A popular Mossberg model made from 1949 - 1957. It uses a 7 shot mag and will load and fire S, L and LR 22 ammo. It weighs around 6 pounds, 18" barrel, Monte Carlo stock w/ pistol grip with sling mounted on the left side. Unique feature is the fold down forearm that can be used as a hand grip or a uni-pod when shooting prone. It used a military looking Mossberg S109 front sight and a S108 receiver sight.
The early model 142a's used a T handled bolt handle, changed after a few years to be replaced with a more traditional ball on the bolt handle. Mossberg used wood for the fold down forearm for most of it's run but was changed to a black plastic forearm the two to three years.
The 142a shared most of it's features with the semi auto Model 152.
Value? Hard to answer that one. On average and nice all original and complete 142a goes for $200 - $300. I have seen the same sell for much less and some higher. Mossberg rimfire prices are crazy and very hard to predict.
1950 Mossberg catalog page