over size .25 pellets. (6.35mm?)

[Collector]

I had my Supersport .25 breech modified to accept H&N FTTs perfectly. An excellent job done by Airmasters. I went on to write an article about it which was published in Airgun Shooter magazine.

[MartynB]

Hello thank you all for your help, that has given me something to think about.
Mr Gen would you kindly expand on your statement that a pellet expander may be available, may I ask from whom?
All the best.
Geoff.

You could ty speaking with Terry Robb if he's still around as he made adjustable pellet sizers, I have one for .22, well made and solid

[Shed tuner]

I don't know how you can say that,
Marksman were 6.2mm when I measured them about 18 months ago & were a good fit in my BSA Supersport .243" barrel, when FTT's & JSB made pellets were almost impossible to load.

notwithstanding the measurement disparity (batches do vary, and soft skirts are hard to measure consistently), I think the key with marksman is the skirt is thin, and the lead is soft. So regardless of size, they are much easier to shove into a tight bore, and more likely to expand into a larger bore. As stated, they are also an excellent weight for sub 12, which combined with the softness gives good efficiency. As a bonus they are dirt cheap, so pretty well the perfect vintage .25 for plinking