Question about bolts

[1075 tech]

Still new to the Grendel and getting some ideas together and making my list of options shorter to begin my first build.

I did a (very) quick search on the site but didn't find what I was looking for.

About the Grendel bolts: If I am correct, there are 2 types of bolts, the Type 1 at .125 and the Type 2 at .136 bolt face depth. Other than the obvious, what are the differences between the two? Pro's? Con's? Does one have significant advantages over the other?

[VASCAR2]

Type 1 (.125 face depth) are typically used in 7.62 X 39 AR-15's. When Colt sold 7.62 X 39 AR-15's they used .136 depth bolt to have better extractor clearance and for added strength. When AA intially started selling 6.5 Grendel's AA adopted the .136 bolt face depth which has since been standardized by SAAMI. Black Hole Weaponry sold 264 LBC barrels and chambered barrels with both bolts and coined the Type 1 which they produced the most. To satisfy customers BHW sold barrels which used .136 bolts which they identify as Type 2. Upon 6.5 Grendel being SAAMI type accepted AA has released the marketing rights to using the 6.5 Grendel name and chamber. If I remember correctly the typical 5.56/223 bolt face is .125 and is why some 7.62 X 39 bolts end up being .125. Both type bolts are compatable with the various 6.5 Grendel ammunition however you have to use the appropriate bolt for how your rifle is chambered, Type 1 or Type 2. You can not use a barrel chambered using a .125 bolt then swith to a .136 bolt or vise versa.

[1075 tech]

Thank you VASCAR. So is the Type 1 the 264LBC? And is the Type 2 better? I understand the bolt/barrel thing.

[LRRPF52]

This all arises from the after market naturally following the path of least resistance to getting into Grendels.

Since every company other than Colt ignored the requirements of the 7.62x39 rim thickness, and thought that .124" face depth would be fine, that is what a lot of companies started going with. The 7.62x39 AR world is filled with broken extractors as a result. Even the .308 after-market suffers from extractor problems, and those are substantially wider than an AR15 extractor.

The terms "Type I" and "Type II" originated with BHW as best as I can tell having followed this over the years, as VASCAR describes.

No matter what face depth you go with, you need a tool steel exctractor that is produced by a shop that knows their heat treating well, and has very tight QC on parts. That applies to any cartridge/caliber in the AR15 and self-loading weapons in general. Extractors take a beating, especially with shorter gas systems.

Les Baer uses .136" bolts. 264 LBC-AR refers more to a chamber design, not a bolt face depth.

[1075 tech]

So... either will do as long as the bolt and barrel match and I get a quality bolt?

[LRRPF52]

You are less likely to see extractor lip breakage with a .136" bolt.

LMT makes probably the strongest 7.62x39 bolt on the market, but it uses a .124" face depth since that's what everybody but Colt did with that cartridge.

There's a guy who likes to shoot a lot of full auto 7.62x39, and posted a picture years ago of all the bolts he has broken. The only one he hasn't broken was the LMT enhanced 7.62x39 bolt, but he did break the extractor, and couldn't get a replacement for it without buying a complete new bolt assembly.

[1075 tech]

LR52, thanks for that info. Gives me a better direction to head in as I piece this thing together.

[customcutter]

OK LMT? Lewis Machine & Tool? Maybe a link?