[imajeep]

This is a thread that which i am writing with the intent of explaining both the cartridge as well as the rifles available.

I own and operate a Custom AR15 shop, Trident. We build Custom big bore AR-type rifles which function under high pressure and big bores.

We have recently had an interest in the 300 wssm or 300 ossm.
The 300 ossm is a once wildcat, now commercially offered by olympic arms in an ar 15 type upper which fits an ar15 lower.
The 300 ossm is essentially a 25 wssm necked up to .308.
there is a little more to it than that, but heres the facts.
45.7g of "xbr" will push a 150 core lokt @ 2825fps out of a barrel.
this makes the cartridge fall directly between a 30-06, and a 300 win mag.
We have found this cartridge to struggle with accuracy with the factory barrels from olympic. factory dies will resize a 25wssm case up to the right size with no more than a touch of teflon or dry lube inside the case mouth. Factory loads for this are available thru olympic, and appear to be loaded by the reputable HSM company. They do however struggle to achieve any better than 2" groups at 100 yards.
the big struggles with this rifle and cartridge are the limits of the platform, the maximum cartridge lengths are limited by the magazine length. Usually this is about 2.3".
Dont worry about seating depth, as we have achieved good accuracy with some loads seated all the way to the base of the ogive.

The magazines supplied with the uppers from olympic are made by promag, and though they are a nice mag, because they allow a fairly long bullet inside them, they are sloppy in the mag well, and frequently cause the misfeeds.
In short, its a spectacular cartridge, and an ok rifle/upper. olympic has done a great thing for the world here, but could have done more by creating a more accurate rifle to shoot it in.


please continue to read some of the reposts below

 

[broom_jm]

OK, so if I buy a really expensive rifle that weighs too dang much I can then mess around with what is STILL essentially a wildcat cartridge that won't group under 2" at 100 yards? Oh, and the gun will jam because the modifications made to the magazines aren't done correctly.

I'm not sure how you would characterize this as "spectacular", unless you pair that with the term "failure". If I spent that much on a shortened 300WSM and got what amounts to a hot 30-'06 round with mediocre accuracy, I would definitely be disappointed. Also, how do you get to those velocities w/o exceeding the pressure limits of the AR15 model? Am I missing something here?

I was hoping you were going to say you had some tricks up your sleeve to make them shoot better and not jam? Frankly, from what you described, I would have absolutely zero interest in that round, in an AR platform or anywhere else. If I wanted a short 300 magnum, Lord knows there are plenty of options out there! There are lots of great cartridges available for other platforms. If I wanted an AR-anything, it would be an AR-10 in a boring old 308 cartridge. I can't conceive of anything the 300ossm would do better.

 

[fred243]

Not sure how it gets between the 30-06 and anything when a standard factory load for the 06 is 2910 fps with a 150gr pill. The high energy or superformance loads will push the 06 to 3200 fps with 150gr bullet and that's way over 2825 fps. I'm with broom_jm and just don't get it.

 

[Big Bore]

I too fail to see anything spectacular about this. I, and quite a few others not to mention DTech, have built custom .358 WSSM under various names to comply with Indiana minimum caliber and length laws, with sub MOA accuracy and perfect feeding from AR-15 and LR-308 rifles. My own .358 HDH (WSSM) throws a 225 gr. bullet at 2300 fps and groups five shots into .750 to .875 inches all day long at 100 yards and a hair over 1 inch at 200 yards and built on the LR-308 platform, which in all honesty turned out to be longer than needed and the AR mag is big enough even for 225 gr. bullets, feeds perfectly from AR or LR-308 mags with very minimal modifications to the feed lips and follower. It takes the 180 gr. pill and launches it at 2500 fps with slightly over 1 MOA groups due to the rifle being throated for the longer 225 gr. TSX bullet. If one were geared mainly for the 180-200 gr. bullets then the AR platform is more than big enough. I went with the LR to be able to seat the 225s way out there but it really was not needed. Even seated way out there there is a lot of room between the front of the bullet and the front of the mag. If doing over I would have used the AR platform instead of the LR and just seat those 225s a little deepr, so from my experience I see no earthly reason the .30 WSSM would need the longer LR platform even with the heaviest of bullets.
It is Olympic's lousy barrels that will kill the .300 ossm, not the round itself. Olympic does not exactly have a stellar reputation for producing accurate firearms and in my personal dealings with Olympic I will never use any of their products again.

 

[MZ5]

I agree that it is a spectacular idea for a cartridge, because it allows the ballistics it does through a std. AR-15 lower receiver, rather than forcing a change to an AR-10. It's also a very quick cycler in a bolt gun like a Browning (short bolt-lift, super-short action length).

The 300 ossm is essentially a 25 wssm necked up to .308.

Can you please provide a SAAMI-acceptance drawing of the 300 OSSM? The 300 OSSM was based on the 223/243 WSSM cartridge when Oly started producing it, which uses a 28-degree shoulder. Dtech offers a 30/25 WSSM with the 30-degree shoulder, though.
Did Oly change their cartridge dimensions and forget to tell us?

 

[Fullboar]

The 300 ossm is essentially a 25 wssm necked up to .308.
there is a little more to it than that, but heres the facts.
45.7g of "xbr" will push a 150 core lokt @ 2825fps out of a barrel.
this makes the cartridge fall directly between a 30-06, and a 300 win mag.

Not trying to be a smart a** but depending on barrel length I have a number of different 308 handloads that are warm (not maximum) that get more velocity then 2825fps. But like I said barrel length matters

 

[MZ5]

Actually, it really doesn't. The WSSM/OSSM case will always be more efficient than the '06 or 308, and it'll always run through the AR-15 lower, whereas the other two never will.

 

[bsn]

28 or 30 degrees for the shoulder doesn't mean much I reform .223WSSM & .243WSSM to 25WSSM all the time using standard loads. After the first firing its a moot point. The 30WSSM's allow you to have AR10 performance in the lighter and less expensive AR15 platform.

 

[Fullboar]

Short Fat cases are more efficient and always will be. Like a 300WM vs 300WSM, the WSM can get the same velocity as the WM with around 10% less powder. Not only that you can have them in a short action and you dont get the head space problems you do with the belted magnums as they HS off the belt so they need to be trimmed and resized more oftern (depending on how hot you load them).

 

[MZ5]

28 or 30 degrees for the shoulder doesn't mean much...

OTOH, if the OP is a manufacturer, we should at least help him to provide correct information to his potential customers (and his employees, and his suppliers, etc.), don't you think? If a rifle or ammunition manufacturer isn't using the correct specifications for their products, even if they're 'pretty close,' that's the kind of thing that could easily lead to large problems for them (or their customers) down the road.

Also, there's the 'minor' point about how I think a manufacturer had ****ed well better know what their product is based on, and how it's supposed to be made!

 

[imajeep]

please allow me to back up and eat one of my shoes and begin to explain a little more.... i wrote this thread to simply give the general population a good idea of what is going on with this concept during a google search.

many of you are correct in your replies. I have been using oly uppers with this concept in my lowers, and placing custom barrels on them for a bit now.. and i will tell you that most of the oly uppers/barrels ive shot do struggle with accuracy.. they are generally no more than a 1" gun.
i have built 6 of these rifles that are currently shooting regularly in the sub 1" neighborhood, which is good enough for most.
when i documented accuracy, i was simply posting generic numbers. I have hotter loads that will send the 150 at a little over 3k fps... but the accuracy declines here. so yes, some 30-06 numbers will beat this, but no 30-06 shell will ever get into a 2.3" mag.
Next is the issue of the shoulder, you are correct with the 30' versus the 28'
but if you arent loading extreemly hot loads or to shoot match grade ammunition, it simply wont make a difference. We use 25wssm brass just the same as HSM does in their loads, we dont change the shoulder. Usually i can reload a shell 15-25 times before it becomes an issue.
the 223wssm brass generally is just too weak to expand this much and retain a wall thickness at the neck to handle more than a few reloads. and it must be done in multiple steps with annealing in between.
the 243wssm brass works quite well, but seems to be hard to find. here again, you with MOST brass, need to be doing the expansion of the neck in a two step process.
I apologise to those of you who are in the "know" and felt that this was not enough information, but i was attempting to be as superficial as possible and only express pertinant information.

 

[imajeep]

I, and quite a few others not to mention DTech, have built custom .358 WSSM under various names to comply with Indiana minimum caliber and length laws, with sub MOA accuracy and perfect feeding from AR-15 and LR-308 rifles. .

did you know the oly upper is simply a DTECH upper?

I have been working on an upper that will work with these cartridges and more in the big bore stuff for about a year now... we dont work with standard ar components in any of our rifles, we only use billet aluminum, and are hoping to increase wall strength to the platform by doing so.


the oly rifles in this caliber arent meant to be sub moa, they are meant to be sub MOD(m. o. deer) and they do that well.

that is why my custom shop is always busy, because some people want a little more.... so we rebarrel them and play with the bolt lockup a bit.... and address the magazine problems... and so on...

 

[imajeep]

what oly and DTECH have teamed up on here really is something spectacular, id argue that point all day. im not saying this is an incredible product, but saying this is the FIRST.... the one that will get everyone talking about big power, big bore cartridges in this platform.... this upper has anchored the wssm cartridge in this platform... that is spectacular. does the rifle have flaws, yes, is it accurate as ****, no.... does it shoot better than most of the guys behind its trigger....yes, even before we get our hands on em.

 

[MZ5]

Thank you, imajeep, for your return and further posting/info. As I said up the thread, I think the WSSM cartridge series is a spectacular idea, and I'm very glad that some of you are extending it into the realm I wish it would have been taken to begin with. This cartridge case really shines with ~25-cal bullets and up. Put it in the AR-15 platform, and you have an outstanding system. I suppose the case profile might be too fat for military use(??), but this case allows the AR-15 to be one h311 of an assault rifle! The flexibility is amazing!

I'm curious to hear that you have such long life from 25 WSSM brass. Most of us at the WSSMZone forum can't get but a couple to maybe a few loadings out of WSSM brass before annealing is necessary. Some have had to anneal factory-new brass right out of the bag to avoid neck or shoulder splits, and many of us (including me) have had factory 223 WSSM ammunition split badly on first firing. Do you think the brass quality is improving in general, now that we're past election panic buying, or are you guys simply demanding better brass from Olin?

It's also interesting that you (seem to?) think that 25 WSSM brass is made from a different button than 223 WSSM brass. That's possible, I'm sure, but I wouldn't have expected it, given the extremely similar quantity of brass in each case.

243 WSSM brass was marketed by Federal at one time, and that brass was dramatically better quality than the stuff marked Winchester. Unless you're already doing it, perhaps you could get that spec brass back? We handloaders would really appreciate you if you could.

 

[imajeep]

no, i believe that the 223 wssm and 25 are buttoned the same, i forget the wall thickness at the neck of a 223, but when you try to expand it, it seems to thin a touch each time, and not necessarily always evenly, thus my concerns... i think when you expand 223 up to 25, its fine, but that next stretch at least for us, is a doozy.
i get a lot of reloads by annealing, i use a pot full of lead to anneal every 3rd time.

 

[Big Bore]

did you know the oly upper is simply a DTECH upper?

Yes, I did know Dtech uses an Olympic upper for their basis for which to build on. In fact, as much as I respect what Dtech does to the base Olympic product the fact that the base upper was Olympic is partly why I went with my own version of the WSSM instead of having Dtech build it, that and also since he did not wish to work on the LR-308 platform, yes, I asked.

Anything Olympic leaves me with a very bad taste in my mouth after two personal dealings with them so while it is partly a personal dislike as well no respect at all for Olympic products (based on my experiences and those of two custom AR rifle builders I know quite well who have had many problems with Olympic products from base parts to barrels) which makes me not want anything to do with any Olympic product. They do have great ideas and their larger bolted ARs is a brilliant one. If only it were not for their poor execution.
Regardless of that, with proper barrels properly made and installed there is no reason I can see why the .300 W(O)SSM would not be a sub MOA shooter the same as all the other larger caliber AR versions such as the 6.8, 6.5 Grendel, .300 Whisper, .300 BO, .338 Spectre, .358 WSSM, .458 SOCOM, .450 Bushmaster, and .50 Beowulf... Lord, the list is almost endless. With quality barrels properly installed it boggles my mind why the OSSM would not be a sub MOA shooter also. While a sub MOA shooter is not really needed for deer hunting, rifles that can be capable of sub MOA accuracy and then not achieving it makes me wonder what the heck is going on? After all, as was once said and I fully agree, only accurate rifles are interesting. Although I suppose one's definition of "accurate" is in the eye of the beholder.

 

[imajeep]

the prototype for our new upper in this line is proving to be fairly accurate with 338 projectiles, but the one that is getting me excited is what we are going to call the 555... or triple nickel....
a 50 cal wssm.... yum!

 

[pruhdlr]

May I Ask

How will that compair to the 50 Beowulf in performance ?? --- pruhdlr

 

[Ko Improbable]

Heh. I hope this .50 WSSM will be a rifle cartridge and not a handgun cartridge like the .50 Beowulf is.

 

[imajeep]

currently we expect it will be far outproducing the bewulf.... testing is showing it at 300-400fps faster, depending on powder....

Hey ill try to get pics up soon, but a lady who bought a pair of our rifles took a moose with a 300 the other day, 874lbs dressed, and 59" spread...

she hit it with the first shot, and double lunged it, the second shot broke both shoulders!

using Trident Armory Custom Ammunition, the 180s both passed thru at 88 yards.