High pressure troubleshoot

Y

Yosemite Steve

New member
So, as some of you know, I shortened my Savage 30-06 chamber recently when I put a new bolt head on my gun. The quick fix was to shorten the shell holder which ended up .007" shorter.

I resized some Nosler brass to fit and primed the cases with CCI200 primers.
I loaded the brass with 53 grains of IMR 4350 and seated 180 gr SST bullets on top with a COL of 3.310 which is kissing the lands. The usable case capacity is 59.690 grains of H2O.
I purchased a pound of IMR4350 at the gun shop the other day and decided to test it on my newly cleaned and slightly altered gun. I got the starting load data from Hodgdon's website which called for a 53 grain starting load. Quite a few other books had lower starting loads but I though I would go with the manufacturers most recent data.

To my surprise when I tested it I got a stiff bolt lift and super flat primer flowing over the bevel of the primer pocket.

I have seated to the lands ant worked up many a loads to near max and never had signs this bad. My velocity was 2611 fps.

I am thinking that the combination of a slightly smaller case volume combined with no jump lead to the pressure spike. Hodgdon gives a velocity of 5385 fps and 57,200 PSI. I am unable to duplicate the numbers with Quick Load.

Can somebody throw me a bone on this one?
 
I really can't tell you. With IMR4350 giving that velocity...it should be good.

Maybe we could start with what gun it is,and why did you replace your bolt head?

Might the old bolt head have set back a touch into the receiver? I asked you twice to coat your bolt locking lug surfaces with magic marker to see if your lug surfaces were bearing. Did you do that?If you did,you didn't say anything.


Picture this.Your old bolt head set back .007 into the receiver.Made sort of a pocket.
Your new bolt head is only resting on its sharp edges.You have .007 space between the lugs bearing.

You pull the trigger. Primer pops out .007.Pressure slams the case back,the primer gets its corners reformed sharp.

Bolt sets back into its pocket just a bit. Your lugs have to climb out of the pocket to open the bolt.Its hard.

So,lets start at the beginning. Why a new bolt head? Answer that,and do the marker thing...or I'm wasting my time.
 
The new bolt head was to replace the old one that had a concave face. When you say the bolt face sets back into the reciever do you mean it may need to slide back as the bolt closes?
 
Did you pop a go and a no go gage in to make sure the headspace is still within specs? I have swapped out at least three bolt heads on my Savages and I always checked headspace just to be safe. I have never had to reset it but I assumed that was due to teh floating bolt design of the Savage. Check the headspace then full length resize your brass at least for the first firing with the new head.

If the headspace checks drop the charge down to the minimum then rework the load with full length resized brass and SAAMI specced COAL just like it was a new gun
 
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You need to check with go/no-go gauges any time you take the barrel off or alter the bolt face.

Also don't stick the bullet into the lands. Give your SST about a 0.020" lead.

And i'm hoping you typoed with the 5,385 fps!!!
 
I and the gunsmith checked the headspace. It's short. We agreed to give this a whirl as it might be more accurate with the tight fitting chamber. I still have the option to have it reamed. That's beside the point.

And it was 2586... sorry... for 53 grains of 4350 pushing a 180 SST.
 
HiBC, I tried the marker thing, I think, and it scratches the back of the lug on one side in the same place it did on the old bolt head. The old bolt head has a little bevel cut on one side of the back of each lug about 1/16". The new one does not. The gunsmith said he didn't think they were necessary. I'm still not entirely sure what you want me to look for.
 
Welcome, you may have just entered the twilight zone. I cut short chambers, I have chambers that came in rifles that are longer than a field reject length chamber. One of the chambers is .016" longer than a minimum length/full length sized case.

None of this locks me up or drives me to the curb because I am the one that understands what happens between pulling the trigger and the bullet leaving the barrel.

F. Guffey
 
Thanks, Guffey. I knew you'd understand. It's not so complicated. I had a high pressure spike... or the signs of it. HiBC might be onto something if I understand what he is saying.

And then there was this guy who said, "Hey you can't do that!" :p
 
HiBC, I looked very carefully and the bolt head cannot move back as it locks in, nor the old one. The receiver where the bolt locks in has no recession. I think that your idea of the primer moving back and then the case slamming back is a good idea, but I'm sure that is not what happened. There is .001" for the case to move in the chamber back or front. I could find no way to simulate a pressure spike in Quick Load to get the pressure or the velocity that high other than to give the shot start pressure 7000PSI. At that point it gives me 2611 fps muzzle velocity and a peak pressure of 56,237 PSI. Funny how that is the exact velocity my chrono gave me.

I am thinking I should go back to 50 grains of powder, check my lands measurement again and seat .020 off as Std7mag suggested and do a careful work up to see how things perform before testing anything else. I recently tested my Enfield for depth velocities and accuracy and that information was very useful to me for that gun and that bullet. I would like to do the same with the Savage but need to make sure there are not other issues at hand.

The peak pressure difference between the two unfired cases is due to the volume difference is about 400 PSI. A fired case of the same lot from my chamber as it is now vs. before holds the same exact volume of water. I checked 3 of each case. That 400 PSI is not much. Somehow, even after bringing the neck back .007" the fired cases hold the same volume of water. This leads me to believe that the pressure spike was from the lands.

As I write this I still think of what HiBC suggested. What if there was never a short chamber to start with? What if the bolt head was in fact the same length and something was not allowing it to "set back"? It would indeed do what he suggested because the bolt would be forced back when fired and the shortened case would have excess headspace. But I can not find that void!
 
I just measured the bolt heads AGAIN. There is a .007" difference. It took exactly .007" to get the shell holder to size the brass .001" less than "no feel" length in my chamber. This also jives with the other gunsmith's comment that my chamber was on the tight side of the tolerance. According to my math, correct me if I'm wrong, The primer can only move .001" beyond the case head before the it is slammed back in. If the bolt head lugs were to be "set back" and the bolt was not doing that, the amount that I would have had to take of the shell holder to shorten the case shoulder would have been more than it is. The measurements add up.

This also leads me to suspect the powder. It was on consignment. I did inspect the seal and it was stuck to the bottle but they all kind of do that. Maybe I should go get a sample form a friend to see if it performs the same as well. I have stuffed bullets right up in the gun so tight the bolt didn't close easy (testing jams) and they worked up to some pretty stout loads but never reacted this severely. 2611 fps does not seem hot to me and it's only 30 fps more than the suggested starting load. Imma go to bed.
 
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The Nosler website lists 63.9 grs water. You brass has less capacity, producing more pressure.

The Hodgdon data list a 180 gr Sierra SPBT. Your using a Hornady. Higher pressure?

Drop to 50 grs IMR 4350 and try again. Back off the lands too.

2 bolts with primer problems, strange. Maybe time to retire the 30 year old rifle.
 
The Nosler website lists 63.9 grs water. You brass has less capacity, producing more pressure.
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I'm only 1 grain off from where I was.

Nosler must have been using sissy brass from somebody else. My Nosler brass holds 59.9 partial sized for my original chamber.
 
First,to the folks advising a headspace check,this is not the first post on this case.It will help if you go check the post about grinding shellholders.No sense going over all of it again.

HiBC, I tried the marker thing, I think, and it scratches the back of the lug on one side in the same place it did on the old bolt head. The old bolt head has a little bevel cut on one side of the back of each lug about 1/16". The new one does not. The gunsmith said he didn't think they were necessary. I'm still not entirely sure what you want me to look for.
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OK. Your bolt face was concave.What causes that? I'm not sure.It could be an extreme pressure event. Ever have one?
Or it could be just a really worn gun. Are there any other ideas?
In either case,inside the receiver there are the" flat" places the bolt lugs rest on. Are you picturing them? Now,imagine your old bolt face locking lugs sitting on that "flat" surface. What if the same wear or pressure that concaved your bolt face did its work inside your receiver? Maybe you have some locking lug shaped dents in that "flat" surface that is not quite flat anymore. I'm going to call this dent(if it exists) "setback"
Wouldn't this "setback" match the locking lugs of the bolt face that made it?

That bolt face,you said,had a 1/16 in chamfer on one edge,yes? Your new bolt face lacks the chamfer,or it has less. Yes? Is the lightbulb starting to glow?
If the impressed "setback" was formed by the old bolt,and if the new bolt head has sharper corners,the actual locking lug flat surfaces will not be in contact when the bolt is in battery. The only contact will be at the mismatched corner conditions.
No,I'm not going to advocate lapping the lugs as the solution....but the concept might help you envision what might be the problem.
Those steel locking faces should make good contact,we would hope 70% or so on both lugs.Working the bolt should wipe most of the ink off both lugs. The floating bolt head should easily contact both lugs.If you still have a fair amount of ink,it may be the high spot of the sharp corner is the only working locking surface. Not so good.
When you open the bolt,if the bolt has settled into the setback pocket,you have to cam it up out of that pocket.

I'm thinking its also possible for your primer to set back and then get flattened.

The lockup of your lugs is "mushy" because that corner contact is not enough.

Nothing you do to the bolt head will fix setback in the receiver.However,if you carefully match that chamfer from the old bolt face lugs to the new one,you may get better lug contact. That will let your bolt set back a bit,and you may not need your ground shellholder anymore. Your primers might look better.

But its likely opening the bolt might still be hard.And I cant help but wonder if that rifle got hurt with an overpressure event.
That or its fired a whole lot of ammo...many thousands of rounds.

OR!!! Maybe I'm wrong.I'm guessing about a rifle I've never seen or touched.

Update: I read your recent post..Consignment powder is definitely a concern.Unfortunately,the factory seals ...leave something to be desired.
Your powder supply chain is critical.You don't buy material for aircraft parts at the recycler.

IF indeed your powder is IMR4350,....you still have SOME form of problem,but its hard for me to comprehend you would get excessive pressure at 2611 fps with a 180 gr bullet using 4350.now 4895...maybe.

1) How is your brass length? Seems like I recall you had it trimmed short.True? If its long,that could be a problem.

2) Is there any story about the concave bolt face? An overpressure?
 
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I don't think there was any big over pressure event. There have been a few others out there who complained of having concave bolt faces. Some have said they had them come from the factory that way. I am the only shooter of this gun and yesterday was the only time I've seen that kind of pressure signs.

The chamfer on the old lugs look to be an aid in smooth closing on the bolt the wear mark on both heads back of lug is concerning though and as my coffee brews I will investigate more. The way the bolt opened after firing was textbook overpressure. The brass was all 2.480". Should have been .007" under my new trim length.
 
I honestly don't know why a "gunsmith" would send out a rifle with improper headspacing. We are literally talk I,g five minutes with a piloted finish reamed to fix it.
 
I honestly don't know why a "gunsmith" would send out a rifle with improper headspacing. We are literally talk I,g five minutes with a piloted finish reamed to fix it.
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I have that option free of charge. He suggests that keeping it like it is will give me potentially better accuracy and certainly longer brass life. Right now that is besides the point.
 
Picture of wear on edge of bolt lug.

The wear mark is the same on the old lug. What is troubling is that there is no wear on the lug on the other side at all. none of the marker wiped off. What you see here is it.
 

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UncleNick correct me if I am wrong here but isn't a short chamber referencing a barrel that has not been completely machined ? I thought the term "short chambered" refers to a barrel that not completely reamed so that the barrel can be installed by finish reaming the chamber without needing a lathe to cut back the barrel shoulder.

Since the Savage barrel is adjusted and locked into place using a barrel nut not by machining the shoulder it seems to me the cure is loosening the barrel but and screwing the barrel .007 away from the bolt then relocking the nut
 
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