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Discussion Starter · #1 ·
Hey guys I picked up a used 16 from a fellow member a few weeks back and finally got a change to Trim the Fat off this girl, this is a PMM 10.5" SCAR 16" (including the threads.)

Normal PMM Barrel work with the exception of having to machine a custom tapered Delrin coller Spacer to hold the Barrel in the chuck as there was real flat to clamp onto with the Soft-jaws, Total run out from OD to ID .0005" 1/2x28x.625" deep Threads.

I also machined some of my own different sized Gas screws out of Stainless for this application and will have bot of these services/Parts up on the Site soon if anyone is interested.
Automotive exhaust Pipe Auto part Metal Pipe insulation

Auto part Cylinder Tool accessory

Auto part Tool accessory Cylinder Hardware accessory Nozzle

W?AAC Flash hider
Gun Firearm Airsoft Airsoft gun Trigger

Gemtech Halo on a Standard Birdcage.
Gun Firearm Trigger Airsoft Airsoft gun
 

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Looks good! Are there any issues with accuracy from trimming or is it just the falloff in velocity from a shorter barrel? Could I send just a barrel group to you once you are up and running or do I need to send in the whole rifle?
 

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Discussion Starter · #3 ·
I will be finishing up my testing and tuning on this Rifle in the next week or so. I will also be offering some gas screw options to go with it/them.
The accuracy of all shorter barreled weapons pales in comparison to the longer units,But that is not the point of them, SBR's are for close work and this thing will still be very accurate out to a couple 100 yards.

When I have the PMM SCAR CQC16 Barrel specific option up on the site I will price it as just a barrel Cut,Crown thread job or full upper with tear down and re-assembly/TQ settings on barrel bolts etc. Logistically not having to log in a serialized upper in is better for me but I can deal with it either way as that is what i do.

Final note: this barrel has been cut to the EXACT specifications of the FNF SCAR 16 CQC barrels the only difference between the two is the gas block volume.
As I understand it the Factory Gas block units has a little larger volume area inside to help aid in dwell time and cycle rate of the weapon.

I don't have access to a Factory CQC gas block off hand to do a CC Volume test as a comparison to the Standard Gas block and since this was a standard 16" rifle to start with having the option to use a difference sized Gas screw should help mitigate any foreseen cycling issues based on the ammo being used.
~Jrod.
 

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I will be finishing up my testing and tuning on this Rifle in the next week or so. I will also be offering some gas screw options to go with it/them.
The accuracy of all shorter barreled weapons pales in comparison to the longer units,But that is not the point of them, SBR's are for close work and this thing will still be very accurate out to a couple 100 yards.

When I have the PMM SCAR CQC16 Barrel specific option up on the site I will price it as just a barrel Cut,Crown thread job or full upper with tear down and re-assembly/TQ settings on barrel bolts etc. Logistically not having to log in a serialized upper in is better for me but I can deal with it either way as that is what i do.

Final note: this barrel has been cut to the EXACT specifications of the FNF SCAR 16 CQC barrels the only difference between the two is the gas block volume.
As I understand it the Factory Gas block units has a little larger volume area inside to help aid in dwell time and cycle rate of the weapon.

I don't have access to a Factory CQC gas block off hand to do a CC Volume test as a comparison to the Standard Gas block and since this was a standard 16" rifle to start with having the option to use a difference sized Gas screw should help mitigate any foreseen cycling issues based on the ammo being used.
~Jrod.
I've got to chime in here about your comment that I highlighted in red. I have seen just the opposite as long as the barrel being changed out has the twist rate of the rifling compensate for the shorter length. Many rifles I've seen in the 5.56 platform have gone from a 1 in 9 twist 16" bbl that shot MOA out to 200yrds, and then change it out for a 10.5" bbl that is a 1 in 7 twist and shoot sub MOA all with factory ammo. As known in bench rest circles, a shorter bbl is a stiffer bbl if all diameter and material of the bbl in question is the same. Stiffer or more ridged bbls flex less and shoot more consistently for group. If longer bbls shot better groups then all benchrest competitors would be shooting 26" 28" or 30" bbls in the 200yrd matches and not the usual lengths of 20" with their 6mm PPCs rifles.
They say a picture is worth a thousand words so, here's the latest groups shot from my ACR with a factory 1 in 7 twist Remington Defense 10.5" bbl. (can you say sub quarter MOA?) Don't ever believe shorter bbls with the right twist rate and bullets can't shoot as good or better than the man behind the trigger. (groups seen here were shot at 100yrds with 60gr V-max BlackHills ammo)

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Discussion Starter · #8 ·
I've got to chime in here about your comment that I highlighted in red. I have seen just the opposite as long as the barrel being changed out has the twist rate of the rifling compensate for the shorter length. Many rifles I've seen in the 5.56 platform have gone from a 1 in 9 twist 16" bbl that shot MOA out to 200yrds, and then change it out for a 10.5" bbl that is a 1 in 7 twist and shoot sub MOA all with factory ammo. As known in bench rest circles, a shorter bbl is a stiffer bbl if all diameter and material of the bbl in question is the same. Stiffer or more ridged bbls flex less and shoot more consistently for group. If longer bbls shot better groups then all benchrest competitors would be shooting 26" 28" or 30" bbls in the 200yrd matches and not the usual lengths of 20" with their 6mm PPCs rifles.
They say a picture is worth a thousand words so, here's the latest groups shot from my ACR with a factory 1 in 7 twist Remington Defense 10.5" bbl. (can you say sub quarter MOA?) Don't ever believe shorter bbls with the right twist rate and bullets can't shoot as good or better than the man behind the trigger. (groups seen here were shot at 100yrds with 60gr V-max BlackHills ammo)

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Lefthanded7 Great post , My statement was to broad and I should have been more specific, That is why I am doing some more testing on this for my own purposes.
Based on some of the articles I have read data varies wildly based upon a bunch of variables like ammo Grain for bullet the twist rate and the barrel thickness etc. which you pointed out.


I have a close friend that is much smarter then I am when it comes to Ballistics(I'm just a machinist!) and the things tied to them,we just had a conversation about this the other day and schooled me on some stuff I did not know.It's a good thing to know at age 36 I still have alot to learn and I am enjoying the process.

My apologies for the blanket statement as I said I should have been more specific like your post.
~Jrod.
 

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Lefthanded7 Great post , My statement was to broad and I should have been more specific, That is why I am doing some more testing on this for my own purposes.
Based on some of the articles I have read data varies wildly based upon a bunch of variables like ammo Grain for bullet the twist rate and the barrel thickness etc. which you pointed out.


I have a close friend that is much smarter then I am when it comes to Ballistics(I'm just a machinist!) and the things tied to them,we just had a conversation about this the other day and schooled me on some stuff I did not know.It's a good thing to know at age 36 I still have alot to learn and I am enjoying the process.

My apologies for the blanket statement as I said I should have been more specific like your post.
~Jrod.
A lot to learn at 36!? Heck I'm 54 and learn every day! The day we stop learning is the day we are either too prideful or stubborn in our ways or we are just plain dumb.
I for one love learning new stuff - (I'm an info / knowledge, and data junky I guess). I pray I am always humble enough to listen well and retain all the true knowledge that's out there that good people like yourself are willing to share with me.
Good shooting to you Jarod, and may you and your family have a blessed and Merry Christmas!
 

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Discussion Starter · #10 ·
A lot to learn at 36!? Heck I'm 54 and learn every day! The day we stop learning is the day we are either too prideful or stubborn in our ways or we are just plain dumb.
I for one love learning new stuff - (I'm an info / knowledge, and data junky I guess). I pray I am always humble enough to listen well and retain all the true knowledge that's out there that good people like yourself are willing to share with me.
Good shooting to you Jarod, and may you and your family have a blessed and Merry Christmas!

To be green is to grow and to be ripe is to die, I like growing.
Gonna do some Shooting in the next two days by nature with racing I will be meticulous in the data collection. And will post it up when I am done.

Merry Christmas to you my friend.
 

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Discussion Starter · #11 ·
cross post.

Gents, As some of you may know I had posted some images of a Barrel Cut,Crown,Thread job I did on a PMM SCAR 16s and several members were wondering about the accuracy of doing this to an existing barrel and if the weapon would cycle properly.

Weapon Info:
SCAR 16s W/ PMM/CQC 10.5"-1:7 Twist cut,crowned,Threaded Barrel.
PMM B.C.D, Selector Leveres LH&RH QD mounts,KeyMod Rails.and associated furniture.
Geissele Superr SCAR Trigger.
Optic for testing:SWFA 3-15x42 scope
Supressor:GEMTECH HALO


Here is the data collection I did in the last few days.
AMMO:
Wolf 55 Grain Military classic.
Lake City XM855-556 62Gr steel core
PPU Remington 75Gr Match ammo


Weapon Cycle Testing:

In the last three days I have been doing just some standard pinking at my Place to make sure the rile functioned well, After I Machined the barrel I made a jig and mounted several Allen head 316 Stainless set screws and drilled ports in them with various sizes to test the rifle.
Based on some feed back I got from trusted sources the 2.5mm Gas screw was a good place to start and I never changed it as the rifle ran flawlessly suppressed and non suppressed with the exception of 1 FTF while lying prone and resting on the Magpul P-mag Aprox. 500 Rnds were sent through it in three days and based on the data the FTF was a direct result of resting on the mag while shooting.
Gas Screw Port Data:
Factory 16s-1.5mm
PMM 2.0mm SS Gas Screw
PMM 2.5mm SS Gas Screw

The PMM2.5MM gas screw is the option I am going to leave in the weapon as it ran Very well with or with out the GEMTECH installed.

Accuracy Testing :
Ambient Temp: 30-32*F
Wind-NA
Distance 150FT-50Yrds

By no means do I consider my self a precision shooter but I do well enough.

The Lake City XM855-556 62Gr steel core performed Well and I attribute the straggler on this target to me, the last shot in the group just did not feel right and I should have reset,granted throughout testing process I did get the occasional Strangler on the target.


PPU Remington 75Gr Match ammo, Constantly Yielded tighter grouping and I never got the occasional straggler using it.


Conclusions:
Based on what I saw out of the testing the rifle functioned extremely well and the better ammo showed better results. The PMM.CQC performed well and I am very happy with it.
I will be adding the PMM/CQC SCAR 16S Barrel Service to the site shortly and will include the Barrel Cutting, Crowning & Treading, 2x Gas Screws (2.0mm & 2.5mm) and optional engraving for your upper in the place you choose I did this one on the rail up top as seen below.


Thanks for looking
~Jrod.
 

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Discussion Starter · #15 ·
Yes an AAC Miter mount to be exact.

Based on what I see on AAC's website I am not 100% sure on the shoulder mounting depth of the MITER Mount and there are no specs to go off of other then two thread styles(1/2x28 -5/8x24) for appropriate calibers.

I bring this up as I would like to see the Flash hider in person to place the pin in the appropriate location without interfering with the Flash hiders thread for a suppressor at a later date.

I suspect based purely on looking at the Flash suppressor that I will have to integrate the pin into the barrel/hider somewhere in between the can threads, or behind them ideally at the low six o'clock position then stake or hit it with the tig real quick making sure it is flush with the OD of the Hider. Not hard to do but I would like to see it first.

If any of this makes sense to you and you still are interested in the job please send me an E-mail and we can work out the logistics for it there.
Thanks ~jrod.
 
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