I posted this in the Big Bore Section, but I am hoping for a little more feedback here. I am using 3 different bullets and the same brass, powder load, primer, and die settings. For the Cutting Edge 450/420 grain bullets, I have loaded 3 times without trimming. For the Barnes 450 grain bullets, I had to trim after the first loading of new brass. The Barnes have to be seated much deeper and all shoot to the same point on the target.

So, is excessive pressure from deeper seating making my cases grow? Bolt lift is easy and no blown primers, seating of primers might be a little too easy.

What am I missing? Why do only the Barnes make the cases grow?

Thanks for the help, straight walled cases are new to me.

Sounds like the second bullet is generating more pressure than the first.

Being a straight-walled case, the cases must headspace on the belt. There is almost always excessively "generous" headspace on belted chambers (which has always been a mystery to me.)

The firing pin pushes the belt against its recess in the chamber when fired and the straight-walled case grips the chamber walls under the pressure of firing. The case will stretch rearward to the extent that the chamber pressure overcomes the elasticity of the thicker brass just ahead of the web. If pressure is low enough, then the case head will not be pushed back all the way to the bolt face, thus the stretching is minimal.

With a higher pressure load the case walls again hold the case in the forward position, but this time the pressure is great enough to push the case head all the way against the bolt face, stretching the brass at the web somewhat more than the lower pressure load. This results in a longer case which may require trimming.

Your higher pressure loads may be fully "safe" in terms of pressure, but if the same case is fired repeatedly with such loads then its web will get thinner and thinner with each firing and eventually (maybe in just a few firings) reach the point that the head separates -- an ugly situation which can be dangerous.

The only cure for this (other than keeping loads to lower pressures) is to set the barrel back slightly and rechamber, being careful to make the belt cut the very minimum necessary to allow the belted cartridge to chamber.

By the way, this is not at all limited to belted straight-walled cases. The same thing occurs with a rimmed case if the rebate for the rim is too deep. It also occurs with bottlenecked belted cases (and bottlenecked cases of any kind of base) if the loader pushes the shoulder back so that the primary headspacing surface is the belt recess.

Try to reason these things can be complicated, and the answers vari a lot on these blogs..

The main thing is your probably getting more pressure in some of your cases or whatever..Based on your results and your post, Id sugges that you trim the long cases to spec and keep an eye on your brass, if it continues then cut that specific load by one grain..nothing will change with a one grain change as a rule except your brass will stretch no more hopefully...You have to play with these problems to get the fixed.

I like Stonecreek’s explanation but I wonder if it also possible for the bullet to drag some case wall forward as it moves out of the case?

stop full length sizing them.

measure a fired case.
measure a sized case.
where do you think that difference goes if your pushing on the bottom of the case?

just size the part you need to hold the bullet.

Even on "low pressure" loads the case head is pushed against the bolt head. Being pushed back is NOT the reason the web of the case thins. The reason it thins is that when resized after the case has expanded under pressure, is that the brass as the case is squeezed in the die has to go somewhere. That somewhere is not going to be back toward the thicker brass toward the case head but in the opposite direction. Thus, the web gets thinner and the case gets longer. This happens until after several resizing/trimmings the web gets so thin you have a case head separation.

So, the best way to minimize that is either have a chamber that closely fits, the cartridge, don't full length size so the case isn't resized as much or decrease the powder charge so the case doesn't expand as much.

As for head separations being dangerous; it depends. In a strong bolt action rifle with a fully supported case head it's a non event. For rifles without a fully supported case head, it will be a disaster. I check all of my cases by the bent paperclip method after every firing since I'd rather not have head separations. The cases should be checked after resizing, by the way.

Can you explain the bent paperclip method?

I can. Straighten out a p clip. Form a small hook on one end that can be inserted into your case. Feel for thinning or cracks on the inside of the case near the base. A dental probe works well too. Thinning you can feel is a warning. Cracks are an all done now.

That bullet combo is absolutely DEVASTATING in the .458 Lott! You'll love it.

I found a bent scratch awl at a garage sale years ago I keep just for that reason, but paperclips are ubiquitous, cheap and easy to make...many things with a ≈90° bent angle will work to find that elusive crack, but you should see the "bright line of danger" ringing the case diameter just above the solid portion of the case base...VERY noticeable.

Fit your sizer die to your chamber by polishing out the sizer so it sizes only enough to chamber and only size the mouth enough, diameter and length wise, to hold the bullet firmly, then use a taper crimp die or Lee FCD to keep the bullet from moving during recoil...or have a die maker/gunsmith make you a sizer die from a fired case or "fix" your sizer die.

You also need to re-evaluate your reloading procedures...using the same powder/seating etc for three different bullets is a possible sure way to get pressure/dangerous spikes. What you need to look at is the USABLE CASE VOLUME below the bullet base in relation to the powder amount and seating depth you are using...the bullet's overall length in relation to the cartridge overall loaded length, the COAL...and what a reloading manual for WHICH Barnes bullet and Cutting Edge bullets says about the powder amount and COAL. You might also use a chrono to check the velos to see just whatthehellandwhy.

Variation in bullet OAL can cause a real difference in USABLE CASE VOLUME especially with a case a large as the Lott and bullets with a OAL length differences using the same COAL...which leads to pressure excursions of the third kind.

Run some numbers by and someone with QL or other software might be able to add something...need bullet over all length, brand type(TSX, solid etc), weight, LOADED overall cartridge length, type and amount of powder, other pressure indicators, etc.


Just saying.

Good Hunting

The problem is the straight case, it has no shoulder and you need to full length resize a DG round, as feed and function take precidents..

The Lott headspaces on the rim, rims vari in size so then does the headspace, and that's the problem in the nut shell...

just keep cases trimmed, as you have enough powder space and extra velocity to load the Lott down and still have all the punch in the world. Its what the 458 win should have been to start with..the milder pressure loads should pretty much solve your problem one degree or another and still thump a big bull pretty hard..

I would never not full length a DG round that I intended to shoot DG with..I also crimp the Lott.