This is an appeal from a conviction for forging and uttering. 18 U.S.C. § 495 (1952). The alleged error on which appellant relies — failure to charge that *584 a certain witness was an accomplice and that his testimony should be viewed with caution — was not raised in the District Court, and we find no sufficient reason on this record to exercise our authority under Fed.R.Crim.P. 52(b), 18 U.S.C., to review it here.

Affirmed.