Tuesday, September 09, 2014

I have a somewhat messed-up elbow Updated: that was fast

which is preventing me from doing some things I really need to, so I decided to do a little more checking on the .30-30 project idea.  Specifically, the bolt, which I thought of as the big problem.

Son called last night, and after other things spoke a bit on this(he's building a .308 AR), and during discussion he suggested check some numbers, which cleared things a bit.  Specifically, the first 7.62x39 AR-15 setups used a .223 bolt with the face opened up to hold the wider casehead.  A bit of checking gives
.223 rim diameter .378"
7.62x39                .447
So it had to be opened up .069"

.30-30   .506"
.308      .4728"
So a .308 boltface would only have to be opened up .0332", less than half as much.  My, my, that should be doable!  Especially since the .308 bolt is set up to handle ~60kpsi, whereas .30-30 has a max ~42kpsi.

So, having heard DPMS has the AR-10 down pretty well, I decided to ask them if they saw any problem with a .308 bolt being opened up that much.  That went well:
it will not work as there are no mags or receivers that will let that happen
Why would the receiver not work with it?
the case is too small
I assured them I was not thinking of trying to fire the one cartridge in the other chamber, I'd be using a barrel properly chambered for .30-30.
it will not work
I am a stubborn bastard at times, so I've sent one last question(I promised): since the .30-30 case is the same length as .308, why not?  We'll see what they say.  I'll have to ask some other manufacturers as well; any suggestions?

Update: that was fast, and disappointing:
  the two cases and rounds are completely different
Well DUH!, as daughter used to say, I'd never have noticed that!  And that's a singularly uninformative answer, considering the number of different cartridges the AR-10 platform is chambered in.

Other thoughts: I'd probably have to get a barrel bored for .308 and threaded for the barrel extension(I'm learning all kinds of things here) or with it installed, and have the chamber cut so it headspaces properly with the bolt.  And a adjustable gas block, because I'm sure that will need fiddling with.  Everything except barrel, bolt and magazine would be off-the-shelf parts, and the magazine, I think, would primarily be a matter of adjusting feed lips to work with the cartridge.

I think this is workable(aside from scraping up the money to buy the stuff, of course).


Anonymous said...

It might just be a case where for DPMS "It will not work" means "Our lawyers would gut us for even looking at this."

What were you planning to do for magazines btw? If you talked about it before I might have missed it.

Anonymous said...

Sorry, I did miss it. So adjusting the feed lips on a 308 mag? What happens to the rims on the 30-30?

Firehand said...

It's possible, but I'd appreciate a 'We can't help you with this' instead of "It won't work. Because we say so."

I'm hoping a .308 mag would work, would have to see. For the rim, thinking the same thing the Romanians do on mags for the PSL: about 1/3 up from the back of the lips there's a cutout on both sides; you place the rim there, then push the cartridge down & back. That makes sure the rim of each is in front of the cartridge below. And it does feed nicely.

KM said...

Just for grins I loaded 10 30-30 rds into a 10rd DPMS 308 mag, taking much care to get the top rim in front of the others.
If you haven't done this yet, you need to cuz it won't be a quick fix.
It. Is. FUBAR.

The too small front (mucho taper + rim) makes it wiggle in the mag. Wiggle means the rim above gets BEHIND the rim below and needs a bic pen to shove them down out of the way. Two even got their rim in front of the next round but behind the *3rd* one in line.

0007 said...

If you have enough time, money, and the services of a good smith, most anything can be done to anything.
My guy down here just finished redoing an SKS platform in .357 Sig for somebody.
He's currently redoing a P-14 in 7.62X54 Russian for me and I bought a P-14 in 30-30 Win from him.
Admittedly the 30-30 still has mag/feed problems but we're working on that, heh, heh, heh.

Firehand said...

Yeah, the mag may be the most problematic part; the bolt & barrel I'm not seeing a real problem

tkdkerry said...

the two cases and rounds are completely different

Sigh. I frequently get similar answers from support types who obviously didn't really read what I was asking, and apparently assumed I was just an idiot wondering if I could stick a square peg in a round hole. Good luck.