OAL Impact on Headspacing

This is in reference to the “plunk test” sticky on the reloading library of wisdom by Walkalong. I am not a novice, but far from an expert. My ammo always goes bang and I can get 1.25” or less groups with a stock Milspec at 50 ft. Any error is probably mine. However, one thing always bothered me when it came to loading 9mm and .45acp.

How does OAL impact the head spacing as shown in Walkalong’s sticky? If the round headspaces on the case mouth contacting the end of the chamber (where there is a step that reduces diameter) why would OAL matter as long as the bullet does not engage the lands?

My rounds pass the plop test, but I notice that they may “stick” just a bit in the chamber of the barrel. They may not drop out cleanly when I invert the barrel unless the OAL is very short. They are easy to extract, but factory rounds don’t exhibit this behavior even if I push them in hard with my thumb.

I used Tilos method to determine theoretical max OAL and I am a good 35/1000 or more short of that at 1.165 OAL on a .45 with a flat point having a large taper. Even allowing for error in that method I don’t believe the bullet is contacting the lands.

My gut tells me not to worry about this too much as long as the base of the cartridge is at or slightly below the breech and I get good results, though comparing mine with Walkalong’s pictures I may be spacing on the extractor if anything. Maybe I should just try for flush or just below?



As far as hard data with the particular round I am using right now:

0.451” 185gr plated flat point diameter

OAL = 1.160-1.165”

Tapered to 0.469” at the mouth of the case.

Cases trimmed to SAMMI min of 0.888.

Any insight would be appreciated.

Wow! A far greater response than I could have expected during a holiday weekend. I think we have some high road junkies here…

It’s funny how “talking” things out provides us with those “aha!” moments. I think I worded the original question poorly. I should have said: What impact does OAL have on how deep the cartridge inserts itself into the breech. (Yes I am trying to avoid the word headspace here, even though I have the definition right in front of me. In some cases it seems to add confusion)

Walkalong said:

Assuming correct mechanical headspace for the pistol, the case determines the head clearance, which we often call headspace, unless the round is too long and won't chamber.

You can reduce the OAL all you want without affecting mechanical headspace or head clearance.

Click to expand...

That’s what I thought and wanted to confirm. It seemed at odds with his sticky and now realize I misinterpreted his comments there. What he did was to simply keep reducing OAL until further reductions did not allow for the round to sit deeper. At that point you know the mouth of the case is against the step down in diameter at the muzzle end of the chamber.

That lead me to realize that if I could insert a sized piece of brass into the chamber and measure how far below flush it is. If I then insert a loaded round using the same brass (or one trimmed to the same length) and the depth below flush is the same then the mouth of the case is contacting the step of the chamber, and the bearing surface is not contacting the lands or at worst simultaneously touching along with the case mouth on the step down.

When I first started reloading 9mm many years ago I tired to use the max OAL because I was told small cartridges are sensitive to bullet depth and I like to err on the side of caution. I am sure many of those rounds were contacting the lands. I probably got away with it because as Wreck-n-Crew says, I ALWAYS start at min load, even if I am only changing one brand of 200 gr LSWC to another. In fact, as long as the gun cycles properly and the load is accurate I generally leave it there. I have fired a few hand cannons and I just don’t get the rush from a super loud report and heavy recoil that some do.

I have always thought of distance between bearing surface and lands as more of a rifle thing. But after Livelife’s post I am now compelled to work up a bunch of different OALs and test for accuracy. Not sure if he did me a favor there or not. Another thing to OCD on

At any rate, thanks to all you guys. I think I have a better picture of what’s going on now.

Do you trim your cases? I did this for the first time with my last batch of Starline and they have stayed a pretty consistent 0.888, or SAMMI min. They came in at about 0.894 but were not consistent. I guess you could trim them in different lengths for different purposes.

Sounds like I blew it when I trimmed all my Starline brass to SAMMI minimum. Of course the fact that I consider an 80 on a slow fire target grounds for a bottle of Lagavulin makes that the least of my my problems.

Actually, I consider making a legal right hand turn grounds for a bottle of Lagavulin