Misfires with a specific ammo

[F&H1821]

Greetings, I am breaking in a Winchester Model 70 Alaskan, 375 H&H. This gun is a strong candidate for a back up on an upcoming CO elk hunt this fall. I will soon do some load tuning but now have an issue with misfires. I have discharged 60 rounds of Federal Premium, 300 gr Nosler Partition, with no issues. Best group is 1.7 MOA but am confident with hand loads that I can get it pretty close to 1 MOA. This weekend, I tried Hornady Outfitter 250 gr GMX. Of seven attempted firings, 3 were misfires. Hornady customer service looked at the attached pic and stated:
"Thanks for the inquiry. At first glance we notice that the pin strikes on the primers aren't centered on the primer and do appear a little shallow. We seat the primers slightly below flush about .005" to .007" but this increases the sensitivity of the primers. Currently we don't show any other known issues with that particular lot# at this time."

In the pic, the three misfires are on top, beside an unchambered round, four normal fired cases on the bottom. As you can see from Hornady, no consideration of the fact that the gun performed without issue with another type of ammo. Winchester said to go ahead and ship the gun to their service center in Missouri. However, I may consider having a local smith give it a look. I can also try another type of factory ammo (not cheap however these days, at 4+$ per round), or try some hand loads. Any thoughts or advice? I can also get the comparators out and compare head space/case length for fired and unfired cartridges with both ammo types on hand. Could the Hornady cases be a tad short, too much room in the chamber? Both types are nickel plated cases. Any similar experiences with Hornady Outfitter ammo (which they claim is durable and dependable enough for an outfitter to use).

Thanks in advance for your help.

 

[xsn10s]

I'd use a comparator to measure the shoulder distance/ headspace between the two ammo and then check primer depth of each unfired. I'd also take the bolt apart and give it a good cleaning to make sure there's no debris causing an issue of light primer strikes. My two cents worth from the peanut gallery.

 

[F&H1821]

Thansk xsn. Comparator measurements underway. Can do the Hornadys -- fired, duds, and unfired; the Federals -- fired n=60 and unfired n=20; and also one new box of Nosler brass (not nickel plated).

Was going to disassemble the bolt and give it a good cleaning in the ultrasonic cleaner, with metal parts cleaner solution. However, I may shoot it some more before cleaning if the comparator data indicate a possible smoking gun (hah, hah, pun intended), in an attempt to ID the source of the problem. I have a science background, so like to keep the picture as unconfounded as possible. I have another fresh box of that Hornady ammo, so can test that box after bolt cleaning. This gun only has a total of 67 rounds down it, and has been kept in a humidity controlled gun safe, so a dirty bolt is unlikely, thought still can't be dismissed as a possible factor.

 

[Azrael]

It'll take a few seconds to field strip a M70 bolt. Spray off the striker assembly and inside the bolt body with just about anything and scrub inside the body with a bore brush. dry and lightly oil. Your don't have to go crazy; it's a bolt not the space shuttle. Packing grease and crap could be slowing it down. You can check firing fire protrusion easy enough. Chances are you have a box of dud ammo.

Factory belted magnums cartridges should be headspacing on the belt, shoulder location means little on the first firing.

The Alaskan is a nice retro gun, I'm liking mine. Mine weights less than one of my 270 Win Feather-weights.

 

[xsn10s]

It'll take a few seconds to field strip a M70 bolt. Spray off the striker assembly and inside the bolt body with just about anything and scrub inside the body with a bore brush. dry and lightly oil. Your don't have to go crazy; it's a bolt not the space shuttle. Packing grease and crap could be slowing it down. You can check firing fire protrusion easy enough. Chances are you have a box of dud ammo.

Factory belted magnums cartridges should be headspacing on the belt, shoulder location means little on the first firing.

The Alaskan is a nice retro gun, I'm liking mine. Mine weights less than one of my 270 Win Feather-weights.

That is true. The headspacing would be off the belt on first firing.

 

[xsn10s]

He could do the scotch tape method to check headspace in that case. A comparator would come in handy for reloading.

 

[LoneTraveler]

The bolt tear down and check would be my first thing to check. A chip of metal in the firing pin channel bouncing around could be the problem.
A new rifle needs the bolts firing pin removed. Clean the firing pin channel and remove any heavy storage grease from the firing pin spring and channel. Coat spring and firing pin with a light oil.

With a micrometer or dial caliper. Check from the head to front edge of belt on these cases and compare against the shell casing of the other lot of ammo that fired properly. To prove the problem, The scotch tape on the case head would be a good way to prove the present problem shells are out of head space, To take pictures and show manufacture of the problem shells.

Good Luck finding the problem.

 

[TennJed]

Hi, sorry for my ignorance but what is the scotch tape method?

 

[xsn10s]

Hi, sorry for my ignorance but what is the scotch tape method?

Scotch tape is roughly .002"-.003" thick. So if you stick it to the base (of an unfired case) and carefully trim any overhang it can help check headspace. You need to take out the firing pin assembly so you can feel any tension while closing the bolt. On a Winchester pre 64 type or Mauser I slide the case under the claw and then insert the case and bolt back into the action. Pay attention as you slowly close the bolt for resistance. If there is no resistance pull the bolt out and stick another piece of tape onto the first piece and trim. Repeat until you feel tension. It's not perfect but it can give you an idea in the differences of the ammo's dimensions.

 

[F&H1821]

Hi, sorry for my ignorance but what is the scotch tape method?

I will take a shot at this one, given that I started the thread. If you have head space issues with a specific brand or lot of ammo, you can add a layer or two of scotch tape to the head of the cartridge, to make it a bit longer, about 0.003" per layer of tape added. You then chamber the round and test how tight the bolt closes. I will do this after removing the firing pin from my bolt, for obvious safety. I will also do it with the two types of ammo I am working with (Federal and Hornady), and test for the feel of the bolt closing on each ammo type with and without the tape added to the end of the cartridge.

 

[johnnyk]

I'll put my money on contaminated primers. From your picture it clearly looks like the rifle/firing pin is doing its job.
I ran in to this same thing with Norma ammo.
Tried the ammo in two different rifles and results were the same; about half the ammo functioned properly and half didn't.
I contacted Norma over a year ago, sent the unused ammo to them for testing, agreed on compensatory ammo and nothing......crickets.....
They can keep their ammo, I won't spend my money on that name again if I can help it. That goes for brass, bullets, powder or ammo.

 

[Muddyboots]

Light primer strike can be firing pin drag in bolt. I agree with @LoneTraveler to tear down bolt, clean the inside of the bolt body, shine light in bolt body to make sure no corrosion, clean firing pin assembly with good degreaser to make sure not gummed up, look at firing pin hole on bolt face to insure it is free and clear on inside of bolt.

I would try the ammo again after deep clean.

 

[TennJed]

Scotch tape is roughly .002"-.003" thick. So if you stick it to the base (of an unfired case) and carefully trim any overhang it can help check headspace. You need to take out the firing pin assembly so you can feel any tension while closing the bolt. On a Winchester pre 64 type or Mauser I slide the case under the claw and then insert the case and bolt back into the action. Pay attention as you slowly close the bolt for resistance. If there is no resistance pull the bolt out and stick another piece of tape onto the first piece and trim. Repeat until you feel tension. It's not perfect but it can give you an idea in the differences of the ammo's dimensions.

Thank you!

 

[TennJed]

I will take a shot at this one, given that I started the thread. If you have head space issues with a specific brand or lot of ammo, you can add a layer or two of scotch tape to the head of the cartridge, to make it a bit longer, about 0.003" per layer of tape added. You then chamber the round and test how tight the bolt closes. I will do this after removing the firing pin from my bolt, for obvious safety. I will also do it with the two types of ammo I am working with (Federal and Hornady), and test for the feel of the bolt closing on each ammo type with and without the tape added to the end of the cartridge.

Thank you!