Bullet Setback when chambering

Ape_Factory

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Wasn't sure if I should post this here or in reloading but considering it's an AR-style gun, thought it'd be best here.

Having an issue with bullet setback in the case, Hornady Sub-X, 190gr. 300 blackout.

I was getting ready to load a bunch of rounds and was experimenting with neck tension and crimping. On a whim, I loaded up a dummy round with the bullets in question and dropped the bolt on it. After ejecting it there was significant bullet setback along with a gouge in the bullet (see photos). I tried crimping the bullet, really crimping, same result. So I pulled the firing pin and loaded a factory Sub-X round. Same thing, bullet setback and the gouge.

I then took another sub round, S&B 200gr. FMJ. I've shot just under an MOA at 100 yards with the S&B's so I know they work. Did the same thing, dropped the bolt on one and no bullet setback, no gouge.

Interestingly enough I did shoot the factory Hornady Sub-X load and was sort of surprised at how inaccurate they were in comparison. There are very few expanding 300 blackout sub bullets that are available and somewhat affordable so I went with them figuring I could improve on the factory load.

Barrel is a Faxon match grade stainless/nitrided. The gun shoots everything and I've never had a FTF with it. I've also shot a bunch of hand-loaded Berry's 220gr bullets and I haven't notice any issues with them and for the price, they're pretty darn accurate, enough for fun plinking anyway.

I tried two different bolts, same results. I'm guessing it's down to the bullet's profile? Anything I can do short of changing the barrel? I have about 800 of these suckers and it'd be a blow if I couldn't use them. The rifle is also a form 1 so I'm stuck with the length at 10.5" which really limits my options as well.

Solutions?

Photos...my load, super crimped (intentionally).


S&B's, one on the right has been chambered.


Factory Hornady round chambered
 
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Ape_Factory

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So I walked over to my neighbor's house and we put a round of the Sub-X in the mag, loaded it into the gun and slowly lowered the bolt. It looks like the bullet is tilting too far up and not hitting the top inside of the the barrel extension but rather deflecting off the face, catching slightly, then making its way into the chamber. The longer S&B's do not have that issue.

So right now I'm looking into loading the Sub-X longer, pre-cannelure. If that doesn't work, he recommended slightly filing the feed ramps and polishing them back up.

I am using 300 blackout specific magazines (Magpul).

I just loaded a round up at 2.172 COAL (factory is 2.065 approx) and that did the trick. Will still likely polish the feed ramps to help as if I go shorter than that, I get a bit of setback and it'll leave a smaller mark.
 
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Im2bent

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    Be extremely careful how much you take off the ramps or you will definitely start having ftf.....don't ask.....
     
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    bfoosh006

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    Weird for me, to see horizontal gouges.
    On a long shot... can you permanent marker one half of the case head face , and carefully rechamber a round ( taking note of where the marking is ) to see if the gouges are from the top or bottom ?

    Could the entrance to the chamber be "sharp", at the radius in ?

    And what is the "comma" looking mark on both the Hornady bullets, at the top of the brass neck, on the bullets ?

    Edit... you other guys type a lot faster then me !

    I would polish the edge in question... a over sized bore mop ( so it can't go in chamber ) , at that edge , with polish has worked for me. Spun via a piece of USGI cleaning rod.
     

    Ape_Factory

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    There are horizontal marks which are light scratches and not deep. The comma is where it's digging in to something and causing the bullet to set back into the case. The longer I seat the bullet, the smaller that mark but it's always just before the case neck. I cleaned the barrel/throat just to make sure there wasn't something in there but it did it even after cleaning. The gouge/mark is definitely deep enough to catch a nail on it.

    I haven't loaded up any duds of the small Hornady 110gr. VMax rounds to test out. I have 25 loaded with various powder charges, hoping they don't have the same issue.

    I compared it to my other Faxon barrel which is in 223 and they look similar. But yeah one of my thoughts was whether the edges were sharp enough to cause issues.

    I'll do the sharpie trick tomorrow. Good idea.

    I posted over on the 300 blackout forum too as I figure those guys may have lots of experience loading this particular bullet. Want to see if others have had this same issue or if it's simply a ramp angle issue with the Faxon.

    The nose of the bullet kinda gets bounced around (almost flicked downward) and I think it's slamming onto the lower portion of the throat, causing that mark. It seems to happen, if I'm doing this in slow motion, right as the round pops out of the magazine completely, past the feed lips. Maybe I can try to shoot a slow motion video of it.

    Duly noted Im2bent! I'll remove as little as possible when polishing.
     

    Ape_Factory

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    Ok...the marker test. I did half black half blue. Sharpie. Loaded the blue side up on a cartridge with the bullet seated to factory depth (2.065).


    Blue side up in the mag.


    Blue side up in the chamber (duh, it's still in the mag!)


    I dropped the bolt and tried to pull it out as slowly as possible and it appeared the blue side was still mostly facing up.

    The horizontal "ring" marks were mostly on the black side but bordering on the blue side (up).


    The normal big gouge wasn't there (I reused a round that already had the gouge) but it appears as though it did it to the neck this time.


    I'm beginning to wonder if the actual chamber was finished correctly. I have a few boxes of the Sub-X which are now mostly worthless in this particular rifle. I'm going to reach out to Faxon and see what they think but I might just snag another 10.5" barrel from another brand. I'm not sure polishing the ramps is really going to solve the issue unless I load the bullets longer and it still appears to be beating them up on the way in (rings).
     

    Odysseus1911

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    Can you get a close-up, straight-on pic of the feed ramps? And a second pic of another rifle's feed ramps for comparison? I'm thinking one or both sides of your feed ramps may be out of spec and the bullet is slamming into the sharp edge of a ramp which would also explain why it is minimized by seating long, as the bullet nose would hold the ogive off the ramp.
     

    Ape_Factory

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    I'm actually going to take the rifle apart today and I'll do that. Faxon is sending a new barrel, free of charge (great customers service from them), and I'm sending along a few dummy cartridges/bullets so they can examine. I have a second 223 Wylde barrel from Faxon that I can compare along with a POF barrel. I also ordered a Rainier Arms match barrel just as a backup.

    I've now loaded a "factory" 110 grain round and no setback. In fact, it went a bit longer on a bolt drop (Gorilla ammo, not a fan!). I also tried a 125 grain FMJ plinking round and no set back there at all.

    So setback with 190 grain sub-x bullets and marks on the longer bullets. I have tried various headspacings. Chamber is about 1.080, maybe a tad longer, and I usually do reloads at 1.076. I have a few cases that were processed by someone else and those came in at 1.066. Same result. Factory ammo varies too. I have Hornady Black 208gr. Amax subs which measure out at 1.078. I actually haven't run those in the rifle yet. Just bought two boxes for experimentation and dissection for my own loads.

    Will keep the thread updated. I really liked this barrel otherwise. Was very accurate with everything BUT the 190's although admittedly, my first 110gr. test loads were all over the map from both a grouping and SD standpoint.
     

    Powder_Burns

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    This may be a dumb question and possibly unrelated to your issue but have you measured your chamber’s throat?
     

    Ape_Factory

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    I have not. I did check with a go/no go gauge but did not measure the throat.

    Edit: I have the Hornady system for measuring throat but I don't have a 300 blackout modified case. Just a .308 and .223.
     
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    Powder_Burns

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    The marks on the bullet don’t really look like they were made by rifling lands, but anything is possible I guess. Measure your freebore, it is possible the bullet is getting jammed in the lands and getting pushed into the case.
     

    Ape_Factory

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    It's only setting back with the 190 sub-x bullets which are quite a bit shorter than say the S&B 200 grain. It could be the contour itself though...Faxon is going to let me know. It'll mark up both rounds but the S&B 200 grain does not get set back but does get the horizontal gouges in the bullet. I'll pull out one of the 208 grain A-max rounds and drop the bolt on it. They're the longest by far but honestly, sitting here looking at them side by side, they have a more narrow profile from the ogive to the tip than the sub-x or a 125grain fmj bullet.

    I think it has a lot to do with the steep entry angle and the shorter nose on the sub-x too.
     

    Ape_Factory

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    All three, sub-x left, 125 FMJ center and A-Max 208 grain right.


    I chambered two of the Hornady 208 grain rounds. They both grew in size slightly. Both have small marks near the tip and the horizontal marks closer to the case mouth but not as much as the S&B's. The 125 and 208 grain are factory loads.


     

    GreenGO Juan

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    Image 9-9-21 at 5.35 PM (1).jpg


    When you are here try pushing the cartridge into the chamber with your finger, and see if it tries to bind on the feed ramps. I assume you were dropping the bolt on it.
     

    msgriff

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    This is my hick method for measuring max OACL without a modified case, don't judge.
    Accurately measure from bolt face in battery to muzzle, be careful not to measure from the ejector. Then gently drop a loose test bullet into the chamber, keep very light tension on the back of the bullet with a section of cleaning rod, and accurately measure from tip of bullet to muzzle. Compare the distance between the two measurements (-jump) and your loading length. I use a brass rod with a square face as a "story" stick and mark at the muzzle with a razor blade.
     

    GreenGO Juan

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    I wonder if its catching, pushing the projectile in and off center and a some point contacting the throat which is putting that mark(in the black sharpie area below) as the projectile is forced straight. Maybe try to heavily crimp the canneluar and see if it still does it. I am not a gunsmith and just throwing out Ideas.

    Image 9-9-21 at 6.18 PM.jpg


    I have some dud rounds made up to test cycle with out the chance of an unwanted ignition. After 10 or 15 cycles(or so) thru an AR they loosen up and the projectile starts moving around and creating all sorts of not good marks/similar marks, I re crimp when I notice it. I played with different neck tensions and is when I decided I would crimp all of my loads for semi. IMO too much force to rely on uncrimped neck tension alone.
     

    mtrmn

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    Just a stab in the dark here. Does your EJECTOR have sharp, squared-off edges? I have been told that square ejector edges could catch on the cartridge base for just an instant during the feed cycle and hold the cartridge at too much of an upward angle and cause issues with the bullet entering the barrel extension/feed ramp/chamber area. Which causes the cartridge to catch a sharp edge that it would normally slide right on past. I don't know which brands, but some "enhanced" bolts come with round-faced ejectors for this reason. I have removed my ejectors and chamfered the forward edge by chucking them in a drill and holding them against a sharpening stone. This seems to be more problematic in large frame ARs.
     

    Ape_Factory

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    Chamber photos. Completely forgot I had a bore scope.

    300 Blk



    223 wylde


    POF Revolution DI (308)


    Ok here's a series of photos moving the bullet out of the mag by hand. Had to use my pinky and it was still difficult to get a digit in there. This is in consecutive order.







    So the above sequence was moving the cartridge really slowly. What I think is happening is the cartridge, when being pushed faster is nosing up off the ramps and catching the throat. At that point the bolt is still slamming home so it pushes the entire cartridge UP, the bullet hits the lugs, leaves marks, and ultimately pushes the bullet back into the case. Here's me pushing the bullet a bit faster and at the critical point where the nose of the bullet is actually on the outside wall of the throat.



    Is it possible the magazine (it is 300 blackout specific) is contributing? The longer bullets likely catch on the more beveled portion of the throat's opening and slide in, although they still get marked pretty good.
     
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    Ape_Factory

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    Just a stab in the dark here. Does your EJECTOR have sharp, squared-off edges? I have been told that square ejector edges could catch on the cartridge base for just an instant during the feed cycle and hold the cartridge at too much of an upward angle and cause issues with the bullet entering the barrel extension/feed ramp/chamber area. Which causes the cartridge to catch a sharp edge that it would normally slide right on past. I don't know which brands, but some "enhanced" bolts come with round-faced ejectors for this reason. I have removed my ejectors and chamfered the forward edge by chucking them in a drill and holding them against a sharpening stone. This seems to be more problematic in large frame ARs.
    Rainier Arms enhanced bolt


    RCA enhanced bolt


    JP Enterprises enhanced bolt (new)


    I tried the first two with the same results. Have not tried the JP.
     
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    Ape_Factory

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    Just shot a slo-mo but it's inconclusive. I'd need video at around 1000fps as opposed to 240 to really get a clear idea of what's going on.
     
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    Odysseus1911

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    C1319A27-4C1E-4194-B6EA-772BB19AD632.jpeg


    Going left to right: 1st circle looks like a burr, 2nd circle looks like a burr, and I think one or both of these may explain your longitudinal gouges. The 3rd circle looks like coppering on the feed ramp edge, and I think this may be where your horizontal ring marks are coming from.
     
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    mtrmn

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    Rainier Arms enhanced bolt


    RCA enhanced bolt


    JP Enterprises enhanced bolt (new)


    I tried the first two with the same results. Have not tried the JP.
    The Ranier and JP both appear to have well rounded edges. I was just thinking the ejector could be causing a hiccup for a millisecond and allowing other geometry to get a bit out of sync during the feed process.
     

    supercorndogs

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    I have had magazines that need cleaned start doing that to me. Have you tried them in a different magazine?
     

    Ape_Factory

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    I have a six Magpuls, they're all brand spanking new. I think they're gen 2's. The one I was using to test for changes in COAL was, I believe, new and had never been used in anger. I'll check it though. Thanks for the tip.

    Rainier barrel is arriving tomorrow, I'll probably take the time to disassemble the rifle and get better, high resolution shots of the chamber. Not sure when the new Faxon barrel is arriving. I'm assuming this week if they have them but it could be a while if they are not in production yet.

    I did one more dummy test load, with a decent crimp, probably a bit more than I'd prefer, and it didn't set back the bullet. Marks are still there including the gouge but it was literally at the point where the bullet intersects with the neck. I may test the 110 grain v-max bullets tomorrow.
     

    Ape_Factory

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    I haven't tried other mags. I may give that a whirl as well.

    The Rainier Arms barrel just arrived and the chamber/feed ramps look exceptional. I'll have photos later. Not sure what the gas port size is as I don't have an accurate way of measuring but it looks to be about .110 or thereabouts eyeballing it with calipers. Will compare to the Faxon once I have the rifle apart. Into the freezer for the Rainer!
     
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    BuildingConceptsllc

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    I haven't tried other mags. I may give that a whirl as well.

    The Rainier Arms barrel just arrived and the chamber/feed ramps look exceptional. I'll have photos later. Not sure what the gas port size is as I don't have an accurate way of measuring but it looks to be about .110 or thereabouts eyeballing it with calipers. Will compare to the Faxon once I have the rifle apart. Into the freezer for the Rainer!
    I've had similar type issues with mags in some rifles that I either had to adjust the follower so it gave the bullet a slightly different angle, or use a different mag. Some of them put the round a touch higher (or lower) inside the action and as a result makes the round present at the wrong height/angle. I'd try some different ones if you can before I did anything more invasive. Just a thought
     
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    loveha

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    I just compared my Proof and DD barrels. I shoot the same Sub-X bullet out of my Proof barrel, and the ramps on that barrel are wider like your POF. The ramps on my DD barrel look like every other AR15 barrel.
    Proof barrel. How every 300BLK barrel should look in my opinion.
    20210913_220453.jpg


    My DD barrel. Looks like your typical ramps for 223. I should probably clean that up some.
    20210913_220609.jpg
     
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    Ape_Factory

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    Ok...new Rainer barrel arrived yesterday. Both barrels have the wider feed ramps. The main difference between the two is the Rainier looked smoother. The edge leading into the throat has a smooth radius and not a sharper edge but otherwise the Faxon barrel extension and feed ramps look good to me. The Rainier looks like it was hand finished, which it is.

    One thing...I took the photos of the Rainier extension in "live" mode so it makes things look sharper/more contrasty than they really are where the Faxon was shot in raw mode on the iPhone. Less artifacts and contrast.

    The gas ports on both are almost identical with the Faxon being slightly larger. The later photos of the Rainer are with the barrel frozen. It's definitely an interference fit like the Faxon so good news there.

    Faxon


    Rainier






    Frozen Rainier at the bottom.


    Visual gas port comparison. Both seemed to measure about .110 or thereabouts, me using calipers and a magnifying glass to line everything up. But visually the Faxon looks larger but maybe due to the nitriding.
     

    Im2bent

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    You can use the shank of a drill bit to check size, basically a poor mans pin gauge. Then measure the bit shank or look up the decimal equivalent.
     

    Ape_Factory

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    Faxon sent the new barrel two-day air on their dime, awesome customer service.

    New barrel left, old right. Really can't tell a difference between them honestly.


    Turning to the outside, this is the only real difference I can see and you'll notice the notch for the feed ramps on the new barrel are smaller than the old. Critical difference?


    Versus the Rainier, you can see the milling marks on the Faxon in the entrance to the throat area whereas on the Rainier, they look hand finished and smoother on the transition from extension to throat.

    I'll try both and see what works. I had to make a few adjustments to accommodate the shorter barrel but it was otherwise bolt-on. And yes, I have a special wrench to get the silencer off from the front. With the OSS, you're able to install it so that when it bottoms out, no need to torque it any further. The gasses exit in such a way that it keeps it on and it won't thread off while shooting. Hand guard is carbon so it doesn't heat up like a metal guard would.

     

    Ape_Factory

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    Headed to the range tomorrow. So far looks promising with the new barrel.

    Couple more photos just because!


     
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    Snuby642

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    I'd like reports on those 190 sub-x.

    I can't remember why I had not tried them, something in the load data?

    Using the hornady 220 rnfb in bolt and ar sbr. They are hitting 1 moa regularly but don't expand at 1050 fps (1015) at 12.1g cfeblk both guns 7 twist.

    No known feed issues.
     

    Ape_Factory

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    I have a few VMax 110gr. loads worked up with three different primers. I also have the 190 Sub-X's loaded up with three different charges using CFE Black. I should have loaded another 15 with H110 just to compare. I have some factory Sub-X rounds that I'll take data from as well.

    Hodgson's web site had load data for the 190's although I'm not going to seat them at 2.050 since the factory loads are more like 2.065. I took measurements from the ogive on the factory rounds but can't remember what that number was off the top of my head.
     

    Ape_Factory

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    Went to the range yesterday with a mixed bag of results.

    The 8.5" barrel is attached and I switched to the JP bolt. Never switch two things at once.

    Went to set up function of the rife. I have some "factory" loads, 125gr. fmj's from a non-big name company (aka not Hornady, Winchester, Nosler, etc..) to use for this process. Primers were blowing out the back. I've never had this happen before and I was going to pack it up. Everything was chambering fine but obviously something was off. I took the BCG out, adjust the gas block to the recirculation setting, fully closed and started from zero. Fired one round. Stone cold case of course which was nice. Opened it up a few clicks, rinse and repeat til the bolt locks back on empty mag. No blown primers. I fire three more and on the fourth I get a click but no bang. Sure enough, another primer has come out. The rims look beat up too. I'll post pics later.

    I brought some Barnes 110gr. cartridges with me as I wanted to chrono a few. Shot four of those, ZERO blown primers. Ejecting at 4pm. I take note of gas block setting.

    I then went to subs. Five factory subs. Opened up the gas block fully in recirculation mode. It won't cycle with the subs like it did before. So I did not run any of the 190gr. sub-x test loads I brought.

    Going back to supers, Hornady VMax 110gr. with H110, I turn the gas block back down to where it was before. I work up the powder ladder, zero issues, tested three different primers as well, 50 rounds in all. I think I have a promising load for those but not if the current barrel won't shoot subs.

    So after all of that, the rifle sat for a bit while I tested a .308 load. I then remembered I had Hornady Black A-Max 208gr. subs in my bag and I wanted to shoot a few of those as they had the highest headspace of all the factory cartridges I've measured. I go to adjust the gas block back up to full and it's frozen. It won't budge at all. And I thought this wasn't supposed to happen to Superlative Arms gas blocks.

    It was stiff once before but I managed to break it free. This time, it feels like the Allen wrench would snap first. So the rifle is coming apart and I'll see if there are any issues with the SA block and gas port alignment. I'll clean the gas block and see if I can unfreeze it. If not, it'll be going back which'll probably take two months given the current climate.

    I have a bunch of cheap Berry's subs loaded up for function checks so I'll likely check everything, put it all back together and work on that next. If that doesn't work, I may just go back to the Faxon barrel and check it with the 190 sub-x dummy rounds. That barrel shot everything and always locked back on an empty mag. I suspect my new issues are a combination of the SA gas block and possibly the JP bolt. Test, test and test again!
     

    Ape_Factory

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    Took everything apart and reassembled with the 8.5" barrel again. This time I used a video bore scope to verify everything was lined up. And I measured. Twice. Pulling off the gas block, and judging by the residual carbon, it was aligned properly the first time. I managed to unfreeze the gas block and I gave it a thorough cleaning.

    I took out the JP bolt and went back to the RCA bolt.

    Gas ports...both barrels have the exact same gas port size which looks to be .109. I can't slot a 7/64 bit into the gas port but a 3/32 slides in easily with room to spare. I'll try one last time to make it cycle with subs. If it doesn't, I can either enlarge the port or switch back to the 10.5" barrel.







     

    Snuby642

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    Were these your reloads?
    That's a large percentage of blown primers.

    I recently had a froze adjustable gas block. My guess was that a large burr from threading got under one of the screws and was partially blocking gas flow as well.

    The vendor made it right quickly replacing it so I can't fault them, excellent cs. The new block in place everything functions properly.

    I would check into that with the manufacturer.

    I remembered why I didn't run any sub-x, they are not flat base. I belive flat base to be more accurate in subs.

    I wish Hornady would fix them.
     
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    Ape_Factory

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    Were these your reloads?
    That's a large percentage of blown primers.

    I recently had a froze adjustable gas block. My guess was that a large burr from threading got under one of the screws and was partially blocking gas flow as well.

    The vendor made it right quickly replacing it so I can't fault them, excellent cs. The new block in place everything functions properly.

    I would check into that with the manufacturer.

    This was factory new ammunition. I tried two other brands, no blown primers with Hornady or Barnes rounds. No blown primers from any of my hand loads either.

    I did take the gas block completely off and cleaned it fully. I didn't change the setting from when it was on the 10.5" barrel and only adjusted it after I saw the first few blown primers. After adjusting the gas block to the correct setting in restrictive mode, I had even more blown primers. The block only froze after I'd shot another 60 rounds or so of my test loads and other factory ammo. The rifle functioned fine (except for subs not cycling) after I switched away from the initial rounds with the blown primers.
     

    Snuby642

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    16322411840516519592787437520996.jpg


    220 rnfb hornady interlock sitting on 12.1g cfeblk 2.1 coal cci 400 primers. Ref Lee book pg 518.

    @spife7980 introduced my to this round early in my reloading start.
    Thanks.

    I use a light crimp as when I tested them it was the best. They are running 1015 fps in cold weather from a 16 inch bolt gun, fully cycle my sbr with or without can.

    On a 100 degree day they remain subsonic. Actually my first true 1 moa round (in the bolt gun).
     

    Ape_Factory

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    May 23, 2020
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    What sort of expansion do you get with those at subsonic velocities? Bullet is nice and long, would probably solve the issues I have with the short 190 grain sub-x rounds.

    I haven't started my own load development with sub yet, just supers.
     
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    Snuby642

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    Minuteman
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    That's the problem, zero effective expansion.

    Hornady needs to put the sub-x technology on that 220 flat base bullet. Or at least put the flat base on the 190's.

    A boattail is of little use at short range and subsonic.

    The manufacturers of expanding bullets should know that but market to the mass appeal instead of reality.
     
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    Odysseus1911

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    Feb 14, 2019
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    Were these your reloads?
    That's a large percentage of blown primers.

    I recently had a froze adjustable gas block. My guess was that a large burr from threading got under one of the screws and was partially blocking gas flow as well.

    The vendor made it right quickly replacing it so I can't fault them, excellent cs. The new block in place everything functions properly.

    I would check into that with the manufacturer.

    I remembered why I didn't run any sub-x, they are not flat base. I belive flat base to be more accurate in subs.

    I wish Hornady would fix them.


    Look at the impressions on the case heads -especially the bottom middle case with brass flow into the ejector plunger hole. With this being factory ammo, you think maybe excessive headspace? He has been swapping bolts.

    OP -get some go/no-go gauges before you go any further, and let us know what you find.

    IMG-8894.jpg
     
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    Snuby642

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    Good call.
    I was kind of wondering how you get over pressure signs on sub-x.

    I'm not going to say the one thing so many of these problem threads have in common.

    Don't feel like playing soccer.
     

    Ape_Factory

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    Good call.
    I was kind of wondering how you get over pressure signs on sub-x.

    I'm not going to say the one thing so many of these problem threads have in common.

    Don't feel like playing soccer.
    Those are not Sub-X rounds. Those are 125gr. FMJ supersonic rounds, factory loads. I didn't have the same issues with anything shot AFTER those rounds, factory loads from different manufacturers or hand loads.

    And there are numerous rounds from the same batch that failed that didn't have the ejector marks and the primers weren't blown out.

    I will check headspace.
     

    Ape_Factory

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    Forgot to mention but I did order a few Lancer mags. Look like theirs are 223/300 blackout unless you get the 300 blackout-specific mag which is for 220gr+ subs. Given that I'm going with the 190's, I didn't order one of those. I may try a Magpul 223 mag as I have a ton of those.
     

    Snuby642

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    FWIW
    I had to use magpul 300 blk mags to get things to feed right. The 223 mags gave me problems.

    For the 220 subs
     

    Ape_Factory

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    Strangely enough, I started out with 223 Magpuls and just stumbled across an article online about a 300 blackout specific mag so I bought six of those! They're all fairly new, wondering if the spring strength is contributing to the setback. I need to load some dummy rounds for the Rainier barrel but I don't get the heavy markings I did with the old Faxon barrel. I may swap the new Faxon barrel in for test purposes and especially if I can't get the 8.5" to cycle factory loaded subs without drilling out the gas port. Those two extra inches make quite a bit of difference!

    And then of course there's powder. I have no idea what the factory loaded ammo uses but I'm using CFE Blk for subs. I also just picked up a pound of Lil' Gun to try and I do have H110. Need to look up which one burns fastest. But with that said, I'd rather have a rifle that runs everything and isn't powder/bullet picky. I'll give back 2" of overall length to achieve that.

    Anyone have a link to a really good video on polishing feed ramps or otherwise cleaning up a new barrel's throat and barrel extension?