I've owned a 1891 7.65 Argentine rifle since the 1960s. For last 15 years or so, I've spent quite a bit of time reading internet posts about this rifle and its ammunition. I'm hardly an expert on the rifle and its ammo, but have found these two past posts on Parallax Bill's Curio and Relic and Miltary Surplus Firearms Forums back in March 2006 interesting.
"If you get chamber reamer prints from JGS #3021 Belgian 7.65 and #3504 7.65 Argentine you will see they show a total of 3 different headspace measurements. Whats funny to note is on the Belgian chamber print, done by Winchester in 1940, notes 1891 chamber is .010 longer than model 1909, which makes me think they meant argentine. On print 3504 they show even longer headspace for modern cip spec argentine and larger chamber size. They also show shoulder angle of 22-30-0 for one and 23-0-0 for the other. Norma ammo is speced minimum and will fit all 3, but will stretch alot too in all but 1909s. 1940's argy ammo is more uniform in base to shoulder length. I measured some of the 1980's SF stuff with a stoney point tool and find some of it a bit longer from base to center of shoulder. Also, I have seen max case lengths of 2.09 for norma, 2.10 for 1940's SF and Orbea ammo, and 2.11 for the 1980s SF ammo. Confused yet they also show 2 different bore specs, .303 to .3105 for Belgian and .3012 to .3118 for the Argentine."
In 1990 an article appeared in issue #132 of Rifle Magazine that featured the 7.65X53 Mauser. Gaulden, author of article, mentioned having a headspace problem with the SF 81 ammo in his 1909 Argentine rifle. "Months later, a letter to the editor was posted which should prove definative on the issue." " Under the heading 7.65 mauser update, Captain Luis A. Garcia Bourimborde, who was at that time the Argentine Defense Attache in Tokyo, who describes himself as an Ordnance Officer, states that the only designation for military ammo that was in use during the time all the rifles were manufactured was 7.65 Mauser, with no case lenght designation attached, and so all rifles were made to one chamber standard, within tolerances, whether 1891, 1909, or 1935 contract. The case lenghth denomination didn't enter into the picture until the 1950s or 60s when NATO started so designating their ammo (7.62X51), and in the case of Argentina, they simply measured their case length and applied a two digit approximation by rounding up. Bourimborde goes on to state that he is of the opinion the the SF 81 ammo is likely out of spec., which he had also previously found when inspecting prior lots of Argentine (SF) manufactured ammo, but never with the old DWM, FN, HP nor Rem-UMC. He also states, "I can tell you for sure there were never two different 7.65 cartridges, only different denominations or headstamps." He also further states, "Any 1891, 1909, or 1935 Argentine Mauser is safe with any military ammunition you can close the bolt on, no matter what effort is needed." I'm not sure I wholly agree with that last statement, but I think the general meaning is correct.
Personally, from my readings of posts over the years, have reached conclusion, the chamber of a 1891 is cut slighly longer than that of a 1909.
