.458 frustrations

[nbowlin]

I have a 16" .458 socom. I have a thing on the end to help with noise. I ordered some 400gr sbr subsonic and it's supersonic. I ordered some black butterfly 500gr subsonic and it's supersonic. I ordered dies and bought some cheap Speer 400gr spfl stuff for the sake of science. Started at 11.5gr of unique and large pistol primers. Went backwards to 10.7 and got that air compressor nozzle being depressed noise I was looking for. Loaded some more to work on getting the thing to cycle. Well the first 3 were air compressor sounding. I am cutting down the buffer spring between firings. Then there for after back to super sonic. I went all the way down to 9.5 from 10.7 and never got back to sub sonic.
Nor does it cycle but that's another aggravation.
How can this be a thing?

 

[yorke-1]

Have you considered using an adjustable gas block to address the cycling issues? That would let you focus on finding the velocity you want and then resolve the cycling issues separately.

 

[Zen Archery]

Contact Tony Tromix. He's been through it all with the .458

 

[nbowlin]

Doesn't work Saturday.....or answer the phone.....like a smart guy I spose.

The adjustable block I think would be more for taming exhaust down? I have opened up the gas port on the barrel and hacked the spring into a form of useless I believe.

 

[yorke-1]

Doesn't work Saturday.....or answer the phone.....like a smart guy I spose.

The adjustable block I think would be more for taming exhaust down? I have opened up the gas port on the barrel and hacked the spring into a form of useless I believe.

Cutting the spring down only made things worse. Unless you're very experienced with ARs, modifying gas ports and buffer springs is a bad idea. An adjustable gas block would have allowed you to tune the gas system to suit your needs without permanently modifying anything.

Your best option is to replace the buffer spring and buy a good quality adjustable gas block. Work on a load that gives you the velocity you're looking for, then adjust the gas block to give the proper cycling.

 

[Dean2]

TRy using Trail Boss. It will go subsonic NO PROBLEM. Whether it will cycle the gun I have no idea as I shoot levers and bolts but it does produce pretty good pressures even at fairly low speeds. I have used it in 17 HH all the way to 460 Bee and no problem getting subsonic on any of them and no problem getting the cases to seal the chamber..

 

[mtwarych]

Like the post above, I would suggest trying a different powder.

 

[cohunt]

Trail boss most likely wont cycle an ar--- check with Tony for proper powder and gas port size when he is available.. patience is a virtue

 

[ntsqd]

Bought a Superlative Arms Adjustable Gas Block for one build. Dialed in the cycling extremely easily. Now I won't use anything else. Recommended.
https://suparms.com/collections/adjustable-gas-blocks-direct-impingement

Sprinco buffer spring solved the cycling problem in a .40 S&W PCC, also recommended.
https://www.sprinco.com/ar-buffer.html
EDIT: Sprinco makes quality springs in different spring rates, read their page for recommendations.

 

[T3ninja]

One thing that hasn't been mentioned is the gas system length. I'm assuming we're talking carbine length. This might be near impossible to get cycling AND subsonic. Think .300 BO. Even most rifles have a pistol length gas system.

Cutting springs generally only ever makes a problem worse. I haven't looked so I can't say if it exists, but I know these things usually help with working up loads for subs, and getting cycling. Get a heavier bullet, you will get the same pressure (for cycling) with lower speed. Try a different powder. You can open the gas port as you described and as long as you don't go TOO big, you'll be fine and won't have any adverse effects because you can always throw an adjustable GB on and tune it down for supers. You need this anyway.

Other option, maybe try a super lightweight BCG.

 

[jfloyd]

I've had the 458 for 6 plus years but never wanted subsonics for it. Who's parts are you using? Tromix is THE authority on the 458S. Unique is not the correct powder either. Do not modify anything until you use Reloader 7, or IMR 4198. I would not modify anything either then until you speak with the manufacturer of the upper/parts or Tony. A proper upper will function without any modifications to the gas port or springs with the appropriate powders. Again Unique is not appropriate to function as the round was designed. Way too fast so you port pressure will be too low to cycle the action. Same for TB. Use the 458 SOCOM forum search function. You will find most issues discussed there as well.

Good luck!

 

[Hookdown]

Another vote for contacting Tony at Tromix. Since he built the very first .458, and it was for SOCOM, I doubt anyone knows more than him about the caliber AND getting it to make those air compressor release sounds reliably.

 

[jfloyd]

One other note, big bore AR's cannot be tuned like a 556. In almost every case, modifying to correct a problem turns into throwing money at a problem that should not be there and will eventually result in fixing the original problem only after you have wasted a lot of time, money and components trying to put a bandaid on the problem. Many people give up and sell the problem to another owner which has resulted in an untrue reputation for feeding issues. These issues are again almost 100% caused by bad chamber reamers, botched barrel extensions and wrong gas ports or port locations.

 

[MZmoose]

Most of the subsonic loads I've seen for the 458 are with 500gr to 600 gr bullets. I suspect those heavy bullet loads would have enough pressure to cycle the action and still be be subsonic before your modifications. I think trailboss would be a better powder, unique is a pretty quick burner.