MoRivera

Right, so as I said, I don't quite know how a hydraulic would cause the same, unless something in the piston action was interfering with the return stroke somehow. A misalignment of the piston/plunger hanging on the tube walls or kinking within the spring, maybe?

When I was putting my first PCC together, I tried different springs/buffers, and a regular carbine spring/buffer apparently wasn't returning the BCG strongly enough, so it seemed the extractor wasn't fully grabbing the case/rim, and I would get a stuck case and double feed. So in that case I guess the spring was too weak and/or the buffer is too light. How a malfunctioning hydraulic would simulate that I don't quite know, but if it's worth anything there's this example.

As I mentioned above, the Stern Defense magwell converter has been very reliable and they also now make a flared well that you can attach to it, which helps a lot with mag changes. https://www.brownells.com/rifle-parts/receiver-parts/magazine-parts/magazine-hardware/ar-15-9mm-mag-ad-flared-magwell-prod123398.aspx But still, if given the option like in other states, I would have started with a dedicated unit.

That's an interesting thought on this....so with less bearing surface and the 9mm in particular, do you think that the bullet may drag/skew a bit in the barrel after the 10 or so inches in which it's burnt all its powder?

And what you had for breakfast......? Sorry.

Living in CT, we can buy 'other' AR formats, but they have to have an arm brace, which will officially exclude them for use as PCC in many competitions. So I went with a pre-ban AR lower for a dedicated PCC (as it was the only way to legally put a stock on) and use a Stern Defense magwell converter for 9mm Glock mags. The relocated eject button takes a little getting used to, but for me it became very intuitive. The Stern has last-round-bolt-hold-open, which I find useful because I live in a state that bans 'high-capacity' magazines, and some IDPA matches that I shoot PCC in have stages with mandatory reloads after six shots or what have you. My only complaint about the Stern adapter was that the magwell opening was rather tight and it would be nice to have it more funneled for mag changes. But now Stern also sells an attachable delrin magwell funnel, and that helps tremendously. Altogether it was a lot to spend. If I lived in a free state, I would most definitely have started with a dedicated lower. or just have gotten a Sig MPX or CMMG Guard.

Here's a recent thread on the topic.....goes through comps, but also discusses brakes as well IIRC....

Do you think that the barrel needs some 'break-in' or the like?

I have not tried it off a rest at that distance, but between 15-20 yards off-hand, I could consistently tear a ragged hole the size of a lemon out of a paper target with 100-250 rds...maybe a few flyers outside of that main hole by an inch. This is with a 6MOA-dot C-More. I might try some 25-yrd stuff off a rest to really sight in the red dot, but like with most PCC's, I think it'll consistently put hits in the center A/Zero at various distances if I do my part. Frankly though, I got this barrel as a sort of 'placeholder' while I get a Taccom featherweight tension carbon fiber barrel repaired....and the accuracy for me and my limited abilities seems the same. So if I get the Taccom back, I might be selling the MBX. I got it more because it was a light barrel that was a total 16" with a comp pinned/welded. The only thing I could possibly think of for poor mechanical accuracy is maybe barrel whip/harmonics since it is so thin with a bulbous all-steel comp at the end of it. As I mentioned, it does have some ring to it when you knock it with your finger/knuckles.

I have one.... It shoots fine, I just think that with factory 9mm (115-gr Blazer) it's still kicking too much for me to notice any effect of the comp.

I'm using a regular Kynshot 5000 with an X-power carbine spring and a wave spring behind it. Was looking to try the heavier .308 carbine one. This is in a regular blowback.

Yes 115-gr Blazer ....could no longer edit that post. As for the MBX, it may just mean that the Taccom comp is doing something as well and that's why I didn't feel much difference. Either that or again, full-power factory ammo jolt may be overwhelming the effect.

Fired around 200 rds today to test, and just like the B-G2S, the B-GRF works fine with my 9mm PCC Glock-mag setup. Not problems resetting or anything. Just as when dry-firing, it feels to me sort of like a lightened MilSpec trigger. It's a nice and controllable pull, but with a certain 'roll' to it and a bit more overtravel than, say, a POF single-stage. It can fire pretty fast but I can't really ride the reset like I do on others, you just sort of let it all back and yank as fast as you can....so I can see how it's not recommended for slow-steady accurate shots. But again I like the curved shape and somewhere down the road I may try a Hiperfire 'Reflex' (24G I think). But chalk this one up as working with PCC, at least with my BCG.....which I think is a Foxtrot Mike or something, don't really remember.

Yes I was recommended the A5 in a similar conversation a while back and I may look into it. I have also tried my current buffer spring + wave spring combo with a heavier 5.4 oz carbine-sized buffer, and it still 'jolts' when it comes back to close (even with interior weight movement) whereas the hydraulic has a more shock absorption when hitting the breech. But the A5 interests me. And yes I check reset dry firing whenever I put in a new trigger or buffer. I think with the case I mentioned, it was an issue with the Rise Armament trigger group I had i there at the time, as that started to get finicky afterwards in another gun with more 'standard' setup. But still, with the longer 5007 and a both a) a longer rifle spring and b) normal carbine spring and wave spring in the carbine buffer tuber, it was a real chore to even cycle the bolt back past the ejection port. Whereas with the 5007 and just a carbine-length spring, it would get back far enough for both reset and lock back.

I'm giving a Geissele B-GRF 'Rapid fire' trigger a try. Now I did some research and saw that the S3G and S3G-E (on which this trigger is supposedly based) are not reliable in 9mm PCC's....BUT.......I have a B-G2S that I tried in the same PCC with the same BCG a while back. And even though I ended up putting the G2S in my 5.56, it ran flawlessly through around 400 rounds in PCC before I switched it. Reason why I point that out is that the hammer profile of the GRF looks to be identical to the G2S, but different from the S3G and S3G-E. From the research I did it's the hammer profile on the S3G that wasn't allowing reliable reset upon cycling, and from personal experience the profile on the B-G2S works fine. Only concern is I'm using the lighter trigger spring in the GRF, so I'm wondering if that will affect reset with 9mm. But dry-cycling so far seems to have a very definite reset, whereas I've felt trigger groups that are very light on felt reset and have failed during live-fire. Dry-firing, the 'break' on the GRF is interesting...like a highly polished mil spec, but with virtually no take-up and less travel. Not a sharp, super-short glass-rod break with no overtravel like some like. Definitely more of a 'roll' than the sharper shelf of the POF flat-faced that I had in there before. Kind of reminds me of the single-action break on some of my CZ pistols. Reset has a bit of travel, but once it resets there's again very little to no pre-travel before the break again, so I guess that's why they call it the 'Rapid Fire'. Will test out tomorrow and see how she runs. Reason why I switched out was a) The POF flat-faced still feels a bit heavy, and b) I just like curved-face triggers more than flat-ones. If the GRF doesn't work out, may try a Hiperfire Reflex.

I have both the 5007 which is the longer 9mm model and the shorter 5000 which is intended for 5.56 carbines. I use the shorter 5000 combined with a .308 carbine spring and a wave spring at the rear end. Although the 5000 is lighter than the 5007 at 4.3 oz vs. 5.9 oz respectively, I still feel more jolt from the 5007 and just the buffer spring (it's too long to also include a wave spring) when it reaches the rear end of the cycle, compared to the lighter 5000 which is both 'padded' by the wave spring at the rear as well as shortening the stroke enough that it doesn't go way back of the bolt catch. I tried a rifle-length .308 spring with the longer 5007 once (carbine buffer tube), and the buffer wouldn't go back far enough to reliably reset the trigger....like it was being too short-stroked or something. Run all with bolt weight in. Blitzkreig seems to only sell the 9mm versions, whereas Kynshot (which I assume is the original manufacturer) has all the other models. Was an earlier version of the 9mm-specific model shorter?

That's what I understood a short while back when I shot my PCC in a local IDPA match, but I actually decided to shoot my 10-rders in a stage that had specific mag changes because I wanted to work on them and also I'd be self-conscious if all the other shooters had to do one and I didn't. Actually, I also shot it both strong and weak one-handed on a stage that called for it. Still did well as it had a very light carbon-fiber barrel.

I also notice a considerable difference in 'jolting' when the cycle returns to battery compared to 'normal' type buffers.

This is why as a CT resident, I had to splurge on a pre-ban lower.

Well, technically as I gather, an AR with a brace is either a pistol if it doesn't have a vertical fore grip, or an 'other' if it has a barrel 12" or longer and has a vertical fore grip. As far as IDPA... 8.2.7 Pistol Caliber Carbine Division (PCC) Requirements: Rifles permitted for use in PCC must be semi-automatic and have a minimum barrel length of 10”. Carbines must be designed to be fired from the shoulder and have a butt stock installed. Authorized pistol caliber cartridges include 9mm, .357 Sig, .40 S&W, 10mm, and .45 ACP. Magazine capacity is 10 rounds plus one in chamber to total 11 in carbine at one time. Starting condition with PCC is locked and loaded at the low ready, unless otherwise specified on written stage description. PCC Division Permitted Features and Modifications (Inclusive list): It’s an “Inclusive list” so that means it includes almost everything and is not necessarily excluding any modifications if they are not listed here. Iron Sights, Optical and Electronic Sights are allowed Lights and Lasers are also authorized Muzzle Devices such as Flash hiders, Compensators and Muzzle Brakes are allowed Action work may be used to enhance trigger pull as long as safety is maintained Reliability work Internal Accuracy work Aftermarket Extractors and pins may be used Aftermarket Triggers and Trigger Work that result in the trigger being forward or rearward from the stock trigger position. Externally visible trigger over travel stops Checkering, serrated and stippling Extended and/or ambidextrous bolt releases Custom finished and engraving may be applied Aftermarket safeties Magazine base pads may be modified by reshaping, texturing, or adding bumper pads. Aftermarket magazine base bumper pads may be used provided they do not make the magazine weight more than 1.00 oz over the same capacity factory magazine. PCC Division Excluded Features are firearms not designed for use with a butt stock; for example AR pistols with Sig Brace or equivalent. Bipods are not authorized. Butt stock must remain attached to the firearm. I think for USPSA, unless it has changed recently........ Appendix D8--Pistol Caliber Carbine Division 1 Minimum Barrel Length **see Special Conditions** None (See special conditions.) 2 Approved/Permitted Calibers 9mm, .357 Sig, .40 S&W, 10mm, .45 ACP 3 Minimum Power Factor 125 **Minor Scoring Only** 4 Maximum Velocity **Minor Scoring Only** 1600 FPS 6 Must have stock attached and be capable of being fired from shoulder position. **Note: Sig Brace and any variant thereof is not allowed** Handgun to carbine conversions are allowed, provided they meet the criteria above.**see Special Conditions** Yes, see 5.1.10. 7 Sling use authorized Yes 8 Optical sight/electronic sights permitted Yes 9 Compensators /Muzzle Brakes permitted Yes 10 Flash Hiders permitted Yes 11 Suppressors permitted No 12 Rules References All references to “handgun” are deemed to apply to PCC as well, except where the terms “holstering”, “drawing”, or “re-holstering” are referenced, and where otherwise noted. PCC specific rules are in the PCC rules addendum. 13 Lasers/Flashlights Yes 14 Magazine and Magazine holder restrictions No side-by-side magazine couplers allowed. Magazines must be carried on the belt or in apparel pockets. See rule 5.2.4. No restriction on location on the belt. No thigh rigs or tie down magazine holders. End-to-end coupling/extension is allowed. 15 Full Auto/ “Burst” Capabilities (one trigger pull fires more than one round--see special conditions) Permitted, but semi-auto function only, see PCC 5.1.11, PCC 5.1.12, PCC 10.5.18 16 Binary Triggers (firearm fires once on trigger pull and once on release) Not Allowed So I guess the question is in regards to those rules being based on the former BATF ruling the the brace wasn't allowed to be shouldered....and now that it can.....

Yeah I have both a 5000 (regular carbine-sized) and a 5007 (PCC sized). The 5007 has noticeably less hydraulic damping than the 5000, and when I asked Blitzkreig about it I was told it was because of the higher buffer velocity with PCC's, and the the less fluid pressure reacted more gradually or something. I'm currently using the 5000 with a .308 Carbine spring and a wave spring in the rear of the tube. The difference I feel between that and the 5007 and just the spring is that I get more of a jolt at the rear most travel with the longer 5007. The wave spring, for me, cushions that hit at the rear and my dot isn't jolted as much, as well as keeping the stroke length short enough not to slam onto the bolt catch (use a Stern Defense 9mm adapter which does lock bolt open on last round). My only concern is if I'm putting too much pressure on the 'stiffer' hydraulic chamber of the 5000 which is intended for the 5.56. But from the looks of it with the 5015, they've gone with more pressure anyway. Shot a lot of rounds so far though and it seems to be holding up fine.

Well, I look at that little generic pistol comp as basically no comp since I didn't notice it having much affect when I used it on other PCC's before. I just put it on there to maybe help with sound pickup on a timer. The total weight of the BSF is the same as the MBX, maybe because it's longer or maybe a little extra weight of a longer (13.5" vs. 12") handguard affected things. But all I know is that I shot better with it.

So I shot a few hundred this afternoon sighting in my C-More and with the new MBX barrel/comp. Frankly, it didn't really feel much different than what I remembered with the Taccom carbon fiber one with comp. I'm still shooting factory stuff (Blazer Brass 155gr), so maybe it's still too hot to keep the reciprocating mass from dominating the feel of the cycle. But yeah definitely didn't noticeably stabilize the barrel like on a 5.56 brake/comp. Not that it's bad or anything, or that I was expecting miracles. But considering that the MBX cost nearly twice what the Taccom combo did....I dunno. I also have a 16" BSF carbon fiber barrel that I got off a helpful member here, and I only attached a generic pistol comp that I had in a parts drawer, and I have to say that barrel (in another upper, but using same bolt/lower/ammo) seemed to come back on target better and I shot tighter groups. So I'm sending the bent Taccom back to see if they can repair. If they can....I'll probably end up putting the MBX up for sale. Again, not because it's bad, but it's just not twice as good as the Taccom...at least to me and my admittedly limited experience. Definitely keeping the BSF though.

I get that too sometimes. Haven't noticed any issue with performance/shooting. The rear of the receiver is also where shooters often get a lot of gas in the face when shooting suppressed, so it may just be some fumes from standing lubricants or whatever escaping.

It's actually around the same give or take an ounce. Little heavier towards the muzzle obviously with a thicker steel comp, but feels good to handle so far. If anything, the Taccom felt a bit too light. I'm still going to send it in for repair (if possible). The 12" rail seems to be the perfect length for the MBX.