Please note that this article looks at research and testing done by a variety of sources. Extreme caution should be taken when creating loads that go against accepted load data. This article looks at theory and our experience, and should not be considered recommendations about primers for the 300 Blackout. When developing a new load for your 300 Blackout, or any caliber, you should start with smaller amounts of powder and pressure and work up gradually.
What size primer does 300 Blackout take?
The 300 Blackout cartridge takes a small rifle primer. Some reloading manuals, like the Lee and Nosler handbooks, list regular small rifle primers in their load data, while others recommend either small rifle magnums, or the #41, which is a harder magnum small rifle primer with a thicker cup.
Hornady Handbook of Cartridge Reloading
Can you use small rifle magnum primers in 300 Blackout reloads?
Yes, some reloading data are made with small rifle magnum primers. Hornady is one example of one that has their load data calculated with small rifle magnum primers, namely the Remington 7 1/2 primers. In theory, magnum primers are more efficient and require slightly less powder to get the same velocities and power. If they cost the same and your manual is calculated in magnum primers, I’d use magnums. The powder savings is only a couple tenths of a grain, but that can add up. It’s good to see how different powder for 300 blackout will shoot with a primer and with your rifle though, so test.
I asked my personal gun smith, who also taught me to reload his opinion on small rifle vs small rifle magnum and this is what he said about it: “I’ve tried both. Small mag is if you want fast loads. You need to burn a lot of powder quickly. You can over pressure the case quick so be careful. In the end if you are following good reloading procedures, load light and build up to what you want with either one.”
Can I use #41 small rifle primers in 300 Blackout reloads?
Yes. The #41’s have a harder cup and are very popular for reloaders who shoot primarily out of an AR15 platform. Most reloaders are able to use these interchangeably with the magnum small rifle primers without adjusting their load data, but you do your own testing if you choose to use the #41 small rifle primers in your 300 Blackout loads.
Berger Bullets Reloading Manual
Will small pistol primers work in 300 Blackout?
We have seen some reports that yes, many people have gotten small pistol primers to work in their 300 blackout loads. Some report that they can even chronograph at faster speeds than with small rifle primers for that cartridge, though we haven’t verified this for ourselves yet. Your main problem with small pistol primers is the cup thickness and the free float firing pin in an AR style rifle. The free float firing pin makes contact with the next round’s primer when the new round is chambered. There isn’t enough force to set off a factory 300 Blackout round, but that may not be true if you have small pistol primers.
Essentially, this could mean that you pull the trigger once and it could empty the whole magazine. At least that’s the theory. I’ve never actually seen it happen, though you can always get someone on a forum to claim that they’ve seen it happen. As with all reloading, if you decide to try this proceed with caution. Also, when test firing, load 1 in a magazine, then try with 2 in the magazine, then 4 or 5, before you try a full magazine. Every gun is different, so see how your gun will react before you just full send it with 300 Blackout reloads with small pistol primers.
Can I use small pistol magnum primers in 300 Blackout?
We’ve also gotten reports that yes, you can also use small pistol magnum primers to develop your loads. We also read a report that said for one manufacturer, they’re identical to the regular small rifle primers. Specifically, the CCI 550 Small Pistol Magnum primers and the CCI 400 Small Rifle Primers are the same size, with the same cup thickness. They’re also made from the same material and use the same explosive.
As always, do your own testing to confirm using safe load development practices.
What Primers Do I Use?
I initially developed my 300 Blackout loads using regular small rifle primers. Now I either use #41 primers, or, more frequently, I just load all my .223 and 300 Blackout brass to .223 load levels.
Other Frequently Asked Primer Questions:
Will small rifle primers work in 300 Blackout reloads?
Yes, the 300 Blackout cartridge is made to take a small rifle primer. Some recommend an AR specific primer, with a thicker cup, but we haven’t ever had any issue with using regular small rifle primers in a 300 Blackout.
Can you use CCI 41 primers for 300 Blackout?
Yes. It loads about like a regular small rifle primer. It is a popular primer in AR type rifles. If you have light firing pin strikes, you may have problems with these, as they have a harder cup, but the 300 Blackout was originally designed to shoot this harder nato style primer.
Can you use CCI 450 Primers for 300 Blackout reloads?
Yes, you can. Small rifle magnum primers, like the CCI 450, will certainly work in the 300 Blackout cartridge. If you usually use a regular small rifle primer, we recommend not going straight to a max load after you make the switch. Work up loads safely like you otherwise would, but the magnum primer shouldn’t be an issue.
Where can I find 300 Blackout primers for sale?
I buy from Sportsman’s warehouse and several local shops by where I live.
CCI primers for 300 Blackout
CCI 450, 400, and 41 primers are all the commonly used cci primers used, and there is standard load data for each. Look at your specific load data and see if what it specifies.
What Winchester Primers should I use for 300 Blackout?
We recommend the WSR primer, or small rifle primers. They do have a thinner cup, at .020, so if you have a heavy striking free float firing pin, you may want to consider something like the CCI #41s.
Can you use CCI BR4 primers for 300 Blackout?
Yes. BR 4 primer are good to go. They’re a match grade primer, so they’re a more expensive option, especially if you’re just planning on using them for plinking, but they work. In fact, some prefer them for precision loads.
What Federal primers can I use for 300 Blackout?
- Federal 205
- Federal 205AR
- Federal 205M
- Federal small pistol and small pistol magnums at your discretion and at your own risk, but they fit and some have reported success.
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