AR barrel throat depth

[NugginFutz]

I was doing some load development for my 20” Radical firearms upper today.They use the type 2 clambering. I found my overall length to be 2.223 to clear the lands. My 16” Faxon barrel clears at 2.243. I was quite surprised.

Kind of makes you wonder what all the buzz about the Grumble II chamber solving all the short throat issues was supposed to be about.

As as far as I’m concerned, the GII was a solution in search of a problem, and only muddied what used to be clear water until all the type2 and GII nonsense started.

[Drillboss]

I was doing some load development for my 20” Radical firearms upper today.They use the type 2 clambering. I found my overall length to be 2.223 to clear the lands. My 16” Faxon barrel clears at 2.243. I was quite surprised.

The group buy Faxon barrels did vary toward the maximum allowed by SAAMI. They still have the compound throat, but max COAL is a bit more generous.

[zcostilla]

Mmm. SALAMI.

My auto correct hates me

[grayfox]

Auto correct is more like Auto confuse.

[just_john]

beastep, have you measured to be sure that the correct depth bolt is, in fact, what you have? A .125 bolt will put the bullet into the lands.

[NugginFutz]

beastep, have you measured to be sure that the correct depth bolt is, in fact, what you have? A .125 bolt will put the bullet into the lands.

Likely, it would not. With a chamber headspaced for a .136" bolt face, the case shoulder would be set against the chamber, just as it would with a properly surfaced bolt. The bullet would not present any further into the throat. If anything, the bolt would be prevented from going fully into battery.

[beastep]

I was doing some load development for my 20” Radical firearms upper today.They use the type 2 clambering. I found my overall length to be 2.223 to clear the lands. My 16” Faxon barrel clears at 2.243. I was quite surprised.

Good to know. This short throat thing on all these barrels really surprises me.

[beastep]

beastep, have you measured to be sure that the correct depth bolt is, in fact, what you have? A .125 bolt will put the bullet into the lands.

I have not but they were both ordered from BCA and the bolt is marked Grendel II. I dont think that would make any difference on presenting the bullet too close or into the lands anyway. But correct me if Im wrong.

[beastep]

BCA's chamber is a SAAMI chamber. They say type II to reference the 0.136 bolt face depth. I was confused about it at first, and wrote an email to them for clarification. As cheap as BCA is producing Grendel barrels, you might want to contact them, after all, they won't be out a ton of cash and labor, like Lilja would be.

I will contact them for clarification.

[LR1955]

Guys:

Lets say you have a piece of empty Grendel brass. Sized and ready to load.

If you tried to chamber it in a Grendel chamber using a 7/62 X 39 bolt, it would NOT chamber. The empty brass itself would not chamber, let alone a loaded round.

If you used a Grendel bolt (.136 face depth) with a chamber cut for the 7.62 X 39 bolt, it most certainly would chamber and would shoot. You would note the shoulder got blown out enough for you to see it with your own eyes. Kind of like shooting a .308 out of a 30-06 chamber but not as blown out. You will not blow up your rifle, either. I blew out a few pieces of Grendel brass this way deliberately many years ago in an experiment I was running. The experiment was a failure but I was never worried about damaging the rifle. No, I would not shoot a diet of ammo through this combination of bolt and chamber.

Short throating and head space are two different things. You can have a perfectly headspaced chamber with a short throat that won't let you chamber a live round without having to seat the bullet way deeper than any loading manual would advise.

Short throating is generally cured using a finishing reamer.

LR55

[Mytie]

So is the op going to be safe seating his Bullets that deep? Have you shot the new rounds seated below the minimum?

[beastep]

I have and Im having pressure issues due to less case capacity I do believe. With a book max of 31.2 of CFE I loaded some at 30.6 and higher but I had pressure signs at 30.6 so Im not shooting the rest. I have to drop down and see if I can get something to shoot without pressure signs and that holds a nice group. Im also thinking about changing powder to maybe something a little slower to help that out. Maybe AR Comp. Not sure yet.

[grayfox]

I'd go with '55s advice, a short throat is short no matter if it's G1 or G2 or xyz... nothing will really be able to compensate for that other than lengthening it back to where it ought to be. The GII aspect only means it has a straight cut throat rather than SAAMI cut throat, I've had 2 GII's and their throats were plenty long enough... now the SAAMI spec chambers shoot better in general than my GII's did IMO but that is irrelevant to whether there is enough leade to properly seat your 6.5 bullets. I'd call up BCA (use the 833-number on their website not the "customer service" one) and see if they will take care of it for you.

[Redomen]

I checked my 18” Faxon and COAL came to 2.255 with 123SST without hitting lands. I. Re checked my 16” and found a comfy spot at 2.250 COAL. Just worked some loads up for testing on my 20” Radical build. The Faxon barrels will be next.

[beastep]

I'd go with '55s advice, a short throat is short no matter if it's G1 or G2 or xyz... nothing will really be able to compensate for that other than lengthening it back to where it ought to be. The GII aspect only means it has a straight cut throat rather than SAAMI cut throat, I've had 2 GII's and their throats were plenty long enough... now the SAAMI spec chambers shoot better in general than my GII's did IMO but that is irrelevant to whether there is enough leade to properly seat your 6.5 bullets. I'd call up BCA (use the 833-number on their website not the "customer service" one) and see if they will take care of it for you.

Im going to start another round of load development next weekend. Im having to wait on brass and bullets right now. I also think Im going to get away from CFE to maybe lessen my pressure a little bit and get more temp stability. Im thinking about AR comp but Im not sure yet.

I called them Thursday and I havent heard back from anyone yet.

[LRRPF52]

I've had to ream several 6.5 Grendel barrels so far that people sent me.

They had short throats that would jam factory ammo into the lands.

Funny how out of all the barrels I own or have owned, they all allow factory ammo to drop free from the chamber with ease.

This happens in .223, 5.56, 7.62 NATO, and every other chamber you can imagine when one of a few things happens:

* Finish reamer with the barrel maker gets worn and no longer cuts to the minimum spec for throat location. (Every rifle maker I know of has had this problem occur if they crank out any kind of volume.)

* Whoever/whatever did the reaming operation didn't ensure that it was done correctly, which is usually because of the above.

I built an SPR clone upper for a guy with a barrel from one of the main go-to SPR clone builder barrel providers that had a short .223 Wylde chamber. It shot 69gr and 77gr SMKs into bugholes no problem, but blew primers with M193.

[Redomen]

I measured my 20” with he Hornady gauge I had and got a measurement of 2.340 to the lands. I came up with the earlier measurement of 2.223 by coloring a bullet with a sharpie and clambering it and looking for marks. I was making loads of varying lengths to test and decided to seat one at 2.245 since that is the max norm for 123 SST. I chambered it and had no marks and it measured the same afterwards. I’m kinda stumped. I’m thinking when I chambered the first colored rounds that the bullet may have moved forward a smidge from the bolt slamming closed and caused the marks and extra length. I originally thought I was into the lands and the extra length was from the bullet being pulled when I ejected them. This is confusing the hell out of me. The best groups I got were with 28.5 and 29 grains of CFE at COL 2.223. I loaded some at 2.245, 2.230, 2.225, 2.218, and 2.210. Before I blow myself up or ruin my barrel is ther a minimum recommended COL? I’ve been reloading for bolt guns forever but semi autos is new to me.

[Steve390Gold]

I have a Satern 5R liberty 20" barrel that also has a SAAMI spec chamber with the very short throat (produced about 3 years ago.) Hornady Black is jammed 0.025" into the lands. Considering it shot right at 0.75MOA at all yardages including 625yards, I didn't complain, and instead worked up loads that also jam the Hornady ELD-M 0.025" into the lands. Thus far I have not been disappointed - 0.5 moa when I do my part at all yardages out to 625 yards. (Furthest I can shoot for groups currently.)

Neck tension is pretty good with my reloads so no issues with bullets being pulled when removing a chambered live round.

[Steve390Gold]

make a load ladder at the bottom of the load spectrum working up with the bullet jammed into the lands - my gun seems to like 0.025". You may see pressure sooner than without jamming into the lands, but I went up to 32 grains of CFE223 under a 123, had a wildly compressed powder charge, and jammed 0.025" and still had no pressure signs. My good load with cfe223 is currently 29.8grains IIRC, COAL is 2.245" or something analogous to that. That particular load is about 1.5 minutes lower at 625 yards than Hornady BLACK, so it is moving a tad bit slower.

[Steve390Gold]

I measured my 20” with he Hornady gauge I had and got a measurement of 2.340 to the lands. I came up with the earlier measurement of 2.223 by coloring a bullet with a sharpie and clambering it and looking for marks. I was making loads of varying lengths to test and decided to seat one at 2.245 since that is the max norm for 123 SST. I chambered it and had no marks and it measured the same afterwards. I’m kinda stumped. I’m thinking when I chambered the first colored rounds that the bullet may have moved forward a smidge from the bolt slamming closed and caused the marks and extra length. I originally thought I was into the lands and the extra length was from the bullet being pulled when I ejected them. This is confusing the hell out of me. The best groups I got were with 28.5 and 29 grains of CFE at COL 2.223. I loaded some at 2.245, 2.230, 2.225, 2.218, and 2.210. Before I blow myself up or ruin my barrel is ther a minimum recommended COL? I’ve been reloading for bolt guns forever but semi autos is new to me.

Make a load ladder at the bottom of the load spectrum working up with the bullet jammed into the lands - my gun seems to like 0.025". You may see pressure sooner than without jamming into the lands, but I went up to 32 grains of CFE223 under a 123, had a wildly compressed powder charge, and jammed 0.025" and still had no pressure signs. My good load with cfe223 is currently 29.8grains IIRC, COAL is 2.245" or something analogous to that. That particular load is about 1.5 minutes lower at 625 yards than Hornady BLACK, so it is moving a tad bit slower.

(The main reason I cant remember the COAL is because I use the ogive gauge that hornady sells - as someone else mentioned, seating to a specific case head to ogive length is far more consistent than COAL.)