Sorry if I come off sounding argumentative, but this board is used for infornation as well as entertainment. Therefore, for the sake of clarification I feel a real need to interject into this conversation.
The tape method is shadetree/kitchen table gunsmithing. While it may give you a clue to whether or not there may be a problem, it certainly will not verify one. There are too many variables involved.
Not all brass is created equally. Brass thickness itself can throw off any true dimensions. Shoulders angles, rim thickness etc can vary from lot to lot and maker to maker. Thay can even vary slightly within the same batch. The same goes for the tape. Paper or mylar thickness varies as does the amount of adhesive at any given point along the roll. Tough to measure tape when glue compresses. Tough to trust it when some comes off on the calipers.
If a single piece of tape goes in along with the cartridge, odds are good it passes Go. If it doesn't enter and chamber, there is a slight chance the headspace may be tight. That's all it can tell you. Only a properly gauged or gauged and measured action can tell you where the headspace actually is. Gauging alone tells you what range the headspace is in. A headspace gauge and feeler gauges combined can get you to within +/- a thousandth or two.
Now, if four pieces of tape don't go but three will, that only indicates it might be worth getting the headspace properly checked to see if there is a problem. It may not be a problem with the rifle at all. It could be a problem with the ammunition being used.
Seeing a ring form above the web that looks a bit out of normal can also be loose chamber tolerances, or thin undersized brass, overworked brass, and even improperly annealed brass. I wouldn't jump to headspace problems yet. However the headspace is where to start checking if a problem turns up. If it passes the FR gauge, then a chamber casting and/or an entirely different batch of brass should be the next thing(s) to try.
I have used a piece of tape in the past a time or two. I didn't have gauges on hand so the tape told me it appeared good enough there for test firing. Even that was a guess. That's all it can tell you. A cartridge with a measured and close to true head thickness used with a feeler gauge can tell you more, but that's only certain with that particular cartridge.
Respectfully,
JB
