What would you have told him ?

[44man]

Firing pin hole has to be checked too.
There is a lot of pressure inside the primer cup. A revolver can have the hammer blown back to almost full cock with still a good indent showing in the primer. We took pictures of this happening before recoil started. We found double pin strikes on S&W revolvers, some outside the primer on the brass. This is why some .500's doubled, the hammer bounced back, cylinder unlocks and turns backwards and if there is a live round there the hammer will fire it.
If the pin is blown back, the cup will try to flow into the hole.
Bolt guns need a very strong mainspring for top accuracy. The worst thing to do with any gun is to reduce the hammer or mainspring, looking for a lighter pull.

[Ballistics in Scotland]

The inertia firing pin (some call free floating) follows different rules. A stronger firing pin spring will show signs as shown more so than a weaker one. The fallen hammer has NO influence on this as the firing pin is shorter than the breech bolt's length. (unless the 'extrusion' becomes so great as to take up firing pin length clearance)

I think the longer time pressure curve (from the 4831 powder) is the culprit. Tight case fit (headspace) will aggravate what you are seeing.
Some cases fired with faster powder or even factory loads in the same gun would tell us a lot!.

Eutectic

I have never liked the idea of an inertial firing-pin in a high-pressure firearm. A return spring in front of it should indeed be as weak as will do the job, and I would feel happier with the system seen on some falling-blocks, whereby operating the lever cams the firing-pin out of the primer. I suppose dirt in the firing-pin channel or a deformed return spring might produce the OP's problem.

But the faster the hammer, the faster it makes the firing-pin move, and the more inertia it has.

[44man]

The firing pin on the 760 and 740 do not have pin springs but are NOT inertia pins. There is no gap at the back of the pin when the hammer is against it. Yet the pin will blow back and take the hammer back from internal pressure. That leaves a hole for the cup to flow into. The pin on these rifles should be long enough to keep the hole blocked unless the hole is large.
When the pin is pulled all the way back, it should be flush with the bolt face.
The reason a 740 will not slam fire is because the pin does not get a running start, unlike an SKS that will with a thin primer cup. I have turned SKS and AK pins for a spring and stopped slam fires with our primers.

[upnorthwis]

Some chrono data would be nice. If it was only going 2100 fps you could eliminate high pressure as a cause and look for something else.

[41 mag fan]

I've got a Remington model 700 Boon and Crockett in 300 win mag that has the same problems. Interesting read on this

[Ballistics in Scotland]

Some chrono data would be nice. If it was only going 2100 fps you could eliminate high pressure as a cause and look for something else.

True if it was really the load described, but it is possible to get low velocity with a load giving excessive peak pressure, if you really work at it with some determination.

I have "The NRA Gunsmithing Updated", which is mostly a very valuable book, as long as you don't expect it to be updated anywhere near the pressure. Unfortunately the price nowadays on www.bookfinder.com, both new and used, make me wince. But there is one article by a US service pistol team member, which more or less takes the unusual tack, for that book, of advising the amateur to do no gunsmithing whatsoever. He does say, I remember, that it is very useful for the reloader to recognize the different powders by appearance. A good many other people advise us never to have to.

[robg]

measure case head and compare to unfired case , primers are not an accurate indicator of pressure,

[TXGunNut]

Overly large firing pin hole in the bolt. Or soft primer cups.

My thoughts exactly. Sometimes primers lie, other times they're just misunderstood.

[Motor]

The firing pin on the 760 and 740 do not have pin springs but are NOT inertia pins. There is no gap at the back of the pin when the hammer is against it. Yet the pin will blow back and take the hammer back from internal pressure. That leaves a hole for the cup to flow into. The pin on these rifles should be long enough to keep the hole blocked unless the hole is large.
When the pin is pulled all the way back, it should be flush with the bolt face.
The reason a 740 will not slam fire is because the pin does not get a running start, unlike an SKS that will with a thin primer cup. I have turned SKS and AK pins for a spring and stopped slam fires with our primers.

This is correct. It DOES NOT have a inertia firing pin. It simply free floats. The hammer very likely bounces back a little from recoil as well.

IMHO: Everything looks fairly normal for this type of rifle. Yeah the firing pin hole is chamfered or maybe even worn a little. Its really NBD.

Guys really need to read the thread. This is a Remington 760 PUMP ACTION RIFLE. Not a bolt action. In fact its almost identical to the self loading 740 series except you pump it instead of it pumping itself like the semi's do.

Why is this thread in the "Cast Boolit" forum?

"He said he shot 56.0 grs. of IMR - 4831 with a 180 gr. jacketed in 30-06 brass."

[Eutectic]

The firing pin on the 760 and 740 do not have pin springs but are NOT inertia pins. There is no gap at the back of the pin when the hammer is against it. Yet the pin will blow back and take the hammer back from internal pressure. That leaves a hole for the cup to flow into. The pin on these rifles should be long enough to keep the hole blocked unless the hole is large.

I believe you are correct 44man..... I say it this way as I didn't have a 760 to look at but I do have a 7600 .35 Whelen. It indeed has a spring loaded firing pin of a rather unique design with twin sleeves that prevent the pin from going forward until the bolt is closed. Then there is enough clearance for the pin to reach the primer. I wouldn't call it a 'floating' firing pin either.

The hammer is very light in mass and the firing pin has every mechanical advantage to 'push' the hammer back (as compared to a bolt gun). So that could indeed be happening.?

My comments about firing pin spring pressure and pin touching the hammer are also incorrect if the 760 and 7600 are designed the same way.

My 7600 Whelen mentioned doesn't display this primer 'flow' as Ben's picture. It does however, crater primers quite easily as maximum loads are approached. Loads at similar pressures in my bolt gun or even my Ruger #1 .35 Whelen do not crater at these pressures. I'm talking 'crater' here with a sharp edged corner... not primer 'flow' as Ben's example.

Sorry for the bum steer guys.... Guess I just looked at too many Remington 870's!

Eutectic

[Motor]

I believe you are correct 44man..... I say it this way as I didn't have a 760 to look at but I do have a 7600 .35 Whelen. It indeed has a spring loaded firing pin of a rather unique design with twin sleeves that prevent the pin from going forward until the bolt is closed. Then there is enough clearance for the pin to reach the primer. I wouldn't call it a 'floating' firing pin either.

The hammer is very light in mass and the firing pin has every mechanical advantage to 'push' the hammer back (as compared to a bolt gun). So that could indeed be happening.?

My comments about firing pin spring pressure and pin touching the hammer are also incorrect if the 760 and 7600 are designed the same way.

My 7600 Whelen mentioned doesn't display this primer 'flow' as Ben's picture. It does however, crater primers quite easily as maximum loads are approached. Loads at similar pressures in my bolt gun or even my Ruger #1 .35 Whelen do not crater at these pressures. I'm talking 'crater' here with a sharp edged corner... not primer 'flow' as Ben's example.

Sorry for the bum steer guys.... Guess I just looked at too many Remington 870's!

Eutectic

Not really but they are close. The 7600 is updated and improved. Go to gunpartscorp.com and study the Schematic (s) of both rifles.

The 760 does not have the spring on the firing pin. It will dimple primers when briskly loaded.

Motor

[Hickok]

I've got a Remington model 700 Boon and Crockett in 300 win mag that has the same problems. Interesting read on this

I know this doesn't pertain to the Remington Pump that is being discussed.

Remington has purposely beveled the firing pin hole on their Model 700 rifles for last few years, "supposedly" it is an added safety measure in that it makes the primer less likely to pierce, because the bevel creates a thicker radius when the firing pin strikes and the cartridge is fired.


NOW, I agree this just doesn't make sense, but that is what Remington is saying. I have two newer Model 700's in .308 caliber, one is the 26" heavy barrel, and the other standard weight 24 barrel, and both give the same primer protrusion. In fact, you can remove the bolt from either rifle and see the bevel/chamfer around the firing-pin hole.


I have several other older Model 700's and they do not have this bevel/chamfer around the firing pin hole. I don't like it, but I just don't let it bother me, as it does no harm, but it does go against my way of thinking.


As to the OP's rifle, I agree that firing pin hole may be large, or hammer spring may be weak, allowing firing pin to push backwards on firing.

[Hickok]

Attachment 130752 Bevel/chamfer on 700 Remington Bolt.

Forgive me Ben for thread drift, just wanted to help 41 mag fan.

[Smoke4320]

Overly large firing pin hole in the bolt. Or soft primer cups.

I agree .. may also be a combo of large pin hole/soft primers and slightly overcharge for YOUR gun
That would explain why the primer edges are not flat .. classic sign of overcharge

[41 mag fan]

Hmmmm... I'm going to have to take a look at it and see. .. this rifles between 6 to 8 yrs old iirc.... Thanks Hickok... I'll see what it looks like. ..I've not worried about it as it has not showed issues of over pressure. ..

[Hickok]

41 mag fan, no it is nothing to worry about, as Remington is deliberately doing this. I just go on shooting my newer Remington's too, but I hate the look of the primers! Too me, it is a fix for a problem that doesn't exist.

[EMC45]

Overly large firing pin hole in the bolt. Or soft primer cups.

Beat me to it!

[Pilgrim]

That .244 load is beyond max. in that rifle (post #59)! The firing pin shows definite cratering, the primer edges are flatter than normal, PLUS you can see the ejector hole on the case head. That load is probably in the 70kpsi range if not a bit higher.

[BrianL]

It looks mechanical to me. Worn out firing pin hole? I had a similar looking condition once with a long firing pin thinning the brass so that it flowed backward. I actually had several pierce.

[Eddie2002]

I'm betting on soft primer cups, maybe he used large pistol instead of rifle primers and an oversized firing pin hole which caused the dimpled pimple.
Haven't see anything like that with my BDL 700 in 30-06 but the rifle was built back in the 80's not recently.