Mauser Trigger Issue II

[DonHowe]

I have mentioned this M95 before. It is barreled/chambered for. 257 Robert's. Yesterday while attempting to fireform brass I noticed a further issue with the trigger. More often than not the trigger simply will not break. I'm using the Mauser trigger, as-issued for now. Pull weight measures 4-4 1/2 pounds. If dry fired the trigger action is normal, every time. With round in the chamber, mostly it will not fire. Take up is normal then the trigger stops hard and no amount of effort will move it. I am stumped.

To complete the picture, I formed cases setting the shoulder so the bolt just closes with resistance so the case heads pace is correct whenfireformed. Back home I chambered an empty formed but not yet fireformed case and tried the trigger. The mechanism functioned normally.

I am at a loss. Ideas?

[405grain]

On an M95 Mauser there is a small slot cut into the bolt that matches up to a projection on the sear. If the bolt is not fully closed the front of the sear will not engage this slot, and the trigger will not be able to pull the sear down. This is to prevent out of battery firing. It's a no-brainer but I gotta put this out there: when investigating what's going on do not use live rounds. make up some dummy cartridges with no primer or powder. Do you have a sporterized welded on bolt handle? Make sure that the root of the bolt handle isn't preventing the bolt from rotating all the way into the closed position. Is the headspace on the chamber correct? If the chamber is just a little too short the bolt won't fully close. Are the cartridges sized properly? If the shoulder is too far forward that could be a problem too. Are you using a factory M95 bolt? In a pinch I've seen people grind the chin off a M93 bolt to use in a M95. The problem there is that some M93's don't have that slot for the sear. It could be any number of things, but the first thing that I'd check is to see if the bolt is rotating all the way closed.

[Gtek]

Not knowing all the details, are you using converted brass? What is the possibility, you say naked brass will drop, loaded up no correct? So loading up and chambering creates a no-go, what about neck thickness (conversion brass) and not letting bolt rotate all the way into battery. Safe checking, pull firing pin assy from bolt and chamber the different scenarios and look at bolt handle position (measure) to stock.

[DonHowe]

405grain: the projection on front of sear not etrring that slot in the bolt would explain what I am experiencing. It has to be ammo related as it only happens with a round in the chamber. The chamber is cut to correct heads pace. A case sized normally, ie die screwed down to contact shellholder, chambers correctly.
Heads pace on formed cases Is long intentionally. The case shoulder was pushed back slowly, try ING a case in the chamber at each interval until the bolt just closes. After a near case separation once due to improperly forming cases I routinely use this method

Gtek: I am using cases converted to. 257 Robert's from 7x57 and from 8x57, the parent case. As stated above the formed (necked-down) cases are carefully fitted to the chamber to minimize stretching at the first firing.

What I realized while reading both replies is that I should final-check my case-forming method by seating a bullet in the formed case and check chamber ING as the increased diameter from seating the bullet may make the case too long at the neck shoulder juncture. It is likely that only minimum length cases make up the rounds that function. I will check that and all the things mentioned but am confident the issue is headspacing of the case.
I also need to improve my proofreading before submitting a post!

Thanks gentlemen!

[TurnipEaterDown]

The dimensions of your formed cases should be checked.
The dimensions of an 8x57 are such that, depending on your forming / trimming operations, you may well end up w/ cases unable to chamber in a 257 Roberts, if made directly from 8x57. Parent case relationship does not imply reform in one pass in a die and it will function. Several cartridges have dimensions that make forming from the parent more complicated than 1 pass through a die. SAAMI has an online reference w/ all cartridge and case drawings available. These can be invaluable.
Also note your neck thickness when you check your loaded rounds. OD w/ a bullet loaded will be more than sized empty brass. Sizing down an 8mm neck case to 25 cal (0.066" reduction in nominal neck diameter) could leave your neck too thick when loaded in final 256 Roberts form to freely chamber. You should not have an issue w/ movement of the shoulder / neck junction enough when seating a bullet to make the round unable to chamber. If it cams in w/o bullet w/ little to no resistance and doesn't cam in w/ a bullet seated (dummies: no primer), I would look at neck thickness.
With a dummy you can check full function of the striker as well. No primer or use (spent) primer, and dry fire is fine to check function. I never leave my rifles cocked on empty chamber for storage. When I put them away, I ensure it is empty, close the bolt and pull the trigger. Dry firing a few times doesn't hurt common CF bolt actions.

[atr]

good post! all the respondents "hit the nail on the head"

[Texas by God]

What about necking up 6mm Remington brass? Would that work?

Sent from my SM-A716U using Tapatalk

[TurnipEaterDown]

I don't think 6 Rem would work well. The shoulder-body junction is close, but w/ a steeper shoulder on the 6 Rem the shoulder of the reformed case would move away from the shoulder area of the chamber, and it would likely not control headspace well.
Of course, necking up is Usually less problem prone than necking down (though shoulder walls that become neck may give an issue w/ a thick neck at the bottom, or a "doughnut"), so perhaps a 6 Rem could be necked up to 7mm, then 30, then back to 257 to give a good false shoulder and headspace well.
BTW: SAAMI drawings give you no clue as to internal case tapers, shoulder or body thickness, or internal head form. These can all vary from manufacturers, and even from one case to another in the same manufacturer. They can use different tools to draw the same basic, and I wouldn't put it past them to do that at times.
Dummies, a caliper, and SAAMI drawings are your best buddies when reforming cases...

[Gtek]

Measure your neck wall thickness, if it is fatter than about .011"-.013" may want to look around there.

[DonHowe]

OK, investigating. Chamber neck diameter is 0.2920-0.2925. Not fron Saami print, but physically measured from a lead slug of the chamber neck. Necks of several loaded rounds rounds with mIcrometer were 0.285ish at the mouth and 0.2885 just ahead of neck/shoulder juncture.
For the record, cases formed from 7x57 cases were formed in one pass with. 258 Robert's die. I would not dream of trying/going from 8mm to . 257 in one pass. That was done as follows:. 308 sizer yo move shoulder back, reduce neck with 7x57 die then final sizing with Robert's die.
Don't have all the answer but not my first rodeo.
I broke down 5 rounds, dumped powder deprimed then seated the bullet's again. Ran all 5thru the action from the magazine. The firing mechanism worked perfectly. I think I am onto the problem but want a trip to the range to verify it. I believe the cases are heads paced correctly given that I am fireform ING. So far as I know 3 1/2 to 4 thou is plenty of neck clearance. As often happens picking the brains of others helps to refocus. As often as have looked at that little slot in the bolt I never gave it much thought until it did what it was there for.

Thanks all!

[Gtek]

Hard to focus, you should see what it looks like from here. Sounds like something appeared before you, please let us know when confirmed.

[DonHowe]

Not about hard to focus, just that it is easy for any of us to look at a problem over and over and get nowhere because we look at it the same way each time. The various thoughts presented here merged into one: start over and check every step, assuming nothing. The first comment told me the mechanism is fine now look elsewhere.