Is an adjustable gas block generally needed on a Grendel?

[cb4017]

Over the years I've built my fair share of AR pattern rifles in .223/5.56, 6x45, 6.8 SPC and .308. Now I'm collecting the bits for a 6.5 Grendel.

I've always looked at an adjustable gas block as a crutch to fix an over sized gas port or a gun with some other unusual condition. Of the rifles I've built I have only needed an adjustable gas block on a couple of the .308 rifles.

My question, have folks found it generally necessary to use an adjustable gas block on a 6.5 Grendel build?

Thanks!

[jcjarmon]

Yes. Grendel runs an oversize gas port(.125). Makes the whole system very over-gassed with most factory loads. Seekings, Radical, and Anderson make a dirt cheap adjustable gas block that works well. JP makes top of the line variants for all barrel sizes.

[Bwild97]

My philosophy has always been, better to have it and not need it, than to need it and not have it. But generally, no they are not necessary for proper function in the Grendel. Gas port sizes will vary from one manufacturer to another. A properly sized gas port is dependent on a few variables, port position, dwell.

[biodsl]

Yes. Grendel runs an oversize gas port(.125).

Again, please? That's an eighth of an inch.

[rabiddawg]

If jcjarmon is correct, you will need the adjustable block. I recall LRRPF52 saying the brownell's barrel made by the planet company(won't give them a mention) was notoriously known to be oversized at .094 and needed adj gas blocks.

Bwild97 makes good sense.

I'm running two adj blocks because I changed the blocks myself. My two precision firearms uppers do not have adj blocks and run just fine.

I'm editing my post after reading jcjarman's post about confirming his port size. However, to say that the Grendel runs a .125" gas port is not exactly correct.

[Nicaburns]

I have only built three Grendel uppers but all functioned smoothly without it... Have not read specs on one yet that was .125

[jcjarmon]

I had to conform it myself. The first Grendel I built was so over gassed it was unshootable. I had to tear it down and measure the entire gas system before I noticed the size of the gas port. I measured it with a drill bit blank at .125 inches(number 30). When I called Black Hole, and was mad as fire, they told me the gas ports on Grendel are oversized to allow for lower chamber pressures, and lower overall gas pressures from the rifle length gas system and the Grendel round. When they changed the gas system, they just assumed that everyone building a SPR would be using an AGB, so they went much larger that the maximum port size for an 5.56. When I ask about wear on the barrel, they said if it starts to open up before 5k rounds they would replace it for free. An Anderson Gas block on the 5th click made the rifle shoot like a dream. Now I use JP's, because they work just a little smother that the cheap ones.

[cb4017]

Thanks Gents. I ordered a 20" Criterion from Mark at PF. I would like to think he has gas port size figured out. I also ended up with one of the first group buy Faxon barrels. With calipers it appears the gas port is around .073". It doesn't quite fit my idea of a rifle for casual precision/target shooting so I haven't decided if I want to use it or sell/trade it off.
I had one BHW barrel in 6x45. It was not a great experience and I would not buy another one.

[Motorhead]

I'm running a 24 in satern barrel with a non adjustable gb. Absolutely no problems. Bought mine in 2016 so maybe they got with the program.

[LRRPF52]

Yes. Grendel runs an oversize gas port(.125). Makes the whole system very over-gassed with most factory loads. Seekings, Radical, and Anderson make a dirt cheap adjustable gas block that works well. JP makes top of the line variants for all barrel sizes.

No. Not sure where you saw this, but 6.5 Grendel uses several different port sizes depending on barrel length, and .125" is not one of them.

RLGS 20-24" use .094"
MLGS 18" uses .076"
MLGS 16" uses .078"

.125" is the ID of the port in an actual gas block and is huge.

I had to conform it myself. The first Grendel I built was so over gassed it was unshootable. I had to tear it down and measure the entire gas system before I noticed the size of the gas port. I measured it with a drill bit blank at .125 inches(number 30). When I called Black Hole, and was mad as fire, they told me the gas ports on Grendel are oversized to allow for lower chamber pressures, and lower overall gas pressures from the rifle length gas system and the Grendel round. When they changed the gas system, they just assumed that everyone building a SPR would be using an AGB, so they went much larger that the maximum port size for an 5.56. When I ask about wear on the barrel, they said if it starts to open up before 5k rounds they would replace it for free. An Anderson Gas block on the 5th click made the rifle shoot like a dream. Now I use JP's, because they work just a little smother that the cheap ones.

I see where you got the bad info from now. If someone is purposely using .125" gas port diameters in 6.5 Grendel, it is and can only be with the intent of using adjustable gas, because that is so overgassed, it will not work. I didn't know they were doing that.

Gas port diameters are pretty much like 5.56 at the same barrel lengths and gas system lengths. While it operates with much lower chamber pressure, it has way more case volume and capacity than 5.56, so port pressures are very similar.

You absolutely do not need adjustable gas on a correctly-built 6.5 Grendel barrel.

There are quite a few barrels out there in the 18" MLGS combo that are way overgassed with MLGS/.094" ports, and they do need to be tamed somehow.