Case bulge/splitting on rim-fire ammo?

[AMT]

I am wondering what would cause the case(s) to bulge on the end of the rim-fire ammo on this 17HMR ammo? (I hope you can see the few rounds that have bulged ends in the picts.). It happened with a few different rounds from a couple different manufacturers, and different types of loads.

The Winchester rounds were the only rounds that split. The Winchester rounds did not bulge. The CCI and Hornady did NOT split but they had bulged ends.

I am guessing that the only way this can happen is from the pressure inside the barrel, between the back of the case and the bullet as, as the bullet is travelling down the barrel. Once the bullet leaves the end of the barrel the pressure drops to near zero almost instantaneously (at least within a fraction of a second).

I shot a total of [maybe] 20 various 17HMR rounds. These 10 (or so rounds) are the only ones with "issues". I was at ecstatic to see that none of them had the back end blown off (or ripped off during ejection).

These are being shot out of a semi auto pistol. 6 inch barrel. Stainless steel - NO PLASTIC or POLYMER on it except for the grips.

Anyone with more knowledge of ballistics and the way things work, please chime in. I am working on a project and would like to know if I can eliminate this from happening.

I am thinking a stiffer recoil spring to keep the slide against the back of the shell longer? Until full action to eject the shell?

While shooting, it did not seem "violent" when the slide was working on ejection and loading the next round. If it were "violent" I would assume that the gun was being beat up and a stiffer spring would be a must. This wasn't the case, and everything felt normal.

Any help is appreciated.

I am going to be getting a chrono from Santa this year. I can't compare printed velocities with what I am actually shooting from my gun, yet, but I will be able to after Christmas. I would assume that higher pressures (in my gun) would show higher velocities than printed on the ammo boxes?

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[jordanka16]

I'm assuming this is a blowback and not a locked breech semi auto? If so they are probably extracting while pressure is too high causing stress to the cases and making them split or bulge. Heavier bolt (slide) or stronger spring should help.

 

[ageingstudent]

I'm assuming this is a blowback and not a locked breech semi auto? If so they are probably extracting while pressure is too high causing stress to the cases and making them split or bulge. Heavier bolt (slide) or stronger spring should help.

Those Winchesters look like brittle brass. Almost looks like a bad annealing job. If it's a blowback action the other two brands do look like early extraction.

 

[ma96782]

"These are being shot out of a semi auto pistol. 6 inch barrel. Stainless steel - NO PLASTIC or POLYMER on it except for the grips."

I would suspect the pistol has a lot to do with what you are seeing. But then, the ammo could also be "defective". Of course, the ammo manufacturers don't like to admit that their ammo is "defective".

Funny.....
But you didn't mention the pistol manufacturer by name. 17 HMR pistol......does it fire from a locked bolt/breech? Or is it totally dependent on the bolt weight and spring pressure to keep the bolt closed?

Anyway.....take a look. This was with Hornady (First Production Run) and with CCI .17 Mach 2 ammo in a converted Ruger 10/22. Fun times huh?








Aloha, Mark

PS.....my solution was "better ammo" and to clean my rifle more frequently.

 

[Member 34319]

I've shot all three of those out of my bolt action and can tell you one thing, that's 100% semi auto related.

I'm gonna guess this pistol has fallen prey to all semi auto 17s, the dreaded pressure issues.

I'm gonna guess it's the Excel Arms Accelerator? Asthats the only 17hmr semi auto pistol I know of that was produced. If you do a search online you'll find they all had issues with chamber pressures blowing up cases.

Only 17hmr semi I know of that does not have these issues is the A17 by Savage. As it has a delayed blowback design.

 

[AMT]

I am actually working on a re-barrel (new barrel) option for my AMT-II pistol. The 22WMR works perfect, i just want something "different". If i can get this "figured out" i may opt for a threaded barrel too.

I know it has to be pressure build up related, just curious how to correct it.

Jordanka16, I was also thinking going to stiffer recoil spring and see what happens.

Any and all help is greatly appreciated!

 

[AMT]

I've shot all three of those out of my bolt action and can tell you one thing, that's 100% semi auto related.

I'm gonna guess this pistol has fallen prey to all semi auto 17s, the dreaded pressure issues.

I'm gonna guess it's the Excel Arms Accelerator? Asthats the only 17hmr semi auto pistol I know of that was produced. If you do a search online you'll find they all had issues with chamber pressures blowing up cases.

Only 17hmr semi I know of that does not have these issues is the A17 by Savage. As it has a delayed blowback design.

When i fist got this wild idea i did as much digging as i could. I could find CUP pressure for 22WMR, but could only find PSI pressure for 17HMR. i could not find a way to convert the 2 findings so i could compare CUP to CUP, or PSI to PSI. So I'm winging it and hoping for the best. So far, these few "issues" are the only thing i've run into.

I have come to the conclusion that i will continue to test the Winchesters, but may not use them as a "routine" round to use.

Thank you for your input. It is appreciated.

 

[AMT]

"These are being shot out of a semi auto pistol. 6 inch barrel. Stainless steel - NO PLASTIC or POLYMER on it except for the grips."

I would suspect the pistol has a lot to do with what you are seeing. But then, the ammo could also be "defective". Of course, the ammo manufacturers don't like to admit that their ammo is "defective".

Funny.....
But you didn't mention the pistol manufacturer by name. 17 HMR pistol......does it fire from a locked bolt/breech? Or is it totally dependent on the bolt weight and spring pressure to keep the bolt closed?

Anyway.....take a look. This was with Hornady (First Production Run) and with CCI .17 Mach 2 ammo in a converted Ruger 10/22. Fun times huh?

View attachment 524410
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Aloha, Mark

PS.....my solution was "better ammo" and to clean my rifle more frequently.

This is one of those "clean the shorts after that" times?

 

[Member 34319]

If you can do something like Savage that would be best. Otherwise it's a game of weighted slide and heavier springs.

 

[Member 34319]

When i fist got this wild idea i did as much digging as i could. I could find CUP pressure for 22WMR, but could only find PSI pressure for 17HMR. i could not find a way to convert the 2 findings so i could compare CUP to CUP, or PSI to PSI. So I'm winging it and hoping for the best. So far, these few "issues" are the only thing i've run into.

I have come to the conclusion that i will continue to test the Winchesters, but may not use them as a "routine" round to use.

Thank you for your input. It is appreciated.

Reading something about why no semis for 17 existed, before the A17, I recall it having to do with the time the pressure occurs vs peak pressure. 17s peak pressure isn't too much over the 22mag, but it's curve is longer and has higher pressure for a longer period of time.

 

[AMT]

Reading something about why no semis for 17 existed, before the A17, I recall it having to do with the time the pressure occurs vs peak pressure. 17s peak pressure isn't too much over the 22mag, but it's curve is longer and has higher pressure for a longer period of time.

Odd, as i assumed the heavier 22 bullet would take longer to exit the barrel - because its heavier and slower fps. This would allow higher pressure build up in the barrel cavity because the area is greater. With a lighter 17 bullet, and faster fps, i assume the pressure would peak faster, but not remain as long in the barrel.

I thought about a garden hose. Imagine a 22 nozzle and the water stream. Then imagine a 17 nozzle and its stream. The pressure build up waiting to "escape" is greater. This is my thinking of heavier spring as jordan mentioned too.

I will have to poke around more and see what tests were done, what comparisons, what barrel lengths, annd what firearms.

That Excel Arms slide doesn't look like much mass. The AMT-II has a fairly beefy stainless steel slide (maybe not beefy enough?). I'd like to see what sort of bolt the A17 has, and how heavy it is for comparison.

I guess prototyping is a lot of thinking, a little luck, and a whole lot of hit-and-miss?

Again, thank you for your help!

 

[coyoteman5]

On my Remington 597 17 HMR Semi auto I too had split cases bulging cases and it's due to bolt timing and the 17 HMR high-pressure so I bought a 22 mag barrel for it and that one away and I converted my bolt action 22 mag into my 17 HMR bolt action.

 

[Member 34319]

Odd, as i assumed the heavier 22 bullet would take longer to exit the barrel - because its heavier and slower fps. This would allow higher pressure build up in the barrel cavity because the area is greater. With a lighter 17 bullet, and faster fps, i assume the pressure would peak faster, but not remain as long in the barrel.

I thought about a garden hose. Imagine a 22 nozzle and the water stream. Then imagine a 17 nozzle and its stream. The pressure build up waiting to "escape" is greater. This is my thinking of heavier spring as jordan mentioned too.

I will have to poke around more and see what tests were done, what comparisons, what barrel lengths, annd what firearms.

That Excel Arms slide doesn't look like much mass. The AMT-II has a fairly beefy stainless steel slide (maybe not beefy enough?). I'd like to see what sort of bolt the A17 has, and how heavy it is for comparison.

I guess prototyping is a lot of thinking, a little luck, and a whole lot of hit-and-miss?

Again, thank you for your help!

Your hose analogy it makes sense, at least in my head.

A 22lr and mag is a straight walled case so the pressure builds and drops, in my head, linearly.

17hmr is bottle necked, so again in my head, all the pressure is in the case as it is pushing the bullet through the neck and down the barrel

 

[jordanka16]

Your hose analogy it makes sense, at least in my head.

A 22lr and mag is a straight walled case so the pressure builds and drops, in my head, linearly.

17hmr is bottle necked, so again in my head, all the pressure is in the case as it is pushing the bullet through the neck and down the barrel

The biggest problem with the 17 or any bottlenecked case in a blowback is that as soon as the case moves any at all, a lot of space opens up around the neck and since there is still pressure it often results in split cases or outright failure. This is why the A17 is delayed blowback and why straight .22 mag to .17 conversions don't often work.

I would run the heaviest spring you can that it will still cycle with, that will probably help a lot.

 

[edzz]

Use rings cut in chamber to retard blowback? Heaver hammer spring to delay slide?

 

[po18guy]

The CCI and Hornady look like the slide might not have been completely in battery when fired - as if it was closed enough that the disconnector was not activated and allowed the hammer to fall, but still not up against the base of the cartridge. The longitudinal splitting (W-W) looks like either brittle brass or a borderline large chamber. Were these rounds cleaned or polished with anything?

Better pics and emails to the manufacturers will undoubtedly lead to some good answers. All of this points to a weapon problem. As well, it might be time for a chamber cast.

 

[Member 5605]

I saw a guy at the rage last week who had this issue from a bolt rifle.

His ammo was some older stuff about 10 years old he said.

 

[Lilhigbee]

I have two friends and one of their friends with Volquartzen .17HMR semi-auto rifles and all three have this problem and all three have sent them back to Volquartzen more than once. I don't know what-all Volquartzen has done to try and fix them, but they have not been successful. @AMT good luck in your quest to fix it. If you are successful there are a lot of people who would be grateful for the information!!