: H&R HandiRifle
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technical cartridge drawing
A commercialized wildcat. One of many 25 and 6.5mm caliber wildcats from the 1920's based on the 30-06 case. Developed by Neidner by simply necking the 30-06 down to 25 caliber. Others from that era include the 25 Griffin Howe and 25 Whelen. Neidner's work post-dates Newton's 256 (6.5-06) by 8 years. All suffered from the lack of slow powders at that time; and didn't come into their own until the introduction of imr4350 (1945), and 4831 (1948). Until then all were hopelessly overbore and under performed per their case capacities. Remington commercialized without alteration and introduced in 1970 as a chambering for their model 700.
The 25-06's case capacity [66.1 gr (of water) full case, 62gr with bullet seated .300"] fits midpoint between the 257 Roberts (55.8gr and 51.8gr, respectively) and the 257 Weatherby Magnum (76.9gr and 72.9gr). The 25 Gibbs represents the maximally "improved" 25-06 (69gr and 65gr).
The 25-06 is nominally chambered with a slower twist barrel (1:12) vs the 6.5-06 with a 1:8 or 1:9; making the two a pair - the 25-06 for lighter varmint bullets, the 6.5-06 for larger game and heavier bullets. 25-06 bullets tend to run between 75gr and 110gr, where the 6.5-06 runs 120gr up through 160gr. The 25-06 makes an accurate varmint thru deer size game cartridge. Nominal bullet diameter is .257"; SAAMI lists the maximum pressure at 64kpsi.