Mike,
around half the calibre is usually regarded as enough, so 0.11" in this example. Actually, most cartridges work happily with bullets seated into the neck by a tenth of an inch irrespective of calibre. I reckon even that could be reduced a little assuming the rounds are treated gently and single-loaded. Rapid bolt manipulation and/or a magazine rifle that doesn't have a smooth feeding magazine obviously risk putting sideways pressure on the bullet and producing serious runout.
I used 80gn 0.224 SMKs and Nosler Custom Competition match bullets in a manually operated AR15 for a long time with only a tenth of an inch seating depth, and there was never any problem single-loading them off an original Bob Sled single-shot loading platform despite the bolt whacking the round fast and hard into the chamber after its release catch was operated.
So far as retaining 0.005" jump in a .22-250 is concerned, you obviously won't! There are two answers, one expensive, one cheap. The former is to rebarrel once throat erosion goes beyond your comfort zone. The cheap answer is not to worry about it until the groups 'go off' which might see a lot more bullets through the barrel than you expect. At that point, try different bullets to find one that accepts more jump into the leade than the one that has stopped working. Most tangent ogive bullets are very jump-tolerant and the aforementioned .223 AR was still producing very good groups with getting on for 200 thou' erosion and the best part of 100 thou' jump, if not the tiny examples that I got when the barrel was nearly new (0.4-0.7" groups compared to 0.2-0.5" originally).
I've always thought that increased jump through erosion is less important than the nature of the erosion. In long barrel life cartridges like .223R and .308W used in slowfire deliberate competition shooting, the barrel throat appears to remain fairly smooth. Jump-tolerant bullets often continue to perform well at ridiculously high round counts in this case, for example .308W Target / Fullbore rifles shooting into a 2-MOA Bull, 1-MOA V-Bull (X to US citizens). Erode the chamber fast though with a high capacity barrel burning number and the throat becomes rough and firecracked, and the barrel stops performing long before the eroded section reaches any great length. This may or may not apply to a .22-250 which I would call an in-between cartridge in this respect.
The longer / heavier the bullet used, the more rapid the rate of erosion, and also the likely effect that it has on performance. Some Canadian F-Class shooters used the .22-250 with 80gn bullets in fast-twist barrels in the early days of the discipline but reputedly got relatively short barrel accuracy life, around 1,100 rounds. Likewise VLD or other secant ogive bullets that like to be seated into the leade present an obvious problem. Your 52gn Bergers don't fall into either category, so should continue to perform well in az relatively high round-count barrel.
Laurie,
York, England
! They perform well in my 26" 1:9 twist barrel too! I haven't warmed the barrel up too much on this particular rifle but, it hasn't been to the prairie dog fields yet either 
