Mudhen - Check the variety stores, especially after Halloween, can find them close out and buy enough for $1 to last for years. Look for the bags of flat black ones, unless you like the neon colors, .
Another source are the specialty stores for cards, party favors, etc.
I've pretty much gone to using muzzle cover all the time. Even if thinking not going to be in the brush, rose briar junk, seems like I always end up there for one reason or another. Have found too much debri in barrel from the brush junk, especially when tall and overhead. Conditioned me to use the balloon trick all the time!!!
Haven't found it to affect accuracy yet, hunting shots, or shots off the bench.
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