View Full Version : Methods of assembly -- question about gas port alignment
What method ensures proper gas port to gas block alignment? Assuming no pins are present, how do YOU ensure that you have aligned the gas block to the gas port?
I usually trust that the gas tube and gas tube hole should get me "close enough" if lined up properly, but I suppose you could be a millimeter out and never know it...
So how do the "pros" do it? Is there a tool? A feeler gauge? Something more precise than the method I use??
K.L. Davis
08-14-06, 13:36
The best bet is to have a barrel that is "indexed" with a small plunge cut 180 degrees opposite of the gas port... you use the hole in the bottom of the gas block to line up with that hole -- of course, some blocks use a set screw in that hole, which is all the better for alignment and retention.
You can make a jig to hold the FSB or gas block on place on the barrel for drilling the pin holes -- it is a rather simple arrangment really.
If those are not an option... I usually do a quick measurement of the center of the hole in the gas block to one edge, then slap some layout dye on the barrel, make a reference mark for depth and TDC, then line the block up with that.
eta: crap... I just noticed that you asked how the pros do it... disregard my previous.
On every gas block I've seen, the hole in the FSB that mates with the gas port is much bigger than the gas port in the barrel, so there is plenty of room for error without affecting function at all.
I'm no pro, but I always align the FSB by boresighting the iron sights. I mainly do this so that the irons are on target when centered, but I guess a fringe benefit is that it seems to help line up the FSB with the gas port. I check that zero at the range and if no adjustment is needed, I dimple the barrel for the set-screws and apply Loctite. (I guess I'll be SOL if I ever install a low profile sight :) )
Robb Jensen
08-14-06, 20:55
What method ensures proper gas port to gas block alignment? Assuming no pins are present, how do YOU ensure that you have aligned the gas block to the gas port?
I usually trust that the gas tube and gas tube hole should get me "close enough" if lined up properly, but I suppose you could be a millimeter out and never know it...
So how do the "pros" do it? Is there a tool? A feeler gauge? Something more precise than the method I use??
I'm far from a pro.
But what I do is mic the gas port to the shoulder, then mic the gas block to make sure it'll be over the port. I then mark the barrel and the block and then counter sink where the set screws will go so the gas block can't walk forward. Then upon final assembly I use Rocksett to keep them from coming loose during operation. This method seems to work well so far. The gas port in the gas block is usually quite a bit bigger than the port in the barrel so even if it's a degree or 2 off it'll still work.
My hack-Fu is strong, I use a grease pencil and a feeler gage.
K.L. Davis
08-14-06, 22:30
My hack-Fu is strong, I use a grease pencil and a feeler gage.
If those are not an option... I usually do a quick measurement of the center of the hole in the gas block to one edge, then slap some layout dye* on the barrel, make a reference mark for depth and TDC, then line the block up with that.
Okay... so I dont sound all like Mr. FancyPants
*Sharpie
I drill the gas port, then index the barrel 180deg and use a ball endmill for the dimple.
There are no feeler gauges that I am aware of. The only good thing I can tell you is that if it's a carbine gas system the port is small and you have a good bit of wiggle room. You should be able to get it plenty close with your eye, of course I have a machinist eye....
I thought of one more idea.
Get a spare gas block and drill all the way through from the bottom.
Put it on the barrel and line up the gas port in your new hole on the top of the gas block.
Use the forward set screw to hold it in place and use the rear hole as a jig to drill the detent for the rear set screw.
Robb Jensen
08-16-06, 07:40
I thought of one more idea.
Get a spare gas block and drill all the way through from the bottom.
Put it on the barrel and line up the gas port in your new hole on the top of the gas block.
Use the forward set screw to hold it in place and use the rear hole as a jig to drill the detent for the rear set screw.
That would be the very best way. :D
There are no feeler gauges that I am aware of.
Just make one...cut an HG cap in half. This is where Hack-Fu and Dremel-Fu converge.
Get the correct size dimpling jig from SLR Rifleworks, makes the job eazy peazy and perfect!
http://slrrifleworks.com/index.php?route=product/category&path=57_129
Yup,
BRT barrels have a dimple opposite the gas port.
If assembling another brand without a dimple, add one using a dimple jig.
This dimple is key and makes lining up the gas block super easy.
Get it close and start tightening the set screw while jiggling the gas block slightly.
You can feel the amount of movement decrease as the screw is tightened and it centers up on the dimple.
Snug it up, then do the other screw, apply thread locker, etc.
Go back to the first screw for final torque.
This works even on barrels without a shoulder.
I drill the gas port, then index the barrel 180deg and use a ball endmill for the dimple.
BRD (http://brdengineering.com/) Dimple Jig is what I use. Perfect alignment with no guessing, whatsoever.
You realize that this post is about 11 years old, right?
Get the correct size dimpling jig from SLR Rifleworks, makes the job eazy peazy and perfect!
http://slrrifleworks.com/index.php?route=product/category&path=57_129
You realize that this post is about 11 years old, right?
Well, we do now.
What difference does it make? It's still good information and it might help someone.
What difference does it make? It's still good information and it might help someone.
The difference that it makes is posted HERE (https://www.youtube.com/watch?v=dQw4w9WgXcQ). It is greatly informative, and may help you out.
Two, make that three, things I just learned: 1) Rick Astley can't lip sync for shit; 2) I dance better than Rick Astley; 3) where to get a good gas block dimpling jig.
Thanks for the necro, just ordered another toy (wife's description, complete with eye roll).
I added this jig to my tools list. Thanks!
Sent from my Pixel using Tapatalk
You might want to save some money.... Not to mention that link says it's for SLR at .460 but SLR sells .400 and .450
http://slrrifleworks.com/index.php?route=product/category&path=57_129
1 @ $60 or 2 @ $30? I know what my wallet likes best.
I use the SLR jig to drill the dimple opposite the gas port. Then I slide on the gas block and use this tool to mark and dimple the second hole. It doesn't matter what the spacing on the gas block is, this will give you two, (or three) dimples to line up the gas block perfectly!
https://www.ezaccuracy.com/shop
I use the SLR jig to drill the dimple opposite the gas port. Then I slide on the gas block and use this tool to mark and dimple the second hole. It doesn't matter what the spacing on the gas block is, this will give you two, (or three) dimples to line up the gas block perfectly!
https://www.ezaccuracy.com/shop
Why not use the drill bushing from the SLR jig? Are the threads on the SLR jig not 10-32?
My gas block had weird set screw spacing, neither .400 nor .450 probably closer to .475 or so (doesn't really matter), so I couldn't use the jig to drill the second hole. The Drill guide on the SLR jig uses a much larger thread (close to 1/4") than the gas block. The EZ Accurizer is the same thread as the gas block, plus it has a integral center punch to make a small dimple to center the drill on when drilling. Anyway the combination of the two tools worked perfect for me, and I have also seen gas blocks with three set screws, this method would work for them as well. You could probably use the accurizer to drill all the dimples, but I wanted my gas block to be aligned perfectly! And it is.
Hope this helps someone.
Rick
Helped me. Thanks for explaining.
The difference is that there are MULTIPLE CURRENT or more recent threads regarding this issue.
What difference does it make? It's still good information and it might help someone.
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