Comparing 300 blk and 7.62x51

Discussion about rifles in 300 AAC BLACKOUT (7.62x35mm), hosted by the creator of the cartridge.

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Funnyhat
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Comparing 300 blk and 7.62x51

Post by Funnyhat »

How comparable are the ballistics between these two rounds? Would an optic designed for 7.62x51 be usable on a rifle chambered in 300 blk?
ReadyAimDuck
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Re: Comparing 300 blk and 7.62x51

Post by ReadyAimDuck »

If my numbers are correct, the 168 grain 7.62 x 51 has about double the energy at the muzzle (2720 ft pounds) at 2700 fps. Vs. the 110 grain 300 blk at 2400 fps and 1407 ft. pounds. The 7.62x51 at 300 yards has similar energy to the 300 blk at the muzzle.

What type of optic are you looking to use? One that is sturdy enough for a 7.62x51 is absolutely going to be sturdy enough for a 300 blk. if that is the question. Or are you wondering if a BDC optic for 7.62x51 will work for a 300?
Funnyhat
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Re: Comparing 300 blk and 7.62x51

Post by Funnyhat »

I was looking at the Elcan Specter 7.62 NATO model, which does have a BDC. I wasn't sure if that would work with a rifle chambered in 300 blk.
ReadyAimDuck
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Re: Comparing 300 blk and 7.62x51

Post by ReadyAimDuck »

You can make it work, however the reticle shows where the bullet drop is going to be for different yardages based on the 7.52x51 147 gr. load. These are going to be different for 300 aac. So what you would end up doing is figuring out where the bullet drop is for 300 aac at each of those different subtensions.

Its somewhat common for people to use 5.56 BDC reticles for 300 aac and simply do the math for the difference between the bullet drops of the two cartridges. For example, I've used a reticle like this for 300 aac that was calculated for 5.56. It had hash marks listed as 3, 4, 5, 6 to correlate to how much the 5.56 cartridge drops at those ranges. Those bullet drops are different than for 300 AAC. So I had to figure out which each of them meant for the 300 instead. Its not as slick, but you can do it. "3" might mean 275 yards, "4" might mean 350 yards, etc.

I hope that makes sense. Its not as handy that the numbers on the reticle don't equate exactly for your cartridge. Can it be done? Yes. I think there are a lot less reticles on the market for 300 AAC so a lot of people are using BDC reticles for 556 on their rifles. Many of those advertise that they are for both and the manual will tell you how to calculate the difference.
Funnyhat
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Re: Comparing 300 blk and 7.62x51

Post by Funnyhat »

I get what you mean. At this point though I'm probably just going to stick with 556 and throw a suppressor on it.
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