Bolt Lock Up M39 twice!

[swheeler]

I wonder about changes to this powder over the years and manufacturers? It started life as MP5744, then XMP 5744 and now just 5744, maybe they have changed more than the name? Seems like I remember the nitroglycerin content being cut back by about 10% less when it became XMP? Now being made in Canada who knows

[swheeler]

I could say it was a SEE, after all you did start under Accurates published minimum charge for that bullet! This thread could go on for years, loooong time GI!

[30calflash]

Accurate has had surplus powder from different countries over time. Many other popular numbers used in hi power 'changed' when using a new batch. Did not have the same performance and peaked earlier than the old batch.

Too bad they used the same numbers over and over with new powder buys.

[astroturf3040]

I could say it was a SEE, after all you did start under Accurates published minimum charge for that bullet! This thread could go on for years, loooong time GI!

Hmm 25.0 Gr is at #2 manual and above other data starting load but somewhere around 78% of max loads. All conjecture I suppose. I do not want to recreate the experience! I will Tech Inspect Rifles for HS and FPT. The 311466 bullet works great across board with 25.0 5744. Thanks

[swheeler]

If you experienced any delayed ignition upon pulling the trigger I would say a SEE was possible. Have never bought into the only slow powders, only jacket bullet THEORY. I believe the slow powder, large capacity/ low expansion ratio catastrophic failures are just more spectacular. Starting loads are there for a reason, and that reason was that the test rifle started to show signs of erratic burn of propellant/ignition, change your chamber dimensions/ throat/ignition and you have a MINOR SEE, high pressure excursion.

[astroturf3040]

Interesting. Certainly locked up the bolt.
I recall that WW always noted not to reduce the powder charges in the old manuals.

[swheeler]

Have you got a different bolt body ordered, should be plenty available online.


I'm sorry meant bolt head, had a blonde moment

[LAGS]

Just to throw my $.02 into the mix.
I have seen many rifles detonate from too Low of powder charge.
But I suspect that the firing pin protrusion is wrong.
With the MN, if you swap firing pins between guns accidently, they do not have the same protrusion, especially with the screw adjustment design that they are.
I watch for this on my Mosins since I have several MN's and a bunch of spare parts.
Check it with a Gage after re assembling the bolt each time.
And try to set it at Minimum protrusion.
Commercial primers sometimes like a different protrusion than Military, Berdan primers.
Usually Around the Min. for the rifles specs

[astroturf3040]

Just to throw my $.02 into the mix.
I have seen many rifles detonate from too Low of powder charge.
But I suspect that the firing pin protrusion is wrong.
With the MN, if you swap firing pins between guns accidently, they do not have the same protrusion, especially with the screw adjustment design that they are.
I watch for this on my Mosins since I have several MN's and a bunch of spare parts.
Check it with a Gage after re assembling the bolt each time.
And try to set it at Minimum protrusion.
Commercial primers sometimes like a different protrusion than Military, Berdan primers.
Usually Around the Min. for the rifles specs

Will do. Headspace good on both rifles, checked them both yesterday with all three gauges.

[Larry Gibson]

"Same load with 200 Grain .308 R4 and .310 170 311291 Powder Coated with AL GC DID NOT"

Could you give us a better description of those bullets after they were PC'd (sized to, nose size, lubed at all, HT'd, etc.) ?

Going from a 150 - 160 gr regular cast bullet sized .309 to 170/180 and 200 gr PC'd bullets with the same powder charge that "worked fine" with the 311466 might have something to do with the problem.

Larry Gibson

[swheeler]

Here is data from Accurate Manual #2, page 286

7.62x54R Russian
180 GR lead RN/GC
5744 start 25.2 gr-1873 fps, 28.0 gr 2129 fps 35.2 k PSI- 2.830" OAL 311-467 mold.

my 311-467 casts about 182 grs from 50-50coww-pb

I just weighed several, 187 grains full dressed and ready to load. The above data comes with a set of 7.62x54R Lee dies also.

[runfiverun]

powder coating is slicker and generally requires a bump in the load data of about 4% to bring things back into line with a naked boolit.

you could be super close with the P/C but be okay.
I just don't see how being that close wouldn't show some pressure signs.
then suddenly it did.
unless you were just flat jamming the oversized boolit into the steel so hard it couldn't move until the pressure got super high.

[slownsteady22]

Are you crimping these boolits?

Sent from my SM-G925R4 using Tapatalk

[swheeler]

powder coating is slicker and generally requires a bump in the load data of about 4% to bring things back into line with a naked boolit.

you could be super close with the P/C but be okay.
I just don't see how being that close wouldn't show some pressure signs.
then suddenly it did.
unless you were just flat jamming the oversized boolit into the steel so hard it couldn't move until the pressure got super high.

this.....

[swheeler]

Someone on hear has to have Quick Load? Where's Bjorn when you need him I'll take a wild guess that the 200 gr bullet load will show 32k psi and the 170 about 20k?
When the OP told me by PM that he noticed a click-bang I thought auhha, see what I mean.

[runfiverun]

meeah.
click bang and sticky bolt.
that's scary, like a start-stop pressure rise scary.

[swheeler]

With 32.5 grains of 5744 as max listed for 314-299, I really doubt they exceeded CIP max in their load data, 25.0 grs shouldn't have pierced a primer, stuck the bolt and blown part of the bolt head off, SEE what I mean. The 170 gr bullet he fired that pierced a primer was .2 gr below the start load published by the powder company for a 180 gr bullet.

[swheeler]

OK I found a member here that is willing to do a QuickLoad compute on the loads astroturf3040 used. I still need a few specifics from the OP, remember junk in junk out, so we want as close as possible and no skewed results. I have been going through my old load data and have not found any in the 7.62 Russian, funny because I shot up 8 pounder of the xmp version and first I ever bought was in paper bag as mp. But I do have plenty of data in various rifles with full workup on cartridge/ cast combos that no data was available, so with time I will repeat with the same rifle and bullets, everything same as before except the powder, I have an unopened pound of the new Canadian made 5744(just saw it and bought it a week ago) I can not pressure test but want to compare chrony data, difference will be temperature.

[Bjornb]

Having no Mosin experience I won't try guessing what happened in the OP's case, but QuickLoad gives 23631 psi when inputting the 311291 seated 0.25" deep, with 25 grains 5744 powder. That is obviously way below max pressure for this cartridge.

The MV with a 27 inch barrel is calculated to 2063 FPS. I can run other numbers when I get home later tonight.

[swheeler]

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.