Bolt Lock Up M39 twice!

[runfiverun]

the low pressure is somewhat confusing when coupled with the velocity in the 2-K fps area.
that is an intriguing combination to say the least.

but it does point to the click bang being the problem.

it's too bad a chronograph wasn't being used at the time.

[Bjornb]

Bjorn thank you very much for doing this. 23.6K psi with that 170 grain bullet probably isn't burning clean yet. If you get a chance the numbers for 200 grain with same charge would be interesting as that one locked the bolt and blew rim off the bolt head.

Scott,
I ran numbers for a 200 gr bullet (the 311299), because I wasn't familiar with the R4. It showed an MV of 1955 and a pressure of 28.4K psi. Still nowhere near danger zone. If I didn't know any better I'd chalk this up to an accidental overcharge. After all it's not possible to rule it out in hindsight.

[swheeler]

Scott,
I ran numbers for a 200 gr bullet (the 311299), because I wasn't familiar with the R4. It showed an MV of 1955 and a pressure of 28.4K psi. Still nowhere near danger zone. If I didn't know any better I'd chalk this up to an accidental overcharge. After all it's not possible to rule it out in hindsight.

Overcharge is possible but double charge won't fit and this stuff meters well, I think he said he weighed the charges, I know he pulled the others and they were spot on. I'm guessing with the slick powder coat bullet he got a example of stop/start and pressures went way up. I just wanted some numbers for OP to look over, he knew his load was within reason as I did when I first read it. If 25.2 grs is start for 180 grain bullet then one would assume 25 grains should be fine for a 170 grain bullet being 10 grains lighter. This guy posted looking for answers and help not ridicule.

Now back to splitting lodge pole, wonder if I could use 5744.

[Bjornb]

I hope no one thinks there's any ridiculing going on from my side; I'm just trying to wrap my head around the severity of what happened to his rifle bolt. Having used 5744 extensively, and particularly in the 25 grain range in several 30 cal cartridges, it's a load I would share freely.

[MT Chambers]

I believe that 5744 has been associated with some unusual pressure excursions, and learned ones are not using it as much.

[swheeler]

I hope no one thinks there's any ridiculing going on from my side; I'm just trying to wrap my head around the severity of what happened to his rifle bolt. Having used 5744 extensively, and particularly in the 25 grain range in several 30 cal cartridges, it's a load I would share freely.

Oh heck no, as I said thanks for the help! About as soon as he posted someone jumped in with the bold print telling him to get a reloading manual and read it. That just isn't the way we should treat each other, someone asks for help I try to help them best I can.

[CHeatermk3]

When I first began shooting Military cast boolit matches, I shot 5744 in my M39 Mosin. One thing I learned the hard way is that 5744 wants to bridge in my RCBS powder measures.

I STRONGLY advise weighing each and every charge of 5744 unless using a dipper to dispense directly into the case.

[Mr Humble]

A couple of thoughts:
1. the 7.62x54 headspaces on the rim not the shoulder.
2. why not stick with proven powders that have been essentially the same for decades like 4198/4895/4064 etc. ?

[swheeler]

." the 7.62x54 headspaces on the rim not the shoulder."

......and a belted magnum headspaces off the belt, a novice reloader often makes this mistake, BUT after a few years of hand loading for either you should figure out that headspacing off the shoulder will give you longer brass life and better accuracy. Rookie mistakes happen until you get a little powder residue under your belt.

[swheeler]

and it is 7.62x54R if it's going to headspace off the R(rim)! LOL

[Mr Humble]

I agree that any rimmed or belted cartridge is better set up to headspace off the shoulder BUT, in a rimmed or belted case IF the shoulder is set back, there will be no excessive headspace because of the shoulder setback. The reason for rimmed and belted cartridges is to allow for cartridges to be made undersize to function in dirty, nasty chambers yet still headspace properly. A perfect example being the WW I SMLES with very oversized chambers to (hopefully) function in the horror of the trenches with no danger of excess headspace.

[swheeler]

If you keep expanding/blowing them out to fit the chamber on firing, then sizing back down pushing the shoulder back you can still seperate a case releasing gas. We know that isn't/shouldn't be the problem the problem as OP says once fired and is an experienced reloader. Neck sizing or partial full length sizing is a better option in this case pun intended.

[tomme boy]

Powder bridged is what I say. Especially if using the rcbs powder drop with the small outlet. The 54r cartridge is a strange acting cartridge. Especially using rl15. Seen loads that were 2 grs off of max act like a very low psi load and soot the whole case and a collapsed shoulder. Seat the bullet 10 thousands deeper and it acts perfectly fine.

Using 748 and win primers and have misfires. Pull the bullet and the powder turned to a large green chunk.

[runfiverun]

I have seen the round suck dents into the neck and shoulder of the case too.

[tomme boy]

I have had it do that too Run. The case is not sealed and the gasses are pushed back around onto the outside of the case. Usually the case will be black from soot. For me it was RL15 every time it did it.

I found that it was from seating the bullet out too far trying to touch the lands. If you seat the bullet in the neck at least 1 full diameter in length it does not do it. I feel it is on the verge of a SEE or whatever you want to call it when it does this. It will also puff gas back at you in the face when it does this as the case is not sealed. And it was ALWAYS on a fresh full length sized piece of brass. Being that the 54R or 53R depending on which brass you use, headspaces off the rim. But the chamber shoulder itself can and will be fairly deep on some of these. So that extra bump of the shoulder is not sealing off. And that is were the gas is trapped and collapses the shoulder.

I also had the shoulder collapse on 303 Brit. Same thing about a deep shoulder and short brass. That is why I neck size all of my 54 and 53R brass only.

[swheeler]

I guess we all agree then we will never know what happened, can only assume. If it was bridging in the powder measure then when he pulled all the remaining ammo, 2 of them should have been light loaded.

[CHeatermk3]

Or maybe the click-bang was the light one and the blowout was heavy...

But you're right.. we will never really know