400 ARG

[HMC710]

Test fired the 400 ARMax today for function and brass forming and things went pretty well.


We cut the reamer my last trip home and profiled the barrel. Had a chance to chamber it today. I started with 6.8 SPC brass necked up with custom expanders to get the cases opened all the way up. Starline has their Basic Brass so we just ordered 250 of those so all we have to do is trim to length.

I started at 1.600" case length because of the shorter SPC brass. We'll probably lengthen it out to 1.7 to get the OAL up closer to 2" with the stubby 10mm bullets. Using my modified PMag that I use for the 358 ARMax, but we need to open up the front of that a bit more for the large dia rounds.

Tested with a light load of Lil Gun and 200gr bullets to test and we've got about 10 more grains to go according to QL, so we'll see how this goes. I'll get pics up when I post some.

[HMC710]

I formed these cases a few years ago in anticipation of doing this...



Most of the cases come up shorter that 1.600 after forming so I hope they stretch a bit after firing.



We'll get things apart, cleaned up, and then finished waiting for our new brass to show up.

[paulsblackrifles]

That should be a nice round! I have very good luck hunting deer with the 6.8SPC.

[HMC710]

Thanks. We'll see how it fills the gap between the 35s and 45s. Didn't have much 6.8 brass to work with so we got some new stuff coming.

[HMC710]

Got our box of 6.8 basic brass along with a box of 350 Legend brass from Starline so we went to work cutting 400 brass.



The basic brass comes in at 1.725" + so the easiest trim length was settles at 1.720" which still leaves us well under 2.25"

Left the original 10 Max barrel chambered at 1.600" and did up a new one last night at the new 400 AR at 1.720"



The 10mm Family

Test fired today with some light loads and went with a Mid length gas system and 19" barrel on the 400 AR as the carbine port 10mm Max had plenty of gas. Next order of business is making a new seating die as the stock 10mm works..... but def needs some mods for the 400.

Feeing 2 rounds at a time from my modified PMag for now and will probably try a 350 Legend mag to see how it works.

Might load everything up and head for the range for some chrono work, we'll see how it goes today.

Tim

[HMC710]

Went to the range on Saturday for some load and chrono testing for the new 400AR. My Chrono went dead on my so unfortunately no data there.
Put my Burris 2-7 on the 18" upper and set it up on sand bags with 3 different loads, all with the same 200gr FMJ bullet.
Load 1: 21gr Lil Gun
Load 2: 24gr Lil Gun
Load 3: 27gr Lil Gun

According to QL we still have a long way to go depending on what pressure we want to call good for the 400AR with its 6.8 basic brass. To be safe, we kept everything under (per QL) 35,000 psi.

The 24gr load was a great plinker round and cycled nicely. The 27gr load starts to get your attention and the primers were starting to flatten out. That tells me, we'll hold there for a while and get more data.



Started at 25 yards with a hold just under the Black Bull. Next 2 I held on X, then moved out to 50 yd and framed the bull with the cross hairs at 7:30.

Last 3 were the 27gr load with a hold at 9:00 on the edge of the bull

[HMC710]

Hey All,

Picked up a set of Hornady 10mm dies to see if they could be modified easier than the Lee set. We made some new guts for the seating die and also picked up a Lee Taper crimp. The modified seating die lets us use all of the press handle range and did some more test loads for Barrel #1 which we re-cut to the 1.72.

The brass shrinks on fire forming as it expands to fit the taper of the case which is about .010" over the 10mm / 6.8 base dia. This is similar with the .556/350 legend when using 556 brass. That's why Win went with larger dia brass for the 350 Legend.

My once fire brass still chambered and ejected in the test barrel, so we'll see what happens when we reload some once fired brass. The Speers XTP don't have a cannalure so I can't do a hard crimp and try and stretch things out a bit... We'll see what happens...

[HMC710]

Modified the seating die and used the Lee Taper Crimp for final crimp. Feed and fire was 100%. We then went to reload the once fired brass to see if we can "neck size" the brass, but even with the de-capper pin down as far as we can go we still sized about half of the case. We'll keep playing with it, but I'll probably just send some fired cases out to have dies made like the 257 ARS.

Stay tuned.

[HMC710]

Up at the main shop and getting some die work done....

Doing a batch of our 400AR sizing dies and will work on the seating dies after that. You can "just" get by with 10mm dies, but its a pain so we figured we'ld try to spin some up.



1st operations of the 400 AR sizing die



Will review why type of de-capper we want to use and add that in the 2nd operation, then harden them up, finish, and polish.

[HMC710]

Lots of work done on our sizer while at the main shop



worked on polishing both pre and post hardening

might have to update our geometry a bit on the next set and will verify once we get these polished up

[HMC710]

Reloaded and fired about 20 test rounds last night. Had a couple of bad primers that I thought were short cases / excess headspace, but measurements were all good. Not exactly where I want to be on the seating die so I'll have to check dims on that to see how I want to proceed.

Worked on polishing sizing dies and the more I use them the better they get. Necks a bit loose so we'll see what I want to do there.

Left my can of Lil Gun at the range so switched to 4227. Just test loads to make some brass for sizing so no load data or paper punching....

[HMC710]

Loaded up some 200 gr loads and tested new seating die. works good with last mod. will make a new set of guts for the hornady die set.

[HMC710]

Working on another 400 AR build and lamenting the fact powder supply is lacking to say the least.... I guess its time to just bite the bullet and pay the price for powder....

[paulsblackrifles]

Jan 1, 2022 22:17:47 GMT -5 HMC710 said:

Working on another 400 AR build and lamenting the fact powder supply is lacking to say the least.... I guess its time to just bite the bullet and pay the price for powder....

I'm hoping supplies get more abundant with the new year. If not, then it will depend on the election to decrease the panic buying.

You can find many powders for reasonable prices but it takes too much time from building customer's firearms.

[HMC710]

I was thinking the same thing as I reloaded a batch of 357 sig yesterday......