And according to testing, the sabot rounds were very inaccurate. This is taken from a US Army test of the Firefly done during the winter of 1943-1944:
Test 2: Dispersion
The purpose of this test was “to test the dispersion of various types of 17-pounder ammunition at ranges from 500 to 2,000 yards, and to compare the result with similar data computed from 76mm and 90mm ammunition". This was done by setting up 6’x6’ canvas panels at 500 yard intervals, and firing ten-round groups at them...This successfully completed, they went back to the 500 yard target and fired SVDS.
Results were rated "poor", with 8 rounds on target, and two sensed as being about 36” below the panel, but for the purposes of calculation they were presumed to have the same average deflection as the 8 rounds that were on target. Overall deflection was 2.35mil, 4.34mil elevation, with means of 0.5mil and 0.92mil respectively.
Then they tried at 1,000 yards. After firing 18 rounds trying to register, (Successive rounds with the same sight picture were observed as over, left, short) they decided to abandon further testing of the round except for armour penetration.
After firing the 28 rounds SVDS, they decided to go back to APCBC. However, the SVDS rounds had left duralumin fouling in the gun tube, and so before resuming the dispersion testing at range, they fired ten rounds of HE and then ten rounds of APCBC through the tube for the obscuration tests to clean it out. Given the observed results of the grouping (see “Phase B, below), they went back and fired another ten rounds of HE and APCBC. After the 40 rounds had been fired (Phase D), it was considered that the tube had returned to normal, (albeit at apparently a new zero) and the accuracy testing continued at 1,500 yards after an adjustment on the sights on a clean zero panel.