Looking For 6.5 Grendel Reliability Optimizations

[rothgyr]

My 6.5 Grendel seems to shoot Hornady Black reasonably reliably, but once I do reloads with a slower powder (8208 XBR and 123 Scenars), the gun starts to get cycling issues, especially with failure to close the bolt all the way. I ran it a couple of weeks ago with a suppressor and it seemed to improve a bit, but I still got some issues on the last few rounds in the mag. For reference, I'm using an ASC 15 rounder loaded to no more than 12 rounds.

My 6 BRA PRS gun is great, but I'd like to take the grendel to a match some time to shake things up, but screw that if I have reliability issues.

Anyone running an 18" Rifle length gas system and 8208 XBR or similar slowerish powders? What buffer system are you working with?

Picture of the rifle:

I'm using a standard carbine buffer, I want to say it's a BCM buffer tube, but I'm not certain anymore (it's been a while), b5 Sopmod, Anderson upper and lower, BA 18" SPR profile barrel, Area 419 Maverick, standard MK12 furniture, PRI delta forend, USO FDN 10x in an MPA BA mount, triggertech safety and a Larue MBT. PSA bolt carrier, Brownells 6.5 Grendel bolt.

 

[hlee]

I’ve got a 20” rifle length 6.5 G and shoot 123gr ELD-Ms over 8208. I have a JP SCS and an SLR adjustable gas block on that gun. I bought the SCS kit, but it is being used in the standard configuration.

About 1 in 50 or so cartridges will impact the barrel face and bend or shear off the plastic tip on the bullet. If that tip shears and falls into the bolt lock up recess, the gun goes down pretty hard. Had that happen at a match once. “Normally” it’s just a ftf, drop the mag, run the bolt, cartridge falls out, insert the mag, run the bolt, back in the game. (The recovered rounds look like they took a Mike Tyson punch in the nose, but still fly straight enough for most PRS targets.)

I’m switching to BTHPs because the gun is 100% with them in factory loadings.

Even with the ftfs, the rifle is easily more reliable that 50% of the built guns I’ve seen in matches.

 

[rothgyr]

I bought the SCS kit, but it is being used in the standard configuration.

So, the SCS kit in standard configuration, or a standard carbine buffer system?

 

[CaptNemo]

In a carbine buffer system, give an H2 Buffer a try.
How fast are you pushing the Scenars?
I've run 8208, CFE223 and AR-Comp in various loads and haven't had a short stroking issue at the end of a magazine.

 

[hlee]

So, the SCS kit in standard configuration, or a standard carbine buffer system?

SCS in standard config. Rifle receiver extension with the JP supplied Delrin spacer.

 

[rothgyr]

In a carbine buffer system, give an H2 Buffer a try.
How fast are you pushing the Scenars?
I've run 8208, CFE223 and AR-Comp in various loads and haven't had a short stroking issue at the end of a magazine.

I'm clocking 2471 FPS with the Scenars. If memory serves right, last time I loaded them up in Starline brass, I was lightly compressed.

 

[LRRPF52]

For any larger case head cartridge, you want the ejector to be radiused and not proud of the feed presentation of the right side cartridge.

That’s a baseline for me any time I put a Grendel together before the bolt even goes near the carrier.

Next is after I confirm the chamber will feed my 4 different dummy cartridges with different ogive lengths and profiles (tangent vs secant, varmint vs target), I de-edge, blend, and polish my feed ramps while ensuring they blend with the feed ramp roots in the upper.

I don’t want any excuse for any type of cartridge to not feed smoothly up the ramps, align into orientation with the chamber, and allow the cartridge to go fully into battery.

Another thing. You mentioned hand loads. What tools are you using to ensure sufficient shoulder movement during your re-sizing process?

The best tool in my experience for controlling that is the Hornady headspace comparator:

Once you figure out what your shoulder datum location needs to be for reliable feeding, you can use that during your re-sizing process with constant spot checks as your’e sizing. This right here solves 90% of any problems of failure to go into battery.

For RLGS 18”, you will be fine with a standard carbine buffer and spring, as long as your port is within .086” - .094”. Suppressed should run with .086” with a high efficiency can, but is on the edge or under for unsuppressed at RLGS.

For the record, I just haven’t seen feeding issues over the past 14 years of building and shooting multiple 6.5 Grendels in fairly high volume, and I have 7 of them. I haven’t shot the 22” much, but have put thousands of rounds through my original 16”, thousands through the 17.6” Lilja, and thousands through the 12” CLGS suppressed.

RLGS is the easiest on your critical components due to lower port pressure and ideal cyclic rate. I choke the CLGS and MLGS with Bootleg Adjustable Gas Carriers looking at ejection.

 

[rothgyr]

Thanks for the detailed response, I'd never heard of the extractor rounding, but it makes a lot of sense.

So far, I'm getting issues with virgin starline brass, so I never checked headspace. I'll look into the gauge you mentioned.

 

[LRRPF52]

Thanks for the detailed response, I'd never heard of the extractor rounding, but it makes a lot of sense.

So far, I'm getting issues with virgin starline brass, so I never checked headspace. I'll look into the gauge you mentioned.

Ok, if that’s happening with virgin brass, check if you have an O-ring around your extractor and remove that.

They have too much extractor tension for my liking. A legit extractor spring (SpringCo) and insert is all you really need especially for RLGS 18”. The tension fights going into battery if you have the O-ring and also stresses the extractor lip more. If I see O-rings in my Grendel bolts, I remove them and never use them. I’ve never had FTExtract.

The Crane O-ring was a band-aid for SOPMOD M4A1 heavy barrels with tight chambers, especially shooting the KAC NT4 with no way to choke the gas. The first generation of 727/XM4/M4 govt profile barrels worked fine as far [as] chamber dims went, but something was done wrong with the reaming on enough of the SOCOM heavy profile M4A1 pipes to want more extraction power.

For hand-loading, I still like to know where all my headspace is on new brass just for records so you can see how much growth and then re-sizing you’re doing to the brass. That Hornady gauge is great.

 

[DHDeal]

As far as the Grendel goes, LRRPF52 knows a thing or two!

I may be misunderstanding what you mean when you mention having issues with new brass. Will new brass not reliably chamber or is it an issue with your loads? The tool memtioned above is used by me every time I set a FL sizing die.

I tend to consider 8208 to be powder for lighter weight bullets (107-108). LeverRevolution and/or 2520 is what I use for the 120-123 grain bullets but my shortest Grendel barrel is a 20" (Proof).

Are your reliability issues with one magazine? Are the the 10 or so rounds you mentioned cycling normally and the last 2-3 not going into battery constant? Can you load say 12 rounds and fire a 5 round group and it cycle normally for those 5 rounds every time?

As LRRPF52 stated for him, I haven't had an issue with the Grendel cycling. I haven't fired as many rounds of Grendel ammo as he has by a long shot but I have been playing with one since about 2010 (Alexander Arms Overwatch was my first). I will say over 3 different rifles and 5 different barrels they have all been reliable. I tend to load on the warm side and will use a strong spring and at least a H1 buffer. The radiusing of the ejector is standard for me. It will make a swipe on the case head go away (unless you get stupid that is).

You didn't mention your load. Might help to diagnose your issue. Take a long hard look at the magazine in question too.

 

[rothgyr]

I'm running about 28 grains of 8208 in my current load with 123 scenars, CCI #450s, starline brass.

Thus far I've just been using an ASC 15 rounder magazine, but I have some PRI 6.8 mags on order that I want to give a shot with.

I had assumed that since 8208 is a relatively slower powder by comparison, it might not be getting enough gas to cycle properly the RLGS. Most 18" barrels you see for sale with a grendel are mid length systems, so I figured that might be the culprit. The issue I'm seeing is where the bolt carrier stops a few mm short of a full closure, and I have to use the forward assist to get it to lock up properly. I mean, my gun could just be dirty too.

I'll load up a bunch of ammo, clean my gun out, and test different mags and different capacities soon and report back.

 

[DHDeal]

As I mentioned, I consider 8208 my lighter bullet powder though it can be very accurate with the heavier Grendel appropriate bullets. 28ish grains is in line with what I've used it at with the 120-123's. All of my barrels have been rifle length gas systems but longer barrels than yours.

Since you have what you have, run the suppressor while you are figuring out the issue since you mentioned it ran better with it. Rifle length gas and an 18" barrel is a short "dwell time" if you will. That may be part of the problem but maybe not. I tend to like as long of a gas tube, within reason, as possible. I run an intermediate length on one of my 16" 223's and it is completely reliable and what Craddock calls a C+1 on a 11" SBR 223 barrel and it too is reliable. Probably apples to oranges as a 223 is not a Grendel.

The PRI magazines are some of my favorites for both 223 and Grendel. I cut out the front of the 10 rounders for a longer OAL and they are reliable for me when I'm playing with Berger VLD's. It works too but those recipes are not my everyday loads. They are experiments that happened to work as well as I hoped (but that's another story).

Honestly I think you are having a magazine issue. 6.5 Grendel specific magazines can be finicky. I have had a few that didn't cycle without some help. Even when I got them running well, I tended to stick with the one's that never caused me a problem. I have a few 26 rounders but never use them as I run my AR's either off of a rest or a short bi-pod so there is length issues. Others may have different experiences than I but I find 10-15 round magazines the most reliable. As it seems you have only that one magazine for now (??) try doing what I suggested earlier to see if it is that magazine causing the problem. 28ish grains of 8208 and a 123 Scenar is not a creampuff load so gas should not be your problem.

I don't know why the factory loads run reliably while your handloads do not except for a dirty gun, a too long OAL (but you stated it would cycle until the last 2-3 of a 12ish round string), or you have a snug chamber (it happened long ago with the slightly different chambers of Grendels but that shouldn't be an issue now IMO). Do what you mentioned and clean it well and try again.

You never mentioned how it shot with the 123 Scenar and 8208 BTW. I forgot to add, try a H1 buffer in there while you're at it. I've switched to the all-in-one (JP and Armaspec) buffer-springs but still run a heavier buffer with one exception and it's not in the Grendel's.

 

[rothgyr]

Lot of good info for me to check out. My PRI mags arrive today, I'll get some rounds loaded up for testing this coming week and check back.

The 123 Scenars and 8208 XBR seem to group fine. It's been a year since I shot groups, but I was getting 5 shots just around or just shy of an inch. Nothing as great as my custom bolt guns, but pretty acceptable for a budget barrel from Ballistic Advantage. I'd like to swap it out for a CLE/Craddock someday, but I have higher priority expenditures for the coming year, so it'll have to wait.

I'll do some actual group size measurements next time I'm out with it.

 

[rothgyr]

For any larger case head cartridge, you want the ejector to be radiused and not proud of the feed presentation of the right side cartridge.

That’s a baseline for me any time I put a Grendel together before the bolt even goes near the carrier.

Next is after I confirm the chamber will feed my 4 different dummy cartridges with different ogive lengths and profiles (tangent vs secant, varmint vs target), I de-edge, blend, and polish my feed ramps while ensuring they blend with the feed ramp roots in the upper.

I don’t want any excuse for any type of cartridge to not feed smoothly up the ramps, align into orientation with the chamber, and allow the cartridge to go fully into battery.

Another thing. You mentioned hand loads. What tools are you using to ensure sufficient shoulder movement during your re-sizing process?

The best tool in my experience for controlling that is the Hornady headspace comparator:

Once you figure out what your shoulder datum location needs to be for reliable feeding, you can use that during your re-sizing process with constant spot checks as your’e sizing. This right here solves 90% of any problems of failure to go into battery.

For RLGS 18”, you will be fine with a standard carbine buffer and spring, as long as your port is within .086” - .094”. Suppressed should run with .086” with a high efficiency can, but is on the edge or under for unsuppressed at RLGS.

For the record, I just haven’t seen feeding issues over the past 14 years of building and shooting multiple 6.5 Grendels in fairly high volume, and I have 7 of them. I haven’t shot the 22” much, but have put thousands of rounds through my original 16”, thousands through the 17.6” Lilja, and thousands through the 12” CLGS suppressed.

RLGS is the easiest on your critical components due to lower port pressure and ideal cyclic rate. I choke the CLGS and MLGS with Bootleg Adjustable Gas Carriers looking at ejection.

Just took bcg out to check the ejector, and sure enough, it's pretty squared off:

Any recommendations on replacement plungers or new bolts?

 

[LRRPF52]

I remove the ejector if it needs to be radiused, and spin it in a drill slightly until I reach the desired effect.

Bill said they addressed this in manufacturing by making sure the ejector was a specific length, not too long so it couldn’t impinge on the side of the case rim.

Once I’m done tuning the ejector face, I clean it and Cold Blue it so it isn’t left in the white.

The AR-15 bolt disassembly tool is great to have for this job. It allows easy punching out of the roll pin. You can also use a piece of cut-down brass and a vice to compress the ejector and punch out the pin that way, but I just use the bolt disassembly tool.

I have 2 of them, one specific to the AR-15, and one a combo that you can use for both the -15 and the AR-10 bolts. I got them from Brownell’s.

 

[rothgyr]

I finally got out and shot the grendel again, it's been a busy fall.

I replaced the buffer spring with a new BCM carbine spring, and it ran 50 rounds without issue. Oddly enough the ASC mag ran fine, and the two 6.8 PRI mags I picked up wouldn't cycle anything if I ran them over 5 rounds. The bullets ended up binding and nosediving pretty badly when loaded up beyond 6-7 rounds.

 

[rothgyr]

I'll do some actual group size measurements next time I'm out with it.

And as promised, groups size for the 123 Scenars over 27.9gr 8208 XBR, CCI 450s, starline brass. Not as good as my bolt guns with custom barrels, but for a $200 Ballistic Advantage barrel on a gas gun, I'll call it good enough. I still want a Craddock/CLE someday though.

 

[DHDeal]

Who knows, a "better" barrel (more $$ that is) may beat that and it may not.

I've never used my PRI magazines unmodified so I have no idea how they would run otherwise. You may not be willing to cut out the front of them. I think I mentioned why I do it but maybe not. Take a look on Cavity Back's website for their mod on the PRI magazines. With the group you posted, the juice may not be worth the squeeze so to speak. IME, a Scenar is easy to tune, just not as good as a Berger 120 grain BT but nothing else is either (a 120 SMK is close).

 

[Top O' Texas]

Using the scs with the b5 buffer system you will need a spacer (not the spacer included as it's for rifle length tubes). I do think they make a spacer for b5 buffer systems though? Carbine over b5 versions are about 1/2-3/4" longer (b5 being longer as it uses a rifle length spring).

 

[rothgyr]

Using the scs with the b5 buffer system you will need a spacer (not the spacer included as it's for rifle length tubes). I do think they make a spacer for b5 buffer systems though? Carbine over b5 versions are about 1/2-3/4" longer (b5 being longer as it uses a rifle length spring).

I'm kind of lost with what you're talking about. What is the B5 buffer system?

 

[rothgyr]

And an update. I ran my Grendel at a local regional match this weekend, and it ran with no feeding issues other than needing to use the forward assist on full mags a couple of times.

ASC 15rd mags are the way to go for my gun, by the looks of it.

 

[Top O' Texas]

I'm kind of lost with what you're talking about. What is the B5 buffer system?

Sorry about that. B5 us the furniture and A5 is the recoil system. I usually don't talk about the A5 enough and get side tracked. For better explanation search "VLTOR A5". They have their own systems.