Is my Lilja Chamber Throat Long & does it matter?

[brut28481]

I have been working on my 5-shot groups with various loads for a few months, trying to get better, they are somewhat inconsistent. I also ran my first PRS match over the last weekend (wow that was a learning experience!) with the Grendel and was talking to 6mm BR guys about accurate reloading and that got me going to the ogive/bullet jump path. Summary, I measured my Lilja AR24 drop-in barrel lands-ogive with the hornaday OAL tool arriving with the following averages (6-8 measurements)

123 amax - COAL = 2.34, base-ogive=1.75
107 SMK - COAL= 2.35, base-ogive= 1.75

Given all my loads are around the 2.25 COAL, base-ogive= 1.65 (123 amax), that gives me a jump of 0.1! Seems way over most recommendations of 0.02. Haven't messed with longer COAL yet. Looks like the AA Grendel mags are good to 2.8ish?

Lilja indicated this is a SAMMI Chamber, is it out of SAMMI spec?

[ricsmall]

I had a bartlein barrel chambered by Templar custom and it was very close to your seating depths. It was saami as well. It was also the most accurate Grendel barrel I've shot so far. It shot from 76grain to 160 gr pills to almost same point of impact, with great accuracy out to 900 yards, and was never picky about loads. It was definitely long throated, but it was a hummer.

Richard

[Joseph5]

I would trust what Lilja says. The compound throat makes measuring difficult sometimes because it is a very gradual constriction and not a hard stop. You should be able to load out to 2.30 with most mags, check for function but that will give you less jump. I have the same barrel, if I am remembering correctly I am loading 100gr AMAX to 2.20 and 123gr SST to 2.275. It doesnt seem to matter with my barrel. It shoots everything great. Load a ladder to find you most accurate charge then load a ladder for OAL with that charge and you should be able to find your sweet spot.

[brut28481]

Interesting. My barrel seems picky. A lot of the go-to loads from the hoard (123 Amax & CFE for example) don't group at all. Everyone's response seems to be the same with Lilja, shoot great and shoot everything great.....I'll mess with seating depths and see what happens.

[LRRPF52]

That seems long, like one of the group buy chambers.

What do your necks measure in diameter?

[brut28481]

That seems long, like one of the group buy chambers.

What do your necks measure in diameter?

They are somewhat deformed and not uniform, they range from .295-.310 for neck, shoulder is 1.2190" after fired. I am resizing with redding busing die using the .288 bushing and bumping the shoulder back to 1.215"

[Klem]

brut,

That sounds about right.

I have a Group-buy Lilja and have measured the jump for the following bullets as;



I have the same measuring equipment and load to 2.224 - 2.25" base-to-tip (COAL) to feed reliably from the mags I use.

The shortest jump-to-lands is the 95VMax however this is my least accurate bullet. The 107Sierra MK and the 120Nosler BT are the most accurate.

Does anyone have a chamber that is shorter than their mag length?

I've always thought that as far as jump-to-lands in an AR Grendel goes we load as long as the mag will permit to give the shortest jump and maximum case capacity. The popular bolt gun recommendation of a 0.02" jump is impossible in my chamber for all but one bullet I have tried.

My spent cases are averaging 0.2880" at the neck.

[brut28481]

I decided to continue on my journey of loading 0.02" off the lands to my measured chamber for my go to 123 Amax Load of XBR @ 25.1 clocking in at 2,545 FPS. Based on above info, this required a COAL of 2.34 not fitting into the AA/E-Lander 10rd mag. Hence, mag modification required. So goes my Gen 1 Franken Mag (I would assume some on this forum have done this in the past?):


Amazing they fed. Groups don't lie: 2.25" COAL +/- 1 MOA:

2.34" COAL (My personal best ever & with this rifle. Given my experience & skill level, this is outstanding) 0.6 MOA:


Summary, loading closer to lands definitely tightened up my groups. Now the next debate, do I return the barrel to Lilja to have the throat shortened (can they do that or does the chamber have to be re-cut?) Or continue to run the franken-mag when i want to shoot long?

[Klem]

I guess one way to find out would be to fire a number of groups with your .02" jump length from the modified mag, and then fire the same number of groups, same load, with a shorter COAL that fits an unmodified mag.

You will probably find it is nigh on impossible to shorten your chamber without being charged an amount equal to the cost of a new barrel. Shortening the chamber is one thing, until you have to machine it to spec with the gas port still at 12 O'clock.

[ricsmall]

Klem is right on the shorter chamber. It'd b easier to chamber a new barrel than to pick up threads for extension and lengthen the tenon. Then is the matter of timing the extension back to 12:00 to match gas port, which would require a custom length gas tube after the above modifications. Not impossible by any means, but a small pita.

Richard

This is based on my experience of machining and chambering barrels, the Lilja guys may have a completely different take on it.

[Joseph5]

Try 2.30 and see if those will feed from un-altered mags and what kind of groups you get.

[maxxmojo]

I recently acquired a 319 Lilja barrel and I'm seeing similar results. For comparison's sake I also nabbed up an AA 16" Incursion upper. As seen by others the Lilja barrel seems to do really well with 120gr PPU, however I tried some factory 123gr AMAX and SST and it didn't seem to care for either of them. The best SST 3 shot group I came up with was 1.680" CTC, AMAX averaged around 1" (which isn't that bad honestly), and the PPU average hovered around 0.5", best 3 shot group was 0.345". I went with 3 round groups due to having only one box of each type of ammo at the time.

I recently picked up a bunch of 123gr SMK's for reloading, and I've been trying to nail down a load for them for the Lilja. One interesting thing I wanted to share was I loaded an empty shell with an extended SMK at 2.366 COAL. I wanted to see how the cartridge chambered in both barrels comparatively. Surprisingly, the Lilja chamber gobbled it up and I was able to get a closed bolt that would fire. In the AA chamber the bullet was clearly hitting the throat way before I could even dream of getting the bolt in there.

So I'm not sure what reamer Lilja used for but I'm confident it's not SAAMI spec whatever it is, which is a bit disappointing. Necks on fired brass did measure out to either .2995 or .300 though, for what it's worth. My current running theory is that the Lilja throat is opened up for whatever reason, but it should work well with tangent ogive style bullets which is why the PPU runs so good in it.

By the way the AA upper absolutely hates the PPU.

[terrywick4]

One interesting thing I wanted to share was I loaded an empty shell with an extended SMK at 2.366 COAL. I wanted to see how the cartridge chambered in both barrels comparatively. Surprisingly, the Lilja chamber gobbled it up and I was able to get a closed bolt that would fire. In the AA chamber the bullet was clearly hitting the throat way before I could even dream of getting the bolt in there.

So I'm not sure what reamer Lilja used for but I'm confident it's not SAAMI spec whatever it is, which is a bit disappointing. Necks on fired brass did measure out to either .2995 or .300 though, for what it's worth. My current running theory is that the Lilja throat is opened up for whatever reason, but it should work well with tangent ogive style bullets which is why the PPU runs so good in it.

By the way the AA upper absolutely hates the PPU.

Was the empty cartridge shot from the Lilja? If it was that could be one reason that it didn't fit in the AA and doesn't necessarily mean that it isn't SAAMI spec just the AA chamber might be on one side of the spec and the Lilja is on the other.

[maxxmojo]

Was the empty cartridge shot from the Lilja? If it was that could be one reason that it didn't fit in the AA and doesn't necessarily mean that it isn't SAAMI spec just the AA chamber might be on one side of the spec and the Lilja is on the other.

Shot in the Lilja and resized in the dies. It was clear that the bullet was engaging the throat as the shell still had some wiggle room since it wasn't even close to being in all the way.

[SG4247]

I have a gun rack full of custom built Grendel rifles in AR-15.

After exhaustive measurements of several chamber designs, from several manufacturers and most all 6.5 bullets to determine ine the distance to the lands, i determined that my time was better spent making good brass, testing powders, charge weights, primers and bullets. Seating depth is not a variable in the case of the Grendel barrel made with most commercial reamers on the market.

Now, these are very top end builds, with every effort to make them accurate. So, the hardware is the best it can be.

Load length for 90% of them is 2.245". Lighter bullets (if I was to ever shoot them) might be shorter.

All of these rifles shoot between .25 to .5 MOA at this length.

One of the most accurate barrels I have owned, was the group buy Lilja.