First AR Build - 20" Stainless Grendel

[CrisAnderson27]

Hello everyone!

So, about six months ago, I decided to start exploring the AR platform. I went down to my local gun store (Tombstone Tactical), and bought myself a stripped Anderson lower and a basic military type parts kit. I rushed home, found me a YouTube video, and put the thing together in about 20 minutes, lol.

It then sat on a shelf until last week.

In the meantime, I picked up an actual ArmaLite 16" (M15A4CB) gun for $599 at Cabela's, and have proceeded to have a blast blowing holes in 5/8" plate at 50yds with PMC green tips.

This brings us current. During my time playing around with the ArmaLite...I did a lot of research into what options there were for my little Anderson lower sitting on the shelf. I originally wanted a 7.62 gun (come on, they're big!), quickly found out that the .308 wasn't realistic and wouldn't fit my lower anyway...then stumbled over the 6.5 Grendel and quickly succumbed to all of its obvious virtues. My thoughts were that since I had a maneuverable, '100 yard' gun already, I'd build the 6.5 into something that could make use of its ballistics. Something that would make sense for coyote, deer, javelina, or targets.

So I put together a parts list:



For the most part, that's the direction the build took.


All the parts together. The optics are an older Nikon ProStaff, and actually came with my $599 ArmaLite, which now uses an inexpensive red/green dot.


Anderson stripped upper, Strike charging handle (glad I bought the extended one...the scope is right in the way of it lol), and the bolt carrier setup that I ordered with the barrel. The bolt itself is the 750XD from AR15Performance.com, and was checked for headspace with the barrel before shipping.


Squared upper. I don't know if this step is mandatory to be honest...and it actually had caused me some doubt in other parts of the build (the gun feeds fine for the most part though, more on that later). In reading though, unless one goes nuts to the point where the barrel extension protrudes into the upper, it should be a non-issue.

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[CrisAnderson27]

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Completed rifle!!


And some play time at the local shooting spot this weekend. I put 80 rounds of Wolf 100 grain through it, and 40 rounds of Hornady 123SST. It did NOT like the Wolf ammo, at all. And I mean at all. It was jamming regularly. Sometimes I'd have to hold back the charging handle and drop the mag to get it clear, as the spent round and incoming round would be crossed up. It'd go 5 rounds without issue, then jam on the next 2...then run 8 more clean...jam once...etc. Getting through the full 80 rounds was frustrating. After that however, it chewed up the Hornady SST without a second thought.

Which brings me to some questions.

First, what do you guys think would be causing the jamming on the steel rounds? In reading around, I'm seeing a lot of commentary about pressures (with factory ammo I'm thinking this isn't likely unless the barrel or something else out of my control is messed up), and also about gas timing. The description of the setup from AR15Performance.com is as follows:

20" med contour with a rifle length gas system . Barrels ported to run factory ammo with a standard CAR buffer and spring. Optional 750XD bolt, the strongest AR15 Grendel bolt made.

Chamber: 6.5 Grendel body spec with mid spec throat to increase accuracy.
Bolt: uses .135 recess---750 XD(extreme duty) ARP bolt could be an option(will handle 60,000psi)
Profile: SPR-.850/.750/.718
Fluted: No
Barrel Length: 20"
Twist Rate: 1:8.5- Hybrid 5R rifling
Gas System: RIFLE Length
Diameter at Gas Port: .750"
Muzzle Thread Pitch: 5/8x24
Material: 416R stainless
Finish: ss
Process: Button Rifled
Barrel Lining: ss
Barrel Extension: M4

I have all the spent casings (both brass and steel), and can share pictures if you'd like. The primers have a weird half circle flattened spot on them, and there are extractor swipes on some, but not on others. There was a lot of brass on the bolt face, and the markings on the bolt weren't even. There was almost two clear half circle marks on the bolt (I'm guessing these are left by the primer?) around the pin hole. My ArmaLite bolt has a perfect circle centering the firing pin hole. I'm hoping it's simply a gas timing issue requiring a heavier buffer (even though the manufacturer says standard carbine), or maybe my gas block is too far one way or the other? I figured I'd get some input from people with more experience than I have before tearing it apart and possibly introducing a host of other issues requiring trouble shooting, lol.

Anyhow! Other than that I love the gun! I didn't take any time to take pictures with all of the diagnostics going on in regards to the jamming, but at 100yds it does what I tell it to...which is the point . I actually love it so much I'm probably going to relegate the ArmaLite 5.56 upper/barrel to back up, and build a 16" upper in 6.5 Grendel for my 100 yard gun lol.

[CrisAnderson27]

Decided to go ahead and share the casing pictures.

First the steel:


You can see scraped marks on the neck area...and they correspond to the below picture of the squared off mouth. All of the spent casings had a D shaped mouth when recovered.


A picture of the actual mouth. The brass casings are worse.


The primer. None of my 5.56 cases look like this at all.

[CrisAnderson27]

And the brass casings:


Here you see similar scrape marks on the neck of the brass. More exaggerated of course.


And the deeper 'dent' on the mouth of the case. I don't know whether this is from being ejected into the deflector on the upper, or somehow being ejected early and hitting the extension. The way the dings are perfectly spaced and parallel with each other on the neck makes me think the latter. Is this a timing issue or something else?



A couple different angled shots of the primers for you all to diagnose!

Any help would be appreciated. I can't help but think that the odd markings are indicators of whatever issue is keeping the steel ammo from cycling properly. Considering that I can get them around $.28/round vs $1.05 or so for the Hornady, it would be worthwhile for me to figure out the problem lol.

[Klem]

If you want feedback then unfortunately it is going to be a lecture.

With due respect, the photo of loaded weapons the back of a truck (mags on) with barrels pointing towards people turned my stomach. Maybe you've never seen it but there is no lesson better than reality when everything turns to shit in a blink of an eye.

Maybe a portable table downrange of the truck with all the guns pointing in the same direction which is down-range. No one goes forward until all the guns are unloaded. Or everyone behind the truck and all barrels pointing away from your mates and loved ones.

[m796rider]

I have a 11.5" .264LBC barrel from BHW that also does not reliably feed the Wolf ammo. The throat is too tight and the cases just stick, causing multiple malfunctions. Les Baer and AR15Performance, among others, tighten up the SAAMI Grendel throat for "better accuracy," and as you are seeing it tends to be OK with brass cased ammo but the lacquered/polymer coated steel cased ammo really wants that true Grendel chamber.

As for the crescent-shaped marks on your primers -- have you looked at the bolt supplied with your barrel? I'm wondering if it is a standard-pattern AR bolt or if the locking lugs are rounded off, trimmed, etc.

[CrisAnderson27]

If you want feedback then unfortunately it is going to be a lecture.

With due respect, the photo of loaded weapons the back of a truck (mags on) with barrels pointing towards people turned my stomach. Maybe you've never seen it but there is no lesson better than reality when everything turns to shit in a blink of an eye.

Maybe a portable table downrange of the truck with all the guns pointing in the same direction which is down-range. No one goes forward until all the guns are unloaded. Or everyone behind the truck and all barrels pointing away from your mates and loved ones.

Hello Klum!

You are 150% correct in that the picture looks 150% irresponsible. My apologies for that. All of those weapons were empty and had been verified so before being put in the truck during cleanup (part of the process for being placed in the truck). The empty magazines were put back to keep track of who they belonged to.

I tend to forget that online, people can't see the process followed prior to a picture being taken. I'm far from being offended by your 'lecture', if anything, I'm grateful for the respect you've shown for me and mine by pointing out what appears to be negligence.

I will be more careful with my photos in the future, and will leave that one up for clarity in the discussion.

Thank you, again.

[CrisAnderson27]

I have a 11.5" .264LBC barrel from BHW that also does not reliably feed the Wolf ammo. The throat is too tight and the cases just stick, causing multiple malfunctions. Les Baer and AR15Performance, among others, tighten up the SAAMI Grendel throat for "better accuracy," and as you are seeing it tends to be OK with brass cased ammo but the lacquered/polymer coated steel cased ammo really wants that true Grendel chamber.

As for the crescent-shaped marks on your primers -- have you looked at the bolt supplied with your barrel? I'm wondering if it is a standard-pattern AR bolt or if the locking lugs are rounded off, trimmed, etc.

Hello m796rider,

You can see the bolt from the side in the third picture from the top above. Here's another picture I took during cleanup yesterday:



I'll also post some side by side pictures of the bolt faces here in a bit for you all to comment on.

Also, thank you for explaining about the AR15Performance chamber. If that's the case, it doesn't look like there's much I'll be able to do to correct it.

[LRRPF52]

I've never seen primer and case head markings like that. Looks like something isn't square to the bore line, and the firing pin isn't centered to the bore, although you rarely see perfect centering of the firing pin. The crescent moon indentation next to the firing pin dimple is a first as well.

Check that there are no burrs or debris in your firing pin aperture, and that your firing pin head is free from damage. I have seen damaged firing pin heads before, where a cup forms on the tip of the pin, which is a recipe for pierced primers, but nothing like what you posted.

When manufacturers tighten the neck dimensions of the chamber from the SAAMI, you can't expect to be able to shoot factory ammunition, particularly the steel case ammo, which the Grendel chamber was designed to work with from the onset. Another reason why I recommend insisting on the SAAMI chamber, which is already the most accurate chamber there is for 6.5 Grendel and the wide range of projectiles you will come across.

[CrisAnderson27]

I've never seen primer and case head markings like that. Looks like something isn't square to the bore line, and the firing pin isn't centered to the bore, although you rarely see perfect centering of the firing pin. The crescent moon indentation next to the firing pin dimple is a first as well.

Check that there are no burrs or debris in your firing pin aperture, and that your firing pin head is free from damage. I have seen damaged firing pin heads before, where a cup forms on the tip of the pin, which is a recipe for pierced primers, but nothing like what you posted.

When manufacturers tighten the neck dimensions of the chamber from the SAAMI, you can't expect to be able to shoot factory ammunition, particularly the steel case ammo, which the Grendel chamber was designed to work with from the onset. Another reason why I recommend insisting on the SAAMI chamber, which is already the most accurate chamber there is for 6.5 Grendel and the wide range of projectiles you will come across.

Good to know, even if after the fact.

Here's a few pictures of the bolt from different angles, some side by side with my 5.56 bolt out of my ArmaLite.


Standard 5.56/.223 bolt with an unknown number of rounds through it (I've put at least 600 myself, and I bought it used).


New AR15Performance.com XD750 bolt with 120 rounds total, the final 40 of which were brass. The amount of brass shavings and the weird offset witness marks bother me. The brass fits perfectly in the bolt, which I double checked after inspecting it the first time (the marks make it look like the round is clocking itself around the pin somehow while being repeatedly pounded into the bolt...which is of course impossible). I don't understand how the primer could leave an oval witness mark on the bolt face, even if it were being slammed back into the bolt multiple times somehow.



Side by side. You can see that the lugs are rounded as mentioned above. I also verified that the firing pin is undamaged, both on the tip and down the length. Looking at these pictures, I may chamfer the firing pin orifice the tiniest amount to remove what looks like a small burr around it. I'm not sure how that could cause a problem...but I'd rather it not be there either way.

Again, I know only what I've read so far in regards to the AR platform in general, and Grendel builds specifically...and don't pretend to be any sort of expert (barely a novice, actually)...so, I'd love to hear any of your thoughts on the topic.

[Jtmbtech]

I don't know if it's possible but I wonder if it could be happening when the bolt is coming forward and stripping the next Shell out of the magazine? Maybe try one at a time manually dropped in the chamber and see if the Mark still happen

[LRRPF52]

I can see the burr just outside of the firing pin aperture clear as day in your pics. That's where that weird crescent moon indent is coming from.

Be careful with chamfering pin apertures, as you can create a situation where you get more primer flow around the firing pin.

[CrisAnderson27]

I can see the burr just outside of the firing pin aperture clear as day in your pics. That's where that weird crescent moon indent is coming from.

Be careful with chamfering pin apertures, as you can create a situation where you get more primer flow around the firing pin.

Thank you for the advice! I chamfered it today, and was very careful (I would have been either way, but your caution was definitely welcome and helped me resist the temptation to radius more for 'strength' lol) to only barely radius the pin hole just enough to ensure no burr. Luckily I make knives for a living so the task wasn't too difficult .

I also took some video as I felt the pictures weren't accurately showing the surface condition of the bolt face. The video is in 4k resolution, so if you can take the time for it to download that's the best way to watch it.

https://youtu.be/rKIgws541FY

I don't mean to come across as badmouthing AR15 Performance at all. I spoke to him a few times while purchasing products and he was both polite, and seemed knowledgeable and helpful. I certainly don't know what parts of a bolt should be perfectly smooth, and what parts don't matter. It just seemed odd that the bolt face would be left with cutter marks when the rest of the bolt is so beautifully machined.

If you guys see anything else of concern, please let me know.

[diddlyv]

Have you had a chance to test it again, and how does it shoot?

Have a Odin works 20 inch DMR on back order but could be convinced to switch.

[CrisAnderson27]

Going to go put 20 rounds of Wolf through it this afternoon (all I could find locally). I took everything apart down to the bare upper/barrel today...and the gas block was pushed all the way against the shoulder. It's fixed now.



Here's all the Grendel ammo my local Cabela's had in stock. $11 for the Wolf, and $22 each for the Hornady.



/sigh!

I'll let you all know how it goes. Hopefully the short gas was the issue.