This was an interesting post on ringing the chamber on the cast bullets forum:
No wad is necessary. All it takes is a significant free airspace in the case and delayed ignition of the charge.

When I was at Camp Perry, OH in 1967 I witnessed DOZENS of M1 Garand rifles which were turned in for rebarreling, after having fired WCC Ball M2 ammunition loaded with WC852 powder (H380) in which a "ring" had formed adjacent the bullet base, partway up the chamber neck. One of the rifles was MINE! I also had a Winchester Model 70 with ringed barrel and the government paid for it to be returned to Winchester for rebarreling.

I have also examined DOZENS of Ruger No.1 single-shots which had been returned to Customer Service, mostly .45-70s, which had been ringed by shooters using wads pushed down against the powder. The service department had sectioned the barrels and had them mounted on the wall at the New Hampshire factory where they were and probably still are plain to see by students attending the police armorer's school. Some rifles had multiple rings corresponding to the bullet base location of various weight bullets they had tried.

Easily-ignited, relatively fast-burning pistol or shotgun powders, having NO deterrent coating, and which tolerate the free airspace in the case, such as Bullseye, Unique, PB, Universal, SR7625, Herco are not the problem.

Most prone to chamber ringing are heavily deterrent coated, spheroidal powders such as 296, H110, 680, 1680, H335, Ball C2, 748, H380, H450, etc. in which there is a high percentage of deterrent coating, and a small particle size in the base grain.

In pressure testing I did attempting to develop suitable .30-'06 loads to operate the M1 Garand, having correct breech and port pressures, using the government test barrel, I was not able to do so with 150-grain bullets using powders such as 748, H335, or Ball C2. I fact, I RINGED THE $5000 government combination breech-port pressure barrel! The results were EXACTLY the same as those observed with the WCC Ball M2 loaded with WC852.

My advice is that if a powder requires use of a filler in order to obtain acceptable ballistic uniformity, than IT IS NOT SUITABLE for those particular conditions of loading.

For reduced rifle charges, lightly deterred, perforated flake and extruded tubular powders such as #2400, 5744, RL7, 4227, 4198 will give best results. Of these Alliant #2400 is the only one which in my experience, performs normally at loading densities below 50% of case capacity. 5744, RL7, 4227 and 4198 should not be loaded at less than 50% of available case capacity. Extruded powders slower than RL7 or 4198 should not be loaded at less than 70% of case capacity. The Hodgdon 75% rule is sound!

For full charge loads, choose a powder in which a safe charge occupies not less than 80% of the powder space and in which velocity standard deviations of a 10-shot sample fired with the powder uniformly positioned using a "SAAMI roll" do not exceed 1% of the sample average. The military procedure is more severe and consists of 5 rounds fired "base tap" and five rounds fired " nose tap" in the sample.

I punch out wads from the water pipe insulation.
I plug the case mouth to prevent any chance of ringing my barrel.
One Alberta Schutzen Guild member ringed his RKS stainless steel barrel at the base of his seated bullet by placing floral foam directly down on the H108 powder.
He now slices off wads from window foam backer rod and plugs his case mouth to prevent ringing of his new barrel.

  I'm with calledflyer, a sharp knife.

A couple years ago, I was doing a vinyl siding job on a house
of mine. 
Used Fan Fold foam House Wrap under the siding .
When I got the "urge" to go with breech seating, I messed with pipe insulation, and the floral foam.
And then it hit me to try a couple pieces of left over House Wrap. It is +- 0.225" thick. I just peel the very thin film off it and then cookie cut with my loaded cases. I do like to have the case mouths inside chamfered to make better cuts on the foam to plug the case mouths.
Works great, it is also polystyrene like the floral foam, but
is a bit more dense foam and is not brittle and crumbly like the floral foam. No indication of any bad residue in the barrels.
beltfed/arnie

talking about hijacking a serious thread.....
beltfed/arnie

I believe his reference to the percentages of case volume all apply to the absence of any type of case filler.  In my opinion when a weightless CASE FILLER !!! is used those percentages do not apply.
Again it may be helpful to look at a shot shell where the powder charge occupies a very small percentage of the case volume. Since in a shot shell the projectile is 100% internal withing the case the actual case volume might be best measured from the bottom of the shot cup to the top of the case head.  Still it is quite a large volume because most shot ammo is in much  larger calibers that what we generally discuss here..

Red Cent wrote on Jun 4^th, 2023 at 6:48pm:


I thought that a flat laying powder charge was one of the causes of the secondary explosion effect that causes mayhem to rifles

And what happened to all the posts....did the anti humour bandits strike again 
Gumpy