RELOADERS CORNER: 4 (More) Semi-Auto Details

Facebooktwittergoogle_plusredditpinterestlinkedintumblrmail
Facebooktwittergoogle_pluspinterestyoutube

Beyond precision and accuracy, the base goal for any handload is safety: follow these recommendations to ensure yours! KEEP READING

Glen Zediker

Since I sincerely think it’s important to know what you’re up against, in one way of looking at it, when you load for a semi-automatic rifle, there’s more this time. I don’t mean to say “up against” like it’s some sort of adversarial relationship, a fight, but not respecting some of these points can create problems.

The gas port pressure issue was addressed last time, and it’s one of the most influential. Not only does too much port pressure create excessive action cycling, it also shortens case life. The cases take a bigger beating, more expansion mostly, when the bolt tries to unlock too quickly. Clearly, I’m back to using the AR15 as the central example, but virtually all semis succumb to the same set of behaviors (yes, including the gas-piston guns).

nosler brass
My current choice in a go-to for my “better” AR15 brass is Nosler. It’s not exactly thin but it is tough, and, by my experience, holds up to my standard. It’s also ready to load (well prepped).

One: tough brass
Therefore, next on the list is choosing a tough case! Tough, here, means “hard.” Brass is an alloy and the makeup varies from maker to maker.

The reason that a harder composition helps is because it’s more resistant to expansion, not as elastic. That might sound, on the front end, like a bad thing because harder brass is also more brittle so could tend to succumb easier to the ills of excessive expansion. Softer brass will conform more agreeably. True. It might seem like an equitable trade off, but I assure you that it is hardness ultimately that matters most. I notice the softness mostly in primer pocket expansion, or I should say that harder cases don’t open up as quickly.

Thicker cases, by the way, are not necessarily harder. Again, that’s in the alloy composition itself. Some high-dollar cases, Lapua for instance, are relatively soft despite being thick-walled.

The overall best choice for reuse in a semi-auto is probably good old Lake City. It’s exactly what it should be, and that’s been pretty well proven for decades. LC is easily available but, except in rare circumstances, will be once-fired. Most cases left over from commercially-available NATO-spec loadings are likewise fine. Lake City, as a bonus, also tends to be relatively thinner-walled (higher capacity) than many of the commercial brands, and its quality (wall thickness) is pretty dang good.

Check out what Midsouth has HERE

 

Two: adequate case shoulder set-back
Next, and this is a huge source of debate and disagreement amongst my readers, but, since now I’m strictly speaking of semi-auto needs I doubt there will be much dissent: full-length resize all cases! It’s a matter of degrees, and getting handle on port pressure (plus) taming down an excessively functioning gas system, reduces this difference: but most cases from most semi-autos will emerge with a pretty well-blown case shoulder. Make double-sure you’re sizing the cases down to at least 0.003 clearance. There are gages that help, and HERE is a link to one.

If you don’t there are safety and function problems ahead.

Three: adequate case neck “tension”
Likewise, make double-sure the case neck is being reduced an adequate amount to retain the bullet. There should be a minimum net difference of 0.003 inches between sized outside case neck diameter and loaded round outside case neck diameter. Reason: don’t take a chance of inadvertent bullet movement during the recoil and feeding cycles. That movement can be back or forward! It’s easily possible for a bullet to jump ahead when the inertia from the bolt carrier assembly chambers the next round.

sized case neck
Same as said about headspace: a bolt-action can “get away” with a lot, but a semi-auto round has to be constructed with an eye on cycling stresses. A firmly-held bullet resists stubs and intertia-induced movement. I recommend a minimum of 0.003 “grip.”

Four: tough primer!
Choose a tough primer! There’s a floating firing pin on an AR15 (M1A also) that is supposed to be held in check but that system doesn’t always work! If you load and extract a round and see a little dimple in the primer, that’s from the firing pin tapping off of it (again, created by inertia of bolt closing). A combination of a high primer and a sensitive primer cup assembly can create a “slam-fire,” which you do not want.

primer indentation
This always scares me. A tough-skinned primer is a very wise choice loading for anything with a floating firing pin, like an AR15 or AR10.
No! Check each and every primer to make sure it’s seated to below flush with the case head!

Brands? CCI has some mil-spec primers that work well, and I’ve had great success with Remington 7-1/2. Some of the well-respected “match” primers are a little thin. The CCI and Remington also hold up well to the (sometimes) greater firing forces working on the primer (again, from the quick unlocking).

And, finally, make double-sure that each and every primer is seated to below flush with the case head! That’s true for any firearm (because it also means that the primer is fully seated) but imperative for safety in a semi-auto. This is especially an issue for those who use a progressive-type loading press. There’s nothing wrong with the press but it may not give the sensitivity in feedback to know that the primer is fully seated without checking.

Here’s what I use from Midsouth

This article is adapted from Glen’s books, Handloading For Competition and Top-Grade Ammo, available at Midsouth HERE. For more information about other books by Glen, visit ZedikerPublishing.com

Facebooktwittergoogle_plusredditpinterestlinkedintumblrmail

3 thoughts on “RELOADERS CORNER: 4 (More) Semi-Auto Details”

  1. Ja, I size on a T7, because I get more consistent head space that way.

    I also size with all-in-one body and neck sizer die, so I can get a maximum grip on the bullets, without having to modify a stem.

    Then I seat primers with the RCBS Bench Tool, because I can tell if a primer is seated properly .

    Flaring, powder fill, powder check, seating and crimping I do in one step on the progressive.

    It’s worked for me, haven’t had any problems, but I suppose it’s not the only way that works well.

  2. I second the Lake City nod. I and a friend have been reloading LC brass for years and are just now starting to pitch some cases that have head stamps dating back into the late 60’s! Now granted….these haven’t been reloaded continually at or even near max pressures but still that’s a lot of use from a single case without any annealing.
    One other thing I will mention, all I’ve ever used in my semi auto loads is Winchester (plain Jane) Small Rifle Primers and have never had a slam fire, ftf or blown primer. What I am trying to say is their primers are good to go as far as all my testing….. however it is always good practice to keep that muzzle pointed down range when sending the bolt home!!

Comments are closed.