Seneca .308-caliber 135-grain spire-point Lead Bullets, 100 ct.

Seneca is a hunting product line for Air Venturi. These are .308 and based on what you are sharing that's the accurate diameter. These are in fact made in the USA.

Would these work with a umarex gauntlet 2 30 cal?

Actually if you check the diameter with a caliper its in fact .308 caliber but on the box says .30, and they are offering this slugs as .30 caliber and that is completely wrong because .30 is completely different than .308 so the mistake here is not the buyer, and there is no such a thing like LARGE.30 slugs, in this world .30 is one thing and .308 is something completely different!

matthew, people like you are the the reason this hobby doesn't grow much

This is a bullet.

Obviously not a pellet.

Just like a pair of shoes if they dont fit dont buy them and dont wear them. Not every gun out there will fire every pellet out there. its all about finding what your gun likes.

AAAAPLUS Matthew

All of the four air rifles that you listed above that you own OBVIOUSLY wont accept any type of 100-150grn LARGE .30 slugs. You have PELLET air rifles, I dont know how you own FOUR different air rifles and still dont know the difference between the big bore air rifles and what you have. I have a Texan LSS that shoots this ammo perfectly, it was made for that type of Big Bore air rifles. So before you leave a 1 star review just because they dont fit educate yourself, because this is a terrible review that doesnt reflect the slugs true quality and performance. What you said does not matter, at all. Go grab some 50grn .30 pellets and shoot those, then stop complaining that you were ignorant enough to buy the wrong thing.

.30 on its own is big bore. Any gun above .25 is big bore

These are sized .308 for big bore rifles. They are not compatible with 30 caliber pellet rifles.