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Old June 19, 2017, 06:07 PM   #51
stagpanther
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Looks like something you'd shoot at another battleship!!
Exactly--resembles a 16" or 18" main battery shell--I thought the same thing.
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Old June 20, 2017, 02:18 AM   #52
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What charge weight did you use?
Much of the "popular" load data on the 'net is over-pressure.

(Just trying to prevent potential headaches and/or parts breakage.)
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Old June 20, 2017, 06:29 AM   #53
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I'm running 28 to 30 grs. of lil gun driving 300 gr tac tx's seated to a COL of 2.25 (seems to be about where they end up right on the middle of last cannelure) which should put my max pressure somewhere around 33,300 psi. I've dry-cycled in my build and the cartridge makes it in and out without any issues--being such a blunt projectile doesn't seem like much of an "opportunity" for it to hang up in the chamber or throat upon feed. By sheer coincidence--the cavity back mags that I bought for my 6mm predator project--and which seemed to hang up the cartridge's grendel base design--so far appear to work just fine in dry-fire tests in the 458 SC.

I took a look at the 458 socom forum and some of their load data there--and I saw where some folks were bumping up on pressure signs on using what theoretically should be a safe charge. I also took a look at Barnes (quite old) test data--kinda left me scratching my head since QL was returning low numbers.

Looking at the default value in QL for barnes part #30640 it lists a bullet length of 1.280. HOWEVER upon measuring the bullets I have with same part number they consistently come up with a length of 1.239--as well as a slightly shorter shank/seating depth. Why the discrepancy? I then remembered that barnes did the same thing when they rolled out the their "MIL LE" version of the 308 tac tx for the 300 BO--in other words they took the existing bullet and "tweaked it" for specifically one cartridge--changing the box color to black and putting the "MIL LE" designation on it. That 300 BO bullet, by the way, is by far the best shooting bullet in my 300BO pistol--I'm hoping this incarnation in the 458 SC is similarly good.

I have to say though that many of the tac tx's and the ttsx's that I bought for the 458 look a bit crude in finishing--the plastic tip stuff appears to have melted flashing hanging over the sides of the bullet's tip cavity--not impressed with that.
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Old June 20, 2017, 02:03 PM   #54
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28 gr to 30 gr should be in the ballpark. It's possible that the heavier charge weights might show signs of approaching the limit, but they'll probably be okay.

Be sure to keep the ammo in the shade for testing, as well. For some reason, Lil Gun is very temperature sensitive in this application -- as you may have read on the other forum. Several of us that ran, or still run, Lil Gun behind Hornady 325 gr FTXs ended up with two or three different load levels for different seasons. (Summer loads, winter loads, etc. )

In my opinion, QL can't be trusted with .458 SOCOM (and offspring). The predictions are so far off the mark that I've totally given up on trying to make it work.
I've tweaked all kinds of stuff, including the Ba values for specific powders, in order to get the data to at least come close. And it has worked to some extent. ...Until I changed COAL or went to another bullet. Then everything was way off again and had to be completely reworked.
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Old June 20, 2017, 03:02 PM   #55
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I think I understand what you mean--I took my first shot today with 28 grs and was following the Superlative Arms directions for bleed-off instructions (start with no cycled gas and work your way to open so the bolt locks back--more or less the opposite of a DI block)--so basically I had no gas pressure in the system--not sure that was a great idea. The case came out but it took a hard pull on the charging handle--The primer looked fine but I measured .004 expansion at the case head. I'm concerned--and I've learned from experience to listen to that inner voice.

I've loaded lil gun in lots of 44 mag cases--I think you might be right about "unpredictable" behavior in the 458--it seems to need a certain amount of "airspace" inside the case along with the powder volume to get the best burn efficiency--otherwise alot of ends up unburned or going out the muzzle in a fireball. I'm seriously considering pulling all the rest of the bullets--but lil gun does seem to be one of the major "go to's" on the 458 SC forum. Maybe I should look at win296/H110 or 4227??

PS--biggest wallop I've ever felt from anything in an AR 15
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Old June 20, 2017, 06:33 PM   #56
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@Franken--OK--after thinking about it (for maybe 5 minutes) I decided to reverse the gas block approach and start wide open and dial it down as I went--in other words I went out and shot the rest of the test group.

No pressure signs at any of the charge levels--even the case heads looked good--I guess they just stretch a bit more cause of the chamber and don't snap back as readily.

Howvever--I still got problems--the cavity back mag didn't work as well as I thought once I loaded up multiple cartridges--single stacked they had a propensity to pop out of teh mag and jam--so I reverted to single feed. The other issue was ejection of spent cases--sometimes they would go 5 ft away to my 4:00--other times they would barely fall out of the ejection port--and that's whithin the same charge range. I figure there's probably something with dwell time going on--I'll put a higher power extractor and ejector springs in and see if that helps any.

Unfortunately I couldn't get much meaningful data--though this group (29.2 grs) almost came together barring the flier in the lower right.



Without a doubt the most powerful AR 15 variant I've ever fired--the recoil felt like something between a 308 and 300 winmag
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Old June 20, 2017, 10:21 PM   #57
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Not a bad group.
It's a fun one, even if there are teething problems, isn't it?

I'm glad you got the loads to run.

As for ejection...
I have two primary theories:

1. You're over-gassing it, and the small variations in charge weight and chamber pressure are changing the delay until the case releases from the chamber. The lack of brass deflector on the upper may be a contributor to the strange pattern(s).

2. (More likely?) I'd say it's probably a burr on the extractor, or too sharp of an angle on the extractor hook. Both problems (often found together) are very common on extractors made by anyone other than Tromix or RRA (even other "approved" makers). And, everyone makes mistakes. My first Tromix extractor was bad and caused stove-pipes or cases actually stuck on the extractor (smashing mouths on the ejection port and ruining those expensive cases ). Usually a little deburring and stoning can get them to run. Or, you can contact the company and ask for a replacement.
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Old Yesterday, 02:16 AM   #58
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Quote:
Not a bad group.
It's a fun one, even if there are teething problems, isn't it?

I'm glad you got the loads to run.

As for ejection...
I have two primary theories:

1. You're over-gassing it, and the small variations in charge weight and chamber pressure are changing the delay until the case releases from the chamber. The lack of brass deflector on the upper may be a contributor to the strange pattern(s).

2. (More likely?) I'd say it's probably a burr on the extractor, or too sharp of an angle on the extractor hook. Both problems (often found together) are very common on extractors made by anyone other than Tromix or RRA (even other "approved" makers). And, everyone makes mistakes. My first Tromix extractor was bad and caused stove-pipes or cases actually stuck on the extractor (smashing mouths on the ejection port and ruining those expensive cases ). Usually a little deburring and stoning can get them to run. Or, you can contact the company and ask for a replacement.
Thanks for the comments and suggestions. I did stone the extractor and ejector when I first got the bolt--also I'm not getting any notable damage to the case rim where they contact. I'll take the bolt apart and power-up the springs and see if that makes a difference. Got tons of 5.56 mags lying around around--be sure to use one of those next time.

My shoulder is actually a bit sore!

Are there other "go-to" powders other than lil gun for the 458 SC? I know from my 44 mag SBH even in a revolver it has a bit of a "reputation."

I found on Nosler's website their formula for their spitzer which is not listed in QL. Their top load is driven by 4227--which I suspected was a possibility so I'm going to give that a try next/
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Old Yesterday, 11:00 AM   #59
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In my wanderings over to SBR site I could help but notice the 338 Spectre. I took at look at it's ballistics and it seems like it's performance falls off compared to the 458--my guess is that's because the higher BC/SD bullets encroach more on case space.

In my experience in building AR 15 hybrids--so far the 458 socom seems like the top of the heap in terms of energy delivered as a CQB type weapon--I have no trouble imagining it would be a devastating hunting weapon at close ranges as well close being maybe 150 to 200 yds or less.
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Old Yesterday, 12:34 PM   #60
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I usually have a bruise the day after a session with the SOCOM/Tremor.
It makes me look like a pansy, but I can't stand to shoot with any kind of padding between me and a rifle.


Lil Gun, H110/W296, N110, and the 4227s are the "go-to" powders for standard loads.
I've seen loads shared that used everything from X-terminator (too slow) to 800X (questionable). I've seen a few people that say the 4198s work well with 325-405 gr bullets, but I have my doubts and haven't tried it myself.

Most guys, like you and I have done, jump in with Lil Gun, since there's so much more data to get started with; and then we can at least have some trigger time and do some testing while looking for the next load.

For heavies/subs, Reloder 7, H4198, Norma 200, and VV N120 seem to get a lot of talk.
Some guys have had good luck with Trail Boss, but others have had nothing but problems.

My "go-to" load in .475 Tremor actually uses Norma 200 behind a 275 gr Deep Curl. It's a filthy application, since the powder is too slow - especially for the light bullet; but it runs well, is very consistent, has good case fill, burns well enough to not leave a lot of powder granules, the rifle doesn't get fired enough -overall or in a single session - for the fouling to become a problem, and it still provides unexpected velocities (1,800+). ...And it is, at least theoretically, a much "cooler" load than Lil Gun.
One of these days, I'll work that load back up with H110 and see how it does. One of these days.

I really need to get some 4227...


I have not yet been able to take any game with mine, nor has cornbush (the new owner of my .458 SOCOM upper); but we've been very impressed with clay, water, and wet-pack performance. It just seems to do things that calculations on paper say it shouldn't.
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Old Yesterday, 03:01 PM   #61
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Fortunately I have all of those powders--because I load a fair bit of magnum revolver rounds--and when is all is said and done--from what I can tell so far, that's more or less what the 458 socom boils down to--it a BIG pistol cartridge being pushed through an AR 15 but has some pointy bullets.

I've built quite a few AR 15 variants--but it's very rare that a new flavor brings something outstandingly different to the table--but this one does IMO. Except possibly the other big bores like 450 bushie and 50 beowolf--I can't think of one that projects so much power out to the range that it does.

Rest of the parts to complete the build came in today, so the receiver it was meant to have is now mated to the upper. I also upgraded the ejector and extractor springs, as well as installed enhanced buffer and buffer spring.

I'll see how it all works out.

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