The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: Semi-automatics

Reply
 
Thread Tools Search this Thread
Old July 5, 2018, 06:37 AM   #1
JJ45
Senior Member
 
Join Date: June 8, 2015
Posts: 908
PTR91 Trunnion question.

Is the barrel extension actually part of the trunnion or is it a separate piece?

I think the purpose of the trunnion is to anchor the barrel to the receiver, correct?
JJ45 is offline  
Old July 5, 2018, 01:39 PM   #2
ttarp
Senior Member
 
Join Date: January 4, 2013
Posts: 888
There's no separate barrel extension in the G3 pattern rifles, the barrel is pressed directly into the trunnion. The barrel is pressed and then pinned into the trunnion, which is welded into the receiver, the trunnion also has the recesses that hold the rollers when in locked(not really locked) position.
ttarp is offline  
Old July 5, 2018, 01:47 PM   #3
PlatinumCore16
Senior Member
 
Join Date: February 23, 2017
Location: Colorado
Posts: 424
^ What he said.
Curious what the premise of the question was? Attempting your own build or just curious?
PlatinumCore16 is offline  
Old July 5, 2018, 02:35 PM   #4
JJ45
Senior Member
 
Join Date: June 8, 2015
Posts: 908
Just curious, I did a google search before posting because as a PTR 91 owner, I didn't want to post a dumb question The search only came up with complaints about cracked trunnions in the past and not really the purpose of the piece, etc..

I'm no stranger to firearms but somewhat a stranger with this system...I am amazed with the weapon (so far)...it has it's detractions like no bolt hold open and on mine, a button mag release, etc. but I can well live with it.

For some reason it kinda reminds me of an AK because of it's robustness and seemingly no BS construction...time will tell, I guess.
JJ45 is offline  
Old July 6, 2018, 03:08 PM   #5
PlatinumCore16
Senior Member
 
Join Date: February 23, 2017
Location: Colorado
Posts: 424
I understand. I picked up my C308 after I did quite a bit of research into what the cheapest route to a main battle rifle was. I would love an M1A at some point, but they were/are just too expensive for my price range, right now and for the foreseeable future. Not to mention when Springfield Armory pulled that stunt in IL. And I could've gone with an FAL, but I got hooked on the roller action. After much more research, an MBR isn't something you pay $500 for, but my rifle has run flawlessly and all of the measurements check out.

I've been taken with the roller locks so much so that I almost got the 5.56 version of the roller lock as well, but I got an AR instead, due to cost, magazine cost/availability, and modification ability.

MY C308 is still my favorite rifle in my quiver. Probably shoots right around 2-3MOA and it fires a full power round. I would love a free floated PTR 91 at some point, so I probably will pull the trigger on one at some point, but that's a future purchase.
PlatinumCore16 is offline  
Old July 6, 2018, 06:09 PM   #6
dakota.potts
Senior Member
 
Join Date: February 25, 2013
Location: Keystone Heights, Florida
Posts: 3,084
The trunnion holds the barrel to the receiver. The barrel is pressed into , drilled and pinned. The trunnion also has the recesses into which the rollers sit when the gun is in battery. The barrel must be pressed to proper relationship with the trunnion. This controls the gap between the bolt body and bolt head, in turn affecting the amount of force required to unlock the bolt and thereby setting the roller delay timing. Too little resistance and the bolt may cycle early with increased back pressure. Too much resistance and you will have trouble with appropriate cycling.

Hope that helps. I used to have a loose trunnion laying around (for a CETME, but very similar) but I can see if I still have the pictures
__________________
Certified Gunsmith (On Hiatus)
Certified Armorer - H&K and Glock Among Others
You can find my writings at my website, pottsprecision.com.
dakota.potts is offline  
Old July 7, 2018, 03:19 AM   #7
highpower3006
Senior Member
 
Join Date: July 30, 2011
Location: Savannah TN
Posts: 1,217
As I understand it, the cracked trunnions were a problem with early PTR builds and not endemic with HK roller locked guns. I have both a HK91 and a PTR91 and while you can tell that the HK is just nicer , the PTR is no slouch in it's own right.

The trouble with the internet is that any problems with a particular gun tend to be magnified, sometimes way out of proportion, and it gets hard to separate the truth from the general noise. PTR's are quality firearms and are well made. You should have many, many years of service from your rifle.

One thing that has bothered me for years is the tendency of the couch commandos to bloviate endlessly about tactical BS. In reality, unless you are planning on going to war, the magazine catch on your PTR will work just fine to change mags even though it doesn't have the paddle release.
highpower3006 is offline  
Old July 9, 2018, 03:58 PM   #8
PlatinumCore16
Senior Member
 
Join Date: February 23, 2017
Location: Colorado
Posts: 424
Quote:
In reality, unless you are planning on going to war, the magazine catch on your PTR will work just fine to change mags even though it doesn't have the paddle release.
The only problem with the mag release is that it's quite far forward, so unless you have long fingers/big hands, it might be difficult to get to. I don't have too much problem with it. The only problem I have is keeping the gun upright whilst I pull the mag out with my left hand. The rifle is very front heavy.
PlatinumCore16 is offline  
Old July 10, 2018, 09:13 AM   #9
davidsog
Senior Member
 
Join Date: January 13, 2018
Posts: 1,322
Quote:
The only problem with the mag release is that it's quite far forward, so unless you have long fingers/big hands, it might be difficult to get to. I don't have too much problem with it.
It is now standard on the PTR's to include the European Style Mag release as found on the FN FAL, M14, and AK-47 series.

It is not found on HK-91 due to BATF regulations and AFAIK never standard on the CETME series rifles.

The European style magazine release eliminates any ergonomics issues and was standard on all G-3 service rifles. The combat reputation of the design was forged on a different weapon that is in most civilian hands.

Kind of the exact opposite of the FN-FAL where civilian variants have a bolt lock where the military service FN-FAL's do not have a bolt lock.

How are you doing your magazine changes that makes the rifle feel so barrel heavy? Are you bringing the rifle into your workspace or trying to maintain stock weld? Prone or standing? A simple technique change can do wonders.

You have to run an HK product like HK intends. For example, the USP series of pistols is awkward to operate as if it has an American Style magazine release. Operating it like HK intends using your trigger finger and not your thumb to release the magazine not only works very well, it automatically puts the operator in the correct muscle memory of getting your finger off the trigger when bringing the pistol into your workspace.

HK designs primarily cater to government entities and not the civilian market so the "bubba" techniques passed around by tacti-cool crowd may not be applicable, LOL.

Last edited by davidsog; July 10, 2018 at 09:31 AM.
davidsog is offline  
Old July 10, 2018, 11:44 AM   #10
JJ45
Senior Member
 
Join Date: June 8, 2015
Posts: 908
I'll have to adapt to the button mag release and not the other way around...the only thing I added is an HK leather sling. There will be no "mods" on this one.

This PTR91-K .308 is the 16" barrel carbine model without a rail and this is exactly what I wanted, as simple as I could get it....It is somewhat lighter than a 16" barreled PTR32 and other PTRs with rails and heavier, longer tubes.

. and the difference in weight between it and my Russian SKS with bayonet is negligible although they are both a bit "front heavy". The SKS because of the bayonet, cleaning rod, etc.

I've seen HKs, PTRs, CETMES with high optics mounts, big scopes and heavy leather cheek pieces and appearing to need something on wheels to lug around BUT, to each his own.
JJ45 is offline  
Old July 10, 2018, 05:32 PM   #11
PlatinumCore16
Senior Member
 
Join Date: February 23, 2017
Location: Colorado
Posts: 424
Yea, my C308 is probably right around the 9.5lb mark, maybe even 10. I have a tri-rail fore end with an optic on the rail.

David, when changing mags I change them as I would regularly change mags in say an AR: hold the pistol grip in right hand, move finger to the button, attempt to grab the magazine with my left hand and not let the rifle fall forwards, remove mag. This is with the rifle either in my shoulder or, at this point, tucked under my arm to stop it from rotating around the pistol grip. How would you suggest to change mags? Or even rack the bolt?
PlatinumCore16 is offline  
Old July 11, 2018, 05:17 AM   #12
JJ45
Senior Member
 
Join Date: June 8, 2015
Posts: 908
I'M still getting familiar with the weapon so I'll have to work at the best way to dump and insert mags.So I am no reference on the best way. I could use some education on the matter.

It's difficult to retain a cheek weld when changing mags probably even with a paddle. I secure the butt stock in my arm pit gripping the pistol grip with firing hand. Fore finger can easily reach the button and empty mag is released with the help of the support hand. No drop free yet but this may change as the weapon breaks in.

New mag inserted with support hand and bolt worked with support hand to chamber a round....the lack of a bolt hold open doesn't help, but it is what it is.

FWIW, I was informed that the aluminum mags, as sturdy as the are, were designed to be expendable.
JJ45 is offline  
Old July 11, 2018, 07:03 AM   #13
ttarp
Senior Member
 
Join Date: January 4, 2013
Posts: 888
The mags won't drop free, at least they weren't designed to anyway. You should start your mag change by locking the bolt to the rear, this makes both inserting the new/full magazine easier, and chambering a new round easier by simply slapping the charging handle down.
ttarp is offline  
Old July 11, 2018, 08:39 AM   #14
PlatinumCore16
Senior Member
 
Join Date: February 23, 2017
Location: Colorado
Posts: 424
I have also read this, ttarp. I have always tried to make sure that the first thing I do is lock the bolt back. Not quite the same as a last-round, bolt hold open, but as the rifle was designed, that seems to be the best way to do it.

JJ45, that is exactly what I do at this point. Whenever looking at pictures of service members of different militaries holding G3s, they are almost always barrel end down, 2pt sling carried across the front with the firing hand on the pistol grip, canted. This makes it extremely easy to manipulate the safety as it's not quite as ergonomic as an AR is in the firing position. Doable, but much easier when the rifle is across the front of you. So maybe the sling is what makes the difference? Also thank you for that last note. I was unaware and just assumed they were reused because they do seem very sturdy. As a sidenote, I was very pleased to find that they are extremely easy to find and inexpensive. And all of the different variants work with each rifle, a la G3, HK91, CETME, etc.

Still hoping that someone might be able to enlighten us as to what the standard method of removing/changing mags would be with the HK roller locks? The internet hasn't been terribly helpful from my searches.
PlatinumCore16 is offline  
Old July 11, 2018, 07:24 PM   #15
davidsog
Senior Member
 
Join Date: January 13, 2018
Posts: 1,322
Quote:
David, when changing mags I change them as I would regularly change mags in say an AR: hold the pistol grip in right hand, move finger to the button, attempt to grab the magazine with my left hand and not let the rifle fall forwards, remove mag. This is with the rifle either in my shoulder or, at this point, tucked under my arm to stop it from rotating around the pistol grip. How would you suggest to change mags? Or even rack the bolt?
I charge the weapon like a machine gun, Palms up on the charging handle and rack it like a man!! LOL

Some people pinch the charging lever between their index and thumb to hook it back.

Whichever you are most comfortable with use. The important thing is the system is designed to be pulled all the way back and released. Let the bolt slam into battery and do not ride it.

Pulling it fully to the rear and release or the "HK Slap" is purely up to you.


Quote:
I'M still getting familiar with the weapon so I'll have to work at the best way to dump and insert mags.So I am no reference on the best way. I could use some education on the matt
This guys gives a pretty good demonstration of tactical and rapid reloads. The G3 has the paddle release which eliminates any ergonomics issues with magazine changes.

https://www.youtube.com/watch?v=YAwM71383C0

Quote:
I'll have to adapt to the button mag release and not the other way around
Yeah, you are kind of screwed which is why that paddle magazine release is standard on a service G-3 rifle.

Right Handed

If you have long fingers you can manipulate it otherwise bring the rifle tightly into your workspace and use your index finger of your left hand to manipulate the button.

The magazine change will look almost exactly like the standard magazine change or the workspace tactical reload.

Last edited by davidsog; July 11, 2018 at 07:37 PM.
davidsog is offline  
Old July 11, 2018, 07:25 PM   #16
davidsog
Senior Member
 
Join Date: January 13, 2018
Posts: 1,322
Magazine changes from the prone are the same. Use the index finger on the same hand you grip the magazine to press the release button.
davidsog is offline  
Old July 11, 2018, 07:30 PM   #17
davidsog
Senior Member
 
Join Date: January 13, 2018
Posts: 1,322
Quote:
So maybe the sling is what makes the difference?
That is correct. The thinking being in the majority of surprise contact situations, the rifle is going to be in carry mode.
davidsog is offline  
Old July 11, 2018, 07:47 PM   #18
davidsog
Senior Member
 
Join Date: January 13, 2018
Posts: 1,322
Quote:
It's difficult to retain a cheek weld when changing mags probably even with a paddle.
I never retained a cheek weld changing magazines.

In CQB all mag changes are done from a secure position. It is not something you do in the middle of the fight in the room. In fact, at the moment your main goes dry, you have are now armed with a club in the middle of a gunfight.

You arm yourself with a gun by transitioning to your secondary. When the fight is over and you are in a covered position, then you get your main back up.

If you do not have a secondary, they you better seek cover and move at lightspeed to trying to be a more difficult target to hit. You stand there with a club on your cheek, you will be shot if an opponent has a gun before you can change that magazine. In the youtube video I posted, he is not doing tactical reloads or fast reloads in the middle of a fight. It is a very bad day if you have to do that.

Even in the infantry I never retained cheek weld. Unless that club requires use due to the proximity of the enemy, Get that thing out of your face and watch your sector while you make it a gun again!! LOL

That is the reason why you bring the weapon into your workspace. It clears your Line of Sight to look for threats and the weapon if needed.

Only using a bolt action rifle do I retain cheek weld while operating the bolt.

Last edited by davidsog; July 11, 2018 at 08:09 PM.
davidsog is offline  
Old July 11, 2018, 08:21 PM   #19
JJ45
Senior Member
 
Join Date: June 8, 2015
Posts: 908
davidsog, I'm not clear on what you mean by "workspace" Never heard of the term in the context of armed combat .
JJ45 is offline  
Old July 11, 2018, 08:32 PM   #20
davidsog
Senior Member
 
Join Date: January 13, 2018
Posts: 1,322
Quote:
davidsog, I'm not clear on what you mean by "workspace" Never heard of the term in the context of armed combat .
It is the area to his front, a few inches down so the weapon is not obstructing the view of where the most likely threat might appear.

It is an area and position where you can momentarily glance at the weapon if needed or momentarily divide your attention between the direction of your most likely threat and weapon to diagnose/clear a malfunction if immediate action does not work, change magazines, or whatever is required to get the weapon back into operation.

It is the space you "work" on the weapon.
davidsog is offline  
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 08:05 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2021 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Page generated in 0.13543 seconds with 10 queries