Procedures for virgin brass, gas gun

[jlorenzo]

What do you guys do with your virgin brass loaded in a gasser?

I have a small base RCBS sizing die, which luckily enough gives me about .0025" neck tension. Ar10 with a Krieger 20" M110 308 barrel, JP HP bolt (same setup Johhny's reloading bench stuck a case in using regular non small base dies). The Krieger seems to have a slightly tight chamber.

To bump the shoulder .0003-4", the shell holder is pretty tight against the bottom of the die on full cam over. I may have a machinist friend take a few thou off the bottom of the die. Anyone have experience with taking material off the bottom of a die?

I have some Starline small primer match and some Lapua LRP brass, 308. I measure the shoulder and compare with a fired/decapped piece of brass and the new brass never has needed any shoulder bump.

I have been screwing down the case mouth expander in RCBS die, lubing the neck and just running the neck over the expander ball without pressing the entire case into the die.

Other than champfer/debur that's all I've been doing to my virign brass.

Have yet buy an expander mandrel die and mess with that. Since I like to keep things simple and both of my dies for the main calibers I shoot give me around .002-.003 neck tension, I've been sticking with that. I am able to load extremely accurate ammo.

Any thoughts, tips or experience?

 

[243winxb]

Takes about 3 firings, at near maximum pressure , to fully expand brass, head to datum.

 

[DHD]

I chamfer case mouth, chamfer flash hole inside, and run a mandrel on new cases. I won't ever be without multiple mandrel dies, but agree it can be expensive (the die plus multiple expanders)and another step.

The above said, if what you do works for you, and you know you load good ammunition, use what works. I doubt pulling the new cases over the ball one time will cause shotgun patterns.

I don't disagree with 243winxb about fireforming new cases possibly needing a couple three full loads. In my experience that usually is for boltguns, reformed cases (think 6.5 Grendel to 6mmARC), or improved cases. Lapua can take a couple good loads before all is smoothed out as they tend to have hard case heads.

For an AR though, IMHO, the above paragraph may get lost in the noise as there is so much going on. I do load for my AR's the same as for my boltguns, meaning I do just as much and spend just as much time on each load, but I sometimes wonder if I am just superstitious. I don't plan to change what I do, so I can't be superstitious...

 

[jlorenzo]

Thanks for the good response.
I find in my Bartlien barreled 223, I can't see a difference when firing virgin brass.

 

[Mark611]

So far all I have shot is new Starline LP brass from my AR10 308win and SP brass in my 6.5 Creedmoor upper, all I do is run the brass through an expander mandrel .307dia 308win and a .263dia then through a Sheridan slotted case gage to make sure all the cases are in spec, uniform the flash hole trim chamfer and deburr Load a few rounds and check to see if they cycle in the gun, they usually do, then its range time, after I have loaded all my test ammo, Reloading my gas guns, M1A NM, FAL, M77pap {etc} I use a Redding SB die to size all my brass, run them thru a Sheridan slotted case gage then thru a Lee collet die gives 2.5 neck tension, trim Chamfer and deburr, I seat my bullets with either a TC or standard RCBS seating die depending on bullet type, candler or match type bullet, so far I have had no issues with my auto loaders using this method YMMV

 

[64Rambler]

Anyone have experience with taking material off the bottom of a die?

Get a 7/8-14 coupling nut to thread the die into and use the lock ring. A lathe will hold the assembly well without damaging the threads. Take a 0.001-0.002" cut, then debur the ID at the mouth slightly and spend some time with 400/800/1200 grit sand paper and some oil to really polish in a new small radius on the mouth. This will prevent scraping brass off the case.
Another way to get more bump is to put a set of shell holders on a surface grinder and go below the standard "0" (0.125") height. I did a set of 5 in 0.0006" steps. Messing up a shell holder is far cheaper than messing up a die.

 

[Benchrest Braxton]

Get a 7/8-14 coupling nut to thread the die into and use the lock ring. A lathe will hold the assembly well without damaging the threads. Take a 0.001-0.002" cut, then debur the ID at the mouth slightly and spend some time with 400/800/1200 grit sand paper and some oil to really polish in a new small radius on the mouth. This will prevent scraping brass off the case.
Another way to get more bump is to put a set of shell holders on a surface grinder and go below the standard "0" (0.125") height. I did a set of 5 in 0.0006" steps. Messing up a shell holder is far cheaper than messing up a die.

wouldn't it make more sense to take it off the shell holder?

 

[mgunderson]

It isn't common to push the shoulder back on new brass. Shouldn't need it.

Ar10s with the heavy bolt can push the datum back just letting the bolt slam forward in normal operation. Please watch your neck tension.

I personally find these challenging to reload for and shoot well. Can't explain it. Just my limited skill I guess.

 

[Doom]

You can FLS new brass but it isn't going to make every piece uniform. If the datum dimension is shorter than desired it won't be pushed forward unless the body is larger than your die. Even then it may not be enough to get the desired result.

 

[64Rambler]

wouldn't it make more sense to take it off the shell holder?

Yes, but the OP asked about taking it off the die.

 

[jelenko]

I don't do anything to virgin brass for my AR15's. It doesn't impact my groups - all I look for is 3/4 MOA or less.

I do find that virgin brass will tend to scrape some copper off as the bullet is seated - but, again, groups are 3/4 MOA or less.

I also find some case mouths out of round as I'm loading. When I do, I run that case over a mandrel - but running a sizing die just in and out of the mouth would do the same.

 

[Dufas]

Shell holder is really hard steel. Take it off the die. I just used a file as I DON"T cam over the press. Get a case gauge and make real measurements. Insure your brass fits the gun, virgin or not.

 

[SKWERLZ]

Chamfer the mouth and run a .220 mandrel in the neck if it’s lapua brass.

 

[RegionRat]

Chamfer the mouth and run a .220 mandrel in the neck if it’s lapua brass.

OP is asking about 308WIN for AR10.

 

[SKWERLZ]

OP is asking about 308WIN for AR10.

Well then again chamfer and open up the necks a bit if it’s lapua brass,

 

[RegionRat]

The first steps in getting set up to reload for an ARXX of any sort, is to know the chamber details.

There are several ways to go about establishing the brass prep but those all start with knowing the chamber.
I never recommend buying one unless you know the chamber details and if the rig was built for purpose.

Most AR10s and M1A rigs were not built for match shooting, they were closer to Storm Trooper Blasters built to accept NATO ball ammo and run without concern for what they did to their brass.

In order from loosest to tightest, these chambers can be 308WIN commercial, NATO, and Match. A match chamber is rare unless you go looking for one.

A true M110 was meant to be run or tested with the ammo equivalent of M118LR, which is closer to NATO than to 308WIN.

The OP can use sized but unloaded cases to test for ease of chambering. A starting point of 0.002 - 0.003 neck tension will get the rig started with decent virgin LC or equivalent brass. It can be adjusted later if there is any reason, but at magazine lengths with typical bullets there shouldn't be any drama.

There is a gap in philosophy between the M110 concepts versus reloading or match shooting. Uncle Sam doesn't care what happens to his brass once he shoots it, but folks who reload do.

The OP may benefit from catching up on how to establish the basic dimensions of his chamber, ammo, and dies, along with borrowing from the days when XTC was shot with wooden guns.

The Late Glenn Zedicker's old web site had a free PDF on M14 match loading and family now runs his estate, but the older links to his articles on reloading for match prepped M1A and AR10 are now dead links. Here is a link to an abbreviated article by Glenn.

https://midsouthshotreport.com/2017/07/20/reloaders-corner-5-simple-steps-to-m1a-reloading-success/

I suggest the following steps.
Use the GoGage as a reference for all measurements, we want to know how things sit versus 1.630".
Get hold of some FGMM in either 168 or 175.
Measure the ammo in virgin state.
Fire that ammo for a baseline performance.
Measure the fired cases.

In for the range reports and any follow up questions. Good Luck.
Merry Christmas and Happy New Year!

ETA: Had some folks ask again... yes you start virgin brass for a M110 by full length sizing including setting the headspace as well as the neck tension because most sources of brass are not oriented to this type of chamber.

If your virgin FGMM ammo is being crushed to chamber, then set the virgin brass headspace back at least 0.002" less than that virgin ammo.

 

[RabbitSlayer]

Why would a gas gun need some magical initial case prep? Chamfer, mandrel, load, shoot.

 

[Sniper338]

I do the exact same for a gas gun as I do for a bolt gun. If you spent money on a good cut rifle barrel, my belief is get all you can outta it. Worked great for me so far.

 

[RegionRat]

Why would a gas gun need some magical initial case prep? Chamfer, mandrel, load, shoot.

Because some chambers are ridiculously tight and others are sloppy, but that does apply to everyone. You just have to know what chamber you are buying. It isn't magic. YMMV