Interarms Mark X issues

[682bear]

A couple of weeks ago, I purchased a decent Mark X 30.06. Upon firing it the first time, I discovered that the primers are backing out of the cases approximately .020. I initially assumed that excessive headspace was the problem, but I borrowed a set of headspace guages and checked it, The headspace is well within limits.

So, I reassembled the gun and took it out to shoot it again. Every shot resulted in a peirced primer, and the accuracy was @ 4 inches at 100 yards. Would peirced primers result in a loss of accuracy?

After I returned home, I removed the firing pin and checked the tip under a magnifying glass. It was almost flat on the end, and appeared to be made that way. it had a sharp shoulder all the way around the tip and just a very small crown. When the bolt is de-cocked, the firing pin protrudes approximately .070.

The ammo I am shooting is my reloads, consisting of Lake City brass loaded with a 168 grain Sierra Matchking bullet and 45 grains of IMR 4064. The primer is a Winchester large rifle primer.

Also, the cases that I have fired were originally trimmed to 2.494, but after firing are now at 2.481.

Does this gun have two seperate problems, one causing the primers to be pushed back and one thats causing the peirced primers, or is it the same issue? I'm leaning toword one problem causing both symptoms...

Can anyone give me any insight on what may be happening here?

Thanks -Bear

 

[mapsjanhere]

I guess some more load development is in order. 45 gr of 4064 is on the very low end according to Hodgdon's data for 168 gr bullets. So you shouldn't see overpressure unless you're OAL is too long and your bullet sits against the lands. Did you check the correct lands offset for that rifle?

 

[Scorch]

Sounds like two issues:
1- Your reloads are shorter than the chamber and develop relatively low pressure, causing the primers to back out. Primers backing out is often seen in low-pressure loads because the low pressure does not fully expand the brass to fill the chamber and re-seat the primers.
a- Increase your load. Refer to a good reloading manual.
b- Check the distance to the lands when the bullet is seated, or load to SAAMI OAL specs.

2- The squared-off end on the firing pin may be causing the pierced primers. I would radius the end, making sure it is very smooth. Protrusion should be .058"-.065".

In addition, check the action screws to make sure they are tight and that the bedding is even and no areas bearing on the sides of the barrel. Check the scope bases and rings to make sure they are tight and not moving under recoil.

 

[682bear]

I used 45 grains of 4064 because my load manual recommends starting below their minimum load when using military brass. Their minimum load was 46, so I loaded these at 45 grains. I agree that this is definately part of the problem. This ammo was loaded to SAAMI OAL specs.

I chucked the firing pin up in a lathe and used a stone to polish a smooth radius on the end.

I took it out again this morning and fired @ 20 rounds through it. I did not have any more punctured primersand the primers only set back around .005, but I could not get it to group better than 2.5 inches at 100 yards. I shot 2 different types of ammo, Remington 150 gr core lokt,(4 inch groups at 100) and another of my reloads, which was made up of Remington brass, 165 gr JSP, with 55 grains of AA 3100. This load shot the best so far,(2.5 at 100), but still was not up to my standards.

The action is not bedded, I know that will help a lot, but I'm not going to bed it until I decide whether I am going to re-barrel it. I actually bought it to put up for a future project gun, but wanted to see what it is capable of doing as is. I guess some time at the loading bench is in my near future...

Thanks again, guys.

-Bear

 

[oneoldsap]

I have never heard of cases getting shorter after firing ! The trim to length for the 30-06 is 2.484 , 2.494 is the Max length .

 

[hoghunting]

This load shot the best so far,(2.5 at 100), but still was not up to my standards.

Have you worked up different loads for this rifle or did you pick two different loads from a manual? It usually takes different powders, different powder loadings and different OAL to finally get an accurate load.

 

[682bear]

Actually, what I have been shooting in this rifle is loads that I have worked up for my other 8 30.06 rifles. I know they are probably not going to be ideal for this rifle, but thats what I have on hand...

The first load I listed using the Lake City brass shoots great in my m1, and the last load is very accurate in my 03-a3.

I actually have more 30.06 ammo stockpiled than I'm probably ever gonna use, but that won't stop me from loading more... I'm an ammo junky, I guess. I have somewhere around 2000 rounds of .44 mag handloads and only shoot 30-50 rounds per year!

-Bear

 

[hooligan1]

Try IMR 4350, it's worked for me in a couple 30-06's to 1/2 moa and no signs of excessive pressures. I load the 150 grn B-Tip from Nosler with 57.5 to 58 grns of IMR 4350, with amazing accuracy out of a Savage 111, and a Remington 700, respectively. start low and work up, be safe.