Casehead seperation

[Jason B 0]

Hello All,

I am a new member and have learned quite a bit already here; thank you.  I acquired a JSAR that is in good condition that has been sported.  The barrel is 19 inches with a Lyman ramp sight.  There are no markings on the barrel bushings.  The barrel has the markings "8 (one inch of space) 8"  I field stripped the rifle, cleaned and oiled it properly.  I have been firing m2 ball, and various hunting loads at 150 grain or less. The rifle either fails to extract or tears the case heads off.  If I oil the cases, they may eject half the time. I also have case stretching.  I polished the chamber to 1000 grit and installed a new extractor and I get the same results.  If I shoot "factory lite" ammo, the rifle functions most of the time.  I am waiting on headspace gauges.  Any advice on this problem would be highly appreciated. 

Thank You, Jason

[Yuccacapt343 0]

Welcome Jason!

when your Johnson ejects correctly, how far is it throwing the spent cartridge?

Wayne

[Jason B 0]

Hello Wayne Thanks,

It will throw the empties about 5 feet with the lite loads,  The full power loads will be thrown less.

[Yuccacapt343 0]

Sent you a PM

[M48TANKER 0]

Jason,

First I'm not the expert. If Joe Scott reads this he can give you the best advice. The chamber polishing is usually the first thing to do after replacing the recoil mainspring with one which is a full 12 inches long. (available right now on Gunbroker ....make sure you get the one for the JSAR)

Joe always advises to carefully inspect your fired cases. I believe he says to first polish the brass with some steel wool or emery cloth to make it uniform and shiney. Clean the chamber but Don't oil the chamber. Fire the round and then look for evidence of marks associated with pitting in the chamber OR a ring in the walls of the chamber. Even if polished it may still have pits or a scratch.

A weak mainspring will allow violent extraction which can rip the case heads off. Rounds sticking in the chamber will exacerbate the problem. When a round is fired, the brass normally stretches a tiny amount but will shrink back in time to be extracted. If the mainspring is week or the ammo is too hot, the brass may not have time to recover it's original size. I'm not sure but I think an oily chamber will not help... but will hinder the process due to surface tension of the oil.

Since the barrel is a sporter barrel the chamber may not be reamed quite right. Mr. Scott has advised that sometimes it takes quite a bit of polishing to achieve the desired result, but usually it will fix the problem.

If your brass is stretching in length perhaps the roughness is just at the forward end of the chamber beyond the shoulder area.....be sure to include that area in your efforts.

Let us know what fixes the problem.

[Jason B 0]

Tanker,

Thank you for the input on the main spring and diagnosing the brass and the chamber; really good.  I will post when I check headspace. 

out

[Jason B 0]

I received the head space gauges today.  Go, No Go, and Field.  Headspace test were conducted and it failed; The bolt will lock closed on all gauges. I believe I identified the problem of the separated case heads and jamming; excessive headspace.  How do I deal with this?  The barrel has great rifling.

 

Thanks

[Brian Alpert 0]

The bbl has to be set back and rechambered,  This also calls for repositioning the front bbl guide (a spacer is usually needed) and re installing the front sight and bayonet lug.  Occasionally one sees original JSAR of JLMG bbls which apparently failed headspace and required this modification at the factory.  You can tell if they have a spacer behind the guide collar and, if you remove the front sight and bayonet lug, there are additional taper pin groves from  the original mounting. 

[Joseph Scott 0]

To correct excess head space, the barrel must be machined.  removed the rear collar, sight and lug.  Machine the shoulder and rear of barrel back exactly .060" (one turn of collar).  This puts the front sight back on top. You must also recut the extractor slot .060" deeper. Then you must make a spacer .060" thick and install it behind the center guide. Ream new pin location.  Install rear collar,  You can then ream chamber to correct depth head space.  The entrance taper is 82deg, break the edge of chamber slightly.  On occasion, I found it necessary to move collars 1/8"  (.125").  Do not cut the front of rear collar, it doesn't work. 

Before starting, cut some round shims the diameter of shell base.  Try .002, 005,.010" with the go gage and find out how excessive is the head space.  Ream slow with lots of lube and test often.  I am not doing any work or accepting orders  due to blindness.

[Jason B 0]

Mr. Alpert and Mr. Scott,

 

Thank you for taking the time to respond to this matter and set the course on what it will take to bring this rifle back.  I deeply appreciate the knowledge you have shared. I have to digest all of this and make a plan.  I will keep the board apprised.

Best,

Jason

[Jason B 0]

I just got my rifle back from a complete rebuild with new barrel after a few years.  Instead of case head separation, it now throws empties 20 feet(not hyperbole)  I measured the spring and it shows 10.5 inches.  I am at a loss and looking for the goldilocks zone for ejection.  With light recoil loads, it throws them 8 feet, with full power Remington or S&B, 20 feet.

 

Jason

[Blueheeler 0]

With a brand new recoil spring and m2 clone handloads, I get about 3-4 feet.

[Jason B 0]

I think they put my rifle back together with a 70 year old main spring.

The empties also have huge ejector dents in the rim making them useless.

I am going to get a new spring and try again; if similar results, i was thinking of cutting off a couple of inches of the old spring and nesting it with the new one.  Maybe act as a stiff buffer at the end of bolt travel

 

[Whitpusmc 0]

Does your rifle still have the buffer assembly at the rear of the spring? 
 

Whit

[Jason B 0]

Yes, It was restored back to milspec.

[Whitpusmc 0]

Who did the restoration?

 

 

[Jason B 0]

Miltech restored it;  They are sending a new spring.