Which Recoil System? JP SCS Gen 2 vs MBX PCC Buffer System

[Maxamundo]

 

Interally my buffer system looks almost identical to this, except I use an inverted delrin .223 buffer instead of this custom cut milspec one with bumper.
 

[nickbfishn]

12 minutes ago, Maxamundo said:

 

Interally my buffer system looks almost identical to this, except I use an inverted delrin .223 buffer instead of this custom cut milspec one with bumper.
 

What's the extra spring on the backend?

[Maxamundo]

http://www.smalley.com/wave-spring/cs100-h7

[Hammer002]

1 hour ago, Maxamundo said:

EVERY GUN, AMMO TYPE, BARREL, MUZZLE DEVICE, SHOOTER'S STANCE, SHOOTER'S GRIP, ETC drastically affects how the gun will perform with different buffer systems. I'd recommend testing out different spring and travel length with your own setup and measure your times shooting small groups at distance.

 

First, thanks Max for the videos you post on youtube.  They have served as excellent reference for my new found interest in PCC.  Coming from the pistol world a few things are foreign to me, and though I attempt to read as much here as possible, some of the terminology or assumed knowledge is lost on me.  My question is what are you looking for when you are "tuning."  I understand lower recoil, faster splits, etc, but where is the line?  What are you looking for to know you have gone in the wrong direction, or past the right direction?  I have a PCC that runs flawless on factory ammo with higher than desirable recoil of course and am starting to get my reloads working in the gun, working on what will feed well first (Still might need some throating).  I guess I need to know what are you looking for to be right?  I know how to tune a pistol between undersprung vs oversprung, but don't know enough about the PCC platform to recognize it, or other issues there.  Sorry, for the long post, but really liking this new division and would like the benefit of properly running lower powerfactor ammo without screwing something up.

 

Thanks everyone for all the info and input so far.  Learning a ton.

 

By the way, if it helps anyone to know, this is what I am running.  Only thing I know for sure in the buffer system is the buffer is 5.9 ounces.

 

 http://karrisguns.com/Wraith-skm-9mm-rifle-billet.aspx

 

Thing has been flawless except it doesn't like flat nose 147s.  135s on the bench right now...

Edited July 14, 2017 by Hammer002

[Maxamundo]

7 minutes ago, Hammer002 said:

 

First,

I just use something translatable to hit factor scoring. The easiest one for me is 25 yard bill drills. With this setup I can easily keep a group inside less than half the A zone area under 2 seconds from stock on belt. With the heavier 308 rifle spring dot movement seemed a little more inconsistent and my group opened up.

I don't really care how the gun feels in recoil. Only dot return. And I do care if the dot returns fast or slow. Which is why I added the extra spring to block travel and reduce cycle time. Since the cycle time is reduced too, I can shoot this gun WAYYYYY faster more consistently than my rifle. I think it has something to do with the trigger resetting quicker than it would on a .223 but I'm not sure that's just a guess. See here: 

 

When you actually look at the targets that I bump fire on, the hits are nearly touching...

Edited July 14, 2017 by Maxamundo

[Hammer002]

Ive actually seen that entire video, as well as the others for that match, great run.  I think I am getting it as far as benefits chased and how to recognize what is helping.  My concern is making the gun less reliable or not running in efforts to tune.  Specifically speaking, shortening the cycle would be extremely beneficial, but knowing how much is where I would struggle.  So, on that topic specifically, how do you know you have shortened the cycle too much, (likely FTF) and how do you know when you need more?  Same thing as buffer weights, what are you looking for to know when more is needed or less.  If its just dot return, I can handle that, but I dont think I know when I am TOO light or TOO heavy and causing damage to the gun or sacrificing reliability.

[Maxamundo]

2 minutes ago, Hammer002 said:

Ive actually seen that entire video, as well as the others for that match, great run.  I think I am getting it as far as benefits chased and how to recognize what is helping.  My concern is making the gun less reliable or not running in efforts to tune.  Specifically speaking, shortening the cycle would be extremely beneficial, but knowing how much is where I would struggle.  So, on that topic specifically, how do you know you have shortened the cycle too much, (likely FTF) and how do you know when you need more?  Same thing as buffer weights, what are you looking for to know when more is needed or less.  If its just dot return, I can handle that, but I dont think I know when I am TOO light or TOO heavy and causing damage to the gun or sacrificing reliability.

 

You won't cause damage to the gun unless your cycle is way too long and your "gas key" hits the lower receiver or smashes into the charging handle internally.

You will get failure to reset on the trigger long before you start getting FTF, so that's not really a concern. You can test the minimum travel you need by dry firing the trigger, pinning it to the rear, then slowly charging the bolt until you feel or hear the "click" of the hammer catching on the disconnector. That distance plus maybe an extra 0.1-0.2" just for assurance is the minimum bolt travel you would ever want so that the trigger resets reliably.

 

On my gun I have it so I have to fully compress the main buffer spring and the hydraulic piston, and then pull the charging handle back another 0.2" or so compressing the very heavy wave spring and then I can BARELY get it to lock back on the bolt catch.

I've never run LRBHO in this gun, I removed it before even assembling the lower. I don't think it would work reliably with such a short travel but honestly I'm not interested in testing it. 

[Hammer002]

10 minutes ago, Maxamundo said:

 

You won't cause damage to the gun unless your cycle is way too long and your "gas key" hits the lower receiver or smashes into the charging handle internally.

You will get failure to reset on the trigger long before you start getting FTF, so that's not really a concern. You can test the minimum travel you need by dry firing the trigger, pinning it to the rear, then slowly charging the bolt until you feel or hear the "click" of the hammer catching on the disconnector. That distance plus maybe an extra 0.1-0.2" just for assurance is the minimum bolt travel you would ever want so that the trigger resets reliably.

 

On my gun I have it so I have to fully compress the main buffer spring and the hydraulic piston, and then pull the charging handle back another 0.2" or so compressing the very heavy wave spring and then I can BARELY get it to lock back on the bolt catch.

I've never run LRBHO in this gun, I removed it before even assembling the lower. I don't think it would work reliably with such a short travel but honestly I'm not interested in testing it. 

Exactly the type of info I was looking for.  Very helpful, thank you very much.  And mine never had a LRBHO.  That fact alone and how well this thing has run so far on factory ammo tells me they might know what they are doing in assembly, which is why I have been rather hesitant to mess with the set up.  However I am convinced it is built to run on full power factory ammo and that is just a no go.

Edited July 14, 2017 by Hammer002

[Maxamundo]

11 minutes ago, Hammer002 said:

Exactly the type of info I was looking for.  Very helpful, thank you very much.  And mine never had a LRBHO.  That fact alone and how well this thing has run so far on factory ammo tells me they might know what they are doing in assembly, which is why I have been rather hesitant to mess with the set up.  However I am convinced it is built to run on full power factory ammo and that is just a no go.

 

What is the gun?

[Hammer002]

Just now, Maxamundo said:

 

What is the gun?

 

http://karrisguns.com/Wraith-skm-9mm-rifle-billet.aspx

 

Its a husband/wife small company ran right here in my home town.  Olathe, KS even stamped into the lower.  My info is they assemble all of them based on their choice of parts.

 

Recently shot first level II with it last weekend.  11 Stages without a single hiccup.  Very impressed so far.  Had it about 3 weeks now.

[Maxamundo]

Oh okay it's just a rifle built on an NFA lower with a heavy buffer. 

If you replace the buffer and spring with the Blitzkrieg 9mm hydraulic and the JP 308 RIFLE spring you should notice a huge difference and it won't affect reliability at all.

When you start racking up the round counts on those lowers, make sure the ejector screws stay tight. Also, two of the guys who shoot locally had no issues for a few thousand rounds, but eventually the plastic magazine catch started bending slightly and holding the mags in lower than usual. Occasionally they'd get rounds getting hung up and not clearing the corner of the barrel extension. They ended up having me grind the barrel extensions to remove that corner and create a kind of feed ramp like I've done on mine. Completely solved the problem. You also might want to look into the Odin works metal magazine release to replace the plastic one you have now, although it does move the control closer to your hand which I  actually don't prefer.

[Hammer002]

4 minutes ago, Maxamundo said:

Oh okay it's just a rifle built on an NFA lower with a heavy buffer. 

If you replace the buffer and spring with the Blitzkrieg 9mm hydraulic and the JP 308 RIFLE spring you should notice a huge difference and it won't affect reliability at all.

When you start racking up the round counts on those lowers, make sure the ejector screws stay tight. Also, two of the guys who shoot locally had no issues for a few thousand rounds, but eventually the plastic magazine catch started bending slightly and holding the mags in lower than usual. Occasionally they'd get rounds getting hung up and not clearing the corner of the barrel extension. They ended up having me grind the barrel extensions to remove that corner and create a kind of feed ramp like I've done on mine. Completely solved the problem. You also might want to look into the Odin works metal magazine release to replace the plastic one you have now, although it does move the control closer to your hand which I  actually don't prefer.

That's kinda what happens when the 147s fail to feed.  They either just slam into the extension just below entry, or kick straight up.  Twice bent the top of the Glock mag.  Only with reloads though, not one malfunction yet with the Winchester White Box factory loads.  Not consistant failures, but enough they have been rejected as match bullets.  My bullet provider says all his sponsored PCC shooters have gone to the 135s anyway for more reliable feeding.

 

Thanks so much for the advice, I will look into all you mentioned.  Loctite on the ejector screws or no?  Possible pic on the "feed ramp" you mentioned.  I already have a gunsmith lined up to throat the chamber if reloads dont work as well as factory.  Maybe he could capitalize on your idea for mine, if you dont mind.  Whatever will keep reliability high.  Thanks Max!

[Maxamundo]

Throating the chamber is a must IMO. I use a faxon barrel and montana gold 121gr IFP (identical profile to 115gr JHPs). I had to load them MAXIMUM 1.075" OAL to get them to NOT contact the rifling and pass spin test. When loaded too short, the bullets can nose up before entering the chamber and jam vertically. Now I load them to 1.130" and have not had a single issue since throating. No loss in accuracy too

The NFA lower you have is probably the worst offender in terms of the hanging up on the bottom part of the barrel extension. The mag release is actually positioned lower than on more quality lowers like QC10 or JP. You can fix it pretty easily with a sanding drum and a dremel. Don't even have to take the barrel out of the upper.

[Maxamundo]

Oh keep in mind this problem will likely ONLY occur with extended magazines (Taccom mag splice loaded to 46-51, Taylor Freelance extension loaded to 36-41 or so). I've never seen the problem with 33rd glock mags since there is less spring tension slowing down the feeding and allowing the bullet to actually get caught.

[Maxamundo]

Here is an image before I ground the corner down. Notice where there is no fouling. This is where the bullet hits before being chambered. I basically ground the shiny part in this picture to remove the sharp edge.

[Hammer002]

5 minutes ago, Maxamundo said:

Throating the chamber is a must IMO. I use a faxon barrel and montana gold 121gr IFP (identical profile to 115gr JHPs). I had to load them MAXIMUM 1.075" OAL to get them to NOT contact the rifling and pass spin test. When loaded too short, the bullets can nose up before entering the chamber and jam vertically. Now I load them to 1.130" and have not had a single issue since throating. No loss in accuracy too

The NFA lower you have is probably the worst offender in terms of the hanging up on the bottom part of the barrel extension. The mag release is actually positioned lower than on more quality lowers like QC10 or JP. You can fix it pretty easily with a sanding drum and a dremel. Don't even have to take the barrel out of the upper.

Cannot thank you enough for your time and input.  This is exactly what I thought the rifle needed, but wasn't sure it should be done.  Thanks for the confidence to do it.  I have had the same experience with having to load short to stay off the rifling and equated the lack of feeding to the same.  Thanks for confirming and will definitely be throating.  Now that I know for sure that is the issue, I may hold off any further reloading endeavors until throated.

[Maxamundo]

Here are 5 ACME 147 FP bullets at different OALs before and after chambering, but not firing. Notice now one edge of the bullet gets a "shelf" smashed into it by that sharp corner, and the other edge gets an "angle" smashed into it from hitting the top of the inside of the chamber at a steep angle.

[Hammer002]

7 minutes ago, Maxamundo said:

Oh keep in mind this problem will likely ONLY occur with extended magazines (Taccom mag splice loaded to 46-51, Taylor Freelance extension loaded to 36-41 or so). I've never seen the problem with 33rd glock mags since there is less spring tension slowing down the feeding and allowing the bullet to actually get caught.

Mine did it with the Taylor freelance 41 round.  Ran Glock 17 rounders with no problem.  Thought spring tension was at least making the issue worse.  Again, thanks for confirming and making me sure I was headed in the right direction.

[Maxamundo]

1 minute ago, Hammer002 said:

Cannot thank you enough for your time and input.  This is exactly what I thought the rifle needed, but wasn't sure it should be done.  Thanks for the confidence to do it.  I have had the same experience with having to load short to stay off the rifling and equated the lack of feeding to the same.  Thanks for confirming and will definitely be throating.  Now that I know for sure that is the issue, I may hold off any further reloading endeavors until throated.

I tried so many things, changing bullets, OAL, magazine configuration, etc, before finally breaking down and grinding that corner because I was nervous about modifying the actual barrel. 

It literally took me 15 minutes and solved the problem and I've never ever had that issue again with my gun. I was so mad at myself for not just starting with that.

[Hammer002]

3 minutes ago, Maxamundo said:

Here are 5 ACME 147 FP bullets at different OALs before and after chambering, but not firing. Notice now one edge of the bullet gets a "shelf" smashed into it by that sharp corner, and the other edge gets an "angle" smashed into it from hitting the top of the inside of the chamber at a steep angle.

My experience exactly, except mine are black! 

[Maxamundo]

grinding that ramp fixes the feeding issues, but it doesn't change the fact that feeding from a glock mag in a PCC is EXTREMELY rough on the actual cartridges compared to a handgun.

I would still only run FMJ or plated RN if you want the highest reliability. And make sure you're using new or once fired brass for majors and check the casings for those FM stepped casings. Those have blown in half on me multiple times including one time ending a stage for me at safariland a few weeks ago.

Edited July 14, 2017 by Maxamundo

[Hammer002]

2 minutes ago, Maxamundo said:

I tried so many things, changing bullets, OAL, magazine configuration, etc, before finally breaking down and grinding that corner because I was nervous about modifying the actual barrel. 

It literally took me 15 minutes and solved the problem and I've never ever had that issue again with my gun. I was so mad at myself for not just starting with that.

Exactly!  That's why I am so appreciative of you confirming it can and should be done.  Will be on it this weekend.  Again, thanks for all the help.  It feels great knowing I have some specific directions to go in that are proven.  So much learned in just the last hour.  Looked at that Odin mag catch, and thinking that will be an addition as well, although I agree, would prefer the button in same location as used to on an AR15, but reliability is everything!

 

Max, you're an amazing competitor and a hell of a nice guy to be of so much help.  Will keep watching your videos as I learn more and more about moving that long barrel around pistol stages every time I watch.  Best of luck as you continue. 

 

Oh, and by the way.....the video about how to run backwards with a PCC = PRICELESS!  Anyone shooting PCC should learn that!

[Hammer002]

3 minutes ago, Maxamundo said:

grinding that ramp fixes the feeding issues, but it doesn't change the fact that feeding from a glock mag in a PCC is EXTREMELY rough on the actual cartridges compared to a handgun.

I would still only run FMJ or plated RN if you want the highest reliability. And make sure you're using new or once fired brass for majors and check the casings for those FM stepped casings. Those have blown in half on me multiple times including one time ending a stage for me at safariland a few weeks ago.

I remember watching that, right at the end.  Not sure I know what "FM stepped" is.  I am on a budget, so coated bullets is pretty much in order and once fired mixed brass is usually what I have.  Hoping to get reliability acceptable for my level.

[Maxamundo]

6 minutes ago, Hammer002 said:

I remember watching that, right at the end.  Not sure I know what "FM stepped" is.  I am on a budget, so coated bullets is pretty much in order and once fired mixed brass is usually what I have.  Hoping to get reliability acceptable for my level.

 Here you go

IMT or FM headstamps. But maybe not 100% of IMT or FM headstamps... idk

Edited July 14, 2017 by Maxamundo

[MHitchcock]

^^^ Just throw away (or scrap for brass value) any FM or IMT headstamps. It will make your life a lot easier. I can actually feel them in my sizing die on my dillon 650 press if one sneaks by my QC.