More 6.5 Grendel feeding issues

[thedude824]

This is the third 6.5 Grendel I built this year. The two prior builds both used DI and adjustable gas blocks, Craddock RTR barrels, A5 buffer tubes, and A5H2 buffers. Both took about 60 rounds before they STARTED feeding somewhat, but then I moved on to other things so I’m not confident saying they are definitely 100%. I’ve got 30 and 15 round Geissele mags, 10 round Duramags, and 17 round Elanders. Gave up on the Elanders.
Built a 14.5” with a Craddock RTR barrel, superlative arms piston, Rexus bolt, A5, etc for my girl. I’ve triple checked gas alignment. Put 50 rounds through it the other day and only the 15 round Geissele (didn’t use the 30) cycled two rounds in 1 case and a single round in the other mag. Piston is full open and I’ve triple checked alignment. It ejects the rounds at about 330. It jams the new rounds into the feed ramps and in some cases scores the brass case pretty deep. Also using an A5H2. Please give me some ideas. I put some money into this build and I need fresh eyes. Shooting 123 grain Lapua Scenar over 27.8 grains TAC with a COAL of 2.242”

 

[flogxal]

Only insight I have is this: feeding problems seem to come from one of three causes. Magazine feed lips/spring/follower. Too much gas/bolt speed overrun. Too little gas/bolt too slow.

I have seen bolt speed overruns that resembled undergassed performance, feeding wise.

Hopefully someone else has better insights.

 

[thedude824]

Only insight I have is this: feeding problems seem to come from one of three causes. Magazine feed lips/spring/follower. Too much gas/bolt speed overrun. Too little gas/bolt too slow.

I have seen bolt speed overruns that resembled undergassed performance, feeding wise.

Hopefully someone else has better insights.

I was considering this. At first I thought maybe too little gas so I opened it all the way up. I didn’t think to try reducing the gas. I assumed that Craddock used an appropriate size gas port. Definitely something worth trying

 

[flogxal]

When I had a bolt speed overrun, I had only seen poor feeding with choked gas scenarios. Too little gas, I mean. The feeding issue looked like slow bolt. To me. So opened it up further, problem persisted. Assumed "maybe I'm wrong here" and went the other way and it wasn't too long before I had closed it down enough to make it feed happily.

The other factor influencing bolt speed, of course, is buffer spring & weight. If you've got an A5 system you've got it optimized already at the start. In your shoes I would look at the gassing, and see what happens if you choke it down some more. But that's due to my overgas experience mentioned above. I think there are other folks here with more build experience and more troubleshoot experience than I have.

 

[6.5SH]

If you put one round in a mag and fire, does the bolt lock back?

 

[hlee]

Putting up the bat signal. Calling @LRRPF52, please pick up the white courtesy phone…

 

[Markbsae]

I started with an H2 buffer (because the forums) and the bolt wouldn't lock back and it wouldn't strip another round. I switched to a standard buffer and its worked just fine ever since. I have a rifle length gas system and buffer tube.

 

[supercorndogs]

I started with an H2 buffer (because the forums) and the bolt wouldn't lock back and it wouldn't strip another round. I switched to a standard buffer and its worked just fine ever since. I have a rifle length gas system and buffer tube.

Are you saying you put an h2 buffer in a rifle length buffer tube?

 

[Markbsae]

Are you saying you put an h2 buffer in a rifle length buffer tube?

Yes. I have an upgraded spring (can't remember which one) and it cycles just fine with everything from factory loads to warm hand loads.

 

[supercorndogs]

Yes. I have an upgraded spring (can't remember which one) and it cycles just fine with everything from factory loads to warm hand loads.

And this upgraded spring has a spacer in it or something, for using a carbine buffer in a rifle length buffer tube?

 

[LRRPF52]

I’ve never seen the need to mess around with piston systems in Grendel, so I have no experience with them.

I just have experienced 16 years of reliable feeding with:

24” RLGS standard rifle buffer/spring, standard carrier, AA and Maxim bolts
20” RLGS same as above with AA bolts
18” MLGS .076” ports with various bolts, rifle/carbine/A5 buffers/RETs/springs
16” MLGS .076” ports with various bolts, standard carbine springs and buffers/RETs
12” CLGS .062” ports with PDW short tubes/stiff springs/tiny 2.9oz short buffers, and standard carbine RET/buffer/extra power springs/about 100% suppressed, Bootleg adjustable carriers for the past 7+ years

One thing I do is de-edge, blend, and polish feed ramps. Standard or Spingco extractor springs, various types of magazines from the early days of OG CProducts to the present.

The main thing jumping out at me is the piston system. Switch to Stoner gas and don’t look back is the easy button.

Bill Alexander had some Adams Arms piston guns way back in the day, then they quickly disappeared from the site. Not sure what happened.

One best guess is if you’re using a standard Stoner bolt with gas rings, maybe they’re adding friction to the system that isn’t necessary. Due to the lack of precision with piston guns, I prefer to keep any moving parts attached to the barrel at a minimum mass. The basic Stoner design already does this with no real fuss, especially when using adjustable gas.

 

[Jsp556]

I’ve never heard many success stories with piston kits. I’d put it as Stoner intended. At least then you’d have a decent idea on getting it too run.

 

[Markbsae]

And this upgraded spring has a spacer in it or something, for using a carbine buffer in a rifle length buffer tube?

Nope. It's probably the spring rate ramping up as it gets near coil bind.

 

[thedude824]

I’ve never seen the need to mess around with piston systems in Grendel, so I have no experience with them.

I just have experienced 16 years of reliable feeding with:

24” RLGS standard rifle buffer/spring, standard carrier, AA and Maxim bolts
20” RLGS same as above with AA bolts
18” MLGS .076” ports with various bolts, rifle/carbine/A5 buffers/RETs/springs
16” MLGS .076” ports with various bolts, standard carbine springs and buffers/RETs
12” CLGS .062” ports with PDW short tubes/stiff springs/tiny 2.9oz short buffers, and standard carbine RET/buffer/extra power springs/about 100% suppressed, Bootleg adjustable carriers for the past 7+ years

One thing I do is de-edge, blend, and polish feed ramps. Standard or Spingco extractor springs, various types of magazines from the early days of OG CProducts to the present.

The main thing jumping out at me is the piston system. Switch to Stoner gas and don’t look back is the easy button.

Bill Alexander had some Adams Arms piston guns way back in the day, then they quickly disappeared from the site. Not sure what happened.

One best guess is if you’re using a standard Stoner bolt with gas rings, maybe they’re adding friction to the system that isn’t necessary. Due to the lack of precision with piston guns, I prefer to keep any moving parts attached to the barrel at a minimum mass. The basic Stoner design already does this with no real fuss, especially when using adjustable gas.

I’m using a Rexus ultrabolt. The rings are removed. Here is a pic of one the cartridges that was jammed forward. Several had the case gouging and dent in the shoulder. I’m really thinking you guys may have hit on too much gas…
I just assumed the gas port would be drilled appropriately, the A5 system would help with additional “room for error” and the Velos LBP 762 shouldn’t have any additional back pressure.

 

[thedude824]

I’ve never seen the need to mess around with piston systems in Grendel, so I have no experience with them.

I just have experienced 16 years of reliable feeding with:

24” RLGS standard rifle buffer/spring, standard carrier, AA and Maxim bolts
20” RLGS same as above with AA bolts
18” MLGS .076” ports with various bolts, rifle/carbine/A5 buffers/RETs/springs
16” MLGS .076” ports with various bolts, standard carbine springs and buffers/RETs
12” CLGS .062” ports with PDW short tubes/stiff springs/tiny 2.9oz short buffers, and standard carbine RET/buffer/extra power springs/about 100% suppressed, Bootleg adjustable carriers for the past 7+ years

One thing I do is de-edge, blend, and polish feed ramps. Standard or Spingco extractor springs, various types of magazines from the early days of OG CProducts to the present.

The main thing jumping out at me is the piston system. Switch to Stoner gas and don’t look back is the easy button.

Bill Alexander had some Adams Arms piston guns way back in the day, then they quickly disappeared from the site. Not sure what happened.

One best guess is if you’re using a standard Stoner bolt with gas rings, maybe they’re adding friction to the system that isn’t necessary. Due to the lack of precision with piston guns, I prefer to keep any moving parts attached to the barrel at a minimum mass. The basic Stoner design already does this with no real fuss, especially when using adjustable gas.

If this doesn’t fix it I’ll swap the Superlative Arms piston to her 11.5” upper and swap that BCG and a superlative arms gas block to this. I have other systems running the SA piston and they were perfect. The smoothness of the system is really impressive. I’d have to put some replacement gas rings on the Rexus ultrabolt.

If it were overgassing, wouldn’t that mean that a fixed gas block (especially with carbine buffer tube) would ALL have these problems? I’ve not heard of this with the Pangris barrels.
Is it possible my mags still aren’t broken in?
I’m terrified to grind/polish feed ramps etc, but I will do it if someone could provide details on dremel bits, speed, or sandpaper grit and possibly some end result pics.
It doesn’t make sense that the SA piston system is at fault. It uses an adjustable gas block to control the piston. It’s just the piston pushing the BCG back and buffer spring pushing new round forward. It appears the forward motion is the problem.
With one round it DOES lock back on empty.

I tried adjusting the gas at the range, but they are very uncomfortable with the positioning of the rifle barrel and my head that is needed to do that. Granted my 10 years in Law Enforcement falls far short of their two week range officer training… /sarcasm

 

[thedude824]

@LRRPF52 Did you say you’ve had success with Bootleg adjustable carriers in 6.5 Grendel? Did you use an A5 system with them? I have a brand new one in the box after my first required a high back pressure can AND the full open setting to cycle a 14.5” AR with an A5. I sent it in, they said it was fine, put in some tighter fitting pieces and sent it back. It sat in the box since then. Using that would mean I wouldn’t need the AGB if I do switch. I just want to confirm you used it with an A5 and perhaps what buffer weight?

 

[supercorndogs]

Nope. It's probably the spring rate ramping up as it gets near coil bind.

A carbine buffer in a rifle legth tube wouldn't make the coils bind. A rifle legth tube is longer than a carbine tube. Using a carbine buffer In a rifle tube with no spacer leaves room for the carrier to run into the end of the buffer tube. I.E something like the gas key stops movement instead of the polyutherane on the buffer.

 

[Cal97c]

Take a handful of Mobil 1 motor oil and wipe that bolt down real well and run it wet.
Might be a good ideal to work the bolt 100 times or so before loading a live round.

 

[WeR0206]

@LRRPF52 Did you say you’ve had success with Bootleg adjustable carriers in 6.5 Grendel? Did you use an A5 system with them? I have a brand new one in the box after my first required a high back pressure can AND the full open setting to cycle a 14.5” AR with an A5. I sent it in, they said it was fine, put in some tighter fitting pieces and sent it back. It sat in the box since then. Using that would mean I wouldn’t need the AGB if I do switch. I just want to confirm you used it with an A5 and perhaps what buffer weight?

In addition to an adjustable carrier you could also get an adjustable gas key like the below:

Rubber City Adjustable Gas Key ($40)

 

[waveslayer]

I have never had an issue with any grendel I've built. Change out the buffer and spring to match carbine to carbine or rifle to rifle. See what happens

 

[thedude824]

I have never had an issue with any grendel I've built. Change out the buffer and spring to match carbine to carbine or rifle to rifle. See what happens

Is this towards me? Mine has an A5 buffer tube (rifle length) and the appropriate A5 buffer weight and A5/rifle spring.

 

[thedude824]

In addition to an adjustable carrier you could also get an adjustable gas key like the below:

Rubber City Adjustable Gas Key ($40)

The piston/gas block is fully adjustable and can be used in restrictive mode or bleed off. It’s fully open now so I’ll decrease the carrier speed by limiting the gas in bleed off mode. There are 20 clicks of adjustment in restrictive mode (like a typical gas block) then it’s full open, then if you continue turning CW you enter bleed off mode (like the SA gas blocks) and there are at least 20 clicks of adjustment there.
I’m relatively confident it’s either overgassed, a mag issue, a feed ramp issue, or a combination. The observable issue is when the BCG is returning to battery/loading a new round.

 

[hlee]

The bullets jamming on the feed ramp is a mag issue, but no one can tell you what mags will solve the issue for your rifle. ASC mags have been the best in my rifles, but I still get about occasional issues where a poly tip gets woefully bent and maybe breaks off. I’ve been shooting more bthps to get around this problem.

 

[SWgeezer]

ASC magazines specific for 6.8 are all I use with no issues.

 

[Markbsae]

A carbine buffer in a rifle legth tube wouldn't make the coils bind. A rifle legth tube is longer than a carbine tube. Using a carbine buffer In a rifle tube with no spacer leaves room for the carrier to run into the end of the buffer tube. I.E something like the gas key stops movement instead of the polyutherane on the buffer.

Out of curiosity, I inspected things. Here is what I found. As assembled the carrier travel is limited by the gas key bottoming on the charging handle. Here is where that interference occurs. Apparently the spring rate is coincidentally just right to cycle and lock back on an empty mag without bottoming.

Here is where the back of the gas key would contact the lower receiver,

Here is the total travel of the buffer before bottoming on the polyurethane bumper,

And here is the length of the carrier to the key.

 

[hlee]

Out of curiosity, I inspected things. Here is what I found. As assembled the carrier travel is limited by the gas key bottoming on the charging handle. Here is where that interference occurs. Apparently the spring rate is coincidentally just right to cycle and lock back on an empty mag without bottoming. View attachment 8776710
Here is where the back of the gas key would contact the lower receiver,
View attachment 8776713
Here is the total travel of the buffer before bottoming on the polyurethane bumper,
View attachment 8776714
And here is the length of the carrier to the key.
View attachment 8776715

Now, look at the base of the receiver extension tower for damage caused by this corner on your bolt carrier. It will exhibit as small triangles on either side of the tower…

 

[Markbsae]

Now, look at the base of the receiver extension tower for damage caused by this corner on your bolt carrier. It will exhibit as small triangles on either side of the tower…

View attachment 8776723

Here?