Bulging case a sign of over pressure or bad barrel?

[Ullr]

I fired a few of the loads for my new Encore 45-70 (TC Custom Shop) barrel and started to notice bulges on the case about ¼” from the bottom.  This was enough for me to stop and do some further investigation.  

This is what I found.

First the loads I was trying are with two different bullets and powders and were from a light Marlin load up to near Max Marlin load.  (The Encore should be good for Ruger loads as far as I understand so I should be well below max pressure.)

Here are the measurements that I took after shooting.

My sized cases prior to firing measured  .501
The book states it should be  .504

The fired cases at the bulge measured from .504 to just light of .508

The chamber on the barrel at my best estimation of the location of the bulge was  .508
The extreme rear of the chamber was  .510

Do these dimensions seem normal or is something out of tolerance here?  It appears to me that I may have a case of a die on the small side and a barrel chamber on the large side, but maybe each within tolerance at opposite ends.  Or are one of them bad and need to be returned?

I don’t believe that these loads should be anywhere close to getting too hot, especially with the same thing happening with two different sets components.  I was under the impression that this bulge was a sign of over pressure.  Is a slight bulge here normal if so how much is too much?

[savageT]

I think it's wise to try a few factory loads and measure them as you have your reloads.  Did you have indicatons of the primer filling out the pocket, or bulging out?  What about the powder loads....did they fill the case more than 80%?  Can you hear the powder move in the case? I agree that it sounds like your chamber may be on the large end of spec.

Jim

[Sean]

I have to agree with SavageT. Measure the base of the case at the pressure ring on an unfired factory load and then measure that case in the same spot (where you see the bulge)after firing. As I said in my post I believe .006 expansion to be the max that my instructor would let pass, anymore than that and the barrel would be lopped off. Also, measure your brass for length before and after firing (before sizing) to see how much stretch you are getting. One other thing to check is to straighten a paper clip then put a slight hook at the end, run this down in the case. If you feel a low spot then your cases are seperating. I hope this helps. Sean

[Ullr]

The primers look as good as they did new except the little dimple from the firing pin.  I don’t believe that any of the loads were above the 80% full mark you mentioned, even the high end Marlin loads I mentioned (which I did not get all the way to before stopping).  Yes I can here the powder move in the all the cases when I shake them.

I will try some factory ammo and see how that measures and also check these other items mentioned.  I will also take a measurement of the length of my fired brass to check for stretch.  I know the length of it prior to loading, as it was new brass so I sized and trimmed it all.

However, it seems to me that being that the chamber measures as least .508 in this area that the brass would be free to bulge close to this dimension as it has.  Correct me if I’m wrong here, but by my thinking the light loads would be mainly contained by the brass and would show as it did with the .504 bulge.  As the loads go up, the brass will expand until it reaches the barrel dimension where it is contained and then have a slight retraction and show the .507 to .5075 bulge I am getting.

[Ullr]

I found this article that is part 3 on the Model 1895G and I noticed a very interesting picture.  Now I don’t believe it’s just my imagination but in a picture about half way down the article the author compares some fired cases from factory loads and his had loads.  This is supposed to show how his loads burned cleaner but I noticed a faint shinny ring, only on his hand loads, that looks like what I am getting on my cases.  I can’t measure his picture for diameter, but maybe this is common to the 45-70 case.  It still leaves me with the question, how much a bulge is too much?


http://www.realguns.com/archives/038.htm

[savageT]

Since I first saw that same shiny ring on the webs of my 6.5x55mm brass on my Swedish Mauser, I now notice it on all my other guns as well....300 Savage and 30-06.  Can be alarming.  Just give the company that supplied the barrel a call and ask.  Maybe some Cerrosafe casting metal would tell you the whole story?  The case is expanding to fill the chamber and then retracting, but full-length resizing should cure that slight bulge.

[Ullr]

Ok after talking to TC custom shop their response was that this slight bulge is normal on the larger case cartridges.  Also it dose appear that my barrel at .510 is at the high end of their range (.508-.510 at rear of chamber), but still within tolerance.  

Also after firing some factory Winchester rounds the results were very near the same as my hand loads.  

Factory prefired diameter  .501
Fired brass at bulge       .505-.506

Being that this was not a magnum factory load and safe for trapdoors, I feel better seems how the bulge falls in the middle the range of hand loads I tried.  Also I did not feel any thin spots on the inside of the cases.  One thing that did surprise me a first was that all the brass after firing got shorter by.003-.005.  But after thinking about it the metal has to come from somewhere when the case expands, so this makes sense.  

I guess all the alarm was for nothing.

[savageT]

Actually........you were well within your rights to be concerned.  I'm a little put out that the T/C Factory was rather nonchalant about the chamber dimensions.  I would still pour some cerrosafe in the chamber and find out exactly what you have before too much use.  Good Luck and load safely!

Jim
P.S.  That comment about the cases shrinking had me going till I remembered you don't have bottle-neck cases.

[IronKnees]

Ullr... I think you will be just fine. Remember... the .45-70 case is really thin walled and expansion is very different with it than it is with more modern bottle neck or belted cases... I am going to go measure some fired cases from my Marlin 1895, but I can tell you without even doing that that they are expanded pretty good. Also, the white ring you mention is different than bottle neck cases too. With bottleneck cases, the web area is very much thicker than in other areas of the cartridge case, and can easily thin out causing a weak area... In the .45-70, this is still true to some degree, but the ring on the handloads is in all probability causes simply by the full length resizing die... that is, the ring simply shows where the die stopped... Mine all do that, and you will even notice that on bottle neck cases to some degree. There are two safety checks you can do to ensure that it is not a thinning or weakening problem. One, tumble your brass BEFORE and AFTER full length resizing. If it is just a mark left where the die stops, the polishing effect of tumbling the brass will remove it. Second, and I strongly recommend this, cave in and get one of the RCBS CaseMaster gauges such as shown here.

 TRUST ME... I use mine EVERY time I go to reload rifle cases. It has a neat little "feeler" that goes down inside the case and will detect even the very slightest thinning of the web area. (Web area being the area just ahead of the case head) And of course it is also great for checking and correcting bullet runout, etc... Dave[/img]