Hey all! I finally found some ammo and months later was able to shoot my build. On the upside everything chambered nicely, didnt come apart when fired, and the brass looked great.
However, Im having cycling issues. I dont think the bolt is coming back far enough. It is ejecting the casing and resetting the trigger but not picking up the new cartridge. Also the bolt does not always lock open on the last shot.
Im guessing Im under gassed, but need some help!
I am trying to post some photos but havent figured out how just yet.
Shanner,
As you know the carrier must go a fair way further than ejection and reset to clear the rear of the follower, almost to the end of the available travel. As that happens the carrier must be free to ride up to catch. Even if it was a stiff mag making it difficult to strip it should still lock back on last round.
A couple of questions;
Do you have more than one mag? If so, is this happening to all mags?
Where on the clockface do the cases eject (12-o'clock being the muzzle)? 4 o'clock is about right?
Is the gas block adjustable? Who put it together?
I don't expect the factory ammo is the problem. It also eliminates shonky handloads, but if you have another brand that would be good to test also.
If you pull the charge handle all the way on an empty mag does it catch on the follower and lock back (every time)? If so it is most likely undergassed.
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Yes I tried with all mags and similar results. I would occasionally get it to cycle but never more than a couple rounds.
Yes I can pull the charging handle and always get it to catch.
It did eject directly to my right (3-4 oclock) but didnt go very far probably only 3-4 feet to the right.
I put it together. Its a AA barrel with Aero non adjustable lo pro block. I was concerned when assembling the upper because the AA barrel was dimpled but did not line up perfectly with the Aero set screws. I am wondering if the holes arent lining up perfectly.
shannerdrake Wrote:I am wondering if the holes arent lining up perfectly.
It's a common problem so could be. plus it sounds like a new gun, not worn in yet.
Are you saying the block needs to be forward from the shoulder about a credit card width before the screw lines up with the dimple? Have you measured how far into the block the centre of the hole it and do the same for the barrel - shoulder to centre of gas port - are they the same?
Klem, I think that might be my problem. To line the set screws on the block up with dimples on the barrel it pulls the gas block about a quarters width from the barrel shoulder. Im guessing thats misaligning the holes. Im going to take it apart and measure when I get a chance.
Shannerdrake, If you have it apart might also want to plus pin gauge gas port. gauge pin sets not cheap, but imo worth it. guys on sight with more exp. than me could probably rattle off top of head diameter for gas system used in your weapon. I have had a couple under gassed ar builds. BA Hanson barrels are notorious for having small gas ports. Good luck hope you get cycle situation fixed.
shannerdrake... The space between the gas block & the barrel shoulder is there for the handguard end cap used for GI handguards. Depending on the barrel manufacturer, this gap may or may not be present. If the manufacturer makes barrels to GI specs, the gap will be there. It's possible the dimple on your barrel is where it's supposed to be & your barrel & gas block ports are in alignment. Of course, you do need to do some measuring to verify that.
I refuse to be victimized by notions of virtuous behavior.
Klem Wrote:Shanner,
Even if it was a stiff mag making it difficult to strip it should still lock back on last round.
I'm not saying this is shanner's problem, "but I have had failure to lock back after the last round" because the bolt catch spring was weak. After a lot of head scratching and pointless gas adjustment, It took me awhile to figure this one out lol...
08-09-2021, 10:41 PM (This post was last modified: 08-09-2021, 10:48 PM by Klem.)
Shanner,
"A quarter of the width" (of the barrel at the gas port) is 1/4 of 3/4" - yes? That is way more than the width of a credit card, which is what I thought it might be because of Old Bob's explanation in Post#9. Forget that theory - Sounds like you've got a gas block with set screw holes that are just way out of alignment with the dimple in the barrel.
Regardless, you do have to pull it apart and measure the distance from the barrel's shoulder to centre of the hole, and then the edge of the gas block to the centre of the hole. If they are the same then you can push that block right up against the shoulder with confidence and only then have to worry about rotating the block until the holes exactly align. For that you can scratch tiny alignment marks on the shoulder and block to line it up perfectly. Even just slightly out and it's going to choke the gas like it's a smaller hole.
With respect to 'Bullterrier' you won't need a pin set to do this (I don't have one). A set of calipers will do. You can also measure the port size with calipers.
Lining up the gas holes for maximum efficiency is a thread or two on this forum if you want to search. Some guys use bore scopes which means you have to have access to one. Another method is using a toothpick in the gas block. When it is in alignment gravity lets it drop down into the barrel where you crack it out with a cleaning rod. Or you can buy the plastic version of this from HB industries https://www.youtube.com/watch?v=V4f9stp4SWE. I have never used these methods but no doubt they work.
I have just marked and carefully measured with calipers - but whatever method you use you do have to line those holes up exactly, especially in a caliber or gas system that is not as generous with gas as others. If the dimple is misaligned then screwing it tight is going to pull it out of alignment. One solution for this is to replace it with a clamping gas block, which is arguably a more efficient seal anyway. But for that you have to buy a new block. If the dimple is pulling your block out of alignment as you do it up there's not much you can do to fix that. Drill a new hole and screw onto an un-dimpled part of the barrel maybe. That's if there is enough length of block to do this - It's a bit of effort for the sake of simply buying a new clamping block. Up to you and how much money you have.
If you cannot line up the holes without the dimple pulling the block out of alignment then a clamping block is what I would do. As long as it doesn't make contact with the inside of the handguard to keep it free-floating.
That is of course if the problem is the gas holes out of alignment, but it won't hurt or cost to pull it apart and carefully measure, as they say in the emerald isle - 'To be sure, to be sure'.
08-09-2021, 11:29 PM (This post was last modified: 08-10-2021, 12:08 AM by RobertFL.)
I just ordered a Kaw Valley "Dimpling Jig" . I have some uppers that were not dimpled and the Kaw Valley will work for all of them plus the new one I am gonna put together myself... https://www.kawvalleyprecision.com/KVP-A...g-.750.htm Check out this tool, I am hoping it will work well.. it has holes for 3 different screw spacings. 0.400, 0.420 and 0.450. The Odin Adjustable gas block I got on sale has 0.450 inch center to center set screw spacing. Maybe your barrel was drilled for a different screw spacing than your gas block? With the KAW Valley tool you can put the alignment screw into the gas port and see if the set screws are drilled in the right spot.
08-10-2021, 12:18 AM (This post was last modified: 08-10-2021, 09:45 AM by RobertFL.)
***EDIT*** I went back to the AA web site and looked at 6.5 Grendel barrels and build kits..it looks like they have 0.875 gas blocks?? but they also show 0.750 gas blocks?? Since AA dimpled your barrel I guess they want you to buy their Gas Block and gas tube. <img src="https://www.shopalexanderarms.com/icon-img-Low_profile_gas_block_web.jpg" alt="Low-Profile .750 Gas Block"/> This is the 0.750 gas block AA (Alexander Arms) sells. you might have to buy one of theirs or a clamp on style?? [ATTACH=CONFIG]18113[/ATTACH] EDIT** It looks like AA also has This 0.875 gas block for their 16 inch barrel [ATTACH=CONFIG]18114[/ATTACH]
"A quarter of the width" (of the barrel at the gas port) is 1/4 of 3/4" - yes? That is way more than the width of a credit card, which is what I thought it might be because of Old Bob's explanation in Post#9. Forget that theory - Sounds like you've got a gas block with set screw holes that are just way out of alignment with the dimple in the barrel.
Regardless, you do have to pull it apart and measure the distance from the barrel's shoulder to centre of the hole, and then the edge of the gas block to the centre of the hole. If they are the same then you can push that block right up against the shoulder with confidence and only then have to worry about rotating the block until the holes exactly align. For that you can scratch tiny alignment marks on the shoulder and block to line it up perfectly. Even just slightly out and it's going to choke the gas like it's a smaller hole.
With respect to 'Bullterrier' you won't need a pin set to do this (I don't have one). A set of calipers will do. You can also measure the port size with calipers.
Lining up the gas holes for maximum efficiency is a thread or two on this forum if you want to search. Some guys use bore scopes which means you have to have access to one. Another method is using a toothpick in the gas block. When it is in alignment gravity lets it drop down into the barrel where you crack it out with a cleaning rod. Or you can buy the plastic version of this from HB industries https://www.youtube.com/watch?v=V4f9stp4SWE. I have never used these methods but no doubt they work.
I have just marked and carefully measured with calipers - but whatever method you use you do have to line those holes up exactly, especially in a caliber or gas system that is not as generous with gas as others. If the dimple is misaligned then screwing it tight is going to pull it out of alignment. One solution for this is to replace it with a clamping gas block, which is arguably a more efficient seal anyway. But for that you have to buy a new block. If the dimple is pulling your block out of alignment as you do it up there's not much you can do to fix that. Drill a new hole and screw onto an un-dimpled part of the barrel maybe. That's if there is enough length of block to do this - It's a bit of effort for the sake of simply buying a new clamping block. Up to you and how much money you have.
If you cannot line up the holes without the dimple pulling the block out of alignment then a clamping block is what I would do. As long as it doesn't make contact with the inside of the handguard to keep it free-floating.
That is of course if the problem is the gas holes out of alignment, but it won't hurt or cost to pull it apart and carefully measure, as they say in the emerald isle - 'To be sure, to be sure'.
Klem, spot on advise. I would and have used all of it. have a teslong bore scope and had a buddy make me a fiber optic light to run down gas tube to verify everything lined up. I have had three 223 wylde builds that drove me crazy. block ports dimple all gtg buffer gtg spring gtg gas key and tube gtg. and still weak. also had access to a pin gauge sets from work. I can't remember off hand but sets went up like .061 .062 .063 etc just took port up in one increment at a time and boom cycle like a champ. should have logged info in notebook, but once cycle great left them alone after. all I have ever used is ba barrels except one was areo. think ba makes them for areo not sure. this has been my experience with cycling issues each time. just built my first Grendel with a ba Hanson barrel and did not check port upon assembly.I have not tested it yet, but I have an issue that would be my first look. this site is great tons of good info and experience here. happy building/happy shooting !!! My experience is novice at best so don't mean to offend anyone.
Most gas blocks with set screws have the rear threaded set screw directly across from the gas blocks inside port hole. If yours is this type of gas block, then remove the set screws and put the bottom of your gas block"set screw side" directly over the barrel's gas port. Line the rear set screw hole directly over the barrel's gas port. This will give you the distance needed between the barrel journals shoulder and the gas block. You can use a feeler gauge to get the exact distance needed between the gas block and barrel shoulder to line up the gas block and barrel port....
As long as the dimple on the barrel is also exactly opposite the gas port, otherwise it will pull the block in the direction of the centre of the dimple as you do it up.
Sorry I should clarify - the width was about the equivalent of a $.25 piece (a silver quarter) which was about double the width of a credit card.
I moved it back to a CC width which aligned the rear dimple perfectly with the rear set screw hole on the gas block.
This caused the front set screw hole to cover about half of the front dimple hole. I was able to take a spare set screw and buffed the pointed in flat on a stone then screwed it in. My thought is that the face of the front screw being flat will prevent it from wanting to walk down into the dimple.
I have it ready for another trip to the range to see how it cycles. I will post back.
If this doesnt work Ill buy the AA block and tube and try again!
By now you'll have a pretty good idea of all the measurements, bearing in mind some blocks are still designed to leave a credit-card gap for the 'old-school' clamping foreguards.
If it doesn't work I recommend an adjustable clamping block, or if you prefer a non-adjustable clamping block, or at least a cheaper set-screw block than AA. SLR Rifleworks is a popular choice on this forum.
