Why do semi-autos handle ammo differently?

[Bewaffnet]

I keep hearing about how semi-autos are fussy with ammo. One gun will fire a certain brand of ammo flawlessly while another gun of the same make and model will fire that ammo inaccurately or with numerous jams. Anyone know why this is? I've always wondered about this.

[jdonovan]

remember 'flawless' is in the eye of the beholder. I saw a guy at the range who comment that his Jerico was great, and fairly reliable. "It only jams 1x per mag". I guess I just have a different standard as to what 'great' is.

Many of the lower price ammo brands have less stringent quality control, and/or allow a greater variety in what range of tolerances are OK to ship.

Maintenance, care, lubrication all play a part.

[m4a1mustang]

remember 'flawless' is in the eye of the beholder. I saw a guy at the range who comment that his Jerico was great, and fairly reliable. "It only jams 1x per mag". I guess I just have a different standard as to what 'great' is.

Many of the lower price ammo brands have less stringent quality control, and/or allow a greater variety in what range of tolerances are OK to ship.

Maintenance, care, lubrication all play a part.

This.

Operator error can also lead to feeding problems.

In the 1000s of rounds I've fired out of my Glocks they've fed everything you could throw at them. Round nose, flat nose, JHPs of all type... it didn't matter it fed fine. However I have had problems with Sellier & Bellot primers so I don't buy that brand anymore.

[Sensai]

There are a lot of variables in the basic operation of an automatic/semiautomatic firearm, so your question doesn't have one easy answer.

Basically with blowback operated firearms (mostly 22 rimfire) the recoil operates the bolt. Besides the mass (weight) of the bolt, there is a recoil spring that returns the bolt to battery. Both the bolt mass and spring strength are tuned for a particular recoil for proper operation. Anything that causes the recoil to be different will cause the bolt travel to be different in speed and distance. Even the type of lube used and the gun cleanliness can cause a performance difference.

Delayed recoil, like the handguns, are along the same lines as the blowbacks. The big difference is that the barrel and slide are locked together for the first part of the slide travel. The slide mass and return spring tension are still major players in the proper operation of these guns.

With gas operated systems, like most semiauto rifles, the pressure at the gas port on the barrel is the driving force for the bolt. There are at least two different systems of getting this force to the bolt, but basically the pressure at the port is the primary variable. This pressure can be influenced by a different type of powder, a different weight or shape of bullet, even ambient temperature.

This is just a minor introduction to the wonderful world of finicky autos, but it's enough to show that there's a lot more that goes into that auto feeding the next round than a bolt, lever or pump action user has to contend with.

I really hope that this helps in some way to answer your question, or at least get you headed toward an answer.

[Jakeiscrazy]

And to some degree there's a lot of nonsense. My M&P has run everything I've shot thru it no problem same is true with most quality semi autos that friends have. Its only some of the smaller guns that tend to have ammo problems.

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[Sensai]

I hope that my reply didn't seem like "nonsense". Jake is right about one thing, as a general rule the higher quality firearms have a wider range of accepable ammo to use. I wasn't trying to get into the quality of different brands, I was just trying to state some of the reasons for different guns having problems with different ammo. I've had S&W's that would only reliably shoot a few different loads of ammo, and Taurus's that would take just about anything. Go figure! But these were exceptions, not the rule.

[Bewaffnet]

Thanks one and all for the feedback. I guess the primary culprit is the way the ammo is manufactored and not so much the gun. The issue looks to be one of those "go figure" things that help to make guns so interesting.

Thanks again everyone and happy shooting!

[M1A4ME]

While it may be pretty obvious that different models/brands of guns will operate differently due to design differences or difference in materials of construction its also true that the same brand and model can be "different".

Remember, a gun is a manufactured item. Due to manufacturing/machining differences (nothing is perfect - parts are allowed to fit within a range of lengths, widths, depths, diameters, etc. and still meet specifications) and even wear of the tools the parts are made with it is not only possible, but likely, that if you bought 3 guns off the rack side by side of the same brand, model, caliber, you would find that one "liked" different ammo than the others, one was more accurate than the others, one was more reliable than the others, one would be "the best".