.300 OSM - .243 WSSM - .25 WSSM in AR-15


December 16, 2010, 02:49 PM
I was reading up on some other calibers in the ar-15 upper and I came accross these, the .300 OSM is claiming 30-06+ performance out of a ar-15 upper. I was wondering if anyone had looked into this round or the .243 WSSM or .25 WSSM also chambered in ar-15 uppers by Olympic Arms. You can find them on Olympic Arms' website under the Game Stalker product listing. http://www.olyarms.com/index.php?pag...mart&Itemid=37

Thanks for any input.

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December 16, 2010, 03:33 PM
Betcha it won't do it with 180, 200, or 220gr bullets. Case capacity is equal to .308 Win, which also matches .30-06 with 150gr bullets.

But yes, doing it in and AR is cool.

I did a Savage .358 WSSM this year, but I seated the bullets out and COL it too long for a AR-15, might fit seated to the cannelure though. I'm exceeding .35 Rem by ~300fps and I'm close if not matching .358 Win. It isn't going to touch the .35 Whelen. No way.

December 16, 2010, 04:59 PM
I'm exceeding .35 Rem by ~300fps

Does anyone make a 35 Rem. upper for an AR15 lower?

December 16, 2010, 05:34 PM
It's a quarter inch too long, or so. It would work in an AR10 length action, but would require a different bolt.

AAMOF the .35 Rem was designed to be a semi-auto cartridge.

December 16, 2010, 11:34 PM
I've got the .25WSSM and it easily matches .25-06.

December 21, 2010, 12:57 PM
yeah, I'm looking to get a solid deer rifle that I can also, by slightly modifying, take varmint hunting/plinking etc. So far I'm leaning towards the 6.8 SPC. The AR-15 is such a great package, and being able to spend a few hundred bucks and turn it from a deer rifle (OSSM/WSSM/6.8) to a long range tack-driver (.223) or even an extremely fun, cheap plinking round (7.62x39). I like the AR-15, a lot, but I'm not married to it so I'm always open to a better idea, but this seems like a gun that could fill a lot of roles right away and for a long time in the future, just looking for a little guidance at this point as far as which caliber will be the best for what I'm trying to do.

December 21, 2010, 01:43 PM
The WSSM uppers make for a pretty heavy rifle so if you're not stand hunting I wouldn't recommend it.

January 21, 2011, 06:05 PM
Yes I have a 300 ossm. It is shooting a 150 grain at 3050 fps and a 175smk at 2800 fps.I have the bbl version, yes it is a little heavy. After hauling the"pig" around in Desert Storm. I don't mind heavy, if heavy gets the job done;)

January 21, 2011, 10:17 PM
These are very interesting camberings and a great option for many but there are issues. They are ok as soon as you know what they are:

- With good care and reloading techniques the WSSM cases are extremely durable. I know some folks did a torture testing and were able to reload the same piece of brass 30 times even shooting with AR.
- The rounds are very powerful. The claims of speed records and power records over .308 and .30-06 have some foundation but when compared with average .308 and .30-06 loads. Those can be pumped up too.
In any case the OSSM loads that claim those speeds are not accurate. The barrel density in an AR platform doesn't allow for those type of excesses.
I would be more worry about finding a nice milder and more accurate load than getting any new record.
- There is one more option that is not listed below that is the 30-25WSSM. it is nothing but the .25 WSSM necked up to .30. The advantage is that this uppers are a tad more accurate and can shoot both the OSSM and the 30-25 WSSM loads. The OSSM cannot shoot the 30-25loads.
- Some folks get many feed issues but some others don't. Do not be surprised if you get them but they can be fixed.
- Potentially the WSSM extra raw power could be put to good use if it wasn't because there is no way to seat the best bullets w/o running into COAL issues. Because the best bullets cannot be used this presents serious limitations where the extra energy at long range could be used. In the end we do not need to kill the deer twice at shorter ranges.
Check all the ballistics charts before you decide if you want to take long shots. The information is out there.
- Folks with a lot of experience are having trouble getting the uppers to produce MOA accuracy. Sub-moa can be achieve but it is not excellent.
It is not an issue for the average hunter at 100-300 yards but at longer ranges it becomes a bigger issues, with some exceptions.
- While some folks are happy with the OSSM many folks are not so happy and the ones that used the 30-25 WSSM are getting better results than the game stalker anyway.
- While the 6.8SPC is a great option for 100 to 300yards then it suffers some of the same issues of the big bore low grain combination. It is a great option for most folks but if you have to take long shots consider other options. look at the ballistic charts and then decide.

The AR-15 was originally designed for the .223 round and not the other way around. While we enjoy many great options for this systems we need to understand the physical limitations of it.

My comments here are not to degrade or critizice any options. I put them here after long research and to the best of my knowledge so others can use this if they want. Do not take anything to hearht. What works for me might not works for others based on different needs, likes of dislikes.

I am currently working on this thread to see if we can come up with a good long range option in WSSM but we have been hitting the wall with both accuracy and poor bullet selection due to the physical limitations of the AR-15 magazines and the maximum length allowed for good bullets to fit in them.


One somebody says I have the most powerful round ever think..... sometimes less is more in the end.

I hope this helps.


January 22, 2011, 06:26 AM
Thanks First, I thought I had seen you there. There are two different options for the ossm , the game stalker which has a stepped barrel for hunting and th k8 mag upper which has the bbl. The game stalker has not had a load developed that will shoot the moa required for long range. The k8 is shooting accurate loads at 2800 with 175 smk . It also has 150 fmj shooting 2600 and 3050 fps giving 1/2 to 3/4 moa. It is giving the same perfomance as any other rifle, depending on the upper. It is however a project rifle, with alot more tweeks to be done.

January 22, 2011, 10:34 AM
First of all many thanks for your kind and prompt reply. How did you manage to seat the 157SMK w/o stepping into the ogive? We tried many magazines and we cannot come down to increase the .70 length difference w/o stepping into the ogive.
Did you modify your mags?

This has a lot of potential but I believe the OSSM claims for "da most powerful AR-15 round" is a marketing stunt. Personally I am looking first for accuracy and versatility and not any world speed records at the muzzle. This boils down to the simple formula of high grain, high BC bullets that fly well vs low grain, low BC bullets that come out very fast but with the 'landing flaps' down. lol!

Everything starts and ends with a bullet. hopefully a good one.

This would be a nice goal with a barnes TTSX 180gr but so far the COAL is not allowing....

Range Velocity Drop Energy Drift
0 2750 0 3023 0
100 2558 2.65 2615 0.34
200 2380 10.63 2264 0.98
300 2209 24.79 1950 2.09
400 2045 46.11 1672 3.72
500 1889 75.78 1426 5.94
600 1741 115.22 1212 8.82
700 1602 166.16 1026 12.42
800 1474 230.64 868 16.82
900 1358 311.08 737 22.08
1000 1257 410.28 632 28.24

Pretty decent to take down deer past the 700yds. A experienced hunter with a good 30-06 system could pull out the above but the OSSM cannot at least at the moment due to accuracy and COAL issues.

Another option that we are considering is to increase the barrel tune by cutting off the barrel to 20 or 21". This means more accuracy nodes. This is based on this old principal.... http://www.tacticaloperations.com/SWATbarrel/

Definitely these uppers could be fun but are not for the average folks that do not want to fiddle or do not have time.


January 22, 2011, 08:17 PM
Have you tried the cammenga easy mags. They will let you seat to about 2.29 I seat at 2.28 and 2.285.This allows me to use all the vld bullets I have come across.I have also found these mags easier to modify to seat around 2.3. I have not shot these seated to 2.285 , I am using load data posted on another forum

January 22, 2011, 09:27 PM
Many thanks for the reply. Still it doesn't add up. Yes with the cammega we gain some nice real state but so far after converting the magazines we have been able to get .61 maximum when we need .71 and .75.
How did you manage to seat the 175grSMK properly? Do you have any pictures with the round and caliper?
Some folks have a achieved by seating the bullet and running over the ogive and while they seem ok with this for me this is a big NO NO.
There are certain things one shouldn't play with. This is warning in big red letters in any reloading book in the world and that's for a reason.

Any further information on how this can be achieved it would be greatly appreciated.

January 22, 2011, 09:40 PM
While doing more testing with the WSSM I did some other research and I found that the 30Reminghton AR is not bad as most folks initially thought.
I posted this article to see if someone can assist and we can have one round reloaded with a high BC bullet. Unlike the WSSM here the math actually works with this round and also in the ballistics software shows pretty nice potential. Not as powerful but plenty. I believe that remington did a very poor marketing campaign with that ugly camm uppers and rifles and the 4 round mags and the 125gr round when in fact it can take a 168grainer and possibly more. The case is very strong and can take nice bullets....


Reports are of pretty good accuray and DPMS has the 10 rounder single stack magazine, similar (or same, not sure) than the 450 bushmaster but anyway folks say it works flawlessly. Also cheaper than OSSM to buy and to reload and even with the korelokt 150gr much better than the 7.62x39 or 6.8SPC specially past 250yards.


January 22, 2011, 11:35 PM
I understand you concerns. This load set to 2.85 has already been tested and has produced a sub moa. My testing was done with a easymag modified to allow 2.34. I want to test these loads which look fine(no gap or crimp) and have plenty of neck tension. There is no book data on any ossm round. All data states a 2.35 col, which we all know is impossible for this systems standard mags.

January 30, 2011, 10:01 PM
Any progress? I believe the maximum you could run after mag modification and w/o stepping over the o-give was 0.61" ...Makes sense?
I might be wrong.


January 31, 2011, 10:44 PM
How are things going?
here is a picture another fellow WSSM enthusiast who sent me this....
This is a 6.5mm WSSM with a extremely good long range bullet.
Too bad we cannot do these things with the AR-15 otherwise long range would have a new meaning with the AR-15.



February 21, 2011, 08:01 PM
In the long quest for long range accuracy out of the WSSM in the AR15 we are done. I am not pursuing any more research for now as we cannot find a solution. So this project is parked for now. Great cases but it is what it is. The round comes out too darn long for the AR-15 to be a good LR round no matter what you do. It might work ok for many folks but not for my purpose though.

February 22, 2011, 01:30 AM
Well, looks like i got here a little late. I have a 243 WSSM from a custom builder that doesn't shoot great as well. I've only used the 87 V-Max but groups are not better than MOA with virgin brass. Resized some recently but have to get to the range Wed. to see what i can achieve. Gonna try some 80 Noslers as well. The .3+ BC oughtta' get me to 600 under ideal conditions if i can get ~.75MOA or so. We'll see. My take on the WSSM AR-15 is as a damage control long range coyote system. I need something that will perform as far out as i can get it to.

There may be an option to get .25" more COAL out of it, if that's what u guys are looking for. I'll check measurements tomorrow after i wake up and post my idea, roughly based on the old DPMS VLD magazine system that i'm using for my 223 AI AR now.

February 22, 2011, 07:40 PM
1stmarine I have not researched any more mag conversions. I have been getting such good results with the 175 smk there is no need. However I discovered a slight difference in bullet shape for the nosler 168 ballistic tips may have to modify a mag to give me a 2.3 or 2.35. The easy mags are the easiest to modify. Oly has a new prototype lower and mag which give more col... so we will see.

February 22, 2011, 08:45 PM
We have been trying every single trick in the book but in the end the fait is simple. I guess we get so excited with our ARs wildcats that we feel we can achieve anything but the accuracy and good bullet selection is simply not there.
COAL is the culprit and it is sad for such nice brass. I read some folks did the torture testing on the brass and were able to shoot the same case 27 times w/o loosing primer pocket pressure and any other significant signs of pressure until FINALLY the neck split. Even after annealing every 3 loads.
My buddy had the same problems with both the OSSM and the 30/25 match barrel, even worse with the OSSM.
So great concept, great brass but in the end the AR was made for the .223 and not the other way around specially with the big overbored stuff. I am really sad about the long range but still I can use it for short range although I have other uppers and better alternatives for that.

How did you manage to fit the longer SMKs w/o running over the ogive?
I cannot make it happen. Math doesn't add up. Did you modify the magazine or mag well?


February 24, 2011, 07:23 PM
At a col of 2.285 a gap is not visable. I do not have a comparator to tell me where the ogive begins. I have used both 175 smk and 175 nosler cc. Both are giving 1/2 moa. Whether they are into the ogive mathmatically I do not know, however the neck tension is so it does not matter with this minor seating issue. I am sorry it is a big no no for you. I wish I had the answers you seek, however I have shot well over 300 of these loads some of the brass is on it's tenth load. No signs of failer and the accuracy is there. When the weather permits I will be stretching out to 600 yrd shots. Oly is working on a new lower and mag combo that may solve your issues.

February 24, 2011, 07:50 PM
Thanks for the update. I agree neck tension is plenty and nobody with common sense should ever try to put even the slightest crimp over a bullet passed the ogive. Just be careful as you most likely are going over the ogive unless your lower is modified. Remember that things happen to re-loaders normally not by one single thing going wrong, but 2 or 3 thing going wrong all at the same time. So by following the book we are just mitigating possible causes of failure. I do not feel comfortable pursuing those venues but if others are ok with that I understand and respect that.
If Oly comes back with a lower and mag that resolves the issue w/o braking the bank I will look into this. I have also considered cutting down the barrel and this will give me more accuracy nodes all other things being equal and in any case more than 22" is not really necessary with the powders I use.

Stay in touch.

February 25, 2011, 11:52 AM
E. Have u ever used these with your AR's? This is the old DPMS VLD Magazine. I can load the 75 A-Max to just below neck-shoulder junction and it still fits in the mag. I'd often though if a guy could make up one of these for the WSSM it would give .25" more COAL which would help somewhat--


February 25, 2011, 06:30 PM
Hi, thanks. No we didn't try this one but others did. For the best bullets we needed .71 and .75 and could only get .61 tops. I think a friend tested the mags you mention but he was running into some feeding issues so we didn't try them. Not sure if it was the mag itself or his own setup.
We thought about milling the lower mag well and create a brand new custom magazine but that looked like a brand new rifle project so abandoned the idea.
If oly comes back with a solution that feed reliably that would be great.

Again. Thanks for sharing your ideas. I don't think that we can get the .75 difference with any existing or modified magazines. The real state is simply not there. I am open to any suggestions always so many thanks for sharing.

What round is that? it looks improved in the neck?


February 26, 2011, 12:56 AM
Yes. it is the 223 AI. If u need that much then it certainly wouldn't work. Be interesting to see if anything happens down the road.

February 26, 2011, 09:47 AM
We will just have to wait and see. At the moment I have other projects going so the fun is always there.
.223 AI! I am a great fun of the .223 and always wondered about the AI but I don't have one or tested one.

I am also working in this .223 based cartridge in .243 caliber. The barrel is a lothar walter that never arrives! so the AR is still waiting....


Also in the above post I posted some nice .223 bullets for comparative. I have tested some pretty nice .223 bullets in the standard case and found some very nice and pleasant surprises.


April 10, 2011, 02:49 AM
I just got back from the range testing the Ossm at 600 yrds
this was with 175 smk, thunderstorms ran me off before I could test the 168 bt hunting load.

April 10, 2011, 09:25 AM
WOW! Amazing shooting!
Did you work on the magazine or use the same?

April 10, 2011, 12:22 PM
same, still using the 2.285 col and with the results I am getting... no desire to change.

April 10, 2011, 07:50 PM
I can understand the no need to change! Impressive shooting mang!
I am now working in a new magazine project for the .245x223rem and posted the results here....

Unfortunately this solution cannot be applied for the WSSM cases but I have another idea for those that I want to experiment with. I might have to sacrifice a lower but I think I can make it work. At least on the paper works.
That would be even more options to an already awesome WSSM upper.

Who cut the barrel for you? Is that a stock Oly or somebody else?


April 10, 2011, 08:32 PM
It is a stock oly 300 ossm not the 30/25 dtech.

April 10, 2011, 08:44 PM
What length? Maybe you already told me but I might have forgotten.

April 10, 2011, 09:23 PM
It is the 24" K8 mag upper, it was only listed in the catalog and not on the website when I first purchased it. Now it think it is the only wssm conversion listed. Oly says the chamber is the same but the rifling is different than the Gamestalker.

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