30-30 Possible Over Pressure What to Inspect

[Chestnut]

I was shooting subsonic loads from my Marlin 336 in 30-30 today. On the 2nd to last shot i hear a much louder noise and the bullet must have gone through the target sideways. Instant red flag. When trying to eject the brass the lever was stuck and wouldn't eject. I didn't use too much force and just packed up.

Getting home I scoped the rifle confirmed nothing was split in the chamber or anything super drastic had happened. I grabbed a bit of 1/4" brass rod and knocked the cartridge free as i figured it was better to do that then gorilla the lever of the rifle. Couple light taps and the brass ejected. I measured the shot brass and it missed a trim and was right at 2.039". I normally trim to 2.027" so carbon must have built up and pinched the bullet.

My main question is did I damage anything? What should I carefully inspect to ensure the rifle is still in functional order? I'm not very knowledgeable with Marlin 336s so I don't know what to check for.

Again it was a subsonic load. Specifically 6.74gr of titegroup behind a 190gr projectile with CCI200 primer The chronograph didn't measure the velocity so my guess is it was over 1600 fps. Pictures to show the brass in the chamber before knocking out and after removal.

With carbon buildup in the neck what's the best size brush for .30 cal to remove carbo?

 

[Oso]

A couple of quick questions.
How old is your Marlin 336?
Were you using a suppressor while shooting the subsonic loads?
What type of bullet… cast lead?
How much of a crimp do you use?

Hodgdon reloading data says 7.4gr Titegroup pushes a 175gr bullet at 1,071fps.
> You’re loading was with a heavier bullet (190gr) with less powder (6.7gr). It sounds like the cartridge in question might have been traveling 2x the speed…

What’s the chance of a double charge?

 

[Chestnut]

A couple of quick questions.
How old is your Marlin 336?
Were you using a suppressor while shooting the subsonic loads?
What type of bullet… cast lead?

Manufactured 2019 336BL with 18.5" barrel to be specific
Yes Dead Air Nomad XCTI
Hornady sub-x 190gr bullets so copper jacketed

 

[Oso]

I just edited my above post. Barrel is new steel so able to handle pressure.
Any sign of a baffle strike?

 

[Chestnut]

What’s the chance of a double charge?

Slim i cap each brass with a bullet after dumping the charge because of the double charge fear. Running GRT I'd be able to double charge and not over pressure. Though who knows if that's accurate.

No baffle strike, that was my first thought so i inspected the suppressor extensively, removed front cap etc.

 

[Coyotefurharvester]

Bolt would be a much weaker part than the barrel, inspect it carefully. Clean the chamber/bore to bare metal, keep it clean.

 

[Chestnut]

Bolt would be a much weaker part than the barrel, inspect it carefully. Clean the chamber/bore to bare metal, keep it clean.

What size brush is best for the neck / chamber of a 30-30? I have a .45auto brush but that seems too large.

 

[dellet]

Was the primer flat?
Was it sticking out of the case head?

 

[Coyotefurharvester]

Maybe a .410 shotgun brush for the chamber,338 for the neck? I think pro shot makes a flexible chamber rod for lever actions?

 

[dellet]

And what’s the twist rate of the barrel.
You probably have two different probmems

 

[Chestnut]

Was the primer flat?
Was it sticking out of the case head?

No it was not flat no cratering.
It seemed like a regular fired 30-30 brass.

Maybe a .410 shotgun brush for the chamber,338 for the neck? I think pro shot makes a flexible chamber rod for lever actions?

It takes 2 seconds to disassemble, don't think I'd need a flexible rod for it but I'll keep that in mind.

And what’s the twist rate of the barrel.
You probably have two different probmems

For some reason i thought it was 1:10. All my shots previously with the gun and 190 bullets were clean holes.

Thanks everyone for their comments. Rifle disassembled without issue I've inspected everything and reassembled. Function is fine and didn't' find anything upon close inspection.

 

[dellet]

Based on a lot of small clues, most likely it was a double charge. If it wasn’t a double charge, the load is unstable and will happen again without warning. Your load is around 30% density, and that can be a problem.

Your brass that failed is long, but not enough to pinch in a chamber. I would be more worried about that bullet being a hard jam into the land, or the ogive set below the case mouth. The profile does not lend itself to a 30-30 chamber. That’s the exact reason Hornady came out with the 175 Sub X.

It’s normal with a 30-30 cartridge that headspace of the rim, to leave the primers proud of the flash hole after firing. This is indicative of a low pressure load. Since this was not the case, pressure exceeded probably 40,000 psi. Enough to over come the pressure holding the case against the chamber walls and drive the primer back against the breech face.

Primer was not flattened, large rifle primers are commonly used in cartridges exceeding 55,000 psi and not unheard of 60,000 psi. So that’s not surprising.

The chronograph didn’t read. 1600 fps is a problem for chronograph that have pistol and rifle settings, this is the split. Running your info through Quickload, 1600 fps requires about 60,000 psi. And just, over 13 grains of powder.

The 190 Sub X is a fragile bullet. It’s not supposed to be shot over about 1200 fps. But that’s in a 1/8 twist. Most likely your rifle is a 1/12, very common for 30-30 and sammi Spec. Not likely over spun. But the jacket and bullet design needed to insure expansion at 850 fps. won’t hold up to 60,000 psi. If the bullet accelerates too fast and pushed too hard the jacket becomes compromised and will come apart in flight. There’s you’re sideways bullet hole.

Last the action is very strong and factory chambered for cartridges designed to shoot 50-55,000 Psi. 70,000 psi really shouldn’t be a problem a few times. Actions are expected to handle proof loads that are at 1.25 x max cartridge pressure minimum. Repeated use is a different subject.

All that points to a 60,000 psi + load. Basically exactly what you would expect. A brass case rated for around 45,000 psi subjected to 60,000 psi will be deformed. It’s quite possible that it was not missed in the trimming cycle, more likely stretched when fired.

Lever actions have weak extraction, pair that with a piece of brass subjected to almost time and a half it’s designed load, it’s going to be hard. to extract.

Could be completely off the mark, but I’d bet I’m not far off the mark. Be careful, subs despite their low velocity, can be extremely dangerous to load. People assume low velocity equates to low risk. Low risk leads to lack of attention, and that will kill you in the handloading game.

 

[243winxb]

much louder noise

measured the shot brass and it missed a trim and was right at 2.039

Crimped bullet or double charge.

Smokeless powder, particularly double-base powder which contains nitroglycerin, can detonate under certain conditions, although it's designed to burn as a propellant, not detonate like TNT, a high explosive.

The lever controls the rifles headspace. Headspace neededs checked now.

A customer came in with his marlin 30-30. The gun jammed while trying to load the 2nd round to finish off the deer.

He cut the jammed round in half, some how? Bent the lever, causing excessive headspace. (Buck Fever?) May have hit lever against a tree?

Rifle was shipped to Marlin for a new lever & headspacing.