POLL: Type 1 or Type 2

[Texas]

The problem is that there are more things than the bolt where Type I or Type II is used.

Initially, Type I (.125) and Type II (.136) were used by Black Hole Weaponry to distinguish between the 2 bolts. They would cut the chamber to use whichever bolt was available. They were using a LBC 264 chamber.

Then Satern decided to throw another piece in the works and developed a Grendel II chamber. So now we had Type I and Type II bolts, and a Grendel II chamber. That led people to start calling the SAAMI chamber (original) the Grendel I and the chamber from Satern the Grendel II.

Of course new people, not knowing the history, then started talking about Grendel I and Grendel II bolts, assuming that the chambers went with the bolts. (They didn't, Satern always used the .136 bolts to my knowledge).

So now there were all kinds of I's and II's floating around and lots of new people didn't even know they were confusing the descriptions of the bolts with the names of the chambers.

Then other people started chambering guns with the SAAMI type chamber, but set up to use the .125 bolt!

So it became a serious SNAFU as the military nomenclature would say!

The Grendel SAAMI chamber uses a .136 bolt.

Other Variants may use either bolt, or even both, because barrel makers will cut them to headspace with either bolt depth face. This sucks, because inevitably, someone is going to be injured due to the confusion!

Correct, If you look at the SAAMI website:

http://saami.org/specifications_and_information/publications/download/Z299-4_ANSI-SAAMI_CFR.pdf

Page 236 is the SAAMI spec for the 6.5 Grendel reamer. The headspace is a distance between the bolt face and the center of the shoulder.

[mirion]

Not sure how I missed this thread as I was researching the issue the last couple weeks. I purchased a Black Hole 264 LBC from Surplus Ammo and Arms and was looking for a bolt. In my readings from many sources my confusion grew.

I was informed of the following facts (hopefully they are actually facts) concerning the following two variations, 6.5 Grendel with a type 2 (.136) bolt and 6.5 264 LBC with a type 1 (.125) bolt :
- Both use the same ammo
- Both use the same headspace gages
- 264 LBC uses the same bolt as any 7.62x39

At first I was worried, maybe I made a bad choice, maybe I should have read more before I jumped on that barrel. But based on all of the people that are more than satisfied with their 264 LBC, the fact that Black Hole has a very good reputation, the fact that there are some very reputable 7.62x39 bolt manufacturers and the fact that I will gage it before the first firing, I can't wait to get this baby together.

[LRRPF52]

Not sure how I missed this thread as I was researching the issue the last couple weeks. I purchased a Black Hole 264 LBC from Surplus Ammo and Arms and was looking for a bolt. In my readings from many sources my confusion grew.

I was informed of the following facts (hopefully they are actually facts) concerning the following two variations, 6.5 Grendel with a type 2 (.136) bolt and 6.5 264 LBC with a type 1 (.125) bolt :
- Both use the same ammo
- Both use the same headspace gages
- 264 LBC uses the same bolt as any 7.62x39

At first I was worried, maybe I made a bad choice, maybe I should have read more before I jumped on that barrel. But based on all of the people that are more than satisfied with their 264 LBC, the fact that Black Hole has a very good reputation, the fact that there are some very reputable 7.62x39 bolt manufacturers and the fact that I will gage it before the first firing, I can't wait to get this baby together.

The real 264 LBC-AR chambered guns from Les Baer have always used .136" bolts, to the best of my knowledge.

Some of the early after-market parts stores who never looked into the details figured they could whip something up in their specs, and source garbage-grade imitation 7.62x39 bolts (not engineered bolts like Colt did for the 7.62x39 Sporter) and just have some barrels reamed, extensions torqued on, cut whatever port they like, and call it good.

There is no such thing as Type I and Type II if you want the complete picture.

Manufacturers or assemblers need to become familiar with what works, looking at the extractor and bolt length, as well as metallurgy of any bolt that goes into the AR15.

If you want to break extractor lips off when using a cartridge that has thicker rims than the tiny 5.56/.223 Rem, go with a .125" bolt face depth.

If you don't want to break extractor lips off, look at your metallurgy, processes, QC/QA, and use a .136" bolt face depth.

Use destructive testing in batches, with the best alloy you can find for the task that is affordable for your target market.

If you bought a barrel that is chambered for a .125" bolt face depth, I would look at LMT enhanced 7.62x39 bolts made from Aermet. Shooting full auto in 7.62x39 guns, those extractors have broken as well since the lip is so thin, but they should hold up well in 6.5 Grendel. You're going to pay more than twice as much for that bolt, but it will last.

It's a lot easier to just go with the correctly-engineered bolt for this cartridge, rather than trying to reinvent the wheel. You won't find a shop or company that has done the amount of testing that Bill A. did when developing this cartridge, and those who think they can just whip something up better in a few months or even a year need to realize that Bill A. spent over $10,000 just in reamers alone, with test batches of barrels in the hundreds that were never satisfactory. One 200 barrel batch produced zero acceptable results, and that's just one example of one of the main components that needed testing.

You normally don't see that level of testing even in the larger, more recognized companies. They would have thrown in the towel, or moved onto something else by then.

[mirion]

[QUOTE=LRRPF52;147709]The real 264 LBC-AR chambered guns from Les Baer have always used .136" bolts, to the best of my knowledge.

QUOTE]

LRRPF52, Below in an excerpt that is taken from the Black Hole Weaponary/Columbia River Arms web site FAQ which can be found here
http://columbiariverarms.com/frequen...ked-questions/......

What is the difference between .264 LBC and 6.5 Grendel chambers?

Les Baer Custom designed the .264 LBC cartridge to be completely compatible with the 6.5 Grendel, and our head space gauges are marked with both cartridges.

The LBC has a .295 diameter neck, while the Grendel has a .300 neck.

The LBC has a straight taper in the throat, while the Grendel has a compound taper in the throat.

The LBC has a straight taper in the throat, while the Grendel has a compound taper in the throat.



Apparently they have recently dropped the .135 head spacing

[rabiddawg]

Perhaps the key words in LRRPF52's statement were "from Les Baer"

[mirion]

Gotcha, I missed that.

[LRRPF52]

Perhaps the key words in LRRPF52's statement were "from Les Baer"

The bolt face depth is not called out in SAAMI drawings, since a cartridge can be chambered in different rifle designs. The SAAMI drawings call out minimum chamber, and maximum cartridge, so companies will stay within ranges that will allow factory ammunition to function safely through rifles chambered in the cartridge.

If someone is telling you that bolt face depth is called out in the SAAMI drawings, I would like to see what drawings they are looking at.

The layman can look at the diagrams I have shown on why you want a thicker lip on the extractor and come to reasonable conclusions. I've already seen several people in the industry who are in a manufacturing capacity try to make the argument that a .125" bolt face depth is fine, then stating that they don't see failures of the extractors....

....followed by examples of their customers who post afterwards that their extractors broke.

A .125" bolt face depth is fine for .223 Rem/5.56 NATO, because the 5.56 NATO/.223 Rem rim thickness is tiny. There is plenty of room left forward of that to build a substantial extractor lip.

If you just look at the dimensions, it's a matter of basic mechanical engineering. If you paint yourself into a corner, you are left with very stringent options that cost a lot of money from a metallurgy perspective to fix, and you will have a very high reject rate on extractors if you go that route even using exotic materials.

[LRRPF52]

Before the 6.5 Grendel SAAMI there was a 6.5 Grendel (Bill Alexander proprietary) made by Sabre Defence, LLC (Nashville, Tn) that had different chamber specs than the 6.5 SAAMI. Bill Alexander shipped them a different set of reamers to resolve some issues, so I am assuming that LFRP55 has one of those. If my memory serves me correctly, the problem was in the throat and freebore of the chamber (too short). The bolt face was always .136 depth. The stainless barrels had a 1:9 twist and the CMV had a 1:7.5 twist with a few exceptions.

While there is a clear preference for the .136 bolt in this cadre, it would be very interesting to know how many have experienced bolt failures with the .136 bolt and with the .125 bolt. I have both, and there does not appear to be an accuracy difference between the rifles I have based upon bolt. Also it would be interesting to know the bolt failures that were a result of using S7 steel vs, 8620, vs 9310, vs 158 carpenter, vs something other steel. How many failures were due to improper heat treating? How many failures were due to micro-fractures created by excessive powder charges? The answer to these questions would show a clear reason for selecting one over the other.

It is my understanding the .136 was actually developed for the .50 BEOWULF which has extraction issues the 6.5 Grendel does not have. Since the bolt was already developed, it was a natural choice for the 6.5 Grendel.

The 6.5 Grendel chamber that Bill finalized is the one that got SAAMI approved. There were scores of different chamber designs in testing that didn't meet expectations of being able to shoot the wide range of 6.5mm projectiles well. They would either shoot one well, and the others not well at all.

There is no Bill A Grendel chamber proprietary versus the SAAMI. That was a claim by detractors to prevent standardization and sabotage the cartridge since it out-performed everything else, to the chagrin of many.

The deeper bolt face depth comes from Colt, since they actually spent time and money on making 7.62x39 work to the best of their ability in the AR15. Bill A. tracked down one of their engineers who had worked on that program, when Bill was researching for the .50 Beowulf. Rim thickness is what drives the bolt face depth, because it determines extractor lip thickness.

[Bill Alexander]

The Grendel chamber has remained standard from the commercial outset. It was however rather a relief that SAAMI accepted the design without change much more so the pressure levels for the loading.

To be correct and precise, Saber did experience problems with the chamber but it was due to the chrome plating process. If you cut a regular Grendel chamber, electropolish and then chrome the result is not a Grendel chamber. Much like the 5.56 there has to be an alteration to the initial chamber so that the resulting chrome plated chamber is dimensionally correct. This is what we did.

Beowulf rifles extract extremely easily and put next to no stress on the extractor beyond the ejection cycle. Grendel imposes considerably more stress on the extractor and the extractor support.

[Texas]

The Grendel chamber has remained standard from the commercial outset. It was however rather a relief that SAAMI accepted the design without change much more so the pressure levels for the loading.

To be correct and precise, Saber did experience problems with the chamber but it was due to the chrome plating process. If you cut a regular Grendel chamber, electropolish and then chrome the result is not a Grendel chamber. Much like the 5.56 there has to be an alteration to the initial chamber so that the resulting chrome plated chamber is dimensionally correct. This is what we did.

Beowulf rifles extract extremely easily and put next to no stress on the extractor beyond the ejection cycle. Grendel imposes considerably more stress on the extractor and the extractor support.

Bill, thank you for your clarification. I was looking at a 2006 Sabre Defence Catalog where the 6.5 Grendel was offered as a Trademarked cartridge similar to the Beowulf. It was offered in three models (all M4 configuration) with a Mil-b CMV barrel and mil spec chrome lining.I assumed that mil spec meant electropolish - which removes metal from the barrel which is replaced by the 1 to 3 mil chrome deposit. In 2007 Sabre Defence added the 6.5 Grendel to several additional models and was produced with a 1:9 410 stainless barrel as well. These stayed in the Sabre Defence catalog through 2012 although Sabre closed in 2011.

I am a huge fan of the cartridge, and appreciate your development efforts to make it a fine 6.5 SAAMI cartridge.

[phishfood]

Excellent read, I was wondering what all of the different chamber and bolt designations were about.

Thanks much to everyone.

[LRRPF52]

Excellent read, I was wondering what all of the different chamber and bolt designations were about.

Thanks much to everyone.

Anytime you see the misnomers, "Type I" and "Type II", just know that they have nothing to do officially with the development of 6.5 Grendel, and as posted, were terms that BHW used to help customers understand what bolt face depth they were using.

I also noticed the reference to an "industry standard bolt face" for the AR15. Yeah, in 5.56 NATO, there is an industry standard.

6.5 Grendel and 5.56 NATO are two totally different animals that require different bolt dimensions in many ways, not just bolt face diameter for the fatter Grendel, but extractor lip thickness.

Since people don't deal well with complicated explanations and just want to know what time it is, they would like a simple answer and label, hence the traction that misnomer terms like "Type I" and "Type II" attracted.

For all the manufacturers out there who may come across any of this that don't know, a good engineering staff can see straight away the mechanics and metallurgy behind why a real Grendel bolt is the way it is, versus a half-cocked job of trying to wing it with just a cursory inspection of the dimensional differences.

Mark at PF has known this for many years, as has Les Baer, JP, and LaRue.

There are other unique challenges when chambering a dual-column feed presentation magazine with case heads larger than 5.56 NATO/.223 Rem. like the PPC/Grendel. They are easy to address, but are commonly overlooked. Most imitation 5.56 bolts fail in this area as well, talking about the ejector, let alone the ejector spring metallurgy. The Dutch addressed it beautifully with the AR10 in the early 1960s, so good engineering will catch these things and incorporate manufacturing processes to deal with them.

[olde sarge]

I have a few rifles. They are all chambered to SAAMI specs and use a .136 bolt. At this point I am so confused by all of this type 1 and type 2 crap if asked I respond, SAAMI chamber, .136 bolt.