Diagonal shot string with MAS-36

[wadcutter]

I took my new-to-me MAS-36 (Made in June 1940) to the range for the first time yesterday. I shot a 20 round box Pvri ammo. The first three shots were well centered. After that they started to string out, up and to the right. I fired the last 10 fairly quickly and the group was 2-3" up and to the right of the point of aim at only 25 yards.

I'm curious if anyone else has found this? I wonder if this rifle has a barrel design that warps a lot when heated or maybe they were in a rush to build this one as it was made the month France fell. I read that the tension on the stock can influence the point of aim. I properly won't monkey with it, but am curious if anyone else has found this.

Overall I think it's a brilliant rifle and compared to Mauser of a similar vintage they are very cheap. My old eyes really appreciate the aperture sight.

[EMC45]

Sounds like it got hot or something maybe loosened up?

[Multigunner]

Mass produced military rifle bores are often found to be off center at some points down the length of the barrel.
The British normally straighted barrels till production pressures of WW2 resulted in their instead simply gauging the last six inches of the bore. so long as the last six inches was straight and centered accuracy was acceptable.

Mauser got around problems of wandering bores by using stepped heavy weight barrels. I once found a Mauser long barrel had been turned down and shortened to replace a carbine barrel and the bore at the muzzle was so far off center it nearly cut through the barrel wall. the crown had been turned on a lath so the crown was centered to the muzzle but not to the bore.

Its not unlikely that your barrel has bore wander, not serious enough to have been rejected in test firing but enough to cause stringing as the differing barrel wall thickness heats unevenly after firing a few rounds.

[bouncer50]

I have a French auto and two bolt action. Mine have the same problem went the barrel heats up. I wait a minute between shots for the barrel cools to down. From a inch to two with a cool barrel. A four inch plus went the barrel heats up. My thinking they straighten the barrels with a press and then went the barrel heats up they back to went they were bend. Just my opinion on bend barrels that were straighten. You will not notice a restaighten barrel till it heats up.

[ukrifleman]

First check that the action screws are tight, then check to see if the fore stock has any movement in it.

If it has, you will need to remove it and shim the rear lug so that it `snaps over centre` at about 15 degrees to the barrel.

You can make shims from a beer or soda can.

The lower barrel band is critical in its adjustment, as it affects barrel harmonics, they were set up to the correct tension by

armourers and were not to be altered. That's why the screw heads need a 2 pronged screwdriver to move them to prevent troops messing with them.

Once you have ascertained that the fore stock is tight, you will need to shoot a few rounds and adjust the barrel band tension until you are happy with the grouping.

I went through the same process with my 1945 MAS 36 to get it to group plus, I had to change the rear sight aperture to get it to shoot POA/POI

Rifle stocks can dry out over time and shrink, resulting in poor bedding.

If your rifle has a heavy trigger pull, a simple fix is to replace the firing pin spring with one from an M1 carbine.

Cut the new spring a couple of inches longer than the original at first, then remove a coil at a time to get the trigger you want.

Here is a photo of the original (shorter) spring and the longer replacement.
I got my trigger pull down from 81/2 lb to a comfortable 5lb pull.

Don't overdo it otherwise you will end up with light strikes.

Hope this helps and good luck!

ukrifleman

[jessdigs]

I have an MAS 36 that my brother gave me as a gift when he was in the Marines. It is now .308 win. The wood is a little loose, but it is a fun rifle to shoot. I have never tested it for accuracy so I cannot comment on your problem, but I do like the rifle.

Sent from my Pixel XL using Tapatalk

[Scharfschuetze]

Perhaps the barrel was not properly stress relieved. As it heats up, it will relax slightly (and thus unstraighten itself) and start throwing bullets away from your cold bore zero. I've seen this in a US 1917 Enfield (with Elmer's cartouche) several years ago.

[Texas by God]

Glass bed that sucker. I think they are neat but I've never had one. Yet. It can't hurt to try.
Best, Thomas.

[Multigunner]

The military MAS 36 ,IIRC at least, seemed to be a bit too open with the thumb cut weakening the left side more than it should.
The commercial sporter versions and sniper versions don't have the thumb cut (again if IIRC).
This would not be much of an issue if it were a front locking action, though it can affect even front lug actions to an extent causing bullet throw.
The No.4 Enfield had a high squared receiver wall with minimal thumb cut that reduced the effect of action body flex compared to the SMLE.

This might be a factor in wandering zero and stringing.

BTW
Years ago I ran across a Paul Mauser patent drawing pre WW1 that showed a rear locking two piece stock rifle action that appeared to be Identical to the MAS 36 action. Wonder if there was a connection there.