Thread: .17HMR bolt gun splitting cases

I have a Marlin .17 HMR that is splitting cases at the neck and part way down the shoulder, it's a bolt gun not semi, may have been doing it all along for all I know, the bloke that bought it seemed to have the need to closely examine cases and discovered the case carry on. I have never looked at the cases and I (and the wife) have put a few through and it gives good velocity, holds moa all the time, shoots different ammo to the same place. I know Marlin had issues with semi function and cases, but a bolt gun with factory ammo?

What the hell could be going on?, and how to fix?

If I were keeping it, I would not bother "fixing" anything, would just keep shooting it, it's not like you re use the cases.

Check the ammo (unfired) cases for cracks - hard to spot
Hm2 used to have that with certain batches

Use a light to check the necks etc

Its a common fault with the ammo, the brass hardens with age

The American forums covered the problem at length about 10yrs ago

Rimfirecentral.com has a 17hmr page, and you can read about the problem there.

A fresh batch of ammo fixes it.

I had some old CCI that did that. sent it back for some new stuff.

Yeah. Had the same thing happening for years in my CZ but only notice it when I look at the spent cases.
Solution. Don't look at the empty case.

It's a common issue with 17hmr's and certain batches of ammo have also had issues with split necks in loaded rounds still in the box from the factory before firing.
I suspect that the brass they use is worked a lot to neck down to 17 cal and consequently hardens quite a bit and then when fired in a chamber that has slightly larger tolerances, it will be more prone to splitting.
To fix it will probably require re-chambering with a reamer with tighter tolerances.
You could try different manufacturers of ammo to see if one has slightly thicker brass which may fix the problem, but I believe most is made by the same company and just rebranded.

Originally Posted by Matt2308

To fix it will probably require re-chambering with a reamer with tighter tolerances.

I've been down that road with a .17m2, in my experience if you've got a batch of ammo that splits then re-chambering doesn't solve it. Factory chamber, re-chamber of factory barrel done by Arthur Cleland, Clark Custom barrel from the states, custom barrel put together by Dean Maisey - all would split cases with certain lots of ammo. Other lots of ammo will be fine, and newer ammo is likely better.
I have seen split cases coinciding with low fliers on the target with a certain batch of ammo, but most of the time the split doesn't seem to have any effect.
All .17hmr is manufactured by ATK (CCI), other than Winchester. Sellier & Bellot used to make it too but dropped it.

I see a fuckton of .17 cases at the range that are split at mouth and/or neck when I'm cleaning up. Be interesting to see some pics of inside the chamber after a clean. Small place to get a camera into. Might take a borescope along next time and ask if I can do some back end photography hahaha

Was talking the the my gun smith about this problem.
One of the gamekeepers came in with one that had gone and done more than split.
If I recall he fired one round missed and went to fire the next, bullet from the first round (split case on the first round which he recovered after the incident) had not left the barrel so the second blew the bolt. He was lucky in that the cz bolt held and all he ended up with was a burn coat sleeve and beard
After seeing this my dreams of .17hmr went out the window and I brought a cz .22mag.

With the cases it's something to do with not being able to harden/ anneal them during the loading process? This is because the round is so small. They can still do this with .22 rounds.

Something along those lines.

I'll ask me Smith if he has any pics. I think you guys will be interested.

Oh my smiths advise was check all rounds and if badly split then don't use ie if the split is on the shoulder. On the neck seems to be ok.

But I'm sticking with my mag

Case is necked after priming so annealing is not possible, as they arent reloadable and it dosnt seem to affect accuracy does it really matter ?

Firing cci ammo? I have seen then cracked before firing and seems to be common with them. I've fired plenty of Hornady without any issues

Sent from my workbench

A couple months ago I went to my local h&f to get some Hornady and they didn't have any but the sales bloke said he had some cci. Was like "nah that stuff is shit" but he tried again to convince me to get some and even went it the back and got a bag of loose rounds so I pulled them out and looked closely and found two rounds already cracked. Brad at the store had told me in the past about cci doing that and damaging guns beyond repair, that's how I knew about them

Sent from my workbench

I get splits, as I don't seem to notice any affect on accuracy or gas coming back through the action(I taped very light tissue paper around the bolt to check) I have fixed the issue by not looking closely at the cases.

I can understand why someone who just bought a rifle would bring it to the sellers attention but I don't think he has anything to worry about

I'd like to know if moisture would get in? Like when it's raining?
Could maybe end up with hang fire due to wet powder?

Originally Posted by Sideshow

I'd like to know if moisture would get in? Like when it's raining?
Could maybe end up with hang fire due to wet powder?

Just keep them dry, but it's a good point