That’s my current question.
So in trying to work with these Barnes TSX .224″ 53 grain bullets, do I need to crimp them or not?
Do you recommend crimping your bullets?
We usually don’t recommend crimping our smaller-caliber bullets. However, if you choose to do so, a light crimp is best. Heavy caliber bullets (.375 and up) for large game require a heavy crimp, as do most revolver and lever-rifle loads.
From Barnes’ April 2007 Newsletter:
Question: When reloading magnum calibers with TSX Bullets, do I need to set up my die to add a factory-style crimp to prevent cartridges in the magazine from losing their grip on bullets under recoil? I have loaded short-action and long-action rounds without placing a crimp on the bullet, and have never had a problem. I have been told that reloading magnum cartridges is a whole new ball game. Any information you could give would be appreciated.Keep turning out those TSX Bullets and I will keep loading them. Thanks for the help.
—Randall Miles
Answer: In the past Barnes has recommended not crimping anything smaller than .375 caliber if proper neck tension is applied. However, there are exceptions to this rule. Cartridges used in autoloaders should be crimped to prevent bullet movement as the action cycles. Some of the light-for-caliber TSXs require crimping due to their short bearing surface. Sometimes a light or Lee factory crimp will improve accuracy in a standard or magnum cartridge. Finally, with some of the extreme magnum cartridges (e.g. .30-378, .338-378, etc.) it is a good practice to always crimp.
Ultimately, it is up to the shooter to determine what will yield the best results in his or her rifle.
Thanks for a great question.
—Ty
So it sounds like yes I should crimp.
And it sounds like I’ll need to buy a Lee Factory Crimp Die. Or do I? I found this article that shows yes in fact crimping makes some sort of difference. There’s this guy that doesn’t speak highly of crimping (for maximum accuracy). The more I Google around, there’s just a zillion opinions, of course. But one interesting thing that comes up is a lot of people don’t think much of Lee dies to begin with but do like their factory crimp dies. Go figure.
Given these will be shot out of an AR-15, I figure I should crimp. And it sounds like the roll crimp my RCBS dies will do isn’t going to be the best thing. *grumble grumble* More shopping to do.
Stuff From Hsoi 
FWIW, I’ve never crimped for my AR-15.
I *ALWAYS* use a factory crimp die on any loads that will be going into a magazine-fed auto/semi auto for one reason: stovepipes. The likelihood of getting a bullet mashed further into a case by rough impact with feed ramps due to all manner of potential failures (reduced tension/slow speed magazine spring being most common) is greatly increased by NOT crimping. I load for a select fire FN FNC as well as my ARs and I can tell you you DO want crimped rounds when you are firing at ~600rpm.
Theres a reason why all NATO spec ammo is crimped, its in part to protect against possible failures due to bullets impacting too low on the feed ramp and stovepiping, causing a jam. A properly crimped round may still result in a jam under those circumstances, but its less likely to result in a bullet pushed back into the neck of the case and powder spilling out all over the action.
Does it cause increased pressure? Yes, but not enough to warrant changing your loads if you are using standard NATO spec load data (which is written for crimped rounds anyway). Does it degrade accuracy? Maybe, but once again, not enough to really make any difference under normal specification. I load all my FMJ ammo to what I call minute-of-zombie accuracy spec. If I can still consistently ring a steel human torso target at 200m when firing point of aim (from either a bench or various field positions), the ammo is as accurate as it needs to be for the purpose I’ve designated. If you are loading ammo for 1000 yard pygmy prairie dog hunts, well, that’s another story.
Yeah, I’m not going for that amazing benchrest accuracy. Sure I’d like to have better results than with factory ammo (or at least as good as), but I’m not really a benchrest target shooter. As long as it can put down the deer or hog or 2-legged critter, that’s the main thing for me.
I do think it’s best for me to try the Lee factory crimp, especially since that’s coming right from Barnes themselves. They would know their bullets best.
I read about the case mouth tension and how that can often be enough… just all depends about the contrast between the diameter of the bullet vs. the diameter of the case mouth and if you’ll have the mouth small enough to hold it.
But that’s one thing with the Barnes is that with their 3 grooves they give a little less surface area to grip by tension alone. Barnes themselves are saying in a semi-auto to crimp.
So I am feeling I am going to have to buy a set of Lee dies to do the factory crimp.