Barrel stop/barrel/recoup location

[crash520]

Gents,

I have a BRP front end im intendending to fit up with MG53 barrel stop and bits. I have fit the MG53 Cam box to the new front metal firmly up the the cam box stops (top and bottom) and all looks good, comparing this to an MG53 front end I have the barrel stop locator windows are within .020" of each other so i'm figuring all is good.
THEN.... I grabbed the three barrels I have (all 308) I believe one or two maight be MG3, as I wanted to double check on things, particularly recouperator location against the back of the barrel extension etc and found a disturbing thing.
As per the photo below of the barrels, you will notice the area of the barrel that rests agains the barrel stop on these three barrels are all differnt lengths, by up to 0.050"++. so this leads me to question the relation of these barrels, the barrel stops and then the recouperator plunger type etc in order to have the correct set up.

HELP me adn others understand PLEASE!



also here is a photo of the muzzle ends as laying in the previous, I have now what seems two different boosters/bearing ends as they dont interchange with the ends of these barrels.

[roadrunner]

Wow! Crash, even more to consider. I am planning on going .308 on my build too. 8mm is non existent in Alaska. Even if I could find good surplus ammo. Freight and hazmat fee would bring me right up to commercial prices. Now I think I better get a .308 barrel before I set by bushing off my 8mm barrel.
Didn't mean to get preachy about taking measurements. Old habit from work...."apprentices" sounds like your way more than competent.

[crash520]

All good RR,

you dont own a RoadRunner do you?

[roadrunner]

well...Had for 15 years. Ground up resto. 1970 plum crazy, air grabber, white int. sold it last year to bye my new bride a new suv. plan to find another fixer for a father son project someday. take care.

[JBaum]

I still have my RoadRunner that I bought new.



viewtopic.php?f=10&t=10195&p=78902&hili ... ner#p78898

[roadrunner]

Jbaum, Thats a sweet ride, nice color too. RR

[crash520]

OK, Im a Mopar guy at heart as well, nice to have an originally owned car JB, I was just up in Olympia WA with the Rocket Resto mopar guys the other weekend, spent the weekend driving around in an original 69 Hemi 4 speed roadrunner, Freakin AWESOME!!! BUTTTTTT,,,

back to the barrels, the three barrels show each a different shoulder that rests agaianst the barrel stop, can anyone identify these barrels and should they have a specific recouperator plunger to suit?

[JBaum]

The barrels are interchangeable with no troubles. Since the recuperator rides on the barrel extension, the shape of the barrel is irrelevant to it.

[crash520]

JB, I cant agree on that sorry (happy to be corrected as Im not full speed on 42's).

With barrel fully forward it should rest up against the barrel stop I believe, and the recouperator should be applying slight pressure to the back of the barrel extension to hold the barrel forward against the barrel stop. So if this is the case with say the barrel on the left in the photo and then the barrel in the middle was to be used there is a strong chance there could be then a gap between the recuperator plunger and the barrel extension due to the barrel shoulder being significantly shorter. or switch it around, start off with teh center barrel and then try to use the left hand barrel and only to find possibly excessive recuperator plunger pressure or maybe not be able to close the barrel door? ..... maybe?
does any of this matter even?

V/R
C

[www.Prussia.us]

It is an excellent observation Crash520, but I would bet the ranch on jbaum's word.

He is much brighter than he looks in his picture he had taken for his avatar

[crash520]

I know! I feel like i'm taking on the ruler of all things MG,,,, I do it bent forward looking down in a submissive stance of course, begging,,,,,,

[anjongni]

Hi guys, I see that the .308 barrel setup takes a unique front barrel bushing. RTG has them, with the flash hider, quite inexpensive. This may account for the difference in the front bearing area of the barrels. If you are using the 8mm barrel bushing with your .308 barrel, might be in-compatible, or add unwanted length. I have a couple display guns; some barrels go in easily, others have needed a little polishing of the recouperator plunger and a good slam of the door to get them in. I can measure anything you need if it would help. Good luck...Phil

[crash520]

Thanks Phill,

All three barrels are 308 but only one takes the MG3 bearing, the other two take what I believe is the MG42/M53 bearing

Greg

[anjongni]

Hi There, I measured an old German barrel assy. here, 2.565" from flange to end of lock...Phil

[JBaum]

I mostly shoot a .308 barrel with the MG42 WWII style flash hider. Works fine. To convert from 8mm to .308, I change the barrel, feed tray, and top cover (feed pawl spacing is different since the .308 is a fatter cartridge). The front end for the 42 works fine as is for .308. I don't even own an MG3 flash hider.

[anjongni]

John, does one ever need the MG3 .308 barrel bearing that RTG sells? What is different inside it? Do MG3 barrels have a different front profile? Are there barrels out there that are MG42 front profile, but .308 bore? Does this MG3 flash hider use a separate booster cone inside like an MG42? Help please...Phil

[JBaum]

The MG3 muzzle booster goes with the MG3 barrel bearing. The MG3 booster doesn't have a nozzle in it like the MG42 booster. I prefer the looks of the 42 style booster. Barrels are the same profile whether .308 or 8mm. My 42 works fine in either caliber with the 42 booster, nozzle, and bearing.

I suppose from the looks of it, the MG3 bearing is needed for the MG3 booster, because I've heard of problems just putting on the booster without changing bearings. I have no first hand experience with that, but the bearing is different and it would make sense that they are a set that are matched for function.

Without looking at the barrels for a caliber marking or waffenamt, I can't tell my .308 barrels from the 8mm barrels. Profile is the same, and .308 barrels sometimes come with waffen proofed barrel extensions attached. The extensions outlast several barrels, and were reused until damaged.

[crash520]

An MG3 barrel profile is not the same as a 308 MG42 barrel, they differ slightly at the muzzle, the bearings if fitted onto the correctly matched barrel wont slide back and forth on the barrel. off the top of my head I cant remember but, I do know that the MG3 bearing wont fit on a 42 barrel or the other way around as the end of the barrel bearing area is too long and wont alow the bearing to seat parrallel to the barrel, I will try to document this over this coming weekend with better photo's etc.

[Bullwinkle]

You are over thinking this!!!!. .+/_ .050 doesn't matter! The recoup has over 1" of travel and just returns the barrel to the full forward position OFF the cams so the bolt rollers are fully LOCKED in the barrel extension. The recoil impulse pushes the barrel BACK onto the cams (AGAINST the recoup plunger) to retract the rollers and allow the barrel and bolt to seperate. Barrel stop to recouperator plunger is a VARIABLE distance. Your plungers can vary due to wear and tear more the amount you measured!!!

Look at the barrel extension where it contacts the recoup plunger. The extension is beveled at 45 degrees on THREE SIDES...the recoup plunger is beveled 30 + degress...the combined bevels alone = 1/4" or more!!! as long as the barrel snaps into place with the plunger touching the extension when the barrel gate is closed your good to go.

IF you get your rewelds CLOSE...The the other items will fit. If you screw up your major section tolerances...you'll have to grind a few individual parts to fit. (worse case is no Elli Whitney interchangeable parts! BFD!!!) IF the recoup is too long, you will grind a few .10's off the end of the plunger...no biggie but never heard of it being an issue...EVER.

Glad your thinking small, tight tolerances...it will make the large sections reweld easier which means fewer "issues" (with fitting individual parts) down the road. BUT...this is not an area of concern....move on, your barrels WILL WORK. word of caution...CHECK HEAdSPACE on the barrel without the extension if you remount it to a new extension. HEADSPACE is set based on Extension/Bolt/Barrel lock up within the extension...a different extension may have a out of spec headspacing for your particular barrel which = KABOOM

There is a great deal of forgiveness built into the MG42/MG3 system. DO NOT OVER THINK IT!