Case Length/Trim Length

[DubbleTrubble]

Starting the reload process on about 350 cases and have found something that (to me) might point to why I had so many chambering problems and extraction issues with my AR using certain factory ammo and none or few with another brand. But the more experienced here can tell me if I am howling up the wrong tree.

I have about 150 once fired cases, a mix of Hornady (Black) and Remington cases (used in several brands of ammo I tried). I have 200 new cases, also Remington. Or so I think, as there is a card in the box so stating. They are bulk cases from Midway and marked the same as the non-Hornady once-fired... *450* BUSHMASTER They were used by Federal, Remington and others.

I have in my notes a trim length of 1.690" is pretty vital to feeding in an AR. So I sat down to measure case length to see how many I needed to trim. Virtually ALL the new cases are between 1.695 and 1.710". Almost all the fired REMINGTON cases are in the same range.

The HORNADY cases are almost all 1.850-1.880" and the few that are over are just over 1.690 by a couple of thou. I found three REMINGTON cases under 1.690". Maybe not-so-strangely, the Hornady Black ammo fired almost trouble free as far as feeding and extraction went.

So Master Bush Reloaders, should I be shouting "AHA!"? Could the case length be the issue? What trim length do you use or recommend for an AR? Many thanks.

[Hoot]

I personally don't trim my cases as almost without fail, they have shrunk in length below 1.70 by the 2nd or 3rd loading. Beyond that time, their lengths are pretty stable. This is important: I only have an AR platform. I know folks who only shoot bolt actions in this caliber and they see less shrinkage and sometimes lengthening in the cases shot from their bolt actions. That having been said, don't trim new brass before shooting and resizing them at least once. Also, in a dimension where thousandths matter, a caliper isn't the end all for accuracy, unless its had its accuracy checked by a metrology lab. I have mainly used Hornady brass over the 10 years or so, with one foray into Starline for comparison purposes. In that case, the Starline brass on average, shrunk less than the Hornady. Again, I emphasize, in an AR platform. It helps to square off the case mouth with a trimmer to get an accurate reading as they don't always measure the same length as I rotate them. This should go without saying but here goes. Don't measure length with the primers in them and if they have ejector or extractor engraving on their faces, measure somewhere else.

Hoot

[DubbleTrubble]

Thanks Hoot.

To make sure I am clear, you don't think there is a "magic" case length dimension as long as it's at or below 1.70?

While I have you then, what other things can I do in the reloading process to minimize feeding and extraction issues? I know that my rifle and it's chamber dimensions will always be a contributing factor.

[Hoot]

Thanks Hoot.

To make sure I am clear, you don't think there is a "magic" case length dimension as long as it's at or below 1.70?

While I have you then, what other things can I do in the reloading process to minimize feeding and extraction issues? I know that my rifle and it's chamber dimensions will always be a contributing factor.

To be honest, I can count the number of new or 1-fired cases that I've gotten over the years, that were 1.70 or longer, on one hand and have most of my fingers left over. These were from back when the only non-custom platform available was an AR. So, I'm hesitant to predict what the current crop of cases will wind up being. Semi-auto rifles have looser chambers to guarantee successful cycling. The looser the chamber, the more the shrinkage after firing. If I bought a bag/box of new 450b brass and it had even one case longer than the SAAMI maximum length, I would return the entire bag/box for another one. No telling what other issues might be lurking in them. When fired brass arrives in excess of 1.70, you have to ask yourself, "Where did the extra length come from?" The answer is, "From thinning the walls somewhere down their length!" Thin walls are a harbinger of failure to come. It also means someone shot those cases in a rifle that had its headspace incorrectly set. If the rifle you are using has its headspace correctly set, it will not allow the bolt to close on stretched cases. As much as it represents an imposition for you, you should take the cases longer than 1.70 and see it your rifle will chamber them. If it does, you should have your headspace checked. Assuming it does not, if the number of them isn't too great, I would just toss them. If the majority of them are too long, you should return them to whoever you got them from, along with a warning that their headspace is set to an unsafe specification. This is worth repeating: That extra brass came from somewhere!" The rules are different for the more mainstream bottleneck calibers. I have a 300 Win Mag that grows its cases a thousandth or two every time I reload them. Being bottleneck cases, which headspace off of the shoulder, the growth is from the shoulder area getting squeezed as the pressure rises during ignition, before the case locks against the chamber wall. That makes the necks elongate. Par for the course but I never reload my 300 Win Mag cases more than 3 or 4 times. I'm just not that hard up for brass and the primer pockets start to get loose around that time anyway, I'm not a worry wart by any stretch of the imagination but when giving advice to someone else, I always err on the side of caution.

Other than that, any advice I would give you is already contained in any reloading manual worth the paper it was printed on. While there is always a case to be made for too little information, rarely is too much information a problem and there is plenty of reading material available on the topic of enhancing your case life. While SAAMI or CIP are fairly tight in their definitions of what represents the correct chamber dimension that allows the head of the case to contact the bolt face, my experience has been that the extractors will reliably pick up the extraction groove of cases that have shrunk far greater than the headspace tolerance. In the case of the 450b, a lot more tolerant.

Hoot

[DubbleTrubble]

Was hoping to get an answer to my basic question, which is whether or not cases over 1.690 or up to 1.70 would be a cause of chambering or ejection issues? As I said, the Hornady Black ran almost without issue. Lot of trouble with the factory Federal Non-Typical ammo, a bit less with the Remington and lots with the low volume brand whose name escapes me at the moment.

I didn't say a lot of cases were actually over 1.70, but a few were. Now that think about it, there might not have been a fired cases over 1.70 but there was one new case, sitting at 1.710. Again, the new brass I have is the same stuff that Remington, Federal and a couple of the low volume loaders use, headstamped as I mentioned in my earlier post. Maybe that's a problem but if "under 1.70" is all I have to sweat, that's easy enough to sort out by trimming.

I had a report from one volume 450 Reloader that he preferred 1.690" and because all the Hornady cases were in that ballpark, I thought I had an AHA moment.