New Grendel Build Questions

[TexN]

Ok Im looking to jump into the Grendel but being a Grendel newb I want to run my barrel setup by everyone first as these chamberings and bolt types get a little confusing. Im wanting to get a 12.5" and 18", the 12.5 will be my knock around, carry everywhere hunting rifle. The 18" will be just for hunting and target. I hunt deer and hogs but we have recently had a major influx of hogs again, now coming up to the house (may have to use the 300blk) til I can get the 6.5 going. Im planning on just using quality factory ammo, and do have a Sico Omega 300 coming in this month too.

12.5";
-saami chamber
-.136 bolt
-carbine gas
-1:7 twist

18";
-saami chamber
-.136" bolt
-mid gas?
-1:7 or 1:8 twist?

Ive read that the 18" needs the mid length gas system and that 1:8 twist is fine but I see some including AA using 1:7.5, so I dont know if the 1:7 will be that bad in the 18, but I dont really know? Ive been looking through some barrel mfgs but of course would like to get all this hammered out before hand . Sorry if this sounds a little erratic but Im trying to keep all of this straight -Thanks in advance

[Bigs28]

For your short barrel their is a 12.7" group buy going on right now.

[Kswhitetails]

If I were you, I’d head to the group buy section and get in on the 18 and 12.7” group buys and snatch up bolts for both with them. I’d do it soon all three are getting close to full/ sold out: if they aren’t already.

18 mid length can be hard on the system if not properly set up, but I would want to hear from others with more experience that me on that. Twist rate at 1:8 should be fine on both. AA using the 7.5 because after extensive testing they saw incremental gains at distance so they stuck with it- if I’m remembering correctly. The 1:8 makes everything stable so it has more recently been seemingly adopted as the standard. I haven’t heard of any complaints with the 8 twist.

[Jakegsxr11]

I have an 18" in rifle length gas and it functions very well with Hornaday sst and black. I do have an adjustable gas block but it probably doesn't need it.

[TexN]

Well I was originally going to go with the Faxon group buys but then I read that people were averaging a little more than moa with them, my furthest open range shot at my main hunting area is 500ish yds. For a little more money I found a maker that according to various online reviews consistently show sub moa so I thought that that would be the best play.

[Bigs28]

Sounds good, who are you going with? My cousin has the 12" Odin and he shoots at an inch ish with it

[TexN]

Mcgowen, Ive been trying to track down LH bolts but everyone is sold out that I have found. Underground told me to go with the .125" as its in stock and stronger than .136"? I placed an order with Maxim for two LH bolts but nothing has been sent or verified other than me sending him money. So whats the thought on using the .125" from Underground vs their out of stock .136"? Is the .125" really stronger? Also if anyone has a contact number for Maxim Firearms Id appreciate it.

[Kswhitetails]

.125 stronger than .136? Fishy. Stinky fishy. Sales pitches are a dime a dozen, and sounds to me more like they want your money than they want to be real. Bill A designed the G with the .136 bolt face in mind for LOTS of good, tested, and proven reasons. I'd shy away from Underground from now on, unless they can back that claim up with LOTS of good accurate testing data showing truth behind that statement.

My two cents...

[grayfox]

+1, there's no reason to go off the approved track. 0.136 bolt-face-depth dimensions are the way to go, plus those parts are much more interchangeable.
Dbl check with McGowen that they are indeed making your 6.5 Gr-AR barrel for:

1. SAAMI spec chamber - not "264 lbc" or "6.5 match-whatever" etc etc. The 6.5 Grendel SAAMI chamber has a compound throat angle to it, so McG should "roger" that for you on your barrel.
2. Set up for a bolt face depth of 0.136"

This will save you time and trouble in the long run IMO.
My 2 cents'.

[BluntForceTrauma]

Underground told me to go with the .125" as its in stock and stronger than .136"?

There are two parts to the bolt issue. Part one is the bolt body itself, with its boltface depth and the strength of the lugs. Part two is the extractor.

Technically speaking, yes, a 0.125 boltface depth is "stronger" than a 0.136 boltface depth, all else being equal. Less metal is machined away — 0.011 to be exact. All things considered, this is a very small amount.

Secondly, and more importantly, a 0.136 boltface depth allows one to keep more metal in the extractor claw. Practically speaking, this is going to affect your weapon functioning more than the difference in the boltface depths.

Grendel is designed for average pressures around 50,000 psi to account for the larger case head within the AR15 bolt constraints.

The Holy Grail is to have the best of both worlds: 0.125 boltface depth AND a claw that retains the strength of 5.56 claws.

Anyway, best to go with a 0.136 bolt, but you can go with a 0.125 bolt if your barrel is properly headspaced for that dimension and, in that case, I'd recommend having a spare extractor on hand.

[TexN]

Got two LH 6.5 .136" bolts shipping from Maxim today, and Mcgowen site says that they use the 6.5 Grendel saami chamber. So I guess we are good to go? With the only change to the first post specs is 1:8 twist and a longer (rifle) gas system on the 18", over my original mid length?

[grayfox]

That all sounds like its gtg exc one tiny detail:
I didn't see on the McGowen site whether they head space the barrel chamber for a 0.136 bolt face or not... you got the right ones coming in but you might want to dbl check this one spec with them. I think they probably are using 0.136 for the headspacing but don't want to assume anything.

[StoneHendge]

I'd confirm with McGowen which depth they are using. They did a .136 on my 6mm Grrrrrrrr, but I did specify that in the notes when I ordered and reconfirmed by calling them when it was shipping. They answer the phone and respond to emails.

[TexN]

I emailed Mcgowen the other day when I couldn't find any .136" bolts about their views on using the .125". They told me to just send them the bolts and that they would headspace the barrel for them. But yes I will leave the .136" in the notes.

StoneHendge; how do you like your Mcgowen?

[StoneHendge]

Its still in its tube - didn't get it until right before Xmas and haven't been able to spend much on the gun budget since this winter has been a complete disaster. 137" of season to date snowfall at a resort that averages 350" isn't good for a business that relies on people going skiing. I might be able to get to it in a few weeks now that 0.750" clamp on Superlative gas blocks can be found (no one has had them in the past 6 weeks or so but Superlative does now have them on their site). Also need to get a handguard, 6mm dies, brass (was also waiting for Starline so I can have different headstamped 6mm brass), so I've been focusing elsewhere.