6.5 Grendel Upper/Which Bolt?

GuitarmanNick · May 6, 2020

A friend asked me to look at his new acquisition, an AR in 6.5 Grendel.

Well, things are not as they should be.

The previous owner claims it was built for him locally, test fired, picked up from the builder, and stored ever since.

The barrel is clearly marked 6.5 Grendel 1:8. The BCG has a 5.56 bolt in it and I guarantee the rifle was never test fired like that.

Today, I called the alleged builder and confirmed they did not build the rifle. As such, they are unable to provide any additional information on which bolt is needed for this rifle.

I know there are types 1 and 2 and that the bolt needs to match the barrel. The problem is that I cannot determine which configuration this barrel will require.

I was hoping that someone not too far from me may have a live or dummy round, one of each bolt, and be willing to help me. I have nothing in this caliber so I can't even try dropping a round in the chamber to get a measurement. I am in Laurel and happy to drive anywhere within 30 minutes or so. Any assistance would be greatly appreciated and social distancing guidelines will be respected.

Not quite sure how it will look handling gun parts while wearing masks in a public place, but WTH! I would only need to bring the upper assembly.

Of course, if there is another way to figure this out, I would be interested to know.

94hokie · May 6, 2020

If the barrel is marked 6.5 Grendel, then it is most likely a type 2 bolt. That is the boltface that conforms to the SAAMI spec.

outrider58 · May 6, 2020

From what I've read, it all depends on the head space. Type II has a .136 HS. The type I has a .125 HS

I don't have an easy answer unless you have access to at least one head space gauge and two bolts for comparison.

94hokie · May 6, 2020

Do you have any info on the barrel manufacturer?

DavidA · May 6, 2020

As stated if is a true 6.5 Grendel chamber they will required .136” depth bolt face. If the barrel is stamped Grendel SAMMI spec is .136. To satisfy your curiosity, Get you hands on a Type I bolt .125. These bolts were made for the LES Baer Custom .264 LBC chamber and is a standard 7.62*39 bolt. .125 boot face depth. Same as the 5.56 NATO. This was Les Bares way to ge around paying royalties to Bill Alexander,s design along with have a straight throat instead of the Grendel’s complex throat, Put the .125 in you bolt carrier, get a 6”5 Grendel round. Put it in the chamber. Try by applying hand pressure to get the bolt to twist and extend it’s face into battery behind the cartridge. If you have a true Grendel chamber it should be either a forced closure or it will not go. If this is the case you have a true Grendel chamber and you will not be able to use the Type I bolt .125. You could use a type II bolt .136, and used as described but it will not tell you if the chamber is a type 1 because it will close on either chamber. Now from a pure gun smithing procedure advise you should always check your chamber with a go, no go set of gauges. whether the chamber and bolt have been selected properly. Or not this is why some manufacturers offer selling bolt with barrels. Because they have been check with gauges. So if I were building this rifle I would have a set of go, no go gauges and I would check the bolt for proper clearance and function.

Chances are it is a type 2 , .136” Type 2 bolt.

DavidA · May 6, 2020

I have a type I .125 bolt as I have a 264 LBC chamber.

Sent from my iPad using Tapatalk

GuitarmanNick · May 7, 2020

I have no information on the barrel manufacturer. There are no other markings on it other than "6.5 Grendel 1:8". It is 16", blued and fluted.

As I said, I am trying to set this up for a friend. Hence, the plan is to only buy one bolt or BCG once I can determine what is needed. The alleged builder, says they did not put this rifle together. At this point, it is a mystery build that has likely had it's BCG mixed up with a 5.56 AR build. I have warned the previous owner to check his rifles before shooting them. I would not expect a 5.56 with a 6.5 Grendel bolt to be safe.

Anyone willing to let me try either bolt to chamber a round would be helpful. If it works or not, it will provide info I do not currently possess. Yes, gauges would be ideal, but not many shooters will have those.

lazarus · May 7, 2020

Pretty sure it’s type II

If YOU have a type II bolt you can check it by spacing a 6.5 cartridge (remove firing pin). Just slip some folded over and flattened aluminum foil on to the cartridge shoulder to act as a shim. If it can close on a shin like that, that’s at least a few hundredths on an inch thick, it’s a type I. If it won’t chamber it’s a type II.

Or use a bit of silly putty on the cartridge shoulder. Just a little bit. Should be hard to chamber and it’ll squeeze it all out. If it doesn’t, type I

Of course make sure you clean that silly putty out of the chamber and throat.

DavidA · May 7, 2020

Great approach, never though of the silly putty gig.

Sent from my iPad using Tapatalk

whistlersmother · May 7, 2020

I have CIP Grendel gauges. Mistakenly ordered the Min/Max gauges. These are from Pacific Tool and Gauge.

My bolt closes on the Min and does not close on the Max.

My bolt measures .136" deep.

I bought the upper w/ BCG from another member. I don't think it's ever been fired. It comes from Radical Firearms.

I can send the gauges, but you'll have to strip the extractor and ejector.

Do you have calipers for measuring bolt face depth?

Oh, you need a bolt also...

outrider58 · May 7, 2020

Case head diameter of the 6.5 G is .445"

5.56 is .378

Are you sure that bolt is a 5.56? If a 6.5 fits into the bolt, it isn't a 5.56 bolt.

GuitarmanNick · May 7, 2020

outrider58 said:
Case head diameter of the 6.5 G is .445"

5.56 is .378

Are you sure that bolt is a 5.56? If a 6.5 fits into the bolt, it isn't a 5.56 bolt.

Well, I can get a 5.56 or .223 case to snap into the bolt face perfectly. Since I do not have anything in 6.5 Grendel, I tried inserting a 7.62x39mm case and it is way too large in diameter. Since the 7.62 should have matched the bolt face in diameter and did not, the wrong bolt is in the rifle.

Measuring the bolt face with my calipers is how I determined it was a 5.56 bolt. I then compared it to several in my possession for confirmation.

So the answer to you question is, absolutely sure!

outrider58 · May 7, 2020

GuitarmanNick said:
Well, I can get a 5.56 or .223 case to snap into the bolt face perfectly. Since I do not have anything in 6.5 Grendel, I tried inserting a 7.62x39mm case and it is way too large in diameter. Since the 7.62 should have matched the bolt face in diameter and did not, the wrong bolt is in the rifle.

Measuring the bolt face with my calipers is how I determined it was a 5.56 bolt. I then compared it to several in my possession for confirmation.

So the answer to you question is, absolutely sure!

Yup. wrong bolt. I was just checking.

GuitarmanNick · May 8, 2020

A special thanks to Whistlersmother for his assistance, today. Always a great experience meeting other MDS members.

Using his type 2 bolt and gauges in my friend's upper, the bolt closed on both gauges. This indicates to me that there is a type 1 chamber in this barrel and will require the .125" deep bolt face.

I appreciate the efforts of all that replied.

DavidA · May 8, 2020

Just goes to show you assume nothing. Just because it is stamped 6.5 Grendel means what you think it should logically mean.

Sent from my iPad using Tapatalk

lazarus · May 10, 2020

DavidA said:
Just goes to show you assume nothing. Just because it is stamped 6.5 Grendel means what you think it should logically mean.

Sent from my iPad using Tapatalk

Well, or the barrel is an out of spec type II...

Just saying, there IS that chance.

6.5 Grendel Upper/Which Bolt?

The #1 community for Gun Owners of the Northeast

Member Benefits:

Ultimate Member

Active Member

Eats Bacon Raw

Active Member

The Master of Disaster

The Master of Disaster

Ultimate Member

Ultimate Member

The Master of Disaster

Peace through strength

Eats Bacon Raw

Ultimate Member

Eats Bacon Raw

Ultimate Member

The Master of Disaster

Ultimate Member

Users who are viewing this thread

Log in

Forum statistics