Case Seperation after 3 firings?????

[Raptor]

I am at my wits end with a new rifle. I had a 6.5x55 built and have over 300rds through it and can still not find a load this thing will shoot consistantly. Now I am getting case seperation on my new Lapua brass!!! I have a line all the way around the case on this last batch of rounds I shot. Its approximatly .600 up from the base. This is the 3rd firing on these cases.

When I started loading for it I had some extractor marks on the cases but no stiff bolt lift or loose primers. The loads I was shooting were not suppose to be hot. I was shooting from 47 to 49.5grs of N-165 and 46 to 49.5grs of H4831, and 46 to 48.5 of RL-22 which I thought was the hottest loads and left the heaviest marks on the cases.

I am also at .020 case streach on most of these cases. I can feel the grove around the inside of the case with a small pick.
This gun is driving me nuts!!! It is inconsistant and will not shoot the same groups more than twice!! I think I have a good load and it won't hardly shoot it into an inch the next time out.

I have tried it at 100 out to 600yds all with mixed results. I thought it might me the day or me so I took along my 260 and shot some groups with it at 400yds as a benchmark. It shot groups in the 1.5 to 2" the 6.5x55 would do around 2 to 3.5" then one or load would shoot right with the 260 so I would try it again and then it would be all over the place again.

As an example I tried some H4350, a load of 45grs shot .355 and .400 for 5 shot @ 100yds so I think great I got a good load. So I load up 15 and go try it again. I get 3 in a cluster and two out low left next group is horzontal across the paper next group sucks too. All three had flyers and were in the .8 to 1" range. But a group of 44.5 shot 4 shots into 1.25" at 400yd!!!! Now the same load was a .9 at 100yds and if I load up 15 more and go try them they will probabaly be all over the damn paper too. I am ready to use this thing for a tomato stake.

SO... bottom line do you think I have a chamber problem??? Thanks guys!!!

 

[SF340Driver]

What is your resizing procedure? Neck only? FL? If FL, how much are you setting the shoulder back? How are you checking setback?

Case head separations are usually related to setting the shoulder back too far when resizing. It can also happen if the chamber is cut too deep, but this is usually seen after the first firing.

 

[Raptor]

I am full length sizing. I set the die so it sizes most of the neck. Its backed off just a tad from what the manufactuer recommends.

Would the hot loadings have damaged the cases enough to cause the case seperation??

 

[Preacher]

You can bet a hot load will stretch your cases out a lot and in the process cause the separation. Forget the die manufactures suggestion and set your FL die up so you just have a tiny bit of resistance when you close the bolt without the firing pin assembly in it.
If the empty bolt just falls of it's own free will on a inserted case you have FL sized it to much.
It really sounds like your sizing your brass a bit to much for it's own good.

 

[ChuckMiller]

I've got a friend with a 6.5-284 that had the same problem. Lapua brass, by the third firing he would go to extract the case and it looked like he was pulling out a 45ACP. He was using Wilson FL dies in an arbor press. Turns out he was pushing the shoulder too far back and creating 12-14thou of headspace. He was touting the virtues of his Stolle action and how smooth it closed, Ha!

 

[SF340Driver]

I am full length sizing. I set the die so it sizes most of the neck. Its backed off just a tad from what the manufactuer recommends.

Would the hot loadings have damaged the cases enough to cause the case seperation??

The hot loads will cause a primer pocket to loosen or blow out,way too hot).

The case head separations are due to pushing the shoulder back too far. Stoney Point makes a tool for measuring the base to shoulder distance that fits on your calipers. Measure a fired case and adjust the die to resize and push the shoulder back no more than 0.002".

 

[Raptor]

Thanks guys I will reset my die tonight and see if that helps. It just makes me sick to toss close to 100rds of Lapua brass!!

 

[SF340Driver]

Thanks guys I will reset my die tonight and see if that helps. It just makes me sick to toss close to 100rds of Lapua brass!!

The problem is that the damage is already done. If you can feel the ridge inside the case using a toothpick or paperclip I would toss it and get new brass -- it will separate on the next firing. I highly recommend getting the StoneyPoint HS guage I mentioned earlier. It's a cheep investment compared to brass that only lasts three shots. I get 30+ reloadings out of Lapua brass and I FL size every time.

 

[StephenPerry]

Raptor
My take on this is you need to learn how to fire form brass. You probably never achieved a full fire forming and had have created a false shoulder on your brass. I don't lnow if all your cases have 3 firings but you will never reach a full fire forming if not done properly at the beginning. The rest of your cases will fail if you sized all the same way. Get rid of the brass start with new and do things right you will be much happier Nothing is wrong with your chamber new brass if fireformed correctly will form to fit correctly. I wrote a fireforming Thread earlier check the pages for it. No charge for the info.
Stephen Perry

 

[Raptor]

Thanks for replys guys!! It was definatly my die doing it. I learned a hard lesson on this go around!! I have never had this happen before and I still don't know why its doing it. I set the die according to the inst. like I always have and have never had any problems.

This is the first time I have had this happen other than when I had bought some used military brass for my M1A and could not get it to chamber so I really sized it down. I knew I was under sizing it then, but not this time.

I guess this is a hard lesson learned. After I get my load developed I usually go back and fine tune my die to where it sizes the brass so I can just feel a slight drag on the brass. I was in a hurry to get this done because of the weather turning cold so I didn't pay as close of attention as I should have and now I payed the price!!! Thanks again for the help!!!!!!!