Have a question for anyone shooting a 6.5 grendel in AR platform. My brother in law put one together and is having issues. So far these are all factory hornady black he has shot. When shooting it the brass shoots out forward only about 3 feet and most of the time jams the next round to point its damages the brass or bullet. His gas block is non adjustable. I believe its an 18 inch barrel with mid length gas system. He has changed buffers. One was a 5.6oz the other was 3.3 oz. Same results for both. These are armaspec stelth recoil springs. I have not been there when he has tried it. This is what he is telling me. The complete upper was bought assembled he just added it to a lower he put together. Im thinking its a gas issue but not extremely experienced to what direction to take. Any suggestions? Thanks
6.5 Grendel feeding issues
- Thread starter JB10
- Start date
Grendel mags? Maybe a different problem but using 556 mags is less than reliable, ime. If it's gas, play with the gas block a bit. first make sure it locks the bolt back on the last round. If so, you can rotate or move the block just a tad to close off a tiny bit of the port to see if that fixes it or not. If so, I'd fix it right or use an adjustable gas block.
+1. It's possible there are other things going on; but great place to start is the one shot lock-open on an empty mag.
-Mac
searcher
Gold $$ Contributor
A lot of "brand new" A/R bolts create a lot of friction when sliding in the carrier - at least until a few hundred rounds have been fired to break the edge on the gas rings. Starting with least costly methods of diagnosis - if a round is firing, ejecting and the next round is hanging up and jamming - it is usually due to a "short stroke", whereby the bolt is not being pushed all the way back. I'd pull out the bolt carrier and pull the bolt in and out of the bolt carrier about a hundred times. This alone can sometimes be all that is needed to break the rough edge off the gas rings and allow the bolt to move fully to the rear. If that doesn't do it - I'd be sure the gas block is in proper position and that the gas hold in the barrel is not partially blocked by improper rotation of gas block. Then I'd put in a reduced power main spring made by Wolff. That is where I'd start.
As Mac said, insure that the bolt locks back after firing the last round in the magazine. I have had problems in this regard and found the gas port to be undersized. I ended up having to open up the gas port to correct the situation. Unfortunately I have just moved and cannot find my reference as to the recommended port size/position.
These are the recommended sizes. https://www.tacticalmachining.com/learn/ar-style-rifles/ar-15-gas-port-sizes.html
If you find that the gas port is undersized, it is not difficult to open it up using a number drill (available from mcmaster carr) and a pistol drill - being careful not to contact the opposite side of the barrel. The chart shows a mid length barrel port to be 0.078 to 0.081". Start small and work your way up.
Harborfreight.com has number drill sets that are not unreasonably priced. A set of micrometers will help keep you out of trouble.
If you find that the gas port is undersized, it is not difficult to open it up using a number drill (available from mcmaster carr) and a pistol drill - being careful not to contact the opposite side of the barrel. The chart shows a mid length barrel port to be 0.078 to 0.081". Start small and work your way up.
Harborfreight.com has number drill sets that are not unreasonably priced. A set of micrometers will help keep you out of trouble.
Last edited:
If it's locking the bolt back on last shot, and brass is ejecting forward (assuming right hand eject), say 1:00-3:00; then over gas is your issue.
Over gas rears its head in three ways.
1. Case head swipe and beat up case heads
2. Ejection forward and very sporratic
3. Feed problems due to cycling too fast
You may not see all three of these issues, but problems are all the same.
1. Adjustable gas block (plug gas feed at barrel source).
2. Adjustable bolt carrier (vent gas feed at bolt carrier)
3. More mass /spring. Make the extra gas energy move more material.
You pick which method you want to use (or multiple).
You're dialed in when, bolt will just lock back on last round on mag and when the brass makes a nice neat pile at 4:30-5:30.
-Mac
searcher
Gold $$ Contributor
If the bolt IS locking back - that all but eliminates the problems associated with short stroking - such as gas block not aligned, size of gas port in barrel, etc. - so I'd now tend to look at other problems. If the bolt IS going that far back - then the problem is why is the next round getting jammed after being stripped off the magazine on the way to the chamber. Bullets with large hollow points (such as Speer TNT's) will hang up on a sharp forward edge of the chamber on a lot of A/R's. Tipped bullets or sharply pointed bullets can do the same. Even if the gun doesn't jamb - the tips get deformed a bit when loading. Slightly rounding and polishing the bottom, forward edge with a dremel tool will minimize the bullet from getting hung up - then getting crunched from the top by the bolt coming forward. I recently had the gas key come loose on a hunting trip. That particular bolt carrier did not have the screws holding it on staked. Gun jammed about five times before I saw it was only slightly loose, so I'd check that. I'd swap out a magazine - again being sure it is for the Grendel (or SPC). it could also be that the mainspring is not strong enough. Swap out the spring with a heavier one if available for a test. Id check to see that the magazine cannot be pulled out once locking into place. If it is not SECURELY being latched into place - the round can sometimes still be stripped off - but the angle to the chamber is changed - causing the tip to go upwards to hang up before the bolt hits it on the side of the case instead of the base. Trying to stick to the easiest and most common fixes first. It truly is very rare that one needs to enlarge holes in barrels and replace expensive components of the rifle - so best to sort through all the other avenues first. Good Luck
I built a 6 ARC last year and had almost the identical issues as your BIL. If you have a bore camera run it down the barrel and make sure the gas port, etc is all lined up. I will be honest and straight forward. I did everything in the book and finally went to an adjustable gas block and it resolved my problem.
Sandstorm
Gold $$ Contributor
I think this may be your issue. Not uncommon at all.
at least check the size with a drill bit and if your under .062 you may need to open it to .074 aprox
or if oversize adjustable gas block
Last edited:
Lone Hunter
Silver $$ Contributor
I like this chart. Could possibly help diagnose problem.
searcher
Gold $$ Contributor
Just remember - all the gas does is throw the bolt back. If the bolt is locking to the rear - it is evidence that you are getting ample gas to do the job - and the problem likely lies elsewhere. Some people go with an adjustable gas block when getting failure to feed and it helps them - but that is usually because their old gas block was either not allowing enough gas to get the bolt to the rear - OR it was misaligned with the gas port and it seemed the addition of an adjustable block fixed it - which was really not the case many times, but rather the undetected misalignment. If your bolt is locking back - I'd look elsewhere. Lots of folks spend a fortune replacing parts till the problem goes away. The best uses of an adjustable gas block are to stop a heavy load from bottoming out your buffer and to fine tune a load for accuracy. Some just use it to direct their brass in a certain direction when ejecting. Giving more gas than your barrel port will allow is not one of them. Really trying to sway you here........ ha.
^^^THIS^^^. Good info!
Thanks for all the replys. I will pass on this info to him. Think first step would be to check port alignment and possible get an adjustable block in if no issue is seen with alignment or port size hole. I dont think its a mag issue since it is for the grendel and this issue has been with this upper assembly that he got. Ill get with him and let you know how it turns out. Thanks again
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.