Does anyone have an idea why cases would dent? Most were on the shoulder but a few are farther back on the case. These were all shot from a rossi youth model .243.
Brass: new hornady
primer: cci large rifle
powder: imr 4350 39 grains
bullet: sierra 85gr bthp
At first I loaded them to 2.700 oal and 2 out of 19 dented but I didn't notice. The gun shot all over the place which I later found out is common with these. After a little researching I found that these rifles have a long throat on them. I made some dummy rounds and found that i could go to 2.750".
I loaded a few different lengths with the longest being 2.735".
while shooting these different lengths is when I forst noticed the dents so I looked at the first ones shot then. I also tried shorter ones going as low as 2.665". The dents seemed to be more common then.
A friend of mine thinks that maybe the shoulder angle in the chamber is off allowing gas to blow back and the weakest point is denting. they are not always at the same spot ( position on a clock).
I was also wondering if it could be a slight secondary explosion. These are minimum charges and I'm starting to think that 4350 may be a little on the slower side for the 243 case.

Sorry it's a long post. Will put up pictures if I can figure out how.

too much lube can do it

quote:

too much lube can do it

Yep during sizing. I read it as he is getting the dents from firing.

After firing? I checked all cases after i noticed they were dented because my dad told me that he had some dent before from too much lube. But he said they dented while loading. Mine are doing it from firing.
This gun is for my son so I'm not really thrilled with the problem. Not going to let him shoot it until i figure it out.

Post a picture; no it is definitely not a secondary explosion; you are reading too much internet. Case lube, or powder grains in the chamber, will cause it.
Or you are creating them with too much lube and your chamber pressures are too low to iron them out.
Are your necks black from soot; if so, you are not obtruating enough, so go to a hotter load.
I would not expect any rifle to "shoot all over the place". If it is doing that, there are other issues. I guarantee the shoulder angle is not "off" and even if it was, that would not cause dents.
Post a picture, but don't overreact.
Put your pics on photo bucket and then click on the IMG link. Then just paste here.

If you are getting dents in the case during firing you have a combination of a very low pressure load and cases that have hard necks.The brass in the neck area is supposed to annealed so it is quite soft. When the primer ignites the powder and pressure starts to rise the soft brass neck is supposed to expand and form the gas seal between the outside of the case and the barrel. If the case is too hard and doesn't expand gas sneaks past the neck and creates a dimple back around the shoulder or even further back. If you can lay hands on an old Speer # 9 loading manual they show pictures of this and talk about it on page 57. I wouls suggest annealing the case necks and increasing the powder charge in your light load.

Hopefully this worked
[IMG]http://i1376.photobucket.com/albums/ah27/smcguy2/Mobile%20Uploads/20160928_212342_zpsvtz8dmxh.jpg"> [/IMG]

There does seem to be a lot of soot on the cases. Less so on the ones that were loaded longer.

It's the link at the bottom of the 4 choices on PB.

Wrong powder for light loads. Well below minimum charge according to one manual, seven grains below max. When you don't have enough powder results like you experience(d) do exactly what those pics show.

If the rifle handles factory ammo fine, it's the load.

I try to load a powder that gives me at least 80% fill in the case. If the case is not filled enough you will suffer from ignition problems.

You can do a search for successful light loads for the 243. The 250 Savage is a great cartridge for recoil sensitive youngsters.

Joe

That is supposed to be minimum load according to the old sierra manual. I was thinking about making them a little higher anyways so that will be my next step. I haven't shot any factory loads because I wanted lighter loads for my son since he has only shot 22 before. What manual did you use? My dads is probably 20 years old.

Thanks for all the info guys. I'll repost after I try higher loads but it might be a couple weeks.

Yikes; you weren't kidding; those aren't dents, those are massive CRATERS. Yes, it is caused by gas; nothing about your rifle at all. Use more powder; you aren't obturating your brass; might need annealing but try more powder first.
Oh, a 20 year manual is new to me; most of mine are twice that old. If you want light loads, use a faster powder. Get Ken Waters Pet Loads books.

My old Speer #10 shows a minimum load of 41gr of 4350 with 85gr bullet.

Use 18 grains IMR 4198 with a flatbase 105-grainer. Not much more "pop" than a .22 LR and the piggies I shot with them couldn't tell the difference (6mm Remington). Do NOT use boat tails!!

Underpowered:

This is classic under ignition and very poor powder load choice. This could easily lead to S.E.E. (Secondary Explosion Effect).
I don't have my manual in front of me, but, you definitely need to up the powder charge.
I saw this once myself, in 3 7RUM's, no data was available, so we extrapolated, poorly, from other cartridges. Had exact same dents and soot as your cases.

Cheers.

Curiously, I saw the same effect with .375 Wby loads, traced to recoil jamming the bullets in loaded magazine too far into the case for obturation to occur. (That's why I now select loads that yield compressed to semi-compressed loads and crimp at the cannelure -- not necessary for .243 diameter rounds, tho...

I have some photocopied Sierra loading manual pages from about 1998--IMR4350 shows a minimum load of 37.4gr for 2,800fps in this version for 80-85gr bullets. The 90gr FMJ has a start load of 37gr of the same powder.

The OP hasn't stated if he tried any other ammo or handloads that I can see unless I missed that. It would be interesting to note what any other fired loads/ammo looked like.

Is this a new to you rifle?

Does it start doing this on the first shot with a clean bore and chamber, or does it take several shots before the shoulder/body dents occur?

Without any other information, I would cast the chamber (Cerrosafe) and see if maybe the neck or portions of the chamber are too large. It's clear that the dented cases' shots were not sealing off at the neck, at a minimum. But why?

Because his pressure is too low to obturate that brass. ; I guarantee his chamber is not to big. The brass should fill it regardless.

I finally got up to my dads to load a few more shells. Double checked the manual first, the sierra manual does list 37.4 grains of imr 4350 as minimum load but their new manual lists 39.6 grains. I loaded the rest of the cases I had at 41 grains and 2.675" which was the length that had given me the best group before. Now I just need to get out this week to make sure everything is ok since the youth hunt is next weekend.
My brother had also bought some winchester factory loads and only shot 6 of them, but none dented.

Are you sure these dents did not occur when the cases were ejected and struck the ground? I had this happen to me once and I thought they were dented from feeding and all it was, was the cases striking the ground.I am pretty sure the dents were caused by the cases striking the ground.

Positive. The last couple I shot I checked every case before putting them in. Set them in the chamber the exact same way and then pulled the shells out to look at them. The cases don't actually eject you have to physically pull them out. I did that so I could see if they occurred at the same position but they didn't.

I can assure you that it is caused by under-ignition of a too low density of slow powder.
The 243 (yuck) is notorious for pressure problems, either what you're experiencing, then with the same load, it goes to grenadeville cause a bullet starts and stops in the bore, very bad.
There really is no need in modern guns to start 10% below max, 5% is adequate. Powder is held to 3% variation, +/- 1.5% across lots.

The soot is a dead giveaway, it's telling you that the case/load is not making enough pressure to seal the chamber.

Cheers.

I shot the ok ones I had loaded up yesterday and everything is ok now.
Thanks for all the help guys