Is my Lilja Chamber Throat Long & does it matter?

[FW Conch]

^ It is wisdom such as this that restores my faith in the i net ^

Thank You "SG" for a great post and sharing Your extensive knowledge! ;-))

[brut28481]

I subscribe to the "contributing factors" theory. AKA, when the results intended are not achieved, it is typically a series of factors, some major and some minor, that contribute or compound a situation to not achieve the results expected. Furthermore, analysis & response to why the result was not achieved is data & evidence driven. Good data and evidence typically leads to good process change. As it applies to my original post on my Lilja tube, I believe the combination of shooter ability/environment (major factor), reloading/brass prep process (major factor) and gun/barrel/chambering (minor factor) lead to the MOA groups when the expected results would be Sub-MOA. I believe the data I collected regarding the throat measurements supported by cartridges chambering without stick/land marks loaded to 2.34" COAL support the conclusion my particular chamber throat is cut deeper than some & loading closer to the lands increased the accuracy of the system. I also believe that other weapons/shooters with the same barrel/throat dimensions loading typical 2.25" COAL with same projectile/powder will shoot better as many others have posted. My summary: for my ability in shooting & reloading this adjustment to a longer COAL appears to have help make my rig group better bringing me to the conclusion (as a wrap up to the title of my post) that having a longer chamber throat does matter to my ability to shoot sub-MOA.

I have been in conversations with Lilja about my findings and they have confirmed they use an AA/SAMMI reamer and went so far to share the dimensions of the actual reamer used to cut the chamber making this adventure down the rabbit hole even more interesting in that it seems unlikely the reamaer used would produce a long throat in the barrel. Lilja suggested I confirm the headspace as that could be a contributing factor as well. That will be my next step (anyone have a resource for 6.5 Grendel Go/N-GO gauges, I see then can be rented from reamerrentals dot com??).

[LRRPF52]

You can measure headspace with an unfired, then fired piece of brass, using the Hornady comparator.

[brut28481]

You can measure headspace with an unfired, then fired piece of brass, using the Hornady comparator.

This is a series of dots that I have, but yet have connected. I have the Hornaday comparator set (I used it to determine what length to set my shoulders back after fired), fired, and unfired brass and a lot of data on measurements. I probably have everything I need already to answer the headspace. Any chance you could map that process for me or direct me to a read of it? I appreciate the gunsmith lessons!

Side note, my resized brass when set to a slight shoulder bump, which 100% load and function in my chamber, do not fit in my Sheridan SAMMI go/no-go case gauge. Is that my answer to above?

[LRRPF52]

Measure several unfired cartridges with the Horandy tool.

Record those measurements.

After firing those cartridges, measure the spent brass.

Subtract the difference.

Gas guns need some slop in the headspace in order to function reliably, since they don't have the same amount of torque available on something like a manual turn-bolt action, where you can apply off-axis rotational pressure on the bolt handle to force the lugs to cam in and seat a cartridge into battery.

A general guideline is to have .003" of slop in the AR15. You definitely don't want a tight slip-fit with the AR15, like you would have on a benchrest rifle. I've seen BR rifles that don't need the cases sized, because there was literally no growth.

[brut28481]

Measure several unfired cartridges with the Horandy tool.

Record those measurements.

After firing those cartridges, measure the spent brass.

Subtract the difference.

Gas guns need some slop in the headspace in order to function reliably, since they don't have the same amount of torque available on something like a manual turn-bolt action, where you can apply off-axis rotational pressure on the bolt handle to force the lugs to cam in and seat a cartridge into battery.

A general guideline is to have .003" of slop in the AR15. You definitely don't want a tight slip-fit with the AR15, like you would have on a benchrest rifle. I've seen BR rifles that don't need the cases sized, because there was literally no growth.

Got it, I would assume I should be using brass never fired in my chamber (virgin brass) for the "baseline measurement". Brass resized after first firing down .003" shouldn't be in stretching back much more than that?

Once the difference between unfired/fired is measured, how do you determine if you have excess headspace from that reading?

[LRRPF52]

I use my chamber as the final deciding judge in how far I need to size the brass. I don't own a case gauge for this reason, although case gauges can be useful if they were cut at the same time, with the same reamer, by the same competent smith who cut your chamber.

I determine where my COL is with a dummy cartridge, with the projectile colored with a black marker, seated long initially.

I allow that cartridge to be slammed into battery with the action, then extract it carefully, seeing how much land engagement there is. I measure the rifling marks on the projectile, then record that data.

I then seat the projectile .020" deeper than that measurement, re-color the tip with permanent marker, and check function again in the action.

This whole loading process is described in detail in Volume II of the 6.5 Grendel Handbooks, for those that are wondering, in addition to hundred of different projectile and powder combinations.

I have seen the same differences with the group buy Lilja chambers, vs. the SAAMI chambers. Actual accuracy performance for me was noticeable on several barrels from each chamber type, with the long throats normally averaging over 1.2-1.5" for 5 rounds, and the SAAMI chambers shooting 5rds into anywhere from .3" to .8".

There was one particular group buy barrel I had, a 16.5" Wasp lightweight profile, that was a shooter for sure, printing its first 4 consecutive groups into .85" or less, with 2 different types of factory ammo-PPU 120gr MPT and Horandy 123gr SST. The others I tried, including 23" bull fluted and 20" AR740 were difficult to group under 1", if ever.

I switched out one-for-one with a SAAMI chambered barrel from Lilja with the same profile and length/flutes, and it was one of the most accurate AR15 barrels I've ever shot, grouping several times in the .3's-.5's between myself and another shooter. I've posted those groups before here to illustrate the difference.

[Klem]

I agree with 52'...When loading for one gun I use the gun's chamber as the determinant of the headspace, not case gauges.

The Lilja group-buy barrel I have exceeds the headspace of my Sheridan gauge. Sheridan claims to use chamber reamers when machining their gauges and I don't doubt them. So, which chamber reamer is right? I don't think it matters as long as the rifle's chamber is not stressfully larger than the brand new brass you use to fireform and the results on target match your definition of accuracy.

I have taken three pictures of how brass from my Lilja group-buy chamber measures in the Sheridan gauge.



The new 'unfired' Lapua brass fire-forms in the Lilja chamber to measure proud of the 'No-Go' top level of the Sheridan Gauge. The cases are then headspaced down .003" but still sit proud of the gauge. From then on those cases alternate between 'fired' and 'loaded'. After the first firing the cases experience no more stretching than anyone else on this forum who headspaces their cases .003".

I find the case gauge is still useful as a ready-reckoner of whether a round is going to chamber. Slam it in and see if gravity will let it drop back out. It checks axial headspace which is something calipers cannot do. But, it is no substitute for calipers. Like 52', I can live without a case gauge but not calipers.

As for accuracy,
Here are results over five recent shooting sessions of the barrel. I am testing the difference between taper crimping and applying the neck tension before seating, the subject of another thread.

The 18.8" Lilja is giving an average of about 0.8MOA for four round groups. If you shoot three or five round groups you can imagine the metric will be higher or lower depending on what number you use. I have not tested any other 6.5G barrels. There are guys on the forum who are better shots than me but having shot a fair bit of .223 and even though the headspace is longer than the Sheridan gauge this barrel seems OK. And to be fair, there will always be more accurate barrels out there for the finding.



Notes:

• On Target used to calculate group sizes
• No rounds discounted
• Calm wind conditions for all five sessions

[brut28481]

Great response, LRPF52. I have been following your exact process arriving at my 2.34" COL.

Klem, sounds like we have similar chamber cuts. I'm guessing you are running the Nosler 120 BT because you are loading @ 2.25 and this gives you the least jump. Also good data on the crimp vs. no crimp. Seems like we are validating what the experienced reloaders have told us: load close to lands and get consistent neck tension.....

[Kikn]

I had one of the original group but lilja that had the long throat. I have used t hst to my advantage a bit with reloading longer bullets. Although if i use all i got i can load out past mag length pretty easy. But the barrel is still very accurate

[BoxofRox]

I think I'm having the same problem.

I was getting bad accuracy with my hand loads of 30gr, 30.5gr, and 31gr of CFE at 2.265 coal, so I wanted to find the lands. I started out by loading a round at 2.4" and seeing if it would chamber while I have the upper apart and just pushing the bcg forward by hand, and it did. So I loaded one at 2.45" and it wouldn't chamber. I kept shortening it by .005 until it would chamber and at 2.405 it finally did, but it was touching.

So with figuring my lands come into play at between 2.4 and 2.405 coal with a 123gr amax bullet, I loaded some up at 2.365 coal with the same 31gr of CFE I tried earlier with terrible accuracy. I single fed all of them and they chambered and fired fine. The velocity was an average of 60-70fps slower and the group size at 100yds shrunk in half, but is still over an inch. So now I have a problem, the bullet wants to be closer to the lands but there's no way I can load it there and still have a properly functioning AR.

Where do I go from here?

Also, measuring the ID of the necks on my fired cases, they're right around .272, that seems big.

[BoxofRox]

I don't mean to hijack, but I figured everyone in here might be able to help both of us. Anyway, here's my group pics. Only difference is coal.

[Klem]

brut,
I like the 120NBT because it gives the best accuracy of the hunting bullets I have tried. The 95VMax has the best jump of all bullets tested of only .001". Over eight 4rd groups it gave an average of 1.10MOA. The 120NBT is a jump of .006" and over 20*4rd groups gives 0.8MOA. I still have some 95VMax left so should do some more testing. If I find anything interesting I will let you know.

BoxofRox,
Yours is a lot longer jump-to-lands for the 123AMax than my group-buy Lilja. What is your barrel?

What is the outside diameter of your spent case necks? That will give us more of an idea of your chamber necks diameter.

[BoxofRox]

brut,
I like the 120NBT because it gives the best accuracy of the hunting bullets I have tried. The 95VMax has the best jump of all bullets tested of only .001". Over eight 4rd groups it gave an average of 1.10MOA. The 120NBT is a jump of .006" and over 20*4rd groups gives 0.8MOA. I still have some 95VMax left so should do some more testing. If I find anything interesting I will let you know.

BoxofRox,
Yours is a lot longer jump-to-lands for the 123AMax than my group-buy Lilja. What is your barrel?

What is the outside diameter of your spent case necks? That will give us more of an idea of your chamber necks diameter.

It's a Lilja 319 fluted I bought less than 2 months ago. The OD of the necks are right around .300

[Klem]

The specs of a SAAMI Grendel chamber is .300" with a loaded round blueprinted to be around .293" OD neck diameter

https://www.saami.org/pubresources/cc_drawings/Rifle/6_5%20Grendel.pdf

I am thinking, with a bit of spring-back at the time your neck was in full contact during firing it would be fractionally more than .300"