Dangerous Rifle?

[eaglesnester]

I have a Remington P17 converted and re chambered to Norma 308 Magnum. Have been noticing groups opening with more and more flyer's some missing the paper completely at 100 yards while using a gun vise. My loads are mild only 1.5gr over recommended min. load in Speer volume 14 Reloading manual. Have also been getting unacceptable case stretching with incipient case head separation of my brass after only 1 or 2 re loadings. I have also had total case head separation of one shell.,I wear shooters glasses)
I took the rifle to my local gunsmith and he used a go, no go, gage on the chamber. When he tried the no go the bolt would not close and lock. When he tried the go,sup rise, sup rise)) the bolt would not close and lock. I had one deprimed unfired factory shell with me and he was able to chamber the round with no problem. My gunsmith said he had never seen such a thing before and was stumped. He is going to slug the barrel and bore and is sure that this will tell us whats up with the rifle. Any gunsmith types out there that could hazard a guess as to what may be going on with this rifle? At any rate I will not be shooting it under any circumstances until I find out and it is repaired.

 

[Atomic_Cowboy]

You probably already know this but it sounds like you are spiking the pressure if you are using a published load with a smaller volume chamber.

My 2 sense.lol

 

[Cheechako]

Sounds like you have a minimum chamber that will accept brass that is below minimum. But a minimum headspace chamber is not a cause for terrible groups and/or case seperations. That, as the Atomic Cowboy suggested, is probably the result of hot loads. Aggressive re-sizing of your brass is probably causing your case stretching. Use the shoulder to headspace on, not the belt.

Get a chronograph. Start below the minimum and work up from there. The chrono will tell you a lot about what is happening. A lot more than any of us can.

JMHO

Ray

 

[eaglesnester]

I am using RCBS full length resizing dies adjusted per their instructions. Screw die down until it touches the number 4 shell holder then turn down 1/8 to 1/4 inch for cam over on the resizing stroke. I also have a neck sizing die only and I use the neck sizer mostly so I don't think I am aggressively resizing my brass. As for loading below min powder loads Speer does not recommend this practice because of possible dangerous pressure spikes. I have a chronograph and my speeds are around 2740 using 67.5gr IMR4831 with a 200gr Speer SP. Min listed load is 66gr IMR4831 Max Load IMR4831 70gr. I do not know a great deal about guns, chamber sizes, etc. I just shoot them safely, kind of like the person who drives a car but knows nothing about how to fix em.

 

[2506]

Something does notsound right to me. I have a Speer book and it does list 66.0 grs. IMR 4831 as the start load for 200 gr bullets and 70.0 grs as max. But I have a new Hornady 7th edition book and it list for the 308 Norma Magnum with 190 gr bullets that 65.8 gr. IMR 4831 is the max load for 2900 fps. It list for 220 gr bullets 64 gr. IMR 4831 as the Max load.
My Sierra book list for 200 gr. bullets 70.5 grs IMR 4831 as the max load.
Who do you believe????
I think I would back off on the powder some more and see what happens. Or go to IMR 4350 or something.

I just had a thought. Have you trimmed your cases to the proper length. If your cases are too long it will spike your pressure and cause your bullets to go flying.

 

[eaglesnester]

All cases trimmed to 2.549 as per Speers Volume 14. After I get my rifle back from the gunsmith, if he can fix it, I will try different powder and download some more.

 

[Cheechako]

I am using RCBS full length resizing dies adjusted per their instructions. Screw die down until it touches the number 4 shell holder then turn down 1/8 to 1/4 inch for cam over on the resizing stroke.

Eagle

If you are sizing your brass that way you are very likely shortening it's life as evidenced by the stretching and seperations mentioned previously. Even though your cartridge headspaces on the belt,technically), you should size your brass only until it chambers easily, which means you are then headspacing on the shoulder instead. Bump the shoulder only the minimum amount necessary to assure smooth chambering.

JMHO

Ray

 

[Stonewall]

You need to measure your rifle chamber - fired brass and then set the die to push that shoulder back at most .002 .Consider this a rimless cartridge and ignore the belt for proper headspacing of cases in your rifle when setting up your dies.

This tool will give you a way to do this - possibly a .338 Win one could be modified to work.Call RCBS.

http://accurateshooter.wordpress.com/2007/06/20/adapting-rcbs-precision-mic-for-br-cases/

There is a lot of loading data out there for this fine cartridge and some of the older stuff is loaded to quite high pressure. Norma supplied reamers with freebore for gunsmiths to chamber rifles when that cartridge first came out. You chamber must match these specs to use the loading data.
Check out the current Shooting Times magazine for a great story on a Biesen custom .308 Norma rifle.

Clean the barrel -look for carbon in the throat.

Glenn

 

[MOO1072]

Check the throat length in your rifle. There is a lot of variation in this calibre. Some rifles have long throats and some have shorter throats. In some of the rifles with short throats its possible to spike pressures using Norma factory ammo. ,I read this on a post somewhere) I've currently got a project going in .308 Norma and went with a PTG reamer ground to Norma specs.

It may be possible for your gunsmith to turn a thread off and re cut the chamber in your rifle to standard Norma specs if your rifle has a short throat.