Issue : Help : 123 SST Ogvie to Lands measurement 18" Alexander Arms Lite Barrel

[Nachunter]

Hey Horde, let me quickly introduce myself.
I have been trolling around this forum for quite some time (Since mid2012 or so)… I have built 2 Grendels, but took a hiatus for a couple years in reloading since I moved to Dallas. Not much chance to shoot Mid-Long range around the city, and it is hard to drive 3+ hours to my land just to shoot. A lot of good information for reference has been shared over the years from what I have seen. Obviously by my post count, I do not chime in usually… would rather just read and analyze/test my own data.

I have an issue that hopefully the crew can help provide some explanation. I cannot find exactly what I’m looking for in past post...I don’t think.

I’m measuring Ogive length to Lands on various bullets using Hornady OAL gauge and Hornady 264 comparator and insert… I know my Ogive measurements will differ from everyone else’s due to instrument variance… though they seem about .01” shorter than others I’ve seen posted on here.
Upper Assembly:
18” Alexander Arms Lite Barrel 1:7.5 Twist (Bought 2012…AA does not make 18” anymore)

My Ogive to Lands Measurements:
123 AMAX = 1.667 / COL 2.255
123 SST = 1.655 / COL 2.231
120 NOS BT = 1.704 / COL 2.245
107 SMK = 1.690 / COL 2.288

Factory Ammo Measurements:
123 AMAX = 1.656 / COL 2.245 LOT# 3131866 (.01” Jump… which would help explain why Factory 123 AMAX is amazing accurate in this barrel)
123 SST = 1.660 / COL 2.240 LOT#3140581 (.005” should be jammed into lands?) (10RNDS CKd 1.659-1.662 Ogive)

My conundrum is shouldn’t the 123SST be pushed back into the case .005” when chambered, or at least have marks from the lands on the bullet, or be hard to extract? None are the case when I chamber a round.

Is it possible with the compound throat of the Grendel I am not actually hitting lands with the OAL gauge? The bullet is actually stopping in the throat just before the lands start?

[JASmith]

I have experienced similar conundrums.

Try painting from the neck to about 0.5" up the ogive with a permanent marker. You should be able to see whether you have a "light kiss" per Bill Alexander.

The 0.5 degree taper where the freebore would normally be opens interesting possibilities with user thechnique.

[LRRPF52]

Welcome aboard.

All your data looks fine to me based on allowable and typical COLs.

The initial .5 degree angle of the compound throat is a light kiss into the bullet once you touch it, but normally isn't enough to jam the projectile to cause hard manual extraction.

You have to load longer than allowable to jam the lands usually.

Looks like you have a good set of data on where you are at with regard to COL.

[Nachunter]

Thank you gentleman, I was hoping one of you would reply.

I will try the marker technique and see what I come up with. I know .005" is rather small variance in OG length, but figured I would have some evidence of the lands. Checked the length to lands (or what I thought ) multiple times to verify measurement.

I do have some hands loads set at about 2.26. Loaded for my previous barrel. They shot terribly last outing, but I did not think to check throat length. I will chamber some and see if any evidence of the lands are present on them.

[Drillboss]

Nachunter, here's a diagram of the Grendel Chamber:

Chamber Diagram.pdf

The ID of the Hornady comparator is 0.254", so it's contacting the bullet further forward. Like the others indicated, that initial 1/2 degree taper is really subtle and I think you can impress the bullet into the rifling without really feeling it.

It's not on the diagram, but the rifling (0.264" groove diameter) first appears at 1.5707" from the bolt face.

[Rickc]

COL for factory.123 gr Hornady SST is 2.45. I believe that is the recommended COL in the Hornady reloading manual.

I am playing with seating depth too. Trying to find that magic.combination

Anyone out there trying the 123 Lapua scenar

[Nachunter]

Drillboss,
Thank you for providing the diagram... this was a major help in visualizing the chamber... I'm surprised I hadn't seen it previously... After the fact I found where you provided in other threads.

Ok so I confirmed with the marker trick, in my chamber factory 123SST with 1.660 BTOG length is touching the throat. I also chambered some 1.675 BTOG rounds and they were slightly sticking in the chamber.

I resized all my past 123SST loads down to either 1.645 BTOG or 1.650 BTOG (.01" / .005" Jump). We'll see if .01" Jump is more accurate than factory rounds touching the throat. I am assuming so, since 123 Factory AMAX (.01" jump) shoots remarkably better than factory 123SST.

Another note... I use Hornady Dies, with no crimp, I am getting .003" neck tension on 123 AMAX and SST. See where neck tension has been discussed lately thought it might be of interest.

Will finally have the chance to make it back home over the Thanksgiving holiday and do some shooting... I have about 15 different loads to test.. with all different variables (Powder Charge, various shoulder set back, BTOG lengths, bullet weights). I will be checking for Velocity, Pressure signs, and accuracy... Gonna be a longer day on the range

Just a FYI factory 123 AMAX shoots at AVG. 2532 FPS in my 18" AA barrel... Seems a little faster than other 18" velocities I see on here. Again, my barrel is not the 18" lite barrel currently on AA guns. It is a button rifled, non-fluted, barrel that is no longer available to purchase from AA.

Has anyone else shot this barrel? Any data on it?

This is my Grendel and 300BLK SBR

[1911man]

Drillboss,
Thank you for providing the diagram... this was a major help in visualizing the chamber... I surprised I hadn't seen it previously... After the fact I found where you provided in other threads.

Ok so I confirmed with the marker trick, in my chamber factory 123SST with 1.660 BTOG length is touching the throat. I also chambered some 1.675 BTOG rounds and they were slightly sticking in the chamber.

I resized all my past 123SST loads down to either 1.645 BTOG or 1.650 BTOG (.01" / .005" Jump). We'll see if .01" Jump is more accurate than factory rounds touching the throat. I am assuming so, since 123 Factory AMAX (.01" jump) shoots remarkably better than factory 123SST.

Another note... I use Hornady Dies, with no crimp, I am getting .003" neck tension on 123 AMAX and SST. See where neck tension has been discussed lately thought it might be of interest.

Will finally have the chance to make it back home over the Thanksgiving holiday and do some shooting... I have about 15 different loads to test.. with all different variables (Powder Charge, various shoulder set back, BTOG lengths, bullet weights). I will be checking for Velocity, Pressure signs, and accuracy... Gonna be a longer day on the range

Just a FYI factory 123 AMAX shoots at AVG. 2532 FPS in my 18" AA barrel... Seems a little faster than other 18" velocities I see on here. Again, my barrel is not the 18" lite barrel currently on AA guns. It is a button rifled, non-fluted, barrel that is no longer available to purchase from AA.

Has anyone else shots this barrel? Any data on it?

This is my Grendel and 300BLK SBR

That does seem a little fast, my 18" BHW barrel gets an average of around 2480 fps with the factory AMAX. Any pressure signs on the brass?

[Nachunter]

@ 1911man, no nothing that stands out. No flattened primers or extrusion around firing pin hole. No belling or Ejector marks on case head.

Chrono data taken 2 separate occasions with factory 123AMAX out of this upper... BETA MASTER Chrony @ 12ft. , Last outing was 73F / 30.1 BAR Press. in East TX.... not sure of elevation.

[Nachunter]

Update : Factory 123AMAX : Tight Chamber

Ok, so I lied. Shot some factory 123AMAX yesterday and I have flattened primers on about 2\3 of the cases. No extrusion around any of the firing pin holes or ejector marks, but probably pushing the pressure I'm comfortable with.

With regards to my chamber I have come to the conclusion that thus barrel was cut to about min SAAMI Specs. With Hornady Comparator insert, which has a verified .254 ID, I thought rounds should be about .01" from touching the throat. I was incorrect. By looking at chambered rounds there is obvious evidence of the round being pushed into the throat. The shape of the Ogive and measuring at .254" gave my a false conclusion. I should have chambered a 123AMAX, like I did the SST, from the beginning.

Rounds chamber and eject with ease, and will shoot a ragged hole group @100yrd all day long if I do my part. So I'm happy with the tight chamber.

I plan to shoot my 123SST reloads tomorrow, I have verified they are sitting with about .01 or .05 jump. I will update with info then for those who are interested.

I do have a couple questions.
Is there a comparator insert that has a true .264 ID?
Do you'll see anything from the marks on my bullet or cases that sound the alarm?

[JASmith]

...Is there a comparator insert that has a true .264 ID?...

A true 0.264" bullet could slip through a 0.264" gage.

The allowable range of bullet diameters per SAAMI is 0.26113 to 0.2643 inches.

The seating plug is smaller than the 0.254" diameter of the gage.

Add to this that the span of diameters for the 0.5 degree SAAMI throat entry is 0.2617 to 0.2644 (+0.002) inches.

These differences can give us OCD types fits when small variations in ogive radius and / or measurement technique leads to variations in observed readings.

The good news is that we very rarely see a bullet measuring less than about 0.2639 inches.

So, I for one would be happy with a gage and seating plug that both engage at about 0.262 inches. That could make everything line up much better and we could allow the base to tip length vary a bit and still be comfortable.

[Nachunter]

JA, thanks for the input and very good point regarding allowable tolerences for throat and 6.5Cal bullets. I can make do with the .254 insert.

Good news is I will get to do some actual testing. As for us OCD types the only way to satisfy our true technical side is with field trials and data collection.

The compound throat of the Grendel is a very interesting creature and I will have note pads full of data before this is done. Lol

I love having an AR chamber where I can actually adjust BTOG length from touching the throat to over .01" jump if needed.

Thanks everyone for the input and look forward to reading more.

[Nachunter]

Ok everyone, just wanted to give an update of what I'm seeing with my barrel and get some opinions.

All my bullets are showing marks on them from the throat, even the SST's I loaded down to 1.640" BTOG... rounds don't start sticking (jamming lands?) in the chamber until around 1.680" BTOG.
I've reached the conclusion that I have a tight throat. Is this a valid assumption? It seems I cant load anything that does not get throat marks on the bullets. Should I be concerned about chamber being too tight? Is this what is called zero freebore?

The tight throat is resulting in high velocities.
123 AMAX - HORNADY BRASS RESIZED TO ABOUT FACTORY MIN - 1.511" TRIM LENGTH - .003 + .001 NECK TENSION - CCI 450 PRIMER -
4 SHOT STRINGS
26.8 XBR = 2400 AVG
27.0 XBR = 2447 AVG
27.2 XBR = 2467 AVG
27.4 XBR = 2480 AVG
27.6 XBR = 2501 AVG
FACTORY AMAX = 2532 AVG
FACTORY SST = 2511 AVG
WOLF GOLD 123 = 2490

Seems I found accuracy nodes @ 2465-2480 and 2511-2532 (Factory ammo is .50 moa easy)
Should I be concerned about pushing pressure maxs with factory ammo?

All loads have some flat primers... I think this is from headspace not pressure, no blowout around primers, no ejector marks on brass, no pierced or blown primers. Is there any other signs I can look for?

Thanks in advance for any feedback.. I'm just trying to wrap my head around this chamber... barrel shoots amazing.. just concerned I'm over pressured. Though I have read that the compound throat minimizes pressure spikes.

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