extreme pressure,what happened?

[3-300s]

Hello,
Had a problem with high pressure and don't know the cause.

This is a hunting gun. Rem 700 in 260 Remington with a Bartlein 1x8" barrel. It was chambered with a reamer made for my case and bullet combo. Bullet is jumping about .030".
I had a shell blow out the primer and I felt gas on my face when I fired . VERY hard to open the action.Had to remove the bolt to get the shell off the bolt face and primer fell on the floor. 260 rem, 125gr nosler partition (blem), federal case been fired three times, 38gr of IMR 4064, WLR primer. Load has never shown pressure, I had loaded 60 (at one time) of these last year for hunting and shot all of them but 5 or 6.

measurements of high pressure case.
case web .471"
case rim .4755"
case length 2.035

measurements of same load fired case without pressure signs
case web .470"
case rim .471
case length .2.029

measurements of a loaded case
case web .469"
case rim .471
case length 2.032"

No chance of wrong powder or bullet. All charges weighed on RCBS beam scale.
39.3gr is what I consider max load in this gun.
Cases are cleaned with acetone then tumbled after sizing.
Shell was in the magazine when gun was fired 3 times, thought bullet may have slid out the neck.
I tried to make bullet slide out the neck by closing the action HARD ten times on one loaded shell. It didn't move, slim

chance bullet was in the lands. ​

It was raining that day but I carried the gun muzzle down to a covered box stand.
I don't remember if the action was hard to close or not?
Need to get the reamer print and see if case is to long and clamped down on the bullet ?
Have not fired the gun since.

I'm at a loss , no real idea what happened.
My only problem like this in over 40 years of reloading and it scared me.

Robert

 

[mgunderson]

Very hard to diagnose, but you have some good data. Best thing is that you are concerned.

A thought is that the wet brass did not grab the chamber wall as happens when it is dry. Maybe a little water in bore or around the bolt. Happens in the rain.

Unable to comment if that is a hot load.

 

[davidjoe]

I am inferring between the lines this is a new rebarreled job and you haven’t shot this load before in it. If so, I bet you have a bore that is at the tighter (smaller) end of the range. I’ve had brass issues where that was the case and needed to lengthen the free bore with a unithroat reamer, to mitigate the pressure spike.

If that is not a new barrel and the load is a proven one in that barrel, then probably you had a partial barrel obstruction.

 

[Walt Krafft]

I concur on the wet brass theory. I didn't believe it until it happened to me last year. Other wise low pressure loads went ballistic with a little dampness on the case.

 

[davidjoe]

Speaking of wet brass, I’ve never understood how most firearms can be fired completely submerged underwater.

 

[Texas10]

If you've got a borescope, or endoscope camera, I'd chamber that high pressure case and look at where the case mouth falls in the chamber. Does the mouth overlap into the throat?
I see that the damaged case has the longest OAL and you may have pinched the bullet.

Seen it before, has all the hallmarks you experienced.

 

[Willie]

1. Case too long?
2. Carbon ring?
3. Moisture or lube in chamber?
4. Reloading error?

 

[hogpatrol]

As above and check for a carbon ring. Check the headstamp too. Make sure it's correct case.

 

[Dusty Stevens]

Moisture in chamber. Doesnt take much just a change in temp will do it.

 

[gunsandgunsmithing]

Maybe water but if all is as you describe, I'd lean toward the neck being too long or too fat. What does the case neck od measure of a (proper) fired case vs your loaded unfired round? Also, have you actually measured the length of your chamber to establish proper trim length or what are you working from to establish that figure?

 

[T-shooter]

Maybe a stackup of factors. Say your powder charge ends up being nearly a tenth over (withing the tolerance of the scale) and the particular case has a smaller inside capacity by a couple percent, it could put you over the limit if you were on the edge. Possibly a case that was not manufactured correctly. Maybe a bullet that cold-welded inside the neck. How long have they been loaded?

I had a mistake that caused an overpressure several years ago. I reworked the cases and washed them to the the lube off. I left them sit out neck up for a couple hours, thought they were dry. Then I tumbled them in walnut media, loaded, and went shooting. I had a few, not all, kick harder, a bit of an increase in bolt lift, and ejector marks on the rear face. These were all loaded hot right under the limit but never had any issues before. After a couple, I took the rest home and broke them down. What I found was there must have been a drop of water still in a few that made some of the tumbling media stick inside. Some as much as a pea. So the internal capacity was reduced and who knows what moisture turning to steam does in a chamber?

 

[beemanjohn]

How old is your powder? Smell it to see if it has gone bad.

 

[ebb]

Ive never fired a wet case , but I have pinched a bullet in the chamber with a long case. And it did the same thing you described.

 

[Mickey D]

Ive never fired a wet case , but I have pinched a bullet in the chamber with a long case. And it did the same thing you described.

I too have pinched a bullet with a long case. Pressure spiked primer burned out and gas’s hit me in the face. Bolt had to be opened with a leather hammer. Went home got the bolt out checked the bbl for cracks. Looked at my unshot rounds and could see no problem. Then pulled a bullet and weighted the charge. Exactly what it should be. I then checked the piece of brass for length. It was way too long. Checked that group of loaded bullets and I found 6-8 that had to be pulled. Had to be in late 60s early 70s. That scare taught me a lesson.

 

[AckleymanII]

Last years ammo, could have been cold welding of the bullet/brass. I have had this happen twice since I moved back South, never happened out West in 30 years. I also had two cans of IMR 4064 go bad on me.

Extra long brass has some merit.

I saw a 6.5x55 spike pressures where the bolt had to beat open on a minimum book load from excessive copper in the barrel.

Is it possible that a doughnut could have gripped the bullet base? Federal brass is going to flow and grow.

All we can do is brain storm.

 

[Rsadams]

Did you check for a carbon build up..?

 

[JFrank]

Bullet diameter or ambient temperature swing creating moisture on the rounds, it happened to me once , damn near had to get a rubber mallet to open the bolt

 

[riflewoman]

Here is what Hodgdon says.



This would indicate to me that you’re probably over maximum. Since the bullets are blems, perhaps a slightly heavier bullet was in the mix?

 

[Bindi2]

Here is what Hodgdon says.

View attachment 1150726

This would indicate to me that you’re probably over maximum. Since the bullets are blems, perhaps a slightly heavier bullet was in the mix?

I have seen 175gn come out of 155.5 boxes for target shooting where pressures are high for the 155.5 pill. Think about that problem if it had not been found. Blow up if fired disqualification if the ammo police found it in the ammo checks. 155.5 max Palma.

 

[FrankG]

All points made are valid and possible.

My first vote is the ammo/chamber got wet. I’ll also add to this that if it was the first round was the chamber dry/bore dry from cleaning? Any solvent in the chamber will do the same thing. I had a local Police Officer do the same thing. Had so much solvent in the bore/chamber of the barrel they had to beat the bolt open with a hammer. Primer didn’t pop/pierce per say. When we took his rifle a part you could see where the solvent was starting to cake from heat/firing and the threads of the barrel where so saturated they dripped with solvent. I left it that way to show him the problem when he came back in.

Not just weight of the bullet but bullet diameter. I’ve seen plenty of bullets that where fat diameter wise. Possible your other bullets are at .2640” and you had a bullet in the box that was much bigger. Like .2645” etc...

Cases too long?

Welding of the bullet in the case was another good one. An old friend of mine Dan (now gone) was a silhouette shooter. Loaded 7x57AI ammo. Bullets got wet/had slight moisture on them. He was storing his loading components in a old refrigerator in the garage. Loaded the ammo. One week later went to the range with the ammo. First round blew the floor plate assy out the bottom of the gun, cracked the stock etc...other people at the range heard it all come a part and ran over. His bell got rung so bad he was just standing there and had no clue as to what was going on for a few minutes. They had to sit him down and take the rifle out of his hands. Other than getting his bell rung and having minor cuts to his arms here and there he was o.k. He went back and pulled all the bullets and some he almost couldn’t get a part. They literally welded themselves inside the brass case.

If you want to send the barreled action into us we can take a look at it the best we can and see if there are possibly any issues. If your local gunsmith did the work take to him and have him look at it.

According to the Hodgdon data posted your a little over max.

Later, Frank
Bartlein Barrels