Mas 36 Excessive Headspace???

[jwalker7523]

First time poster here,

I am trying to reload for a Mas 36 rifle but have ran into a few issues. The case heads on each of my brass have a slight bulge that is noticeable by running a finger over the area. After sectioning the case, however, the brass in this area looks thick. There is a strange ring around the upper body of each case. This ring is not visible from inside. When full length resizing a considerable amount of force is needed to run the cases through the die. (I am aware that neck sizing is the way to go but dies are $$$ for this gun) Aside from taking this to a gunsmith can anybody give me any idea if this is normal?

- Jerry

 

[edwardware]

I have a sloppy ovoid and oversize .270 chamber that does that, badly enough that I resize the body separately from the shoulder/neck.

If you can just (0.002") bump the shoulder, and rechamber, then you should be ok. Continue to check brass base thickness.

If resizing enough to chamber has you bumping the shoulder excessively, then you'll quickly be splitting cases.

 

[Scooter22]

Is that the original French round or one converted to .308? I've heard the conversions were sloppy.

 

[jwalker7523]

Is that the original French round or one converted to .308? I've heard the conversions were sloppy.

It's chambered for the original 7.5 French round. The gun looks like it saw little if no action. It is parkerized, not sure if that is the original finish

 

[Whiterook808]

The post war rifles were parked, and the pre-war were painted. What kind of brass is this?

 

[243winxb]

Take some measurements.

Factory cartridge before firing.
Shoulder diameter .445" to .437"
Base diameter 0.482 "

Fired should be larger in diameter??
The brass shows signs of high pressure or the chamber is not polished well??

Chamber measurement i converted. Hope my math is ok? http://www.cip-bobp.org/homologation/uploads/tdcc/tab-i/7-5-x-54-mas-en.pdf Note : at link there is maximum and minimum diameters.


12.30 = .484"
11.35 = .4468" Maximums of chamber This is making my head hurt.

 

[243winxb]

CIP doesn't give a head to datum measurement like SAAMI, that i see, to check head space.

H1 - L2 may be there measurement?

CARTRIDGE MAXI 46.42 = 1.827" -.20 = -.0078" 1.8192"

 

[Ireload2]

If you are good with trig you can convert the CIP dimensions to the SAAMI style dimensions.
The easiest way is with Excel. Once the spreadsheet is set you you can get the SAAMI numbers for any round in less than a minute.

 

[243winxb]

trig ,Excel

Whats that? Never heard of them. Are they new since 1944.


I used a Converter-https://www.rapidtables.com/convert/length/mm-to-inch.html slow like us old folks.

 

[Ireload2]

You are converting mm to inches so it is just a change of measurement units.

Using trigonometry you can calculate the distance from the case head to a given datum circle on the shoulder as done by SAAMI. Excel just makes it possible to keep using the same equations over by just filling in the blanks with the CIP data. The spread sheet also converts the units from millimeters to inches.

Whats that? Never heard of them. Are they new since 1944.


I used a Converter-https://www.rapidtables.com/convert/length/mm-to-inch.html slow like us old folks.

 

[dh1633pm]

You mean to tell me that I can use math to solve this problem? And I just said to myself a few moments ago, another day without using trigonometry. I might make light if it, but I added it to my list.

My MAS36 which appeared to be never shot, blew out a piece of brass at the bottom of the case the first time I shot it. It does tend to expand a little bit more than I am used too. I need to experiment some more with it.

 

[entropy]

The gun looks like it saw little if no action.

Only dropped once.
That's not unusual for milsurp rifles; they had oversized chambers to begin with, for sure function in combat; It reduces brass life considerably,and with 7.5 French, that's bad, because brass isn't as common as many other calibers.

 

[Ken T]

What brass are you using?Is it actual 7.5x54 brass?I would try polishing the chamber.It is either rough or really dirty.

 

[jwalker7523]

This brass happens to be FNM, but the same problems appear with PPU as well. It is 7.5 French not a .308 conversion. Seems like reloading for this bad boy might be too problematic to be viable

 

[243winxb]

The case heads on each of my brass have a slight bulge that is noticeable by running a finger over the area.

Full pressure factory loads may do that. Brass will be harder to fl size also.

There is a strange ring around the upper body of each case.

Full pressure ammo, from a rough chamber, will imprint into the fired brass, as yours has.

Taking measurements off fired brass should show if the chamber is oversize and out of specifications.

A Very bad chamber headspace will cause a case separation on the first firing. Possible near case head. Less common in the body.

 

[ping]

I ended up sending mt rcbs dies to rcbs and they modified

 

[Slamfire]

If you can just (0.002") bump the shoulder, and rechamber, then you should be ok. Continue to check brass base thickness.

Agree. Diagnosing dimensional problems from a picture hardly ever works, but I think what you have is a large chamber. The brass is expanding in the chamber, but luckily, your loads are light enough, that you are not expanding the case head. That is all for the good.

For this rifle, on the first firing of each case, lubricate the case and fire it lubricated. A very light coating of your favorite lube, be it sizing die lube, grease, vasoline, etc, just coat the case from the case neck downwards, and shoot the cases. The lube will keep the case from gripping the chamber walls, the case will slide to the bolt face, and the shoulders will slide out and fill the front of the chamber, The end result is, a perfectly fireformed, and stress free case. Incidentally, if your load is excessive, you will have sticky extraction, which is also a good thing. You want to detect over pressure loads, and dry cases in dry chambers have a tendency to disguise high pressure indications. But, if you fully load the bolt,by lubricating your case, you will see the high pressures.

This is something I do all the time with expensive brass, fire form new case by lubricating them, then bump the shoulders back by 0.002" or so.








I did conduct loading for my MAS 36 and came to the conclusion that keeping pressures low is the only way to go for these actions. The MAS36 worked great with issue ammunition, but the thing is a rear locking action and therefore I would recommend keeping pressures less than the 55,000 psia max.

 

[Galil5.56]

I hope you can figure this out. The only time I have ever seen anything approaching something not right, with regard to case swelling in my MAS 36, was using 06 brass as an experiment. A circa early 90's Handloader magazine reloaded for the MAS 36, and used 06 cases for the full power data data. They seemed to think all was well, but when I tried them with gallery cast bullet loads, swelling was WAY more than I was OK with. The dims are so different (esp head/rim diameter), is why I went very conservatively using only gallery type pressures, and glad I did. BTW, what you show looks beautiful compared to what my Ishapore 2A, 7.62x51 produces... Never seen as generous/lopsided a chamber in my life, even beating out my beloved Type 99 Arisaka.

Using 7.5x54 PPU brass, my all original, never refurbished wartime made MAS 36 displays beautiful fired cases, along the lines of any good commercial bolt action would show. This aspect really surprised me, considering it is a battle rifle, and my MAS 49/56 shows a similar condition, which really surprised me. One note is the first set of Lee Dies I used GROSSLY over-sized the brass, so back they went for examination. To Lee's credit, they acknowledged this fact, corrected it, and even sent a CIP type document, showing all of the chamber/case specs they use.