Feeding and Extraction Issues

[squirrelsnpr]

I bought a 22PPC from this site and love it. The rifle is in a MAK tube gun chassis. It is set up to shoot the heavy 22 cal bullets (8 twist barrel) and as a repeater using AICS 308 mags.

The rifle came with two modified mags that don't feed well at all. The have a narrow spacer in the back and another in the front. The front spacer is shaped to assist the round into the chamber. Acting like a feed ramp. Any suggestions on how to set up the mags to feed flawlessly. I've heard of ARs shooting the PPC case so it must be possible.

2nd I am having an issue with pulling the round out of the chamber. I'm running a warm load of Benchmark powder (26.5 grains) but not getting excessive pressure signs. No flatened primmers (using Wolf SRMs) or hard bolt lift. Only expirencing tough extraction. I am using Redding dies that resize the body and control neck tension using the bushings. Using this die I am bumping the shoulder back by .002"

I did notice that some of the cases come out of the chamber with shinny marks on the end of the case neck walls. Almost as if they are touching the lands (?). I have the chamber measurement interts and can't recall needing to trim. Any suggestions?
Thanks,
Mitch. You can also email me at mhellis@att.net

 

[TRECustom]

Mitch, I don't have any experience with this combination of rifle and caliber, but I did have a case of a short neck chamber and I had to trim .040" shorter than SAAMI standard. All my problems went away. It took me way too long to diagnose, but was a simple fix. Can't hurt to try it.

Tom

 

[squirrelsnpr]

Anything I should be checking/taking measurements of to help diagnose?

I did take a measurement of the chamber with the inserts you put into your brass and close the bolt. I am approximately .025 short of this measurement. I did trim my brass to 1.500". This should be .040 from max chamber/neck length.

Should I be conserned about the cleanliness of the chamber or how the chamber was cut?

 

[TRECustom]

As I said, I'm not familiar with that cartridge or a tube gun, but if you have a chronograph, it won't hurt to compare actual velocity with expected load velocity. Higher than normal could still mean pressure. A pretty long shot, but.....

If you have a borescope or know someone with one, inspect your chamber, neck and throat with it.

Chamber cleanliness is critical to smooth extraction, and I've also heard of carbon ring buildup in the throat driving pressures up. Search this site for Sam Hall's bore cleaning procedure. He deals with the carbon ring issue.

Chances are that the chamber was cut well, so that's an unlikely cause, but the Hawkeye will tell you what the surface condition is. Also, something I do on a new chamber is measure a loaded round case length, length to shoulder, diameter at the shoulder, diameter about 1/4" in front of the base, and diameter of the neck. Then I fire that round and measure the same places on the fired case. Compare that to the reamer dimensions. On a good chamber, the diametral dimensions will be about .001" smaller than the reamer dimension, and the lengths may vary from .001" - .003" longer or shorter from the unfired case. Then chamber the fired case with the headstamp vertical, then at 90 degrees, 180 degrees, and at 270 degrees. A round, concentric chamber will close smoothly on the fired case in all four orientations. If the chamber is ovalled or off-center, it will not.

I don't know what action your rifle is built on, but if it has a spring-loaded ejector, that is the best indicator of excessive pressure. If there is a wide, bright, arc-shaped mark on the base of the cases, it's badly over-pressured. I keep bringing up pressure because it's probably the most common cause of hard bolt lift and extraction.

If nothing else, back the load off a couple of grains of powder and see if bolt lift / extraction gets easier. Also, if you are seating the bullet in the rifling, try backing it about .010" - .020" off the rifling.

Can't think of anything else at the moment.

Good luck, Tom

On edit: add backing the bullet off the rifling.

 

[squirrelsnpr]

Thanks for the suggestions. I have chrono'd my loads. With 26.5 grns of Benchmark, wolf SRM, 75 grn A-Maxs .005-.010 off the lands I'm getting right at 3150-3160 FPS. I am getting great results with this load and no pressure signs. The primers are starting to flatten, but they still have a good rounded edge to them. No hard bolt lift, just difficult extraction.

When I worked up this load I started around 24-25 grns of Benchmark. I was getting around 2900 FPS and believe I still expierenced had extraction.

I will take those measurements and give the rotating the brass thing a try. I'll also see about scoping the bore.
Thanks Again,
Mitch

 

[RJinTexas]

Please do let us know what you find is the problem.
RJ

 

[jonbearman]

Are you absolutely sure that the neck was cut as a no turn or tight neck? I will wait for your response or PM me would be better.I just went through this with a no turn neck.

 

[squirrelsnpr]

Oliver 88 check your PMs. I'm having trouble getting a hold of them.