Help troubleshoot 458 socom, lee 340gr, PC'd 12" accuracy

[RobsTV]

The 12" accuracy is at only 50 yards!

First some details.

AR 16" barrel slugged .457, 1 in 14" twist.
Lee 457-340F, sized .459, Powder Coating (from smoke) and sized again to .4585. 13.7 BHN.
Requires OAL less than 2.030 to reliably chamber.

First function and chrono test, 5 of each (based on Quickload for estimates):

28gr 4227, OAL of 2.020, Lee 342gr
1492fps, pf=509, 1696 ft/lbs, ES-79, SD-31


30gr 4227, OAL of 2.025, Lee 342gr
1617 fps, pf=552, 1990 ft/lbs, ES-82, SD-34


32gr 4227, OAL of 2.020, Lee 342gr
1676 fps, pf=568, 2110 ft/lbs, ES-91, SD-34

The 28gr 4227 had 2 FTE, so pushing below min required with this load. The rest tested fine, zero leading. Zero accuracy.

Next test to get some starting point accuracy, 5 test loads from 29gr to 31gr in 1/2 gr increments, 10 rounds each.
All cycled and brass looked great. Zero leading.

At 50 yards, scoped on bi-pod, they all seemed about the same 8" to 12+" accuracy.

Have read 458socom forum, which does not seem too keen on cast boolits, especially when PC'd, and very few posts on subject. Some say never could get accuracy with lead unless gas checked. I can't see how that could make this much difference. On a somewhat related note, switched from GC S&W 500 to PC and accuracy "increased" 4 fold with Powder coating and no gas check, so I hate to go back to old ways now that I've seen the light. 300 Blackout here has only ever seen powder coated without GC, and sub moa with 155gr Lee at 1850fps results every time.

Could Gas Checks really improve accuracy at 50 yards 12+ inches to MOA? Should I try some PB gas checks (they have helped troubled guns here in the past, before I found Powder Coating)?

Or hopefully, I just picked a mold that is no good for this, and simply need to get another mold, which would be ________? NOE around 350 to 425 in stock preferred.

Also haven't seen 4227 posted as a bad powder for this caliber. Have some Ramshot Enforcer to test if it would make a difference this big.

Giving up Powder Coating would be last resort.

Also have a Lee 457-450F but after seeing the results from similar profile 340F, didn't want to waste time unless it is known to work. Won't be running subsonic for at least a year or more.

[44man]

Everything sounds good. Have you checked boolit run out?
Two other things to try, a slower powder and I bet even Varget would work. I got it to work in the 7BR and 7R when I was told no from Hodgdon, they more or less laughed at me.
Then try a harder boolit.
I never had any luck with the 4227's except the .357 max.

[montanamike]

http://accuratemolds.com/bullet_detail.php?bullet=46-350S-D.png


I use this mould for the Socom and it is perfect. Great accuracy and perfect function. Let me know if you want to try them and I'll send you a few. I started a thread on these boolits you can find it here. http://castboolits.gunloads.com/showthread.php?292073-458-Socom-Cast-Boolit-Data

[popper]

PC is fine, brush off the PC from the base - it is NOT a GC. 4227 should be fine. Try a few loaded into the chamber - could have feed issues with dinged noses. The base has to be really good for accuracy at that fps. Might check with Smoke - he does socom. I tried PB 185 pushed hard in BO, got the same results you do - it's 'almost' a straight wall case. That Lee boolit doesn't have much of a rear drive band.

[RobsTV]

Thanks for the replies.

I guess a couple things that have me confused are, the 500 S&W, a much higher pressure cartridge, shooting the same powder in a gas check 440gr boolit at 1350fps without a gas check (shank still present), only powder coated, and it shoots great from 8" revolver. Can say the same for the higher pressure 300 blackout, gas check left off, zero issues simply powder coated at 1850fps, and that thing has hundreds of rounds through it during a typical range session.

With the loads I use, Quickload shows:
458 socom, 340gr 16": 22,000psi
300 Blackout, 155gr, 16": 42,000psi
500 S&W, 440gr, 8": 35,000psi

The alloy used for 458 socom is the same I make for the 500 S&W and 300 Blackout, but if you think harder would be better, easy enough to heat them up.

montanamike, thanks for the link (and the test offer). I see you are traditional lubing though, and the mold has a gas check, both things I am trying to avoid. I do also have the Lee 405gr hollow base mold someone mentioned about in the thread you linked to. But prefer to use something that produces more than 1 boolit at a time. Awesome for trapdoor BP 45-70 though.

EDIT: I really do not like the boolits from the Lee 457-340F much, and prefer more taper in an AR, much like the ones shown from Accurate molds. Also, I will go with a gas check if I absolutely must, but powder coating cleanliness, ease and speed of applying (dry tumble lube) is something I don't want to lose. Lyman 4500's already been switched over for dedicated black powder lube sizer.

[Tackleberry41]

May just not be enough driving band in contact with the barrel without the gas check. Thats the easiest thing to try is some w gas checks.

[RobsTV]

Here is the Lee boolit being used:

178116

[dkf]

Make sure your bullets aren't getting swaged down by the neck. I use the NOE expander plugs but it seems to me even them are little tight.

I'd try out some PB gas checks from Sage or make your own. I'm guessing you probably have a 1-14 twist and they are not known for being the most accurate with light lead and jacketed bullets. That is one of the reason I got the 1-18 twist Tromix barrel, I want to shoot a lot of supersonic cast. I have been using the NOE 350RF, 350gr and 405gr piledriver clones from an Accurate mold with decent results. Accuracy was on par with 300gr jacketed at 50 yards. That was sized .458", going to size .459" and .460" to try too. I've tried bullets at 9-10bhn and some at 22-24bhn, edge seems to be with the softer bullets. Going to stretch it out to 100 now that load development is pretty much done. I've been using Norma 200 and IMR4198 for powder but I have some loaded with Ramshot TAC just to see how they do.(didn't get to shoot them yet) Lube is a 50/50 mix of BAC and Carn red, copper gas checks.

[popper]

You have a 345 neck - where does the L.G. sit?

[RobsTV]

Using the larger Lee expander for 45-70 from Wolf (?). The Lee PTE for the 458 socom uses the 45-70 part number, so Wolf perfect fit and .001 larger than stock.

Thanks for the push. Ordered some PB gas checks from Sage.

[dkf]

With a .459" bullet I'd be using the .461"x.457" NOE expander. You can get away with a little smaller expander on a harder bullet. The Lee expander is borderline too tight even for a jacketed bullet IMO.

[RobsTV]

With a .459" bullet I'd be using the .461"x.457" NOE expander. You can get away with a little smaller expander on a harder bullet. The Lee expander is borderline too tight even for a jacketed bullet IMO.

It's not a normal Lee made expander that Wolf sells.
Wolf has them in several sizes and it was what corrected the soft lead black powder Lee 405 hollow base .459 boolits from being sized down by 45-70 brass. Now using the same plug with 458 socomm and pulled boolits measure .4580.

https://www.trackofthewolf.com/Categories/PartDetail.aspx/1178/1/DIE-458-EXP (http://www.trackofthewolf.com/Categories/PartDetail.aspx/1178/1/DIE-458-EXP)


The wolf expander is on the right. The dark stuff is not rust or corrosion, but simply changed color scar from a ton of black powder case use.

If using the stock lee PTE for 458 socom, it works O.K for shorter boolits, but for boolits like these, because of the taper it does not enlarge brass far enough down into case, causing the brass to resize the bottom of boolit base to .456 (tapers it slightly).

178145

[RobsTV]

Update.
First time back out with a few new loads to try, and now shoots great, thanks to some of the tips given here!

Plain Base gas checks fixed the Lee 340g to now be decent at 50 yards. Cast some 450g Lee as well, using same plain base gas checks, and the slower speed worked best with the upper's 1-14 twist.

Here is photo of two separate 450g 5 round groups at 50 yards. Shot rested on the side of a pickup truck bed with scope sighted in for 300BLK, so just a rough accuracy test to get started with. Looks like could nearly put 5 in a 1/2" hole when using dedicated gear.

181252


This was the best load I could get with 5 rounds of 340g. The flyer was my fault.

181253