Piercing primers with my VKT m-39

[JeffHolt]

Went to the range yesterday to sight in Nancy's Finn VKT M39,
Noticed that the gun was piercing primers using PPU 182 gr FMJ ammo.

Used the Russian field gauge and the pin was between the low and high slots. Seemed to check out. The armorer's markings on the cocking piece aligned also. I'm wondering if the cocking piece was a replacement part (non arsenalled?) or if I can simply file a little off the end of the pin. or is it the PPU Primers being too stiff? My other guns were running the ammo just fine.

Any thoughts or shared experiences with the ammo would be appreciated...

[Patrick56]

First of all I would check that the firing pin is smooth and round. This is easy to check by holding the bolt in your hand and rotating the cocking piece clockwise until it clicks. Now you can remove the locking lugs and the firing pin is visible. The firing pin should be flush with the cocking piece at the rear and I really don´t believe that the problem has to do anything with the length.

[leebuilder]

You may want to try a different ammo too.
How is the headspace?
Be well

[JeffHolt]

LB,
the brass cases appear to be just fine. There are no split mouths or stretch signs down towards the case head. The threaded end of the firing pins is more or less flush with the cocking piece. I'll try some Russian mil-surplus and my own 200gr Lapua D-166 handloads with CCI LR primers and see if they hold up better than this batch of PPU.

[LAGS]

Do not File the firing Pin.
Try different ammo first, and see if you can reset the firing pin Back 1/2 turn on the screw adjustment first.
If you file the firing pin, then you may have locked yourself into using ONE TYPE of ammo from here on out.
Find the Cause of the Problem, and dont just try to fix the Symptoms.

[leebuilder]

JH. Lags is right dont touch the firing pin, but it should be rounded and free from burrs. Headspace is measured on the rimm of the 7.62×54r or 53mm depending which boarders you live within. Being a surplus rifle i would be checking the headspace, look for the easy and obvious. Adjusting the firing pin may be a pillow case full of door knobs due to the shoulder so try and assemble then measure, i have never adjusted a mosin firing pin. Some of the Privy, PPU, NNY ammo is wicked hot, one with the purple paint around the primer is brutal, i dont read Yugoslavian i have know idea what it is.
Be safe

[LAGS]

I have an M-27 that I have to back out the firing pin to the mil spec index flush with the cocking piece to use Surplus ammo, and turn it in 1/2 turn for reloaded ammo or I get misfires.

[Gtek]

Have you measured bore vs. projectile diameter by chance? Pressure issue?

[Patrick56]

I have an M-27 that I have to back out the firing pin to the mil spec index flush with the cocking piece to use Surplus ammo, and turn it in 1/2 turn for reloaded ammo or I get misfires.

Some old rifles has been tinkered with so much that the sear surface on the cocking piece has been reduced a lot. This shortens the strike length. Possibly the spring has been shortened too. Maybe the firing pin has been remodeled too. Excessive head space also causes misfires as much of the energy of the firing pin is used to push the cartridge forward until the rim meets the rear of the chamber.

[Maven]

Have you measured bore vs. projectile diameter by chance? Pressure issue?

Jeff, Gtek's question is well worth considering. (Don't ask how I know!)

[JeffHolt]

Great suggestions guys. I will test other ammo first and if necessary adjust the firing pin half a turn. I noticed the pin is very slightly recessed in the cocking piece and the spring may need to be replaced. It has a slight curl to it so maybe it is compressed a little too much. I will compare it to some other ones.

[JeffHolt]

Ordered a bolt parts kit from milsurpdotcom. Don't mind having a few spare parts since I own 8 or 9 Mosins. Thinking I was off a half turn on my firing pin/cocking knob. I have the marks lined up with the slot on the end of the pin and now it is flush across the back of the Cocking piece. Firing pins appears too be protruding out a little bit less. Off to the range a little later this week...

[Maven]

"Some of the Privi-, PPU, NNY ammo is wicked hot...." ...leebuilder

Jeff, The ammo whose primers were pierced was Hanson/Privi-Partizan with 180gr. FMJ's. The brass, which I'm still using, was marked NNY.

[1johnlb]

Lot's of good info and about every area has been covered and as Maven stated, PPU is extremly hot, couple that with a military rifle designed to shoot military Berdan primed ammo with thick cups then shooting thin cupped high pressure PPU without adjusting the fire pin accordingly you get pierced primers. Especially, if the pin hole on the bolt head has some enlargement from use or just larger for spec than the pin with excessive clearance.

[Gtek]

Just for the safety factor, have you slugged bore, and how was bolt lift on extraction? the Russian weapons bore diameters were usually very generous in the ID and all over the place. You may find your Finn to be in the .309"-.311" area, that coupled with hot fat condom bullets may be taking you to what you are seeing. A fat lead boolit is very forgiving in a couple thousandths fitting down into pipe, hard jacket not so much. I have several and you may find yours to be small also. Fat hard bullet hits throat and slows down as being sized to bore, very steep pressure spike the case is thrust back over riding case wall grab and impaling itself on pin. Your rifle, your nose over pipe, your bolt head eroding pin hole. Surplus rifle and you have not slugged yet? Just hate to see possible weapons and people damage.

[JeffHolt]

GTEK,
Don't disagree with your line of reasoning but I'm going to start with adjusting the firing pin. The barrel is marked with a "D" so it is designated and designed to shoot Russian military ammo as well as the FINN Lapua D-166 (310 dia.). I suspect my firing pin was extended out a half turn. I shot 2 other Russian guns, a 1937 a 1943 with no issues. The brass shows no signs of excessive pressure. if anything the bore would be a little worn I would think to 311-312.

I'm goin to try another 10 rounds later this week.