by Tom Gaylord
Writing as B.B. Pelletier

Part 1
Part 2
Part 3
Part 4

This report covers:

  • Reloading rimfire cartridges
  • Top speed for lead bullets
  • Strip out?
  • Case preparation
  • CUP?
  • Transducers
  • So what?
  • Brass flow
  • 5.56 mm brass
  • Trimming cases
  • Summary

There is a lot of interest in this series. I’m stretching it out over time because it deals with firearms, but it’s useful for all of us to understand in order to better understand airguns.

Reloading rimfire cartridges

Reader Yogi asked about reloading rimfire cartridges. And he was justified in doing so, for the first firearm cartridges in any caliber were either rimfire or needlefire — a type of ignition I don’t want to get into in this series. Centerfire cartridges — the kind we reload today — came a little later in the world of self-contained cartridges.

Actually, Yogi, you not only can reload rimfire cartridges — there are actual kits to help you do it! Since I had no idea any of this was possible, I’m not going to pretend I know what I’m talking about. Here is an excellent article on reloading rimfire cartridges. And here is the place where the supplies and tools are sold.

That said, would you WANT to reload rimfires? It takes a LOT of time to do everything that has to be done to reload a rimfire cartridge. Unless you are huddled in the ruins of a post-apocalyptic shelter and fending for your life I’m going to guess most of you have better things to do. Read the article and you decide.

Top speed for lead bullets

Reader 1st Blue asked me what the top speed for a lead bullet might be. Now a copper gas check can be put on the base of a lead bullet and it changes everything, so what I’m talking about here is an all-lead bullet.

bullet gas check
A copper gas check has been swaged onto the base of the .308 bullet on the left. The .308 bullet on the right is just lead.

I have shot soft lead rifle bullets up over 1,300 f.p.s. with some success. I don’t like going that fast, though, because staying around 1,200 f.p.s. or less is almost always more accurate. But he asked and that is my experience.

Some reloaders believe that bullets have to be cast very hard to go their top velocity. They speak of Brinell hardnesses of 28-30 for their bullets and some go higher than that. My cast bullets are soft — in the Brinell 8-12 range. I do know that the harder the bullet the more lead it will deposit in the barrel. Soft bullets shoot much cleaner — but their top velocity is probably in the 1,300s, where some hard bullet shooters are claiming up to 2,000 f.p.s. Put a gas check on the base and the top speed goes up over 2,300 f.p.s.

Strip out?

Many shooters including 1st Blue are concerned that lead bullets will “strip out” of the rifling at high speed. I have never seen that or even heard of it happening. As long as the bullet is one-thousandth of an inch over groove diameter, it should do well at any speed up to its max. I said bore diameter in an earlier report and somebody brought my attention to it. I’m talking about measuring the diameter of the bore across the rifling grooves.

I have heard that glass-hard bullets (Brinells of over 30) will sometimes shatter from the force of the gunpowder exploding behind them. I have never seen that but again, I don’t harden bullets that hard. I do know that soft lead bullets don’t do that.

Case preparation

Some cartridges are low maintenance and require little beyond cleaning and possibly resizing before reloading. Straight-wall cases are among those that are easy. You can just reload a .38 Special case or a .45 ACP case for a long time before they begin to fail. So the shape of the case is one big part of whether it will last a long time or not.

Pressure is the other big reason for case failure, and it is even more influential than the shape of the case. Load a .38 Special up to +P+ pressures (over 22,500 copper units of pressure — CUP) and the necks will start cracking after a few reloads. Discard the case when you notice that. If you load the .38 Special at or below 15,000 CUP you may get 20 reloads from it. I have a .32-40 rifle case that’s been reloaded about one hundred times and is still going strong, but I doubt my loads for that cartridge ever went above 10,000 CUP. In fact they are so low that the lead unit of pressure or LUP would be used to express them.

Shop PCP Rifles


When we get into the pressure ranges of firearm cartridges we generally don’t refer to pressure as pounds per square inch — even though it still is. We refer to copper units of pressure — which is the pressure that crushes a copper crusher gauge that is held in a test fixture when the cartridge is fired. It isn’t incorrect to express pressure as psi, but CUP and LUP are the more common means of expression when talking about internal ballistics. When the pressure is below 15,000 psi, the LUP is used.


Today electronic transducers are used instead of copper or lead crusher gauges. They are faster and cheaper to use and cause fewer mistakes because careful measurement of the crusher gauge is no longer required.

So what?

Here is so what. Shoot that .44 Magnum with loads that develop about 20,000 CUP and get 10-12 reloads per case. Bump the pressure up to 36,000 CUP and the case longevity drops to 3-4 reloads. Drop it back to 15,000 CUP and get 25-30 reloads from each case.

Okay, all of that discussion was about straight-walled cases — except for the .32-40. What about bottleneck cartridges? Let’s start with a common one — the .223 Remington that is shot in the AR-15. It typically generates around 55,000 CUP/psi if you load it with standard hunting loads. You can go a little higher, but not too much.

Brass flow

At this pressure level the brass the case is made from will move forward under pressure. It’s called flow because that is what happens. At the high pressure the brass will flatten against the walls of the chamber and actually flow (move) forward. The length of the case will grow the more times the cartridge is fired. To offset that growth, we must trim the case back to a standard length before reloading it again. So we measure the length of each fired case and then trim all cases to one standard length before reloading begins. In my experience, the .223 Remington case needs trimming after every three reloads. Trim it two times and then throw it away, because the place it flowed from is getting too thin.

5.56 mm brass

The military version  of the .223 Remington cartridge is called the 5.56 mm cartridge. It is the same size on the outside, but it’s made of thicker brass. It can be loaded into and fired from many rifles that are chambered for the .223 Rem. BUT — the 5.56 mm generates higher pressure than the .223 Rem. It generates 58,000 CUP which doesn’t sound like a lot more — BUT the 5.56 mm cartridge chamber is 0.125-inches longer than a .223 Rem. chamber. Shoot a 5.56 mm cartridge in a .223 Rem. chamber and it generates 65,000 CUP, which is closing in on the proof pressure for the .223 Rem.! Case length and chamber length matters!

Can you reload 5.56mm cartridges and shoot them in a rifle chambered for the .223 Rem.? Yes — as long as you keep in mind that the thicker brass of the 5.56 case will hold LESS powder than the .223 Remington case when the bullet is seated to the same depth. That’s not a bad thing because that thicker 5.56 mm case will generate more pressure with less powder. My advice if you want to hit what you shoot at is do not mix .223 Remington and 5.56 mm cases together, and NEVER load them with the same amount of gunpowder!

I keep my cases separated (the headstamp tells you what’s what) and I develop loads for each type of case, keeping a sharp eye out for any signs of excessive pressure. They would be:

  • flattened primers
  • primers that flow back into the firing pin hole
  • primer pockets that become loose (evidenced by soot around them after firing)
  • cases that are bulged at their base (also a sign of excessive headspace)
  • cases that are split at their base
  • cases that are difficult to extract
  • cases whose heads are deformed (often they flow into the extractor cutout)

If you see ANY of these signs, stop shooting immediately and do not fire the remainder of those reloads.

Some cases REALLY stretch!

Of all the centerfire cartridge cases I have reloaded, the 6.5X55 Swedish Mauser case stretches the most. I had to trim them back after every firing and they started splitting at the base after as few as three reloads. To prolong case life I reduced my loads until they generated around 20,000 CUP. You have to read the reloading manuals and interpolate to figure out things like that. When they were loaded to that level I could get 5 or 6 reloadings before the danger signs appeared, and they stopped needing trimming after each firing.

The 6.5 Swede was such a chore to monitor that I stopped shooting them altogether. Someone asked whether this stretching was due to excessive headspace, but it happened on all 6 Swedes that I owned at one time or another. It was just too much to keep up with.

Trimming cases

I trim cartridges to length with an L.E. Wilson case trimmer. This tool dates back at least 80 years and still does wonderful work. Lee Precision also makes a much less expensive case trimmer that I use for a couple calibers. Where the Wilson relies on a bushing into which the case fits, the Lee has a central rod that limits the depth the cutting head can travel. The Wilson is universally adjustable for length, the Lee only trims to one standard length.

case trimmer
The Wilson case trimmer adjusts to a wide range of cartridge case lengths. Once adjusted, each case that’s inserted into the bushing will be trimmed to the same length.


That’s about as far as I want to go with reloading, unless there are specific things some of you want to discuss. Reloading starts out simple and gradually becomes quite complex as you learn more and more. As I said in the beginning, those who reload can be shooting while others lament the lack of commercial ammunition. Plus, it’s fun!