The pin and weld project I am embarking on will involve a chambered LBC blank without a barrel extension. The gunsmith I will likely be working with believes that even though an LBC is meant to used with a 0.125" depth bolt, it can be headspaced for a 0.135" Grendel bolt when installing the extension . Is this correct? It's not really a big deal for me but I'd lean towards the 0.135" if possible, but don't want to miss out on grabbing a decent 0.125"bolt in this environment if it isn't (I know where there are Spikes bolts in stock). My ability to think it through has been impaired by the people in the unit below me celebrating AZ's legalization of marijuana by smoking even more weed. They're on the deck below, it's open windows season and they start at 9am. I feel like I'm back in CO.
I think it should work. Should. It gonna make your gas tube engage by .011 less in the gas key but that shouldnt hurt anything as I have made pistol gas tubes from carbine gas tubes during shortages and havent had any trouble and they were off by at least that much. Its basically gonna result in your shoulder being set backwards .011, which wont be a problem unless the gas port is already drilled. If so, and your smith doesnt have an LBC reamer, I dont think it will work.
Clear as mud?
Thanks! And that does make sense. Gunsmith will be drilling the gas port, but I had already panicked and ordered one of the Spikes bolts when this was languishing. I had hoped to do a JP Grendel bolt but they are nowhere to be found. But if one pops up now I know I can grab and always use the Spikes as backup for my current LBC.
And a brilliant thought just came to me - if I give him a piece or 2 of sized brass without the shoulder bumped from my current LBC, he should be able to get the Headspace close so the brass would work in both rifles, right?
11-10-2020, 11:25 PM (This post was last modified: 11-10-2020, 11:27 PM by ricsmall.)
Yep. Should be able to match it up perfect. I do that with my personal long range guns so my brass can go from barrel to barrel. I never have to reset the die
ETA: I do always go about .001 longer so I know it will work without being too tight. I just use a pc of fired and neck sized brass as my Go gauge when Im cutting chamber. Works like a dream.
.264 LBC-AR made by Les Baer always used a .136 bolt face depth since he started out using AA-licensed 6.5 Grendel bolts and actual Grendel chambers.
You can headspace it how you want, but .136 face depth will have a stronger extractor lip.
The ".264 LBC chamber does not exist in any industry standard with a published chamber drawing that Im aware of.
The .264 LBC-AR is a chamber specifically made for Les Baer with a tighter .295 neck and a conventional freebore optimized for the 123gr SMK.
Les Baer also contracted Black Hills ammunition to produce a factory Black Hills 123gr SMK load, which was pretty warm.
Given the proven design of the actual Grendel bolt and extractor and the market support for that, it only makes sense to go with a .136 bolt face depth, 2.810 long Grendel bolt of reputable origin.
The misnomer that .264 LBC is correspondent with a .125 bolt face depth is simply not accurate.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
Thanks 52. This is my first foray into having to have an extension installed. The barrels are BHWs so the assumption is that they were chambered with a 0.125" headspace with my assumption based on that the threads cut so that when the barrel extension is torqued to target spec, the headspace will be in the 0.0125" range. Based on your response and Ric's response, my understanding now is that headspace can be adjusted by tweaking the torque (much the way a barrel nut's torque sometimes needs to be tweaked to allow a gas tube to clear it in certain nut/handguard systems). Is this correct or am I off base? I guess shims could also be used.
As to the bolt face depth argument, I didn't mean to get into that. I'll only say that bolts of both types are hard to find. My experience with Spikes products has been first rate - the Horde isn't their target market, but I've found their fit, finish and function to be top notch. I don't have any first hand experience with the manufacturers or distributors of the 0.0136" bolts currently available on the world wide web.
That is an interesting idea - that headspace can be varied by varying the torque on the barrel extension. As I understand it you need at least 100ft lbs of torque on the extension to keep it from coming loose when it heats up and is hammered during firing. I doubt that leaves much headspace left between 100ft lbs and the often recommended 150ft lbs.
That post on Homegunsmith.com where the guy says there is .0035" in headspace is between hand-tight (no torque) and 140ft lbs. Obviously you cannot stop at say 60ft lbs because it has reached the target headspace. I'm not a machininst and don't know how much longitudinal movement there is between 100 and 150ft lbs but I doubt it will be anything useful at all.
