- Jul 29, 2014
- 50,080
10. Honorable mention goes to the MBX Extreme https://mbxextreme.com/index.php?page=Firearm_Accessories_Buffer
For 9mm PCC This is the Way!
- Thread starter calicojack
- Start date
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11. The JP-5. A true roller delayed blowback AR style carbine. Works really well but like the CMMG it is an expensive option. https://www.jprifles.com/1.2.18_JP-5.php
- Jul 29, 2014
- 50,080
Can't believe we missed that. Aren't some of the internals HK parts?
I’m fortunate enough to be shooting the same range and Mon/Wed weekday matches as John Paul right now - at last Wed’s regular steel shoot he brought out their latest, an ULTRALight JP-5 , a 5-1/2” bbl JP-5 with I assume some carbon or other lightweight material extended muzzle, pinned and welded.
He told me they will have just the UltraLight uppers avail to go on existing JP-5 owners’ lowers.
My wife and I both have JP-5’s (hers is the Steel Challenge and mine is the Multi-Purpose) so, I’m definitely going in for at least one of the UltraLight uppers
I can’t post a video but, attached is a screenshot off one of the videos I shot at last Wed’s match - John Paul simply handed the gun off to a regular shooter to use and enjoy for the whole match!
He told me they will have just the UltraLight uppers avail to go on existing JP-5 owners’ lowers.
My wife and I both have JP-5’s (hers is the Steel Challenge and mine is the Multi-Purpose) so, I’m definitely going in for at least one of the UltraLight uppers
I can’t post a video but, attached is a screenshot off one of the videos I shot at last Wed’s match - John Paul simply handed the gun off to a regular shooter to use and enjoy for the whole match!
Attachments
I RSO a match every month and watch this guy shoot this PCC and am in awe every time. Every time he comes up to shoot I tell the rest of the squad to "not blink" or they will miss it.
22-25 targets in staggered formation in 7-10 seconds or less, I've witnessed it now hundreds of times.
Yeah, the locking piece, extractor and roller parts are all interchangeable with HK parts I believe.
If it is like their ultralight blowback barrel it is an aluminum shroud to get it to 16 inches. I am really hoping that they just release the Ultralight barrel. If I do have to go the new upper route route then I will likely go with the side charge this time. It wasn't available when I got mine.
THAT is good to know; adding that to my order, whenever I might be able to make it (I couldn’t find any mention of it on their website and I don’t want to beat the guy up with questions while we’re all sposed to be enjoying the match)
alucard0822
For great Justice
Busy weekend, as far as the OP, retro stuff is cool, but IMO it is about operating a weapon to experience history, and relate to the Men and Women that carried that into combat. I LOVE my M1 grands, they are the last firearm I would ever part with, every pull of the trigger and "ping" makes history come alive. Of course it is also one of the last firearms I would choose as a tool for personal defense. So IMO the OP's H&R 635 and pretty much all the Colt 635 SMG clones should be blowback, because the original was. There are better designs for a PCC now, but outside of their place in the evolution of the design, they aren't really relevant to a clone of a historical firearm.
Doug has competed on and off, and has a background in scientific research, but primarily he is an enthusiast like many of us. I have collaborated with him on occasion in the past(including our experience with the Maxim RDB system), he knows his stuff, but also will be the first to admit what is and isn't in his wheelhouse. I have a similar background as a long time competitor with an engineering background and a few armorer's /gunsmithing courses, but have some tactical training and a martial arts background as well. Point being, the info we have is through our day job skills and firearm experience, and definitely not infallible, especially compared to engineers that design and manufacture firearms.
Mass is necessary to keep the bolt velocity in a nice comfortable and reliable range. For 9mm, that is around 24 oz, all the cushioning, dampening etc really just soften that big heavy mass slamming into your shoulder, then slamming a round into the chamber. Problem is you need the resistance that 24oz of momentum offers for all of 1/4" or less of powered movement to give an ideal bolt velocity, then you need to stop all that mass, and then push it forward to cycle, giving a lot of recoil, and a lot of force to disperse into your shoulder, or into movement of the firearm itself. Delayed blowback just basically applies mass x velocity = momentum. A mechanism, usually rollers and a wedge increases the "gear ratio" of one part of a 2 peice bolt to increase momentum. Basically to get the same resistance offered by accelerating 24oz in a 1:1 ratio aka direct blowback, the mechanism allows the bolt and carrier to separate, and the bolt carrier moves faster than 1:1 to provide resistance to blowback, 2:1 only need 12oz, 3:1 works with 8oz. Once past the blowback phase, the reduced mass moving has a fraction of the force impacting your shoulder, and moving the PCC around when chambering. Some are so effective that a fluted chamber is needed to reduce friction, and help extraction. Less recoil, less gas, less mass might make up for the difference in reliability compared to blowbacks simple bolt and spring. Thing is tuning is important, if a delay system opens too late or early it can be a problem, it may have issues with hot or light ammo, and of course it's expensive.
I have shot or own most all of these.
1. Direct blowback, can be horrible or decent. The original Colt 635 setup was basically a heavy SMG BCG, AR10 spring and H3 buffer. About the same recoil, maybe slightly more compared to a standard M4. Short stroke, heavy buffers and dampening can reduce that substantially. Some use a solid steel buffer, or swap the H3 for a steel bodied buffer with cheaper steel weights, either makes the recoil more forceful, and can have bolt bounce, causing OOB or jamming. My Blitzkreig comp setup is about as soft shooting as a blowback can be, 6oz hydraulic buffer, 2.5oz add-on weight with a short stroke non-ramped BCG, and heavy spring. It is still mass doing the work, but the hydraulic system has advantages. First being the floating mass of the buffer uncouples a little on blowback, dampeing the initial movement, it dampens again when hitting the back of the tube to soften recoil, then dampens when chambering.
Short stroke has the same recoil, but speeds up cycling with slow heavy buffers, and being the rearward, then forward movement is closer together, less dot movement. Standard 9mm Glock mag PCCs use long buffers or spacers to cut the 5.56s 3.75" stroke to 3" being the carrier face acts as the bolt, and there is not a separate rotating bolt. Short stroke reduces this further to around 2" with additional cushions/weights or spacers, it also requires a bolt with a shape that resets the trigger in less movement, My taccom rests in about 1.5" compared to 2.5 for most ramped 9mm bolts, this can offer a little blowback effect with some triggers as the hammer has to be accelerated faster rearward under blowback. Even so, the absolute best blowback system feels like the most basic RDB, almost as soft as my Maxim RDB.
CMMG RDB. This system uncouples and accelerates the carrier/buffer rearward through rotating the cam pin due to the wedge shape of the bolt/barrel extension interface. Problem is mass does the work, but there is a LOT of friction, and it introduces some potential issues with tuning if it is dirty or under-lubed. It is a long 3.75" stroke(same as DI calibers), and does feel a little sluggish to me compared to some other systems. They aren't as common in competition as it should be due to the reliability issues and slow cycling. In use feels similar to, and a little softer than a really good blowback system. Have not fired the dissent, so not opinion yet.
I got one of the first Maxim RDB buffers, and have some correspondence with Maxim's R&D about them, along with some troubleshooting including helping Doug aka blowback9 with his. It is a brilliant system, it is a true delayed blowback, the ball bearings lock in a groove in the guide rod, and allows the rear 3oz portion to separate and accelerate at a higher ratio than the BCG/buffer bearing cage. There is still a LOT of BCG and buffer mass, and the ratio isn't all that high, so not as effective as a delayed design that has a mechanism in the carrier and barrel/receiver, but is is extremely simple being a drop-in buffer. Main issue is that you have to overcome the resistance and leverage to rack the system. On all of mine with raptor handles, and a quick deliberate rack, it is barely noticeable. Some have had them where they were awful and difficult or impossible. It is softer in recoil than ANY blowback, although my short stroke hydraulic comp setup is pretty close. It is reliable, and relatively simple and robust. Perhaps the best application is shooting suppressed, it DRAMATICALLY reduced gas compared to heavy blowback. It has a "standard" PCC 3" stroke, so feels quicker/better than the CMMG RDB, and close to short stroke/heavy buffer blowback. I tried short stroking it, and it ran reliably, but heavier recoil, and not much change in how quick it felt, would have to be re-tuned to make the most of it.
Turns out there are some considerations with this system that were not obvious or in the instructions for the early version(they are considering changes and an addendum to instructions). It is VERY sensitive to the buffer tube length and preload of the system. If it has too much play, it basically doesn't add any resistance for a little bit of blowback, then full resistance, so it can cause jamming, and it makes it near impossible to rack. If there is too much preload, the system is partially unlocked and while much easier to charge, recoil will be harsh. It may need the tube backed out a turn and/or shims(doesn't need the buffer retainer). It should just make contact with slight preload with the carrier when the receivers are closed. There have also been a couple with heavy machining marks and burrs that cause excess resistance, but most are well made and smooth.
JP's SCSS was innovative at the time, one of the first self contained heavy buffers. They practically invented short stroke with their comp setup. Problem is it is still direct blowback, and there is only minor cushioning from rubber washers inbetween the weights, and the plastic bumper, Blitzkreig's hydraulic comp setup flat out feels better. There isn't much difference in feel compared to a 10oz KVP buffer compared to the standard PCC SCSS. Thing is the KVP is $50, the equivalent 11.2oz SCSS (2oz lost from removing BCG weight) is over $200, more than the Blitzkreig comp or Maxim RDB delay, and both are better.
Then there is purpose built HK style roller or bearing delayed blowback, like the JP5 or Mean arms uppers. They are very expensive, but there really is no substitute. Light quick recoil, very reliable, they are not a retrofit, they are designed to have the correct mass and timing. NOTHING blowback can get close, the Maxim has a similar feel but heavier recoil, the CMMG can be tuned to have recoil almost as soft, but still IMO feels sluggish and clunky while still being less reliable.
The Sig MPX is a different system entirely, it's gas op. This is the reason it is both the absolute softest recoiling 9mm PCC, and has reliability issues. Blowback and delayed blowback self tune to a degree to keep consistent bolt velocities. More pressure means more energy to accelerate the carrier/buffer mass, and the faster initial acceleration in turn offers more resistance to give a more consistent bolt velocity, especially true with heavy buffers. My RDB and heavy comp setups feel similar from light match loads to heavy defensive loads. Gas op introduces more pressure, and depending on powder burn rate can give a very wide range of bolt velocities, so some things like pressure vents and engineering some leakage can prevent issues with very hot loads, but can jam with light loads. One system that hasn't really been tried, but should be is HK's own gas delay blowback, used in the P7. That system uses a gas port and piston to add resistance to keep the bolt CLOSED, delaying simple blowback operation instead of being used to cycle the action. This adds 0 resistance over the spring pressure to charge the firearm, offers effective self tuning (hot load= more resistance, light load= less resistance), all the low mass/light recoil of delayed blowback, but simpler with fewer parts, and could fit just fine on top of the barrel or bolt where the gas key and tube would normally be on a Di AR.
Doug has competed on and off, and has a background in scientific research, but primarily he is an enthusiast like many of us. I have collaborated with him on occasion in the past(including our experience with the Maxim RDB system), he knows his stuff, but also will be the first to admit what is and isn't in his wheelhouse. I have a similar background as a long time competitor with an engineering background and a few armorer's /gunsmithing courses, but have some tactical training and a martial arts background as well. Point being, the info we have is through our day job skills and firearm experience, and definitely not infallible, especially compared to engineers that design and manufacture firearms.
This, it is all about the mass and bolt velocity, delayed blowback always has the capability to be superior in function, blowback has the capability to be a simpler, more reliable system. Either system is powered by case "blowback". Basically once it fires, the brass expands to lock in the chamber with friction, then as pressure drops as the bullet heads out of the barrel, the brass contracts, and residual pressure acts on the brass /bolt face like a piston, forcing the bolt rearward until the seal is broken, residual pressure drops, and inertia carries it the rest of the way. Problem is that without a mechanical lock, there is a balancing act of sorts between friction, blowback energy, bolt mass, and spring pressure to force the bolt back forward to chamber the next round.
Mass is necessary to keep the bolt velocity in a nice comfortable and reliable range. For 9mm, that is around 24 oz, all the cushioning, dampening etc really just soften that big heavy mass slamming into your shoulder, then slamming a round into the chamber. Problem is you need the resistance that 24oz of momentum offers for all of 1/4" or less of powered movement to give an ideal bolt velocity, then you need to stop all that mass, and then push it forward to cycle, giving a lot of recoil, and a lot of force to disperse into your shoulder, or into movement of the firearm itself. Delayed blowback just basically applies mass x velocity = momentum. A mechanism, usually rollers and a wedge increases the "gear ratio" of one part of a 2 peice bolt to increase momentum. Basically to get the same resistance offered by accelerating 24oz in a 1:1 ratio aka direct blowback, the mechanism allows the bolt and carrier to separate, and the bolt carrier moves faster than 1:1 to provide resistance to blowback, 2:1 only need 12oz, 3:1 works with 8oz. Once past the blowback phase, the reduced mass moving has a fraction of the force impacting your shoulder, and moving the PCC around when chambering. Some are so effective that a fluted chamber is needed to reduce friction, and help extraction. Less recoil, less gas, less mass might make up for the difference in reliability compared to blowbacks simple bolt and spring. Thing is tuning is important, if a delay system opens too late or early it can be a problem, it may have issues with hot or light ammo, and of course it's expensive.
I have shot or own most all of these.
1. Direct blowback, can be horrible or decent. The original Colt 635 setup was basically a heavy SMG BCG, AR10 spring and H3 buffer. About the same recoil, maybe slightly more compared to a standard M4. Short stroke, heavy buffers and dampening can reduce that substantially. Some use a solid steel buffer, or swap the H3 for a steel bodied buffer with cheaper steel weights, either makes the recoil more forceful, and can have bolt bounce, causing OOB or jamming. My Blitzkreig comp setup is about as soft shooting as a blowback can be, 6oz hydraulic buffer, 2.5oz add-on weight with a short stroke non-ramped BCG, and heavy spring. It is still mass doing the work, but the hydraulic system has advantages. First being the floating mass of the buffer uncouples a little on blowback, dampeing the initial movement, it dampens again when hitting the back of the tube to soften recoil, then dampens when chambering.
Short stroke has the same recoil, but speeds up cycling with slow heavy buffers, and being the rearward, then forward movement is closer together, less dot movement. Standard 9mm Glock mag PCCs use long buffers or spacers to cut the 5.56s 3.75" stroke to 3" being the carrier face acts as the bolt, and there is not a separate rotating bolt. Short stroke reduces this further to around 2" with additional cushions/weights or spacers, it also requires a bolt with a shape that resets the trigger in less movement, My taccom rests in about 1.5" compared to 2.5 for most ramped 9mm bolts, this can offer a little blowback effect with some triggers as the hammer has to be accelerated faster rearward under blowback. Even so, the absolute best blowback system feels like the most basic RDB, almost as soft as my Maxim RDB.
CMMG RDB. This system uncouples and accelerates the carrier/buffer rearward through rotating the cam pin due to the wedge shape of the bolt/barrel extension interface. Problem is mass does the work, but there is a LOT of friction, and it introduces some potential issues with tuning if it is dirty or under-lubed. It is a long 3.75" stroke(same as DI calibers), and does feel a little sluggish to me compared to some other systems. They aren't as common in competition as it should be due to the reliability issues and slow cycling. In use feels similar to, and a little softer than a really good blowback system. Have not fired the dissent, so not opinion yet.
I got one of the first Maxim RDB buffers, and have some correspondence with Maxim's R&D about them, along with some troubleshooting including helping Doug aka blowback9 with his. It is a brilliant system, it is a true delayed blowback, the ball bearings lock in a groove in the guide rod, and allows the rear 3oz portion to separate and accelerate at a higher ratio than the BCG/buffer bearing cage. There is still a LOT of BCG and buffer mass, and the ratio isn't all that high, so not as effective as a delayed design that has a mechanism in the carrier and barrel/receiver, but is is extremely simple being a drop-in buffer. Main issue is that you have to overcome the resistance and leverage to rack the system. On all of mine with raptor handles, and a quick deliberate rack, it is barely noticeable. Some have had them where they were awful and difficult or impossible. It is softer in recoil than ANY blowback, although my short stroke hydraulic comp setup is pretty close. It is reliable, and relatively simple and robust. Perhaps the best application is shooting suppressed, it DRAMATICALLY reduced gas compared to heavy blowback. It has a "standard" PCC 3" stroke, so feels quicker/better than the CMMG RDB, and close to short stroke/heavy buffer blowback. I tried short stroking it, and it ran reliably, but heavier recoil, and not much change in how quick it felt, would have to be re-tuned to make the most of it.
Turns out there are some considerations with this system that were not obvious or in the instructions for the early version(they are considering changes and an addendum to instructions). It is VERY sensitive to the buffer tube length and preload of the system. If it has too much play, it basically doesn't add any resistance for a little bit of blowback, then full resistance, so it can cause jamming, and it makes it near impossible to rack. If there is too much preload, the system is partially unlocked and while much easier to charge, recoil will be harsh. It may need the tube backed out a turn and/or shims(doesn't need the buffer retainer). It should just make contact with slight preload with the carrier when the receivers are closed. There have also been a couple with heavy machining marks and burrs that cause excess resistance, but most are well made and smooth.
JP's SCSS was innovative at the time, one of the first self contained heavy buffers. They practically invented short stroke with their comp setup. Problem is it is still direct blowback, and there is only minor cushioning from rubber washers inbetween the weights, and the plastic bumper, Blitzkreig's hydraulic comp setup flat out feels better. There isn't much difference in feel compared to a 10oz KVP buffer compared to the standard PCC SCSS. Thing is the KVP is $50, the equivalent 11.2oz SCSS (2oz lost from removing BCG weight) is over $200, more than the Blitzkreig comp or Maxim RDB delay, and both are better.
Then there is purpose built HK style roller or bearing delayed blowback, like the JP5 or Mean arms uppers. They are very expensive, but there really is no substitute. Light quick recoil, very reliable, they are not a retrofit, they are designed to have the correct mass and timing. NOTHING blowback can get close, the Maxim has a similar feel but heavier recoil, the CMMG can be tuned to have recoil almost as soft, but still IMO feels sluggish and clunky while still being less reliable.
The Sig MPX is a different system entirely, it's gas op. This is the reason it is both the absolute softest recoiling 9mm PCC, and has reliability issues. Blowback and delayed blowback self tune to a degree to keep consistent bolt velocities. More pressure means more energy to accelerate the carrier/buffer mass, and the faster initial acceleration in turn offers more resistance to give a more consistent bolt velocity, especially true with heavy buffers. My RDB and heavy comp setups feel similar from light match loads to heavy defensive loads. Gas op introduces more pressure, and depending on powder burn rate can give a very wide range of bolt velocities, so some things like pressure vents and engineering some leakage can prevent issues with very hot loads, but can jam with light loads. One system that hasn't really been tried, but should be is HK's own gas delay blowback, used in the P7. That system uses a gas port and piston to add resistance to keep the bolt CLOSED, delaying simple blowback operation instead of being used to cycle the action. This adds 0 resistance over the spring pressure to charge the firearm, offers effective self tuning (hot load= more resistance, light load= less resistance), all the low mass/light recoil of delayed blowback, but simpler with fewer parts, and could fit just fine on top of the barrel or bolt where the gas key and tube would normally be on a Di AR.
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alucard0822
For great Justice
That is awesome, seriously jealous. John Paul seems pretty cool, lots of stories of things like this. I've emailed back and forth a couple times, and was at a couple matches he attended, but never met him personally.
Wow great post. I def learned some things. Thanks for all of the information.
@alucard0822 I was wondering what you thought of Doug's assessment of NOT using a 308 or similar stronger spring (i.e. above and beyond an M4 carbine spring)? He's pretty adamant about that. Me - heck I can't tell if it's any more harsh like he claims. I'm just using whatever works.
alucard0822
For great Justice
Heavy springs can soften recoil, but unlike increased mass, they do nothing to change the initial bolt velocity. They can also make chambering harsh. For most springs don't make a huge difference, and can potentially cause issues, but really are just another part to test and tune. I do still try them, and IMO a DPMS AR308 carbine spring can offer benefits. This is not the same as a DPMS 308 rifle or AR10 spring, same rate, but shorter with fewer coils. For most simple heavy buffer builds, an M4 spring is fine, and easier to rack. Have also met some competitors that like AR15 rifle springs or springco blue and red. An A5H4 buffer(7oz) and ar15 rifle spring in an M4 tube used to be the hot buffer setup early in the PCC game, and it's still good.
A heavier spring can soften hot loads a little, and I found that 308 carbine spring was by far the best in my comp build with hydraulic buffer. In that case I think the fewer coils and slightly larger internal diameter didn't interfere with the buffer movement Where an M4 spring did. That specific spring is designed to compress on a 2.5" 308 buffer, so it does well with buffer setups that have weights in front of the buffer and spacers in the tube compressing the spring more than it normally would be, and the rate isn't far from an m4 spring with a standard buffer and m4 tube. Have had some that feel best with a heavier spring, or function best with a standard spring also. So of course if you have a few springs, try them out to compare. On other builds M4 springs were the best, of course this is for blowback full and short stroke only as other setups have included springs or use different rates.
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