What Does Bolt Bushing Accomplish?


There are three things that Bolt Bushing solves or improves greatly. I list them here with details and in the order of their importance.

  1. Easier bolt lift. This is the biggest reason for me. Because the firing pin and the unsupported part of the primer is reduced immensely you can also reduce the tension on the firing pin. This does many things. It makes opening the bolt much easier. With reduce effort in bolt lift you can better feel when cases start to get sticky in your chamber. I have also noticed that if a chamber is dirty I can feel this with a rifle with an already light bolt lift. With less effort on bolt lift cycling your bolt is faster too. This is possible because you have downsized your firing pin. Making it smaller means there is less for required to dimple the primer enough to start ignition.
  2. A more consistent ignition sequence. If your firing pin is off center in your bolt, and most of them are, your firing pin may sometimes strike the anvil, in the primer, between the legs. This means the firing pin must penetrate deeper into the primer before the ignition sequence starts. In turn this means your harmonics will be different ever time you pull the trigger. Now it is a small change but for those of you that are critical about accuracy and you need avery bit of accuracy you can squeeze out of your rifle, this is a big deal. Just like truing a rifle receiver, having a centered firing pin is important to accuracy. Also think of this too. If your firing pin strikes and pushes your cartridge into the chamber on its side, and not centered, it will cause the cartridge to be ever so slightly crocked in the chamber when it begins its ignition sequence.
  3. The elimination of cratered primers. This is why the vast majority do it though I believe it’s the least important. Bushing your bolt will forever eliminate cratered primers. You will have to work up hand loads from now on using primer flatness as your guid rather then primer cratering. For many shooters this means they can shoot faster, although this should not be the objective. For example I had a customer bring me a bolt once that would not shoot even a mild load without excessive cratering and even blanked primers. When I took his bolt apart it was filled with brass cups from primers. His firing pin was massively oversized and Bushing it fixed this allowing him to shot scolder to book max PSI levels.

Every shooter that is considering getting their bolt bushed is usually a hand loader. I have however had some customers that couldn’t get even factory loads to fire in their rifle without blanking primers, just because the hole was so oversized. If you are considering getting your firing pin and bolt bushed think and ask your self these questions.

  1. Is a faster and smoother bolt cycle important?
  2. Do I need to ring ever bit of accuracy out of my rifle that is possible?
  3. Is achieving the max safe PSI level of my chosen cartridge necessary?

Lastly you need to decide on a size. Most IBS gunsmiths set theirs at .062. I offer a verity of sizes and I recommend them depending on your intended use. If you are shooting strictly from boxed ammo and not hand loads then .068 is a good size. If you’r a reloader then .064-.066. For hand loaders, you know who you are, typically .062.

Last thing to decide is what clearance you want. Clearance is how much room the firing pin has to move through the bolt face. Most factory rifles have monstrous amounts. Like .005 and up. I however have never seen a factory off the shelf rifle with less then .006. Now having a ton of clearance is great if your are dumping mud into your action to impress your friends on your rifles reliability during a stress test on youtube, but for real life its not necessary. For hunters and PRS style shooting,  .002 is plenty and bench rest shooters usually get .0015 or even .001. It all depends on how clean you keep your gun.



A customer testimonial.

I have a Savage 12 .223 that I shoot with 90 VLDs. I was getting significant primer cratering so I decided to get the bolt bushed. After doing some research and learning of Grimstod’s reputation in this area, I decided to send it to him for the work. And because I don’t eject my brass, I asked him to plug the ejector hole while he was at it.

The service, communication, and workmanship he provided were second to none. No more cratering, and as for how well he filled the holes, I’ll let the photo below (not photoshopped) speak for itself.

Dave Rabin


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