Ar10 300wsm

[Jakediesel06]

I’m thinking about building an ar10 in 300wsm. Been doing a little reading on it mostly finding older posts not much on newer info.

In the older posts there were extractor problems and the upper had to be modified to work.

Has anyone on here built one what are your thoughts. Where did you get high pressure bolt parts ext.

 

[STI_1911_Guy]

I was lookign to do one myself but ultimately decided not to after research. KAK industries makes uppers and the reviews are fairly solid. Any of the complaints are more related to the 300wsm as a chambering for AR10 rather than the quality of the upper itself. It seems the 300SAUM was the more ideal AR10 chambering.

 

[Jakediesel06]

What was the reason you decided not to.

The chambering I think can be fixed by modifying the upper receiver.

Not against the 300 saum just doesn’t seem to be as readily available as the 300wsm. Cases between them are almost identical neck on 300saum is a little longer which I like.

 

[STI_1911_Guy]

My reasons were
1. sounds like you cant reap the full benefits of the wsm before you run into over pressure. Not so much from over pressure but timing of the system with that much gas volume. a custom barrel with +2 gas system might be much more beneficial.
2. the WSM is .075" longer case than the SAUM and its hard to fit in and AR10 mag or is severely bullet limited.

I dont believe the 300 SAUM is even really around anymore so its not much of an option any longer.
The KAK uppers come with the ejection port enlarged already.

 

[Steel head]

300 saum

My reasons were
1. sounds like you cant reap the full benefits of the wsm before you run into over pressure. Not so much from over pressure but timing of the system with that much gas volume. a custom barrel with +2 gas system might be much more beneficial.
2. the WSM is .075" longer case than the SAUM and its hard to fit in and AR10 mag or is severely bullet limited.

I dont believe the 300 SAUM is even really around anymore so its not much of an option any longer.
The KAK uppers come with the ejection port enlarged already.

Saum has a shoulder angle slightly better for feeding as well.

7SST would be awesome in a gas gun.

 

[Jakediesel06]

300 saum

Saum has a shoulder angle slightly better for feeding as well.

7SST would be awesome in a gas gun.

You mean 7mm wsm? Sst is just the bullet?

 

[Steel head]

You mean 7mm wsm? Sst is just the bullet?

7 mm Sherman short tactical magnum.

 

[STI_1911_Guy]

I think the sst is the sherman short tactical wildcat

 

[Jakediesel06]

My reasons were
1. sounds like you cant reap the full benefits of the wsm before you run into over pressure. Not so much from over pressure but timing of the system with that much gas volume. a custom barrel with +2 gas system might be much more beneficial.
2. the WSM is .075" longer case than the SAUM and its hard to fit in and AR10 mag or is severely bullet limited.

I dont believe the 300 SAUM is even really around anymore so its not much of an option any longer.
The KAK uppers come with the ejection port enlarged already.

Over pressure is what is breaking extractors because of timing. Over pressure tries send bolt back before it should. Just trying to understand what’s happening

 

[Jakediesel06]

7 mm Sherman short tactical magnum.

That would require making your own carriages right?

 

[Steel head]

That would require making your own carriages right?

You have to load it but he sells brass ready to go.
It’s going to fit in AR10 mags far better than the saum or WSM with better bullet choices.

 

[Jakediesel06]

Really would be nice if the 300prc had a short cartridge. I know there is the 6.5prc just thinking something in 30 cal range

 

[STI_1911_Guy]

Over pressure is what is breaking extractors because of timing. Over pressure tries send bolt back before it should. Just trying to understand what’s happening

Yes. The pressures are still too high to remove the case but the action is trying to open putting stress on the extractor and causing severe case head swipe.

 

[Steel head]

Really would be nice if the 300prc had a short cartridge. I know there is the 6.5prc just thinking something in 30 cal range

The overall length is gonna limit you in bullet choices.

 

[Jakediesel06]

Yes. The pressures are still too high to remove the case but the action is trying to open putting stress on the extractor and causing severe case head swipe.

So would have to have a 30” barrel and have gas block 26”or so down to prevent that? Adjustable gas block I’m assuming is a must

 

[Jakediesel06]

You have to load it but he sells brass ready to go.
It’s going to fit in AR10 mags far better than the saum or WSM with better bullet choices.

I’m looking for something more readily available

 

[Jakediesel06]

The overall length is gonna limit you in bullet choices.

With the 6.5prc too?

 

[Steel head]

With the 6.5prc too?

Do AR10 mags fit a 2.95 oal?

 

[STI_1911_Guy]

So would have to have a 30” barrel and have gas block 26”or so down to prevent that? Adjustable gas block I’m assuming is a must

Not necessarily a long barrel. a +2 gas system is just the gas port is drilled closer to the muzzle to help with timing. An adjustable gas block i would say would be a must.

 

[Jakediesel06]

Do AR10 mags fit a 2.95 oal?

Not sure what a 2.95 oal is

 

[Jakediesel06]

Over all length

 

[Jakediesel06]

Ar 10 mags I believe are 2.8”

 

[Steel head]

Ar 10 mags I believe are 2.8”

Yep

 

[Jakediesel06]

So 6.5 prc is too long. Feel like I’ve heard of that in an ar10. And really 300 wsm is pushing the limits length wise.

 

[Steel head]

So 6.5 prc is too long. Feel like I’ve heard of that in an ar10. And really 300 wsm is pushing the limits length wise.

Yep.

 

[Jakediesel06]

Yep.

What’s the oal of the 7sst.

 

[Steel head]

What’s the oal of the 7sst.

Well my 7 saum load is 2.85 with Berger 168 classic hunters and I think SST is .1 shorter.

 

[Jakediesel06]

Would standard 7.62 mags work?

 

[bfoosh006]

You guys might find this article informative.. ( I did )

https://www.shootingtimes.com/editorial/longgun_reviews_st_ar10ultra_062309/99358

 

[FCS]

Not just a pressure issue (peak) it is a port pressure and gas volume issue.
WSM is just enough larger in diameter than SAUM that ejection port on upper needed to be opened up.
Bolts are an issue, finding an AR bolt with small FP hole and correct diameter recess was a challenge 15 years ago.
When I did mine, used a standard bolt and had a buddy who owns a machine shop turn 300 WSM case heads down to standard dia, allowed me to used a 308 bolt. Helped that buddy had a standard bolt face Barnard action (6BR) and wanted to shoot a 300 WSM so he already had made the form tool, programmed the CNC to modify cases.

I put port 3" farther forward than rifle port location, made a custom gas tube and port was made small so it could be opened up only as much as needed to run reliably.
Still had issues tied to gas port pressure and increased volume of gas since using 60+ gr of powder.

Magazines are a PITA. No, standard 7.62 magazines will not work as follower is incorrect positions cartridges such that they will bind up in mag body.

I used DPMS U/L, 300SAUM DPMS magazines so you are limited to 5-7 rd in a shorter magazine. Put the SAUM follower into a 20 rd magazine, body swells out so bad you can't get magazine into the lower. I haven't tried putting the DPMS SAUM follower in an Armalite (M-14 style / dimension magazine) but I suspect same problem will arise.

Can it be done? Yes.
Is it worth the hassle? IMHO, no but only you can determine that.
Personally, I've found that 308 / 308 parent cartridge is about all the gas volume the -10 platform can handle w/o special gyrations and lots of ibuprofen for the headaches. Granted, things have changed since I did my 300 WSM AR-10 back in '07 and I've gained some additional knowledge. I still wouldn't do any short magnum in a -10 platform as gains are minimal, brass gets beat up faster, getting magazines to work is MPITA, finding correct bolt was (might have changed, I have not looked for a 0.545" diameter -10 bolt in last decade) not easy.

I've done plenty of things that others have suggested were not a good idea. Most times I proved other correct, on a couple of rare occasions I proved them incorrect.

Best wishes on your -10 short mag project if you choose to go forward with it.
If you do build up a -10 short mag, please update us on how it functions, groups, how you got magazines to feed reliably, etc.

 

[Jakediesel06]

So 300 saum would be a better choice but still sounds your going to have feeding problems as gas problems

 

[RyanScott]

Really would be nice if the 300prc had a short cartridge. I know there is the 6.5prc just thinking something in 30 cal range

300RCM?

 

[Jakediesel06]

300RCM?

Looks a little longer the the saum. Has anyone built one. Assuming it’s going to have all the similar problems.

 

[Jakediesel06]

Has one tried jp high pressure bolt. Think I could handle a mag load?

JP - Bolt Assemblies

 

[FCS]

Has one tried jp high pressure bolt. Think I could handle a mag load?

JP - Bolt Assemblies

JP bolts are 0.480 for standard case head, you need 0.535 for SAUM.
I used an Armalite bolt (small FP, 0.480” bolt face) on my 300 WSM as I had brass modified to be rebate rim configuration (300 WSM w/0.480 diameter case head).

 

[Jakediesel06]

JP bolts are 0.480 for standard case head, you need 0.535 for SAUM.
I used an Armalite bolt (small FP, 0.480” bolt face) on my 300 WSM as I had brass modified to be rebate rim configuration (300 WSM w/0.480 diameter case head).

So even with a .480 bolt you had to modify case. Anyone have a bolt big enough?

 

[FCS]

So even with a .480 bolt you had to modify case. Anyone have a bolt big enough?

WSM needs bolt face recess to be 0.545” diameter.
JP bolt is only 0.480” diameter bolt face.
You would have to have 300 WSM / SAUM / RCM case head modified to work with a JP bolt.

I’m not aware of any currently produced AR Bolts with correct bolt face to do WSM / SAUM / RCM / WSSM build. I haven’t looked for a magnum AR bolt in over a decade either so there might be one available.

 

[Jakediesel06]

This is the only bolt I have found. Not sure if kak is good quality or not.

LR-MAGNUM DOUBLE EJECTOR COMPLETE BOLT HEAD ONLY

Enhance the reliability of your magnum caliber firearm with our LR-Magnum double ejector complete bolt head. Designed for optimal performance, this bolt head ensures smooth cycling and consistent ejection, making it an essential component for your firearm build.

www.kakindustry.com

 

[Jakediesel06]

What about using a piston driven system. Think that would gas pressures and timing.

 

[Steel head]

What about using a piston driven system. Think that would gas pressures and timing.

You’d have to tune it just like a DI setups

 

[RyanScott]

Is there a piston system that isn’t overgassed?

 

[Steel head]

Is there a piston system that isn’t overgassed?

Yea, the one designed for a platform and cartridge.

 

[RyanScott]

Is there an example of this? I’m only familiar with 5.56 piston systems, which are all overgassed.

 

[Steel head]

Is there an example of this? I’m only familiar with 5.56 piston systems, which are all overgassed.

Over gassed on purpose just like most DI guns.

 

[RyanScott]

That would make sense of the cyclic rate of piston guns wasn’t higher. They also gain more carrier speed with the same cans.

 

[FCS]

I’d keep it DI.

 

[Steel head]

I’d keep it DI.

As would I.

 

[Jakediesel06]

Ok what if I went with extra long rifle length gas tube and than coiled gas tube around the barrel to say make the gas tube 30” instead of the 17” it is

 

[RyanScott]

Gas expands at 5000fps, you could coil the gas tube around the 25 yard line and barely slow it down.

 

[Jakediesel06]

what do you mine by the 25yard line

What if you went with a smaller id dia gas tube tube if something like that was available. Sounds like this could be the biggest obstacle to this project