Well guys, I decided to build one more LR-308 after all, and wanted something fairly unique and powerful.  So I decided on 300 WSM after a good bit of research and soul-search.  I already have the upper receiver, lower, plus some of the 300 WSM pieces, such as a "Magnum" bolt from KAK.  I couldn't afford one of the boutique, high end setups that have, for example, 300 Winmag as an option, hence the 300 WSM caliber choice in order to stay inside standard DPMS LR-308 parameters.

My only problem now is a barrel.  Nobody is currently making them.  At least none that I've found, and certainly none in my sub 500$ price range.  (This gun will never be used in competition.)  In order to make total, full use of the caliber's possible potential, I want a 26" barrel.

So my simple question is this:  Is there any problem with buying an unchambered DPMS LR-308 prefit 308 barrel, and then having it chambered to 300 WSM and my bolt here locally??  About how much should I expect chambering to cost?

Yeah, I can't really afford to do this, but since when did that ever stop me??

Note that I fully realize that this might not be an easy "slam dunk" build.  I am ready to tune/play with it to get it to run.  I have machining capabilities to open up the upper receiver for clearance, will use an adjustable gas block, have a variety of buffer weights to play with, etc., etc.

Thanks!!
Vettepilot

If I were you I'd reach out to KAK and see if they'd do it.  They have the reamers and all obviously and you're gonna want that magnum gas length and all.  I have one of their pre-built uppers and I'm going to tell you, be READY for the noise.  Its probably the loudest gun I own, and I own a couple lazzeroni's.

Why the 26" barrel?  If youre trying to hunt with it then you'da been MUCH better served with a BAR or the likes.

And honestly.  You say you couldn't afford one of the Nemo/Falkors/Noreens, but if you'll watch gunbroker they can be bought cheap enough.  I paid less than 3k for my Nemo with a NF SHV on it

Deadshot says they will have the Green Mountain blanks back in stock in June. That will be your best ~$500 option.

I already checked with KAK and they said no.  Don't know why.

So any problem having a unchambered prefit barrel chambered locally?  I've never had anything chambered, so I'm out of my realm on that.  Expected cost to chamber?  I contacted one recommended local gunsmith but he said he's too busy.  Maybe later when he catches up...

Actually, that gunsmith said it sounded like a fun project, and like something he would do himself.

Thanks,
Vettepilot

In regards as to "Why?" guys--->   just because that's what I want.  That's good enough right?  I want a very powerful LR-308 that I built myself.  I built AR-15's in all the goofy calibers, up through 50 Beowulf.  I built LR-308 platforms in 243 and 308.  Including milling out and anodizing the lowers myself and you can't tell them from "factory" lowers.  Now I want something more powerful than 30.06 in an AR type platform.  Just because...

I don't mind pro and con comments, but I've made up my mind and paid for 300 WSM pieces to start the project, so you're not likely to talk me out of it.

;~)

I'm kinda fearless (and sometimes stupid).  I would learn how to do it, rent the reamers, and do it myself, but my lathe is too small.  I did recently cut the factory choke out of a shotgun, and cut/threaded it for screw in chokes.  That went well.  Then I silver soldered on a steel Picatinny rail, fitted a red dot and a custom stock.  I have 18" rifled bore adapters for it in 9mm and 45-70 Government.  It's the craziest H&R Pardner you ever saw, and I love it!

Thanks,
Vettepilot

Subscribed. I use 300 WSM for hunting (M70 Classic). This would be a cool project.

Maybe check with McGowen to see if they will do it?

I built mine with a dead shot barrel
Great shooter and wasn't crazy expensive (think the barrel was around 600 bucks delivered)
check 'em out
deadshotbarrels.com

I hope someone that's done one of these can help here.  Deadshot is having trouble coming up with what I want; 26" stainless DPMS 300 WSM barrel.

So I've been looking and looking...  only McGowen seems another possibility.  They want you to send them a "Big Bore" barrel extension and a magnum bolt before they'll make you a barrel.  I have the KAK magnum bolt, so that's no problem, but I cannot find a "Big "Bore" barrel extension.

What is a "Big Bore" barrel extension anyway??  Is it just an extension that has the double slot feed ramps machined out to one wide feed ramp to accept the fat 300 WSM round, or is there more to it??

Deadshot says they just use a standard 308 extension on their builds?  I'm confused and losing patience here trying to source a darn barrel!

Thanks for ANY help!

Vettepilot

Contact Paladin Machine Shop Service, tp555-work(at)vfemail.net.  However, you are going to have to do the procurement.  You are going to have to buy the barrel blank, barrel extension, bolt, and rent the reamer from 4D Reamers along with the headspace gauges, and tell Thomas exactly the profile and gas port size you want and location along with muzzle threads and crown.  He will cut metal and assemble the barrel and it will be done right.

What I have him do is cut the gas port at .060 inch, and it of course will not work.  Then with a load that I think will work, I start enlarging the gas port until it does.  
One of the cats I had him build was a .358 HDH based on the .325 WSM case.  In my situation, Manson made the reamers and headspace gauges, I got the blank with the length and twist I wanted,  and supplied him with the bolt and barrel extension with the exact details of what I wanted and in just a week or two I had my barrel completed and back.

 I used Quick Load that said I should use X powder for Y pressure at the gas port with a 200 gr. TTSX bullet, then started enlarging the gas port until it worked.  It works* like a dream and is incredibly accurate.
 
Thomas can do the same for you but he does not guess or make recommendations on wildcats and I don't know if he would have any input for a .30 WSM barrel.  But you do the homework, supply the goods, and he will make you the barrel of your dreams and do it at a cost that will make your wallet very happy, and the quality of work is second to none.  He has done well over a dozen barrel for me and every one is a work of art.

By the way, you do not need a big bore barrel extension like they use with the ARs in .458 SOCOM and .50 B.  I used the standard .308 barrel extension for my .358 and it never missed a beat.  However, on the .470 Rhino and .500 Phantom the BE had to be modified into a "big bore" configuration.  For a .30 cal on the WSM case, you sure as hell do not need it.
Below is a link to the Big Bore barrel extension TROMIX uses on the .458 SOCOM.  You do NOT need a big bore BE on your .30 WSM.
link

If you are not inclined to do much of the leg work, you might also want to contact DTech

*One more thing.  My only problem has been magazines.  For over 10 years I have looked and tried just about every .308 magazine out there and have modified many, feed lips and followers, trying to get them to work with a full load.  Not going to happen.   Any polymer mag, Lancer and Pmags, swell so much that after three or four rounds the magazine cannot be inserted into the rifle, and if you get it in, good luck getting it out until it's empty.  CProducts, Brownells, Lancers, Elander, and others, they just do not want to play well with the fat WSM cases no matter what you do to the follower and magazine. The best I have been able to do is use DPMS .308 magazines and bend the feed lips out slightly and reduce the "hump" on the follower.  Too much reduction of hump or spreading of the feed lips though and the rounds pop out on their own.  I can load only six rounds and make it feed and function properly.  I load five in the mag, chamber a round, then top off the mag with one more for 5 in the mag and one up the pipe.  Any more than 5 in the mag and feeding problems start.

What one needs is a magazine with a .308 mag outside dimensions with the internal dimensions of an AR mag so that rounds will single stack.  I even tried adding spacers inside the mag and cutting out the follower so the rounds single stacked but my mods were too crude and really did not want to work properly, but they did show promise.  If one made what I mentioned above with a 3D printer along with a custom follower (or an sled type big bore follower some use) and maybe an extra strong AR type spring, I think it would work.  But at this stage of the game, I can live with 6 rounds.  I'm hunting deer, not going into battle.

Something like this is what you had in mind lol? I built this for my 300 Saum, which is a factory dpms.








Laminate an ar15 mag body inside the 308 mag. This is the prototype I made up 8 or 9 years ago with the intent of making a nicer one out of a longer 308 mag to hide all the guts but this one works so well I never bothered, and I don't need more than one anyway. You can probably get the gist of the build from the pics. I think it holds 6 and works perfectly and doesn't swell.

I tried almost the exact same thing, putting an AR mag inside an LR mag, but a designer and fabricator I am not.  My concoction looked like monkey crap and worked about as well.  I used a gen 1 Lancer mag with the front cut out epoxied inside an LR mag with the top cut out.  I think I got every angle wrong because it was a disaster.  I knew someone with skills or a printer could make the idea work but it wasn’t me!

WOW!  Thanks for the kind, super informative reply!

At this time, I just don't have the time and energy to do it "piece meal" as you suggest, though there are benefits.  Plus, I've been having so dam many problems with shipping, plus the high cost of shipping comes into it too.  I did entertain buying a blank and having it done here, but the local gunsmith does not have the time to fit me in.  I can't do it myself, as my lathe is too small.

Just for my education, can you explain how the feed ramps actually work?  Since the platform as designed has side by side stacking in the mag, the original feed ramps have two, corresponding slots.  How is that not a factor when going to fat case, single stack rounds?  Would not a single, wide body feed ramp slot such as used for 458, 50 Beo, etc. work better/smoother, more reliable?  I trust that you say "no, not necessary", just curious and looking to understand.  Hell, if one single slot would actually work better, I'm not beyond machining it in myself.

Here's a somewhat interesting post about creating a modified magazine for 300 WSM.  Being a "maker"/fabricator/tinker, I'll likely give it a whirl.  Why not?  I would also try out the Tromix big bore follower in the modified mag as well.  This modified mag would seem to help address the issues of mag sidewall strength, cartridge centering, etc.  Perhaps worth a try if one is capable of a little metal work.  However, I too am not concerned with having a real high capacity mag with this build; just reliability.  Jams are never fun.


https://www.longrangehunting.com/threads/300-wsm-ar10.300663/  (POST #5)

Thanks again!
Vettepilot

Great minds think alike.  You guys were posting that as I was typing.  Or else my browser hadn't refreshed and your posts were there.  Anyway, yeah, same idea on the mags...

Vettepilot

Well, I jumped in and "pulled the trigger".  (Sorry.)   After about 6 weeks of looking, researching, pondering, corresponding, and waiting for stock to arrive, I went ahead and committed and ordered a Deadshot barrel.  Their Lothar Walther style.  I had wanted stainless steel, but they couldn't source me that in the 26" length I was determined to get.  They said their supplier for stainless, Green Mountain, could only supply it in 24", and I talked to Green Mountain and they would not do me a "one off."  I'm quite surprised this chase for a DPMS 300 WSM barrel was so difficult!  I touched on pretty much every barrel supplier out there.  Part of it was my insistence on barrel length though, with it being far more common in shorter lengths.  But my belief is; why wish for high velocity performance in caliber choice, our loading practices/ammo choice, etc., then give away free velocity by going to a short barrel?

Anyway, McGowen was pretty much the only other choice, but they never got back to me on the barrel extension issue, plus their lead time is like 4 months!!  In the end, the only concessions made were a somewhat higher price than I hoped, and not stainless steel. It should be a good barrel though.  Thanks for your suggestions, and the point to Deadshot.

If someone could, I am still curious about this:

Just for my education, can you explain how the feed ramps actually work?  Since the platform as designed has side by side stacking in the mag, the original feed ramps have two, corresponding slots.  How is that not a factor when going to fat case, single stack rounds?  Would not a single, wide body feed ramp slot such as used for 458, 50 Beo, etc. work better/smoother, more reliable?  I trust that you say "no, not necessary", just curious and looking to understand.  Hell, if one single slot would actually work better, I'm not beyond machining it in myself.

Thanks!
Vettepilot

TROMIX only makes the Big Bore barrel extension for the AR platform, however, a smith who has real experience with modifying BEs for big bore cartridges, Paladin for example, he could modify an LR-308 BE to big bore profile in nothing flat.

The reason why the big bore extension is not needed on the 30 WSM, even though the body is bigger, is by the time the body hits the feed ramps the tip of the bullet is already headed into the barrel.  The bolt pushes the cartridge forward out of the magazine.  It then contacts the feed ramps and is directed into the chamber.  Since the barrel extension feed ramps are designed around a .30 caliber bullet on the LR platform, it does a perfect job as is when guiding the bullet into the chamber.  It even works perfectly on the the .260  as well as the .338 and the .358.

 Now, if one were to make a magazine that center feeds like we discussed, then there more than likely would be an advantage of a big bore type feed ramp, but so long as the rounds are double stacking, feeding from the sides of the magazine, then there is no advantage to the big bore type ramp.  On my .500 Phantom and .470 Rhino, (LR based) they do center feed from the LR magazine just like the .458 SOCOM and .50 B do out of the AR mag, so the big bore type barrel extension is needed on them.

 On the AR platform with the .458 and .450 and .50, the bullet itself is not feeding from the side, but from the center of the magazine and the bullet is MUCH wider than the M4  feed ramps on the barrel extension, which were designed for the .22 caliber bullet.  The normal M4 feed ramps work just fine up to .308 and .33 calibers that still double stock and feed from the side, such as the .30 HRT,  7.62 x 39, .338 Spectre, and .338 GRRR, all of which feed double stacked out of a 6.8 magazine, but when you get bigger than that and with cartridges that center feed, especially the center feed part such as with the .338 SOCOM, .358 SOCOM, .375 SOCOM, .400 SOCOM, .458 SOCOM, and .475 SOCOM, that big gaping maul of the feed ramp is needed but really mainly because they all center feed.

I know it's a little late, but X-Caliber will make you any barrel length you want up to something like 30 inches.  I did my 28" .458 SOCOM on a Black Hole Weapons/CSA barrel blank which Paladin turned into my 28 13/16" AR Buffalo Rifle. X-Caliber and Columbia River Arms both do blanks to at least 28 inches, that I am certain about.

You are a prince!!  Thank you SO MUCH for taking the time to provide this info!!

I think where I am running into a mental block is how the 300 WSM actually feeds as used by most people.  I thought the cartridge was [forced] to single stack and center feed by it's sheer large diameter.  Is this not so, and it actually somewhat stacks side by side??  I had visualized the cartridge automatically centering itself in the mag, much like an AR-15 50 Beowulf does in 556 mags.  Not so in this case?

Thanks again!!

Vettepilot

That is correct, the WSM case stacks side to side in the LR mag, not as much as a .308 sized case but not single stacked like the .500 Phantom and .470 Rhino based on the considerably larger .500 Jeffrey case.  The WSM case can be inserted from the the top and the popped under the feed lips like the .308 case does.  It is not so wide that it has to be slid in from the front of the feed lips and pushed back like the .458 SOCOM does in the AR mag or the Phantom & Rhino in the LR mag.

More than likely a wide feed ramp would not hurt anything, if modified correctly, with the WSM case but IMO try the standard BE first and only modify the feed ramp to big bore style if there is a reason to do so.

Again, thanks so much for the explanations.  Truly appreciated.  My build is going forward!  Only a couple little incidentals left to pick up.  Plus wait for the barrel to arrive.  Isn't something like a 10 to 12 week lead time incredible?  Are that many guns really being made, or re-barrelled??

Vettepilot

Supply chain delays, everything from the raw materials to the smelters and mills to the barrel makers.  This supply chain catastrophe has everything mucked up from baby food to rifle barrels.  Joe’s doing a HELL of a job!

There is a very specific barrel I’ve been waiting for from GM more than a year.

It just occurred to me that one picture could have replaced everything I said about the single stack and double stack feeding situation on the WSM cartridges.

.308 on left, .358 HDH (WSM based) on right.  Both in LR-308 mags.
Attached File

To anyone interested in an AR platform 300 WSM:

The search for a barrel is tough, and if you want to really take advantage of the caliber and use a long(ish) barrel, it gets even tougher.

Here's my e-mail response from X-Caliber, and it was all too common:

Richard,

Unfortunately we do not offer AR10 Barrels in .300WSM.

Best Regards,

-Steve

X-Caliber Barrel & MFG

For a 26" barrel, the only options I was able to find were Deadshot Barrels, and McGowen.  Options are limited, even with them.  Be prepared for outrageous wait times of up to 4 months.  If your local gunsmith is accomodating, probably the best option is to buy a prefit barrel blank, and have him chamber it.

Good luck, and thanks again to all here whom have helped.

Vettepilot

Very nice pic!

Well, I have loaded 308 mags here to look at.  What isn't really self-evident is when the 300 WSM rounds are loaded in, the alternate rounds don't touch/support one another vertically, thus pushing against one another in a sideways direction.  This causes the mag bulging.  This was pointed out and explained to me by "Gunpowder", whom I explicitly thank.

Vettepilot

Well, yeah, BUT.  For example with my present order to Deadshot:  I waited something like 6 weeks for them to get the Lothar Walter stock in, yet the lead time was still quoted as up to 12 weeks for me to receive my barrel.  Bummer!

Vettepilot

Me again. Rounding up the last bits for my 300 WSM AR-10 build. On these mags--> I will likely use standard mags, probably the quoted, usable "P" mags at first, while I play around trying to create a better option.

My question: Since you can apparently only fit 3 or 4 300 WSM rounds in a mag before encountering bulging problems, there's probably no sense in buying 20 or 30 round mags, right??

Should I just grab some 10 round, or even 5 round mags for now? They might be stiffer vertically and work a bit better anyway... ???

Thanks!
Vettepilot

I have used Lancers and P mags in 10 round capacity and putting the WSM case and them, they both swell to the point that they cannot be inserted into the rifle after only two or three rounds. Of the metal mags I’ve used, Brownell’s, CProducts (now CPD or Duramag), and DPMS, the DPMS have easier to adjust feed lips and the follower needs less work, but none of the three swell to the point you can’t use them.  But even the DPMS won’t work with more than 5 rounds, but not because of swelling.
When it comes to magazine swelling the P mags are the worst and Lancers are not far behind. I would have put money that the Lancers would not have swelled much because of the metal insert but I was completely wrong about that. They were not much better than the P mags.  And the 10 R were no better than the 20s.

I have not tried the five round mags because that would limit the magazine capacity of the WSM cases to likely only three rounds.

vettepilot, the fella who started the 300 WSM thread on longrangehunting is a friend of mine in Austin -- a very qualified shooter and talented machinist, he does the barrels for all the Texas Rifle Team shooters (adults and juniors).  He definitely knows rifles and machinery.

That said, he observed that the United States Army Marksmanship Unit had done quite a bit of research to build self-loading 30-caliber magnum rifles.  This was to meet both competition requirements and a certain special operations target set.

We partnered with Mark Westrom at Armalite using his Armalite AR-10T Magnum platform since, at the time, the Armalite's M-14 style magazine gave us some feeding options.  We went to the 300 Remington Short Action Ultra Mag case as its neck and shoulder gave us a little better feeding (while the 300 Winchester Short Magnum was better in bolt actions) and is stronger at the lower web:




Our rifle gunsmiths and machinists used BAT barrel extensions, and I believe settled on a +2 or +3-inch gas tube with a 24-inch barrel.  I'm fairly sure your goal of a 26-incher with a +2 or +3 will work well, partnered with standard or XH buffers.

Before the 185-Berger Juggernaut arrived we had 175 and 190 Sierra Match Kings and the Hornady 208.  There are even better 30-cal bullets out now, including the 169 Match King and several different Tipped Match Kings you should be able to push between 2800 and 3000 fps.

I would recommend a quality blank (Krieger, Bartlein, Walther, Satern, Douglas, Shilen, etc.) and have a professional machinist-gunsmith build it for you.  You want a unique (but not necessarily Unicorn) rifle, so you probably want it built correctly.  We used BAT extensions, but the posters above have mentioned others.  White Oak Precision/Armament has the longer gas tubes.  John Holliger can probably do the work, as well as Frank White, John Scandale, a whole bunch of others.

Armalite's 300 RSAUM rifle:


Armalite AR-10T Magnum

Great info guys.  Thanks a bunch.  This is going to be fun.  All I need to purchase now is the mags, and then wait for the barrel to show up.  I will start machining on the lower receiver tomorrow.  I even have the reloading dies purchased, and of course already have powder, projectiles, etc.

I am building this with beautiful Boyd's furniture, in the style of the Windham Armory wood stocked AR rifles.  As such, it was necessary to go with a standard, rifle length gas system instead of +2 or +3.  As such, to accommodate the high port pressure, I will be using a heavy buffer along with adjustable gas.

Again, thanks for the help!

Vettepilot

Well, I was going to post a picture of the last AR10 (308) that I built in the same style as I just described for my new 300 WSM AR10, but I see it's not very easy to post pics here.  I'm not going to hassle with setting up a hosting service.  Oh well...

Why do they make it difficult like that?  Computer storage is incredibly cheap now.

Mine will be somewhat similar to the "Nutmeg" example here:
https://www.windhamweaponry.com/wood-sets/

Vettepilot

I don't think you'll need a + gas length.  I use standard length on all of my 24 inch barrels, including the 28+" .458 SOCOM.  It works fine with rifle length.  The only + length gas rifle I have is a +2, on a 24 inch .260 Remington LR-308.  It started life as a standard rifle length but there was a problem with accuracy so I ordered another 24 inch barrel.  Blinded and misled by the bandwagon of people saying I should go + length, I ordered it in +2.  Function wise I did not see much difference between the 24 inch +2 gas and the 24 inch rifle gas.  In fact, I have found the +2 to be a little more picky as to what powder will function properly whereas with the rifle gassed .260, it ate everything I fed it without hiccup.  It just was not as accurate barrel as I had hoped, rarely getting below 1.5 inches for 5 shots at 100 yards.  The new barrel rarely gets over 1.25 inch but that has nothing to do with the longer gas length, that I'd bet the farm on.  I do not use adjustable gas blocks and have never found the need for one.  Once I get a few loads that the rifle likes, I don't dick with it too much after that.

Just as a side note.  When I build my first .358 HDH, Indiana state law dictated a maximum case length of 1.625" for deer hunting on public land so my .358 HDH V1.0 was done on the .25 WSSM case and trimmed to 1.620" length.  A couple of years later Indiana lengthened the maximum case length allowable on public land to 1.800 inches, so I had the reamer re-ground for the .358 HDH V2 and the barrel rechambered and switched over the .325 WSM case.  Both cases gave me the same damned feeding problems in regards to the magazines.  The barrel extension and bolt were the same for both rounds and did not need adjusting.  I saw no difference in case life but I set my maximum pressures allowed to 60,000 PSI in Quick Load whereas SAAMI max pressure for the .325 is 63K+ psi.  Case life has been excellent.
Granted, mine is a wildcat and and a larger caliber but I doubt that made much if any difference in regards to the feeding problems I had.

On another side note, I even tried the .300 WSSM follower that DPMS sold for their LR-308 mags for use in the factory .300 WSSM and the follower made no difference what so ever, more than 5 in the mag spelled trouble.

I think you will love your woody.  My .470 Rhino and one of my .458 SOCOMs are woodies.  The Rhino, pictured here, has wood for stock and grip but the forend is dipped in wood grain hydro dip.  The .458 is A fancy walnut by Kincade, but he is no longer making stocks.  His were very close to the Boydes with double cheek piece.  The double cheek piece gives the buffer tube area much more meat and is much stronger.  The .470 Rhino is a DPMS wood stock without the double cheek piece but the wood around the buffer tube is pretty damned thin.  It has held up OK but if I dropped it I have no doubt it would split that stock in half.

.470 Rhino, 24 inch.
Attached File


.458 SOCOM, 20 inch, hidden mid length gas under HG.
Attached File

Do you know whatever happened to the commercial production of the AR-10T Magnum?

I was wondering if it had function issues or just didn't sell very well.

The article that you linked to makes me wonder if the ballistics are enough of a gain to be worth
the extra cost and hassle. The article made it sound as if heavy, long-range bullets wouldn't work.

I spoke with an employee of Armalite, awhile back - He never even heard of the AR-10T Magnum.

On the commercial side it didn't sell well at all but nothing in that caliber really did. There was also no big surplus of parts either so people didn't build their own. The RSAUM was definitely a better fit but I always wondered what would have happened had they chosen the WSM instead. I always thought a 7RSAUM would have been pretty cool too.

Looking forward to seeing your build finished.

I've got most of my parts together for a 338 rcm build. I plan on getting an X-caliber unchambered barrel and chambering it myself. Magazines/feeding is my concern as well. It'll be august before I have time to do anything more on it, though.

I don't know anything about the RCM calibers are they similar to WSM? Same bolt face?

@BigBore:

Ok, I'll get some DPMS and/or C-products mags ordered.  I've have good luck with C-Products mags myself.

You mention feed lip and follower mods.  I've not seen this mentioned elsewhere.  Can you explain what's needed?

Thanks!
Vettepilot

I'm not really sure they ARE needed, at least the follower mods.  On the feed lips, the WSM case seemed to feed a little low and would be sluggish feeding out of the mag and into the chamber.  The shoulder was hitting the front of the magazine and slowing it down as well as the point of the bullet hitting very low on the feed ramp (remember, this was on the .358).  Rather than cutting a half moon in the front of the magazine, which would do nothing about raising the point of the bullet, I used a feed lip tool (or smooth jawed pliers) to bend the front half of the feed lips, both sides, up VERY slightly.  That raised the nose of the bullet by a few degrees and made feeding smoother.  It's a trial and error type thing.
To try and decrease the side pressure on the cartridge from the .308 sized follower, which I thought might contribute to swelling, I ground down the hump on the cartridge side of the follower a bit but I cannot honestly say that helped any at all.  When I put in the DPMS WSSM follower it made no difference at all so I doubt my mods on the follower did any real good anyway.  The hump on the CPD mag's follower is much bigger than on the DPMS mag's follower so a little grinding down and rounding out the hump might be needed but that would be the last thing I'd modify on the magazine.  I think the feed lip mod is the main mod to make but try it first without modifying and only start tweaking if you think it is really needed.  My CProduct mags are from the first company, CProducts, not the CPD company now in existence.

Last night I was playing with a new Lancer 10R L7 magazine.  I could get 4 WSM (.358 HDH) rounds in it and still insert it into the rifle but it required a pretty good pull to remove.  I did not live fire it or even cycle it through by hand but I think it would have fed OK without any mods at all, but put in a fifth round and the top round was very loose and the mag was very hard to insert, and even harder to remove.

Yep. Both the 300 rcm and 338 rcm have the typical .532 rim diameter. Just another short action mag. I could do a 338-300 wsm, but I don't feel like case forming. I wanted the wide variety of 338 bullets, or I would have done the 325 wsm.

Hey guys-->  thanks a bunch for all the super great responses and info here!!

I'm having trouble finding any DPMS 308 mags in stock.  

Are Promags any good for the 300 WSM??

Thanks again,
Vettepilot

I don't think I would deliberately spend ANYBODY's money on a ProMag product.

Maybe a Russian or Chinaman.

Yes, do NOT go with ProMags.  Brownells and CPD are almost as good as the DPMS, just a little harder to adjust the feed lips.  You might want to check out PSA since they now own the DPMS brand.  They have them listed but OOS.  Also, check out D&H Mags.  They look to be near the same as the DPMS but again, OOS at PSA but you might do a deep dive and locate some.
The reason DPMS are my preferred mag is because the back of the feed lips are not made solid into the back of the magazine like the Brownells and CPD are.  Because of that, you cannot adjust the back end of the feed lips whereas the DPMS and looks to be the same with the D&H, they are open at the back and you can tweak the entire feed lip easier.  But if you cannot find them, get the CPD or Brownells.  ProMag have a reputation of their feed lips spreading over time.  They work sometimes for a while then the metal starts spreading and the rounds are ejected.  Decades ago, during the 94-04 AWB, I tried some ProMag magazines and swore never again, for any reason or any price.  They were total garbage in HK USP, AR, and Beretta 92 FS mags.  I picked up a couple of each at Knob Creek and all 6 were total wastes of money.

By the way, I tried heating PMags with a heat gun to adjust the feed lips.  Total fail.  Good mags for the .308, .338 Federal, and .260 Remington; not worth a tinker's damn for the .358 HDH, .470 Rhino, or .500 Phantom.

You are very definitely preventing me from making costly mistakes, and saving me a ton of grief on this project!

THANKS!!!

Vettepilot

@BIG-BORE:

DAM!  I'm so embarrassed!  I was just admiring your super nice guns again.  Then I decided to re-read the posts from there on down.  At that point, I realized I had not commented on your guns.  I'm really sorry.  :~(

They are outstanding; really beautiful!  I bet you're very proud of them, as you should be!  

For those of you that like to have something different, this is it, and sure to garner a lot of attention anytime/anywhere they are seen.

I like, and have had good luck with Boyd's stocks.  I took a gamble back when I built my AR-10 "Woody", and ordered a wood stock set from Boyd's for an AR-15.  (They don't have them for AR'10's.)  I hoped that I could make it work on my AR-10, thinking that if not, I could just use it on one of my AR-15s instead.

As expected, the rear buttstock fit just fine, with no mods needed.  The front handguards needed work to fit, but they did turn out just fine.  About an hours work fiddling around with a Dremel and a sanding drum got the grips to fit perfectly.  BAM!  My own AR-10 "Woody" was born!  I just love how it turned out, and it proudly resides on the wall in my living room.

And so, this next project; my new AR-10 "Woody" in 300 WSM.  AR-10's aren't all that common.  A 300 WSM model even less.  And a wood furniture version?  Pretty rare, heh?  Fun project, and I can't wait to get it done and tuned/dialed in.  I'll be loading all my own ammo for it as well.  (Thank god--> $$$!)

;~)

Vettepilot

Looking at Brownells.  Several have mentioned that Brownells mags are good for 300 WSM, including KAK.  What brand is Brownell's 308 mags?  They don't actually make mags themselves, do they?  I don't see much besides ProMag on their site...

Thanks,
Vettepilot

They do make magazines so it’s possible they make those specific ones.

Sorry, absolutely no idea if Brownells makes their own or not.  They look very similar to CPD, similar shape and even similar follower, but I have no idea if they are kissing cousins or not.  The D&H look closest to DPMS, IF the pictures are even close to being current or accurate.

Thanks for the kind words.  One thing about having a semi-auto elephant gun, I haven’t seen a single elephant in the garden since I got it.  They are incredibly smart creatures!

Yeah, there was a Zombie or three kicking around here in the evenings, but we've seldom seen them since I made my 50 Beowulf.  I don't know WHAT I'll practice on now with this 300 WSM.  Of course, if they figure out the 50 Beo is range limited and start to approach again, that's when the 300 WSM will come in handy!

;~)

So...  there's no mags that say "Brownell's" brand on their site.  Which one would a person choose?  (Sorry to be a PITA.)

Vettepilot

Precisely.

Just because you can't see them doesn't mean they're not there.

Brownells has 10R D&H mags, that would be my choice since they look similar to DPMS with the open back on the feed lips.  The 20R are OOS but they would be my first choice behind DPMS.  The 10R would be my next choice since more than 5 rounds of WSM are likely to be problematic.  
link

I wonder what happened to the Brownells brand mags?  I am going to order a D&H 10 R myself for a try.  If they are as good as the DPMS then I’ll pick up some 20R when available.

DSG Arms has 20R D&H for $18.50! I just ordered two of them.  They cannot be worse than the Magpuls.
link

I got the two D&H LR-308 mags today.  I now "know" who made them for DPMS.  Feed lips are exactly the same, same shape and open on the back.  Floor plates are exactly the same, right down to the God awful tabs that make it almost impossible to remove, and the follower is small and bullet shaped like in the picture on their web site, not as small as the DPMS but not that big chunky follower MagPul and CPD use.  The Brownells mag uses a follower that looks like the D&H.
The ONLY difference I see between the D&H and the DPMS is that while the DPMS only holds 19 rounds, the D&H holds a full load of 20 rounds of .308.  

I tried the .358 HDH (WSM) and as suspected, a total no go without tweaking.  I need more mags for the .308/.260/.338 than I do for the WSM so these will remain un-tweaked.

I've built one in 300 SAUM, and learned a few things.

A Remington (factory) barrel can have the shank machined to accept the 308 pattern barrel extension; I purchased a take-off barrel already chambered for the 300 SAUM. I'm guessing that a Winchester factory barrel would probably work too, but I can't confirm.

The best magazines for the round are the 1919 shotgun mags.

Definitely use a pigtail gas tube: you'll need to make it yourself. The reason is that the chamber pressures are quite high when ignition occurs, and while you can mitigate bolt                                 velocity with your buffer and spring, using a pigtail  tube to almost double the travel distance (and time) for the gas to reach the bolt carrier key allows the chamber pressure to drop off significantly before the bolt unlocks. It will extend the life of your rifle and make it safer in the long run. Autozone carries the correct size brake-line tubing to fabricate one. You can make the coil by pinching off one end of the tubing, filling it with salt, pinching the other end, and then bending it around a mandrel.  

You can get a pretty accurate rifle from this system. It's a highly useful caliber too.