around the gas port, which will show you how far off, (if at all) it was. If you used index marks to allign it you can try using the difference you found w/the burn mark to allign it. I'm working on a similar issue myself, so I know what a pita it can be. |
I use this for my installs:  Works great, good dimples and I absolutely know the port is lined up. Available here: http:///www.rainierarms.com/?page=shop/detail&product_id=1089 |
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I had some SS spacer rings laser cut that are the same thickness as the handguard cap.
I have an old cap that I cut the side out of that I formerly used as a spacer gage. The gas port in the barrel should always be the same distance. I think gas blocks are predominately made to work with handguard caps (some are not). There are always exceptions so it does not hurt to measure things out. All of the gas blocks I have worked with to date have had rails or built in folding front sights so vertical alignment has been easy. |
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Quoted: I use this for my installs: http://www.rainierarms.com//img/shop/product/598baff5016f8f09762b87e660b4c65a.jpg Works great, good dimples and I absolutely know the port is lined up. Available here: http:///www.rainierarms.com/?page=shop/detail&product_id=1089 This works with any gas block? I might grab one for my build... |
| Cheap and easy - go to an auto parts store and buy about a foot of vacuum tubing. If you have the setscrew type, you can put the vacuum tubing where the carrier slips on in the receiver. Then blow through the gas tube while "tuning" the gas block. Lock it in where you have decent flow. |
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I have installed 3 PRI and 1 VLTOR with this, easy as pie. Check with Rainier Arms for the list of what will and won't work. ETA: Install directions are here: http://rainierarms.com/misc/dimple_jig.doc |
| I just had a situation similar to this. I put a Colt govt profile 20'" barrel on a keyhole new upper. Bought a new gas tube, used a used front sight tower. Took it to the range and it would not cycle at all. Swapped a different Colt carrier and bolt and it short stroked. Checked everything and all seemed ok. Swapped out the sight tower and now it functions perfectly. Port must have been partially blocked with the first sight tower. It was allowing gas to flow but not enough. |
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