Bullet Setback when chambering

Small update, been away on vacation for a week so haven't had time to dive back in. I've now used go/no go gauges with the 8.5" barrel and everything is copasetic. No issues there. The ammo in question was made by Freedom Munitions and it was "new", not reman. They gave me a refund on the rest of the unused ammo but probably should have given me a full refund on the faulty rounds just because. I'm fine with it and I've used them before (have a good bit of 9mm ammo from them) without issue so I'll hand this one down to being a fluke in abnormal times. They didn't have replacement ammo which tells me they know about an issue with those loads.

Will try to get to the range this weekend to see if I can get the rifle to cycle with subs. I'd go with a lighter buffer to help but I have the lower working perfectly with my 5.56 upper as well and I want to keep it that way.

Given it's an 8.5" barrel, pistol-length gas port, with an approximately .109 port size, if it doesn't cycle with subs, factory or otherwise, what port size do you all recommend going with if I decide to drill it out? I do have an adjustable gas block as well as a lightweight titanium BCG and lighter buffer (need to weigh it) which worked perfectly on the 10.5" barrel. Just not sure what sort of increments I should be experimenting with and how big is too big.
 
...FWIW, you are making too many changes with too many parts/components at one time. I recommend you start with one barrel, one BCG, one buffer/buffer spring and one bullet/powder combination to start. Also, do it without the suppressor until you get it running right. Adding the suppressor will increase the back-pressure, which you can adjust for with your adjustable gas-block as needed. Pistol length gas systems rarely, if ever, require increasing port enlarging, especially in 8" barrels.

In looking at the Faxon barrels, you can clearly see that the older one has really angular edges at the beginning of the chamber, less angular on the newer barrel. The Rainier barrel was much better, with smooth, slightly rounded appearing edge transitions. It is not absolutely necessary to use "300BLK specific" mags, normal .223/556 mags work. The only concern claimed about using 556 mags was the foremost internal rib, i.e., depending on the particular bullet used and it's ogive location, if seated out too far the rib would contact the ogive at a point greater than a location measuring 0.250" and cause the round to "toe-in" which could affect feeding. This is why it is recommended that bullet seating be to a depth where the rib contacts the portion of the bullet ogive that measures .250". In the early days of 300BLK, people removed some of the material at the top of the rib to mitigate this condition when using polymer mags, steel/aluminum mags were more problematic. Compare your Magpul 556 mags to your Magpul 300BLK mags, you will see the difference. Attached you will find info from AAC & R. Silvers, the developers of the AAC 300BLK cartridge. Remember, the 300BLK was designed to meet a DoD requirement to utilize standard STANAG 556 magazine.

FWIW, I've been using standard Magpul 556 mags (all gens), original Colt AR-15, multiple USGI and Lancer 556 mags for over 10 years with no problems or modifications with a multitude of .308 bullets in handloads for supers and commercial offerings. As suppressors are not legal in my locale, I've limited experience with subs but I've used subs in both commercial & handloads just to "test" in unsuppressed mode.

BTW, the GO/NOGO gauges aren't going to measure the freebore or "leades" on the barrels, just up to the neck/shoulder junction for determining headspace. The freebore is where the bullet ogive shape/measurement makes a difference and affects seating depth (and seating depth affects feeding).
 

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Here’s some data Seekins 8” and Omega can and Seekins AGB
Hornady 190 Sub-X
AA1680
Fed 205M
COL 1.345
COAL 2.140
BTO 1.625
12.4 gr 1094, 1083, 1064, 1057, 1063
12.5 gr 1119, 1115, 1096, 1106, 1086
12.6 gr 1106, 1116, 1132, 1107

25 yrds and EoTech sight fwiw
0F67A2E1-4831-4A80-8987-25A0EFFAED83.jpeg
 
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...FWIW, you are making too many changes with too many parts/components at one time. I recommend you start with one barrel, one BCG, one buffer/buffer spring and one bullet/powder combination to start. Also, do it without the suppressor until you get it running right. Adding the suppressor will increase the back-pressure, which you can adjust for with your adjustable gas-block as needed. Pistol length gas systems rarely, if ever, require increasing port enlarging, especially in 8" barrels.

In looking at the Faxon barrels, you can clearly see that the older one has really angular edges at the beginning of the chamber, less angular on the newer barrel. The Rainier barrel was much better, with smooth, slightly rounded appearing edge transitions. It is not absolutely necessary to use "300BLK specific" mags, normal .223/556 mags work. The only concern claimed about using 556 mags was the foremost internal rib, i.e., depending on the particular bullet used and it's ogive location, if seated out too far the rib would contact the ogive at a point greater than a location measuring 0.250" and cause the round to "toe-in" which could affect feeding. This is why it is recommended that bullet seating be to a depth where the rib contacts the portion of the bullet ogive that measures .250". In the early days of 300BLK, people removed some of the material at the top of the rib to mitigate this condition when using polymer mags, steel/aluminum mags were more problematic. Compare your Magpul 556 mags to your Magpul 300BLK mags, you will see the difference. Attached you will find info from AAC & R. Silvers, the developers of the AAC 300BLK cartridge. Remember, the 300BLK was designed to meet a DoD requirement to utilize standard STANAG 556 magazine.

FWIW, I've been using standard Magpul 556 mags (all gens), original Colt AR-15, multiple USGI and Lancer 556 mags for over 10 years with no problems or modifications with a multitude of .308 bullets in handloads for supers and commercial offerings. As suppressors are not legal in my locale, I've limited experience with subs but I've used subs in both commercial & handloads just to "test" in unsuppressed mode.

BTW, the GO/NOGO gauges aren't going to measure the freebore or "leades" on the barrels, just up to the neck/shoulder junction for determining headspace. The freebore is where the bullet ogive shape/measurement makes a difference and affects seating depth (and seating depth affects feeding).

I agree on too many changes and actually said as much in my first post-8.5" barrel outing. I made two changes at once and should not have done that. Lesson learned!

Headed to the range today, I have the RCA bolt back in and I'll bring the JP along and swap that in if cycling isn't an issue with the RCA bolt. That'll at least narrow it down.

I use an OSS flow through suppressor which has almost no effect on back pressure and does not require any adjustment to the gas on or off. With that said, I tested both ways last time and it did not make a difference.

I started out using 556 mags and stumbled across an article, hence the switch. I now have a handful of Lancer mags to test as well.

Agreed on the go/no go gauges but this is an AR. I'm limited by mag length and will never be able to get the bullet close to the lands like you would in a bolt gun. Irregardless, I have the Hornady kit except for the modified 300 Blk case (out of stock everywhere) so when I do get that, I'll measure just to know. But I've done so on my 556 and 308 AR's and its really a pointless endeavor as it would have required seating the bullet to longer than mag length.
 
...FWIW, heres the link to the Hornady site that lists their load data for the 190gn sub-X, albeit is for a 16" barrel...note the load length they use.

Yep, familiar with it! I have their reloading app as well. Hodgdon also has data up on their reloading site. Here's a link but you'll need to put in the cartridge, bullet weight and powder.
 
Here’s some data Seekins 8” and Omega can and Seekins AGB
Hornady 190 Sub-X
AA1680
Fed 205M
COL 1.345
COAL 2.140
BTO 1.625
12.4 gr 1094, 1083, 1064, 1057, 1063
12.5 gr 1119, 1115, 1096, 1106, 1086
12.6 gr 1106, 1116, 1132, 1107

25 yrds and EoTech sight fwiw
View attachment 7714005
Thanks for that. I'm using CFE Black, for better or worse, in LC brass converted from 5.56 for the subs. I think I have a sweet super load for 110gr. VMAX bullets using H110 that I'll be doing a 10 cartridge test with today as proof of concept. Last time out I tested three different ladder loads, each with a different primer. Looks like CCI400 won over CCI41's and Tula small rifle primers (got those for subs really). But I had well under an MOA at 50 yards with the CCI 400 and CCI 41 primers.

My COL is a bit longer, 1.355, and I don't remember what the COAL was off the top of my head but the ogive measurement looks similar. I took readings off of a box of factory loaded ammo and went from there.

I have a bunch of cheap Berry's 220gr. bullets loaded to test function today. If that all works out, I'll test the 190X's out as I have a test group already loaded. I'll report back later today.

Edit: I also picked up a pound of Lil' Gun and will likely test that with the 190X's as well. I had to wait for my Giraud trimmer to come back (bearing went south) and I now have it so I can finish processing cases.
 
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Using CFE Blk for subs, H110 for supers. I'll check out the other three you recommend. Hodgson lists Lil'gun for subs and I'm assuming, with a shorter barrel, I want a faster burning powder. With that said...I'd rather have a barrel that can shoot anything and I'm not locked in to a certain load/bullet weight despite the fact I'll only load one specific sub round and one specific super round.

Bad day at the range, headed back tomorrow. Short version, it was cycling with subs but did not lock back on an empty mag consistently. That extra 2" of barrel length really does make a difference with the buffer/BCG setup I'm using. The first round, on a stone cold barrel locked back but subsequent rounds did not except for one or two. Chrono speeds were all in the 1000 fps range, less than 1100, with one or two in the high 900's, 220 grain bullet. Plinker rounds so not super precise, just used for fun and function.
 
...if anything after your tests w/LilGun, you may want to try 1680 for your sub loads if cycling issues continue. That powder is the one that has had the best success and least cycling issues since 300BLK came out, generates alot of gas volume which is beneficial for cycling. In my experience with AA5744 loaded for supers in my 10.1" barrel, I had residual unburned kernels, 4227 had complete burning. My preferred powders for supers are LilGun, H110/W296 and 300-MP with 125gn TNT's. I've used Accurate #9 for supers, only took 16gns to hit mid 1900's to 2000 fps in a 9" barrel, but it was erratic and quick to go over pressured in less than 0.2 grain charge increases, YMMV.
 
A few things. . .

Be careful with Lil' Gun. Tons of load data and discussion on the 300 blk forum. General consensus seems to be Lil' Gun gives best velocities (only by a little) but is extremely temperature sensitive. You do load workup in cool weather, then you take your handloads out in summer and get blown primers. Or do some quick shooting and get your chamber really hot, then a round sits in there for a minute before you shoot and boom. No personal experience with Lil Gun, but plenty of reports. Just be careful.

H110 is the bees knees for supers.

Stop banging your head into the wall and put an adjustable gas block on that barrel. Yeah, I know all the "USGI reliability" guys prefer a simple gas block and and a port that is an optimized compromise that will cycle most ammo most of the time. But this isn't the 1990s any more and [good] AGBs are just as reliable as simple gas blocks.

You are combining irrespective and regardless. Irregardless is not a word. 🤓

Good luck at the range
 
I don't understand how you can have a cut/line that is perpendicular to the bore/chamber direction and have it be from the mag or feed ramps without there being scuff marks along the direction of travel. Think stamped as opposed to dragged.

It's almost like you have a burr inside the chamber that then 'forms' that line when its chambered and locked into place.
 
A few things. . .

Be careful with Lil' Gun. Tons of load data and discussion on the 300 blk forum. General consensus seems to be Lil' Gun gives best velocities (only by a little) but is extremely temperature sensitive. You do load workup in cool weather, then you take your handloads out in summer and get blown primers. Or do some quick shooting and get your chamber really hot, then a round sits in there for a minute before you shoot and boom. No personal experience with Lil Gun, but plenty of reports. Just be careful.

H110 is the bees knees for supers.

Stop banging your head into the wall and put an adjustable gas block on that barrel. Yeah, I know all the "USGI reliability" guys prefer a simple gas block and and a port that is an optimized compromise that will cycle most ammo most of the time. But this isn't the 1990s any more and [good] AGBs are just as reliable as simple gas blocks.

You are combining irrespective and regardless. Irregardless is not a word. 🤓

Good luck at the range

Good to know on Lil'Gun. I've not cracked it open yet. I'm in Texas and most shooting days are 90 degrees plus! Maybe I'll develop a load now before "winter" hits.

I have a Superlative Arms adjustable gas block on the rifle.

Today did go much better. I had the gas block fully open, 4.5 turns, and was able to get the bolt to lock back most of the time with two failures to function. I gave the rifle a thorough cleaning and lube prior to leaving today but I have a feeling the SA gas block is not working properly. It once again became hard to adjust and it would not lock the bolt back with supers at 3 turns from closed. With the 10.5" barrel, I think I was at 2.5 turns from closed with supers and 4 turns from closed for subs. I know it's aligned correctly. I measured AND checked it with a bore scope. I have another SA gas block on my 5.56 upper and it's performed flawlessly so I'm beginning to wonder if it's the culprit given my gas port appears to be the same size on both the 8.5" and 10.5" barrels.

I ended up just leaving it wide open for the rest of my time at the range and worked through test loads @ 100 yards. My SD's with subs were around 12 with 12.1 grains of CFE Black having the smallest group. For supers, 110gr. VMAX I did 10 each of my best loads with CCI 41 and CCI 400 primers. Only difference. Pretty accurate but not as good as I'd hoped and my SD was way up there around 43 over a ten shot group. Typically, with my .308 loads, I have between 3 and 6 standard deviation and I've had trouble getting near that with 300 blackout loads. I think it comes down to powder measuring with the H110 and CFE black as they're so fine of a powder. I just have to pay more attention.

Lastly, I tested ten factory loaded Hornady 190gr. Sub-X rounds and had an SD of 4.4. So I have some work to do. The grouping wasn't particularly tight but it's at 100 yards using a 1-6x and shooting into the sun. It's brutal in the afternoon but it's the only time I can make it out there on a Monday. I'm using the Primary Arms 1-6x with the 300 blackout ACSS reticle and the sun can be so bright it's almost hard to see said reticle. I had to turn the illumination on. Here's a photo of the ten shot group, several of those holes are from two bullets. I don't use a sled, just a cheap tripod, a small bean bag and patience. I will say this...the 190 sub-x bullets have a pronounced "thump" when they hit the berm. I don't hear much with the VMAX110's but the 190's are audible.

I may try the new Faxon barrel just to see if I can get back some of the "it'll cycle anything" magic. Right now, as it sits, yes, it's working with the 8.5" barrel but I wouldn't bet my life on it. Definitely accurate, definitely not setting back the 190 sub-x rounds so that's a positive. Not getting the weird horizontal marks on the bullets either.
 
Here's a target, all supers, 110gr. Vmax, various H110 charges with three different primers @50 yards. 19.8 grains and the CCI 400 primers produced the smallest SD and tightest group. Zero pressure signs. If I remember, velocity was in the high 2100fps or low 2200fps range with the 8.5" barrel and the silencer.


Moving to 100 yards, I got this. Some of this is "me" and some is just my setup. I'd probably half the spread using a sled. But my SD over 10 rounds skyrocketed into the 40's.


My sub-x load at 100 yards, needs some improvement as well.
 
...you might want to try the TNT 125gn pills, better pricing than the Nosler 110 VG's and in my experience more accurate than the 110's. One pill that was very accurate in my barrels was the Berger 115gn, but again...pricey!

...during the last "shortage" a few years back I had to look for alternative components and tested the Hornady AK offerings and took their 123gn VMAX (.310") and ran them through a Lee .308 bullet sizer to test. The attached image are the results of that test @~100M from my BA 10.1" bbl, shot off a makeshift rest (GI ammo can), the lines of the cross inside the circle are 1-3/4" long. The 18.5gn load gave me 2139 fps avg, the 19.5gn load 2169 fps avg.

...also tried some of the pills "as is" but they had to be seated much shorter and accuracy was not as good. They were on sale at Graf's at the time and a really good price.
 

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The Hornady 110gr. are fairly cheap and I have a ton of them but I'll take a look at the TNT 125 grain bullets. I've had pretty good success with Nosler stuff in 308 and 5.56 but haven't tried their 110gr. round due to cost and availability. And yes, Berger's are usually a good step up in cost. I haven't tried Barnes either mostly due to cost and the difficulty in developing a good load with a solid core bullet. I worked with a few of Hornady's GMX rounds and they were by far the most difficult to nail down.
 
So someone on the 300blk forum pointed out that the gas ring around the gas port is quite large. I have a "satin" finish on the barrel and it's basically a bead-blasted finish. Pointing this out, I took out my wide selection of micro-mesh (up to 8000 grit!) and worked on the gas block portion of the barrel. I also noticed the gas port had a bit of a raised lip. I knocked that down and smoothed out the finish.

I went back to the range after and things were improved. I was able to get the gas block to lock back with a number of different subsonic rounds. I had a completely different snafu which shut down my testing for the day so I'm not listing it as problem solved just yet.

One other point he brought up is it should be tough to fit the gas block onto the barrel. Even prior to knocking down the surface finish, it was effortless to get the gas block to slide on. I use the set screw version. Going to take calipers to the barrel and gas block to make sure they're in specification. Still a mystery as to why such a change vs. the 10.5" barrel though. Same gas block.
 
So someone on the 300blk forum pointed out that the gas ring around the gas port is quite large. I have a "satin" finish on the barrel and it's basically a bead-blasted finish. Pointing this out, I took out my wide selection of micro-mesh (up to 8000 grit!) and worked on the gas block portion of the barrel. I also noticed the gas port had a bit of a raised lip. I knocked that down and smoothed out the finish.

I went back to the range after and things were improved. I was able to get the gas block to lock back with a number of different subsonic rounds. I had a completely different snafu which shut down my testing for the day so I'm not listing it as problem solved just yet.

One other point he brought up is it should be tough to fit the gas block onto the barrel. Even prior to knocking down the surface finish, it was effortless to get the gas block to slide on. I use the set screw version. Going to take calipers to the barrel and gas block to make sure they're in specification. Still a mystery as to why such a change vs. the 10.5" barrel though. Same gas block.
...even if your barrel is dimpled for the set screws, the uppper quarter of the gas block will be "pulled down" by tension against the upper half of the barrels circumference. Shoot enough supersonic ammo through it and a carbon seal will form eventually. Typically, the gas port hole on the gas block WILL be larger than the gas port hole in the barrel, this accommodates slight misalignments of the gas block or minute adjustments needed to ensure the gas tube alignment through the receiver and seating with gas key. If the gas block was a loose fit on the journal to begin with, polishing the journal didn't increase the friction fit. I'd be inclined to advise just shooting a bunch of supersonics to break it in well before starting your sub load development.
 
Duly noted on shooting supers. Just know micromesh is very fine and doesn't take off a ton of material. I actually checked the gas ring around the gas port and it was much smaller this time around.

I worked on the gas tube a bit as an older thread pointed out that feed issues can sometimes be caused by a gas tube that's misaligned. I had to grind out the top inner groove of the Smoke Composites hand guard as it had been sent to me not fully machined on the inside. I didn't do it enough as the gas tube was hitting the hand guard. This would press the tube downward and make it harder for the carrier's gas key to slide onto the gas tube.

I spent about two hours tweaking the gas tube getting it to the point where a bare carrier, sans bolt and other parts, would slide on to the tube with zero effort. The tube's original bends were not ideal and I had a few mm's, maybe even five, between the bottom of the tube and the barrel nut. I may purchase a few and see if any sit a bit lower than others.

I then machined out more of the hand guard's inner to get it to clear the gas tube. For the price, this thing should fit with no machining work. The CODA hand guard, which I also own, is far more precise and not as finicky if you're looking for a carbon hand guard. The CODA's barrel nut can be torqued to specification, not position, and it doesn't affect the alignment of the hand guard itself. The Smoke requires alignment of the nut irregardless of what the torque specs are. Not the way to do it.

As frustrating as it all is, at least I'm learning so I guess that's a plus. Switching barrels has forced me to look at all the details.

I still may go back to the 10.5" barrel but I want to have someone look at the extension, ramps and throat and smooth out the transitions. You can see all the CNC "steps" in the throat area and I'd like to clean those up.
 
No problem! I have a bunch of cheap(er) supersonics on the way so I can sit there and mess with function and I'm currently trying to find someone in the San Antonio area who's a master at polishing chambers, feed ramps, etc...to take a look at my Faxon barrel.

I did measure the OD of the barrel and I think it came to .748. Forgot to measure the inside of the gas block.
 
Today was a good day.

Found a new range and took the arsenal out for some fun (left the notebook and magneto speed at home) at both the pistol and rifle range. First time shooting reactive targets, firs time shooting out to 300 yards. I had a large pile of brass at the end of my time there so it was also an expensive day!

The good news is other than one Lantac 10 round magazine which will not feed the first round on a dropped bolt, zero issues otherwise. I started by shooting a box of Sierra 125gr. game changer rounds, factory load. Was actually quite painful to use the good stuff but my "cheap" supers supply won't arrive until late in the week. So I went through 20 rounds of that and had no issue hitting various target sizes out to 300.

I switched over to my "plinker" subs, Berry's 200gr. over CFE black, LC cases and Tula primers. They actually did pretty well and I managed to hurl a bunch to 300 and had no problem hitting man-sized targets and a few of the smaller ones.

The bolt locked back on 3 of the four sub mags I burned through. Zero failure to function events other than the Lantac 10-round mag. I tested with both the supers and the subs, same thing. The 30 round Lantac mags had no issues nor did the 300 blackout Magpuls. Nothing funny, the gun just ran. Was nice for a change.

I dropped the lower and swapped it onto my 5.56 16" upper which I haven't shot in some time. Forgot how well it shot! It has a Faxon "gunner" profile, match grade. Ran through a few mags of that and really got the suppressor hot. The CODA carbon hand guard became surprisingly hot as well. First range I've been to where I can shoot a bit more rapidly.

I moved on to the POF Revolution DI with my plinking Hornady 150gr FMJ BT's and those actually did pretty well. I've stepped up my reloading game since I loaded those up so I was a bit surprised. I was able to nail a 6" target at 300 pretty consistently and I really like the Meopta 3-18. I actually found myself dialing it back a bit at 300 yards.









 
Don't take it seriously.

Just a suggestion the zip locks can and will fail and mix your brass that you spent all afternoon keeping separate.

The sturdy plastic jars are free and hold a good working number of rounds loaded or not. You can shove a range data card inside them that wont be lost.

Furthermore the sammich maker wont beat you for taking all the zip locks again.

Those jars hold 120 rounds of loaded 223 with room for a desiccant pkg. They fit in the side compartment of a ruck. Two of them full of 223 brass will take 1lb of powder to reload.


Whatever you do don't let the sammich maker catch you with a pillowcase full of range brass.

Trust me.
 
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Ha! Yes. Have to watch out for the sammich maker. I usually use these medical-grade plastic bags the sammich maker brings home from the hospital for me. About 4X the thickness of a typical zip loc, I just forgot it on that day and happened to have the ziplock in there. I sort everything when I get home under lights so mixing isn't usually a problem. Plus it's very rare I bring four guns to the range. But duly noted!
 
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WTF is on that note pad? Some kind of Dan'l Boone kilt a bar scribblin's? LMAO
Yes that is the worlds worst chicken scratch. Lol

Logging for a local ham net on the computer while talking and scribbling notes for the online report I was putting in later.

My penmanship has always been the worst, like a small child with a blunt crayon. Embarrassing actually.

But as I got older I attribute it to
Age
Arthritis
And Whiskey

All my reloading notes are put onto a word template I made so I can read them.

In grade school my son was sent home with a note about his shitty handwriting. I sent a handwritten note back explaining it was hereditary. Lol
 
Ok wanted to update this thread with a successful outcome. After fiddling with things for months, the third barrel finally did the trick. I had the same feed issues with the Rainier 8.5" match barrel and had just about given up. Ended up selling about 1/3 of my Sub-X rounds and decided to just try the new Faxon barrel that was a warranty replacement.

Just as a reminder, new barrel left, old barrel right. My upper has M4 extended feed ramps (VSeven) so guessing the new barrel has ramps that aren't quite a steep.


I chambered a few of my test loads, at various bullet seating depths and had zero bullet setback by dropping the bolt. They'll successfully chamber with either PMAG or Lantac 300 BLK-specific magazines. At the range, I went through an entire magazine of the factory-loaded Sub-X rounds with zero failures.

I am still using the Superlative Arms gas block but have the JP adjustable on the way. Should be easier dial in the gas since it's a side adjust. I'd go with Riflespeed but it would require me going to a 7 or 8" handguard.
 
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