BallisticianX

From what I understand your looking for the pitch of the fine thread on the extension nut so you can remove the extension tube and put a plug in it? If you wish to eliminate the extension tube and just utilize the factory mag tube for hunting it will be easier to just get the factory cap nut replacement. You can buy one here: https://gunrepaircenter.com/vmax-mag-cap-swivel-assb-power-lock/

Out of pure peer pressure I'm building a PCC for some local steel matches. Im doing this on the cheap and with considerable AR parts lying around I'm going the AR-9 route. So first let me overview what I'm working with so you guys can analyze my questions: Lower; a complete Anderson I have for my 300 ACC, POF trigger group, carbine length buffer tube with 5.56 carbine spring & H2 buffer. Will be using a Stern Defense Magwell adapater block to accept M&P0/P320 mags as I don't own a glock but do own an M&P & P320...cut my expense for mags. Upper; 5.56 WMD NiB coated upper, 15" PCF slim hand guard, Faxon 16" barrel and a KAK Industry weighted BCG. (based on my research the KAK BCG seems to be a good choice in the more affordable $100-$125 range. My questions: What combo generally is the best way to go on the recoil setup? What power factor eliminates finicky function between bullet weight changes between 124 to 147? Should I switch to a .308 spring from 5.56? Swap the H2 to an H4/9mm specific buffer?, Leave or remove the BCG weight? My goal, if achievable, is to get this setup to run reliably with a the same powder (most likely WSF as I have tons of it) but with bullet weights ranging from 124's up to 147's, coated or jacketed. Im trying to prevent having to adjust between bullet weights and not beat on the internals either. I'm basically gonna run this thing as the ammo disposal unit and chew up all the different partial boxes of bullets I've accrued over the years while just having carefree fun...hopefully without changing anything. Ive never messed with AR PCC's so I have no idea what works or doesnt. Or how finicky or forgiving they may be. So whatever info/experience you have is appreciated.

Sounds exactly like my experience. Yeah, that Perfecta brass is a scurge as is CBC & IMI. Perfecta always leave a case wall bulge wherever the heel of the bullet ends up when seating. Im glad you found the extractor, I did not, but considering the situation I would have replaced it anyway. I bought the Lone Wolf "Alphawolf" extractor. It works perfectly and tougher than the factory MIM part. My strong advice is to also replace the extractor pin (the part at the end of the extractor spring that has the notch you line up to slide over the rear of the extractor body). That pin is what retains the extractor. In order for the extractor to be blown out of the gun it needs be excessively hinged out and against that pin. With all that force I wont take the chance of a hairline fracture to the pin. Top gun supply has them and they process/ship faster than SIG. I wont lie, this issue paranoid me and put my gun into a "questionable status". Besides the better extractor and new pin I also changed some things to prevent it from happening again. I bought a Faxon barrel that does not chamfer the chamber entry so deep and wide as the factory one for more chamber support, changed to a slower powder (WSF from A#2), and a tad heavier recoil spring (14# from a 13#). Ive put 300 rounds thru it so far and my cases show less deformity near the web and I actually like the way the combo feels better anyhow. As a bonus the Faxon barrel is more accurate than the Sig. At 20 yards its doing 1.5" clustered groups vs the 3" vertical stringing as was the case everytime with the Sig barrel.

I had a case blowout this past saturday with my P320RX of 2019 manufacture that also blew out the extractor. My load (135 gr RMR JFP over 3.8gr A#2) is fairly mild and does not swell the back end of the case like the pics above but they will grow about .002"-.004". Like others said I never had a problem before this. Its a compounded issue of weakened cases and the chamber design. The chamber on the 320's is horribly unsupported and a questionable design in my opinion. It's bad enough so much case is hanging out beyond the chamber face to headspace just below flush with the hood. But they add insult to injury by a "funneled" cut a good 1/8"-3/16" in from the chamber face. Almost like they used a revolver forcing cone cutter to give it a elongated mouth to enhance feeding. The rear 1/3rd of the case is freely able to bloat. Because of this a case that is weakened has the room to fail whereas the same case in a supported chamber most likely would have survived. Im looking into an aftermarket barrel that at least doesn't have that funnel cut nonsense, just a standard chamfer, for a little more support for my own peace of mind.

The case that had a rupture failure for me was marked "P-A RH". I researched it to a company called Precision Ammunition. God knows where the brass was made or what was loaded in it and how many times it was fired before it made its way into my brass bin. Though my cases have never bulged as extreme or as regular as the OP, Ive taken steps to prevent any future issues. I measured and adjusted my COL for .030" clearance from bullet driving band to lands, moved from a 13lb to a 14lb recoil spring, and completely sorted out brass with any off brand headstamp. The case support in these P320 barrels is a point of paranoia for me. The OP's barrel pics show way to much 45 degree chamfer for my liking. My particular barrel does not have near that much but instead it funnels inward, like they used a revolver forcing cone cutter on the 1st 3/16" of the chamber. Both approaches leave too much area for cases to bloat into in my opinion.

The pistol that started out as a P320 RX I won at match. I built it into a poor mans Legion lol. Aggressive stippled TXG grip, modified the OEM slide cut for the RTS2 dot (including recoil bosses), and some simple top and side window cuts. Threw in a GG trigger kit with my mods to the sear for a 2lb-13oz pull. She's classy!

I know this post is a few months old but just stumbled on it researching my similar experience. I have a P320RX of early 2019 manufacture (not the X5 series). FIrst off the pics are of a correctly seated round. The head should be flush to a few thousand lower than the hood. While at a match this past Saturday I had a case failure that bulged identical to yours that also ruptured the case right in the belly of the extractor groove about 3/4 of the way around. Was surprised it ruptured right in the meat of the web as usually a "weak case" breaks open where the case wall meets the web area. Im running a 135 gr. bullet with 3.8gr of A#2 of which is not a stout load. I can also confirm it was not and overcharge as I visually inspect the powder in each case when I manually set the bullet for seating. It just snapped when fired and between the sound and the slide barely moving I thought it was a squib at first. But when I cleared the gun I saw the deformed case freely drop out of the chamber despite my extractor being MIA. No heavy black residue or blown out mag etc, just a missing extractor. I long suspected the healthy clearance at the chamber on this gun was an issue as my spent cases always slightly bloated a bit at the web and this is just more confirmation. My opinion is my situation was compounded by a piece of brass that may have been weakened by previous firings. The unsupported nature of this barrel wont tolerate much in the way of any weakening from cases that have been reloaded even only a few times. Ive also noticed loading to longer COL's that will still pass the plunk test will exhibit more case bulging than if loaded shorter. Seems like the bullet needs a good amount of bullet jump to buffer pressure to make up for the lack of chamber support. Kinda like a 5.56 nato chamber incorporates bullet jump to prevent pressure. I like the P320 but this chamber design and what I've experienced raises doubts for me. I'm looking into an after market barrel in hopes it may have more support. We shall see!

A few variables to case failure rate. Comes down to brand and their quality as companies will use fillers in the brass alloy to cut costs and it results in quicker failure. Then the load and how much it expands the brass. When you form brass it work hardens, or in other words starts to lose ductility. So the more you size the more brittle and uneven the grain structure will become. Now with increased expansion and the greater dimensional correction to resize will accelerate the ductility loss even further. This applies to what mchapman said about case mouth flare. The more you bell that case mouth the more work hardening you induce for a brittle edge. Another caveat is nickel plated brass; that plating tends to compromise the uniformity in the brass when resized as your compressing a non ductile material into a ductile one upsetting the thickness. Ive found nickel plate brass to last only 50% as long as unplated brass in the same situation. As far as brass quality, hands down starline. Ive fired more rounds thru starline without failures than anyone else consistantly from lot to lot.

I would look to another powder vs Titegroup. I never had any luck with Titegroup in 9mm under any coated bullets. Titegroup has its place but 9mm lead loads has not been it for me!. I currently use A#2 in my 9mm lead minor loads. Accurate, clean, cool, and shoots soft. For 135 to 147gr lead WSF is another one that works well (Wsf is cleaner with heavier bullets at minor pf vs the lighter weight bullets). As another poster mentioned Sport pistol seems to be well acclaimed as well, I personally havent tried it yet.

Spot on. Most standard seating dies are A; seating plug off center in relation to the die body, B; seating plug contour doesn't match the bullet profile and wont allow any self centering. The only way to effectively do away with bullet concentricity issues is to use a floating alignment sleeve type die. I have exclusively started using the Hornady Seating dies as they have an effective alignment sleeve design, are cheap, and agree with progressive presses. I had regular problems with Dillon, RCBS, and Lee (hate Lee stuff) seating dies tipping bullets. When I switched to a Hornady floating alignment die I know have zero bullet concentricity issues.

The mouth of the Catskill Creek at the Hudson River is in the Town of Catskill of which is the next Town North of me.

Check the thumb piece, if the screw is not staying tight enough or the portion that sits in the frames recess is worn it could be rotating inducing drag and binding causing your problem. Take the thumb piece off and see if it moves more freely. Take special care when installing the thumb piece to make sure you center it to the frame recess.

The finger lakes region and Seneca is still a good 200 miles from me. I’m in the mid-Hudson valley of N.Y. about 50 miles south of Albany in the foothills of the Catskill mtns. A.K.A the NYC & NJ tourist region. Sent from my iPhone using Tapatalk

Unfortunately your not close or I’d give you some 158 RN berry’s I got kickin around.

I agree with you, all pistols and even revolvers these days come over sprung. Thats why I had ordered a fat guide rod w/15lb spring for easy spring changes before I had the gun in hand. I never actually fired the gun with the stock spring/guide rod in it. Totally forgot about that. I've since settled on the feel of the 13lb with vigorous ejection.