Something I’ve been working on over the last year or so is an adaptation of the DPMS/Remington RAR upper to .458 caliber……basically, something akin to a SOCOM with a larger rim, made from a little heavier brass - so it can take advantage of the pressure tolerant components of the RAR, and use off the shelf reloading dies and magazines….

The ‘pass-through’ of the RAR barrel extension will allow a casehead diameter up to ~  .670”…...that means brass as large as the Jeffery, Gibbs, or various 'Nitro' cases could be used as the parent….. that would require deep rebating the case rim, opening up the bolt face, or a combination of both……
as the RAR bolts don’t exactly grow on trees, I didn’t want to chance lightening the bolt too much and risk a fracture….or reduce the operating pressure of the cartridge for concern of collapsing the case from deep rebating the rim….

I figured the RAR bolt and extension could tolerate enough pressure to allow the velocity I was looking for with the 300 TSX using a .544”ish diameter casehead….and that would help address a couple other hurdles……it would allow the use of off the shelf magazines and SOCOM reloading dies to form and reload the cases….

There are several rimmed and un-rimmed cases available in the ~ .544” casehead such as the Jeffery, or various 'Nitro' cases that could be used as the parent……..for a few reasons I chose to go with the 404 Jeffery……I already had a good bit of it left over from another big-bore AR-15 project, the rim / casehead dimensions would accept the work that needed to be performed to the rim without getting near the web, could be made to work with the unmodified RAR boltface, and would not require custom reloading dies or magazines….

The first step of making 458 RAR brass is parting the 404 Jeffery case at roughly the 1.650” mark…..a tubing-cutter or chop-saw can be used…..I ended up using a small jewelers lathe…



The second step is the initial forming of the Jeffery brass…… using the Redding SOCOM full-length sizing die without the expander button in place…..



The third step is reaming the casemouth and opening it to the nominal diameter of .458”, and trimming the case length to 1.550”……



The fourth step is to outside neck-turn the brass…..Taking the sizing characteristics of the Hornady SOCOM full-length sizing die into account, the necks are turned down to ~ .013”, this provides die sized neck tension on the order of .003” to .004” depending on the accuracy of the bullet diameter….



The fifth step is to slightly rebate the rim down to RAR boltface dimensions…..



The sixth and final step is to size the brass using a 30 RAR shell holder and Hornady SOCOM full-length sizing die with the elliptical expander button in place, this resets the casemouth opening and ‘straightens’ the case from previous forming and or machining steps…..



After the brass making process it’s pretty straight forward to reload…..I prefer the Hornady SOCOM dies as the elliptical expander button and built in crimp feature of the telescopic seater were taken into account when laying out the 458 RAR with the first bearing groove of the 300 TSX being used as a cannelure…… loaded cartridge length is 2.250”…..



The next challenge was getting the upper together…..I had a few parts available from a previous project, less one or two critical components that I figured I would end up having to scalp or make….. I would of preferred to start the build with a virgin barrel extension, but as it was, I ended up having to strip one from a previously used 30 RAR barrel…..I’ve seen three different feed ramp configurations with the RAR barrel extensions, this one is left offset single ramp…..I may end up making it a ‘full width’ ramp if need be…..but, at least one of the critical components is in hand…..



Next was the barrel nut and handguard….as the RAR uses a barrel nut larger than an. AR’, but smaller than an ‘LR’ that doesn't leave any commercially available alternatives…..I had an odd-ball Rock River nut around here somewhere that I thought would work, or could be modified to work, but I couldn’t find it……so that leaves me with making a barrel nut or re-cutting an ‘AR’ barrel nut…. I chose the latter….



this is one of the items that took the longest as it had to be sent out for anodizing....



Once I had all the components in hand the barrel went just like anything else….after that is was just a matter of fit, assembly, and finish….

What I ended up with was the 458 I’ve always wanted…..something with a heavier bolt and extension that could tolerate a little more pressure in the ‘AR’ chassis, but keep close enough to the original SOCOM dimensions that it could make use of existing reloading dies and magazines…..

Nice work

So for all that work you gained about 300fps over a socom? Its really cool seeing someone with the skill and means to be able to do something like this. Any pics of the completed upper?

Thanks!!.....I appreciate it!!

It came together fairly smooth.....and I was pretty glad.....couldn't afford to lose any parts in the process.....wouldn't be able to replace them  

Thanks again!

It works out to about 800 ft/lbs more muzzle energy....or extends the 1,000 ft/lbs hunting range by about a 125 yds.....whichever one is inclined to subscribe to....

It looks like many of my other uppers.....just a plain ole free-float tube......but yeah, I've got the pics from the rest of the build and range work I'm gonna put up.....

I'm still recovering from doing the first post from my cell phone

The arfcom media server doesn't seem to want to cooperate so doing if from the cell makes it a good bit more laborious.....

very interesting  I love my 458 socom . adding 300-400 fps would be a pretty big step up if you ask me.

I agree.....it 'feels' like a big deal...lol

If the parts were more available I'd probably push one to failure to find the ceiling......

Conventional brass reading doesn't really work.....my guess is the bolt will fail before the primers or brass show anything.....the extension may 'stretch' from the peening....may be able to pick-up some growth measurements from those before they break.....

Quickload hasn't shown much to compare.....

I'm probably gonna hover around 2,000 fps with the 300s for a while and take plenty of measurements.....

Excellent work as usual. From an engineering analysis perspective, the main areas that would be interesting to do FES would be the thread tennon on the extension.

I think the bolt is actually a strong point, and you aren't going to push the peak pressure higher than what the brass is rated for anyway.

One thing about your work is that you are very clean, know how to machine well, and mitigate the interface of different components when tackling wildcats, and it shows. Beautiful project all around.

Tell us more about the billet upper...

Thanks for the kind words.....means a lot!!


I guess too many years of building race powerheads ingrained the importance of 'fit'.....lol

The tennon is a little different than a conventional AR tennon....the threaded and un-threaded sections are more similar to a 308 tennon, just not quite as long....

The lugs in the RAR extension are about half as deep front to rear compared to a 308 extension....

About two or three years ago I picked up three RAR complete uppers.....these were the last remaining parts scalped from one of those uppers....I'll put up more pic....

Thanks again!!!

Nice work!  If I ever get back state side for longer we're going to have to get together over some cold beverages.  But who knows where they send me next, considering we just opened up that lab in S America....

Bet you it does let you know you pulled the trigger

As to which part will fail first, I have seen first hand what a case full of pistol powder does when attempting to home cook subsonic .458 loads (not mine).  QL suggested the peak pressure exceeded 100,000 psi - the bolt lugs and extension lugs were plastically deformed but that was about it.

I have one bolt that used to sit on my desk, it has the lugs starting to all "turn inward" as the result of pushing too hard - it is the bolt that bit my finger off while shooting with the HPD SWAT team.... nothing like bleeding all over the place while doing a demo for the top brass

Very impressive work.  Nice posts and pictures documenting the process, too.  Thanks.

Kurt, your work is impressive as always, but this one takes the cake, heck make it the entire bakery!

Wildcatter extraordinaire!

Thats dedication posting that from your phone. Thats almost as impressive as the build itself

Looks like what I can find so far on the .404 Jeffrey is that it has a CIP pressure rating of 53,000psi, and seems to thrive on lower pressures, with high case volume for a nice "slow push" recoil with heavy projos meant for African dangerous game.

What case volume do you have with this, and what powders are you looking at for the 300gr TSX? 2100fps would basically be faster than a .444 Marlin, and faster than the .450 Bushmaster from a 16" barrel according to what I'm seeing in Hornady's 8th Edition. Seems to match the .45-70 Government out of the 1895 Marlin.

Looks like a .458 to rival most of the legacy .458 cartridges, out of our favorite rifle action, that is now continuing to expand in the hunting market. What's minimum expansion on the 300gr TSX?

1000fps for the 300gr TTSX

If I was a wildcat'er I would have picked up as many 30RARs as possible. Just seems like a blank canvas for so many great ideas. But I was only thinking of opening up the 303RAR brass to 338, or bringing it down to a 6.5.

What you did here is simply amazing.

1,600 fps for the 300 TSX

Sounds good to me!....with new 'roll-outs' at work I've been on about a 40 day stretch....doesn't leave much time in the evenings for gun stuff lately....or cold beverages.....keeping ole Pat pretty busy too....

The project I was working along with / a little before the RAR project was looking to mitigate some of the thrust issues that turn the lugs 'inward' as you described......some of the measurements that I had taken on high pressure x39 set-ups showed that the headspace grew three or four thousandths then the lug to lug diameter shrank by a few thousandths indicating what you described.....the ones that seem to 'move'the most are the ones adjacent to the extractor channel.....and the one on the bottom seems to move the most....
The Jeffery brass was used to make a 'square' base rebated 458 cartridge that 'thrusts' against the center and outer rim of the bolt.....works pretty good....even with pretty stiff loads the the only interface change we saw was a slight headspace growth, but the inward turning stopped....




Has to use a highly modified extractor or the cartridge 45s off the bolt and stays.....you only have to ruin a couple pieces before scrambling for a fix...lol...at four bucks a piece and a couple hours of case prep time it really hurts when one gets ruined...lol

Thank you very much....will try and get a few more pics up of the build....

thanks again

Kurt

Thanks!...I appreciate it!.....

aww man, don't mention cake....it'll start the arfcom running debate of which is better...cake or pie?

but of course cake is....lol

Thanks again!

Kurt

lol lol......I've learned, more like been forced, to rely on the phone for everything over a desktop......it's still a pain..lol

Thanks,

Kurt

The case is ever so slightly heavier than socom brass, but the rim is larger....so it's hard to say how much is mass or metallurgy difference.....the capacity to the shoulder is right at the same best as I can tell.....that was one reason for running the 300 TSX through the cartridge lay-out rather than the TTSX....the TSX has pretty much perfect placement for what I consider 100% load density....

The barrel length is a little over 17" so the powders are the usual socom suspects....H110, 296, 7, lil gun....I'm pretty partial to 1680 and 2200 as I have a good bit of it.....there are recipes out there for 2,000 fps and up socom loads, guys don't usually stick with them for any period of time once they gain a little better understanding of pressure signs not showing up.......it was actually one of these 2,100 fps socom loads that set me on the path to build the RAR....I was really only looking for a little over 2,000 in the summer and right at 2,000 in the winter.....I figured that velocity with the TTSX would be pretty rude to most things

lol...yep, you're 100% dead on....when it first came out I could of cared less about the 30 cal....I wanted to do a 358 and 375.....have both sets of tooling here on the bench...only used once..lol

Again, the thing that set me on the path to do the 458 RAR was some of the really stiff socom loads I found on-line....I figured if that velocity could be obtained with that capacity and be mated to a platform that was a little more pressure tolerant it would be a win / win

I still kick myself in the ass for having a couple of the RAR uppers in my Midway shopping cart and removing them when I decided to work on something else.....they went out of stock a few days later and haven't been back.....

Thanks for the kind words,

Kurt

A couple more build pics....

The RAR extension tennon compared to a typical AR extension tennon




The RAR and AR extensions

Great work!

Tell Pat I said hi, hope he is doing well.

Yes, exactly those two lugs are where it shows first.  Pretty bad when you can see it with the naked eye and headspace is off enough to cause head separation.  That is what did me in during that demo - the back half was stuck on the bolt, I went to pick it off with my finger and the bolt went into battery - that cookie cutter brass sliced the tip off my finger....

Nice on that square shoulder to take some of the thrust!  Yes, finding suitable brass when I first started on the SOCOM was the big challenge.  423 Westley Richards was the other option, as it has the 308 size rim already - that stuff makes the Jeffery brass look cheap!

Very cool! I wish I had the time and money to do this kind of stuff

Some of the parts before finish and assembly....

Thank you....I appreciate it!...

I'll get a few more pics of the build up.....

This is the first day off I've had in a couple months....so it's cleaning bathtubs, toilets, and other domesticated duties today...lol.

That is one of my biggest fears wrenching on ARs.....especially some of the larger frame stuff.....it never fails, I'll be knuckle deep in one and angle it different on the bench and a screwdriver handle or something hits the release perfect

Laying out the tennon.....






Fitting the extension......

You like that cat head chuck alright?

cat-head, spider......works great for most barrel work I do.....using indicating or range rods with a test indicator dialing in less than a thousandth is pretty much the norm....it's a little slow to set up but can be dialed in pretty tight....this particular one is aluminum and steel....it can't be crowded quite as hard as a all steel one, but the spindle on this machine is pretty light so I don't hit it too hard anyway....

With the accompanying spider on the outboard end the barrel can be 'floated' on the brass capped screws without having to use shims....doesn't put any unnecessary stress, bend, or bind on the blank....

Coupled with a coolant system it can be dialed in really accurate for chambering....whichever school of thought one may subscribe to, breech end indexing or muzzle / breech indexing....

Got a chance over the holiday to run some of the 300 TSX loads just a little over 2,000fps...

After a little tuning, they are looking pretty good....



Have been looking for another RAR upper as I would like to find out where the ceiling is, but I'd like a few spare parts in the event this one breaks....til then I'll keep this one under 2,100fps....