6.8 SPC bolt from 223/5.56 bolt

[bj139]

Does anyone have any idea if a 223 bolt can be opened up slightly in a small lathe to function with a 6.8 SPC case?

[Tex Nomex]

Does anyone have any idea if a 223 bolt can be opened up slightly in a small lathe to function with a 6.8 SPC case?

Don't try it. You'll just ruin the bolt and extractor.
The bolt and extractor would need to be thinned in their thinnest areas and the face depth looks to be different. Just find a cheap 6.8 somewhere.

[NugginFutz]

Fpni

[bj139]

Now I've got to try it.

I was asking if anyone knew about doing it not that it should not be done.

The naysayers will always say it should not be done.

[Tex Nomex]

Sorry 'bout that unwanted advice I gave earlier. I guess I didn't read your post closely enough. :o
Good luck. Video please.

[NugginFutz]

One of the overarching concerns would be the removal of surface hardened material. These bolts are heat treated, and grinding / milling / cutting will only compromise the surfaces in one of the areas where hardness is most needed.

Is it really worth the cost of a new bolt to see if you can do this? I'm not familiar with your machinist skills, bj139, but even if you are successful in hogging out the bolt face, are you certain you want a compromised bolt?

ETA:

If you're really convinced this is something you want to try, at least follow the lead of people's opinions you might better respect.

http://www.practicalmachinist.com/vb/gun...ce-198085/

[Randy99CL]

Now I've got to try it.

I was asking if anyone knew about doing it not that it should not be done.

The naysayers will always say it should not be done.

Hey, I'm on your side! You can't know whether someone advising you knows more about it than you do.
Make sure you make a video when you fire the gun for the first time.

[bj139]

NF,
Practical machinist was one of the sites that said any good smith could open up the bolt.

I would not try this with the Grendel because too much material must be removed (0.032") but with the SPC only 0.022" must be removed.

I bought 2 group buy Grendel bolts so I have 2 extra 223 bolts just gathering dust.

[StoneHendge]

It's your face and you can do whatever you want with it, but please be conscious of anyone who might be sharing the range with you

[bj139]

[ATTACH=CONFIG]10790[/ATTACH]

I'm getting some mileage out of this photo. I posted it another thread yesterday.

[Tex Nomex]

From my experiences with 2 6.8 SPC ARs, even when running boxed SSA ammo with an adjustable gas block, the 6.8 SPC is pretty hard on every part of a bolt.

I have an early 'snowflake bolt' that would be somewhat comparable to what you're suggesting. It's face stretched to 11mm in fewer than 1000 rds and I started having extraction issues.

I've run superbolts or something similar since then. Strangely, right now I have a 9 yr-old snowflake bolt in a 16" 6.8 RRA after wearing out the lugs on an ARP bolt (Top in the photo below). Not going to buy another until I see how my new Grendel build performs. Might re-barrel the RRA for 65Grendel or another 223...

Those side walls are gonna be mighty thin if you carve them out...

The worn snowflake bolt below (middle) has a 1.37mm wall at its thinnest point adjacent to the bolt face.

3Bolts:
Top: ARP Superbolt
Middle: Snowflake
Bottom (black): new 223
[ATTACH=CONFIG]10789[/ATTACH]

Not saying it can't be done. Just saying build a 300BLK pistol instead.

[bj139]

That middle bolt looks awfully thin. Are you sure thats not a 6.5 Grendel bolt?
Here is a photo from a site selling SPC bolts of an SPC bolt. They are out of stock.
[ATTACH=CONFIG]10791[/ATTACH]

[Tex Nomex]

That middle bolt looks awfully thin. Are you sure thats not a 6.5 Grendel bolt?
Here is a photo from a site selling SPC bolts of an SPC bolt. They are out of stock.
[ATTACH=CONFIG]10791[/ATTACH]

Those bolts in the photo are mine. Middle is definitely a worn-out 6.8 SPC bolt from 2009-2010 back when SPC bolts were basically just milled out 223 bolts... The face on that particular bolt got pushed in and the sides worn from use.

The takeaway is "what will the sidewall thickness be when a standard 223 bolt is drilled out and how will it hold up?"

Modern SPC bolts now have a greater outer wall circumference so the walls can be thicker - similar to the ARP bolt up top.

"...SPC bolts of an SPC bolt?" (?) Not following...

[bj139]

How about this, "Here is a photo of an SPC bolt from a site selling SPC bolts."



I may just buy this below. Notice how much thicker the bolt web is than yours.

https://www.tracecreekoutfitters.com/pro...rier-group

[Tex Nomex]

Here is a photo of an SPC bolt from a site selling SPC bolts.

Makes sense when I read it now. Sorry. Brain fart on my part.

[bj139]

I still don't have a 6.8 SPC but have ordered two barrels based on the SPC case, the 6x6.8 and the 30 American.
This is similar to the way 224 Valkyrie is based on the SPC case.
I don't intend to buy a 6.8 SPC because the 6.5 Grendel is so much better.

[Tex Nomex]

I still don't have a 6.8 SPC but have ordered two barrels based on the SPC case, the 6x6.8 and the 30 American.
This is similar to the way 224 Valkyrie is based on the SPC case.
I don't intend to buy a 6.8 SPC because the 6.5 Grendel is so much better.

I'm hoping to find that last part to be true. The 6.8 SPC hits hard, but it loses a lot of speed at range. I know of the 30A and 6x68, but haven't shot them. I wouldn't steer anyone toward the 6.8 SPC now. They are great for pigs, though...

Looks like a good bolt, for sure. If that photo is of the actual bolt. :confused: Look up the ARPerformance 6.8 bolt.

Are you going BHW for the barrels? Check the chamber before installing. I have one that was cut a bit deep in the shoulders and was actually sitting on the case mouth - giving me a proper head space reading. Once the throat eroded, head space became a huge flattened primer, near kaboom problem... It'll be a great 18" head-crusher when the zombie apocalypse finally arrives.

[NugginFutz]

Are you going BHW for the barrels? Check the chamber before installing. I have one that was cut a bit deep in the shoulders and was actually sitting on the case mouth - giving me a proper head space reading. Once the throat eroded, head space became a huge flattened primer, near kaboom problem... It'll be a great 18" head-crusher when the zombie apocalypse finally arrives.

Tex - I have a BHW the was cut the other way (tight chamber) and would not close on a go gauge. I called them and they had me send it in. Problem solved within the month. While yours cannot be solved with a simple touch up with a finish reamer, I’d give them a call and see if they’ll make it good. I’ve yet to hear of them turning anyone back.

[bj139]

Tex,
Did you find a place to hunt pigs near Philadelphia? I live just North near Montgomeryville.

I did buy 3 BHW barrels within the last months because of their clearance sale. These high quality barrels for around $90 are a great deal.

They are all wildcats or nearly so. I only received the 6x45 barrel so far. This is the only one which seems simple to form from 223.

I haven't shot a 6.8 SPC so I can't really judge but the 6.5 Grendel is superbly accurate. I have a 24" heavy barrel 223 and I shoot better with my 16" Grendel.

[Tex Nomex]

Tex - I have a BHW the was cut the other way (tight chamber) and would not close on a go gauge. I called them and they had me send it in. Problem solved within the month. While yours cannot be solved with a simple touch up with a finish reamer, I’d give them a call and see if they’ll make it good. I’ve yet to hear of them turning anyone back.

On mine, the throat was cut shallow and the shoulders deep, so for the longest time, I thought the chamber was tight. But after the throat eroded a bit, the case mouth would slide up and brass neck got caught in the throat. My extractor wasn't strong enough to hold and I had to drive a cleaning rod down the barrel to free the live cartridge. Sucks. I'd heard of this sort of thing occurring with reloads if the shoulders get pushed back, but with box ammo?! ARRRRRGH! My other 6.8 - heavier, uglier 16" - never had a hiccup.

I had another barrel at the time (20" Ko-tonics?) back when I had money to burn. I just replaced the stinker 18" and moved on. This was years ago, so I'd feel kinda sheepish hitting them up for another barrel now, especially since I'm moving away from 6.8, anyway. And I'm not knocking BHW. I love their barrels. That one was just a dud. I probably would have forgotten it for another couple of years if I hadn't been inventorying to make a parts list for my new 65Grendel build...

I should have used the go/no-go on it, but not sure it would have caught it. Haven't Go/No-go'ed my new 65Grendel, either. I'll never learn...