Help me while I wait on a go-gauge - 300 prc brass

[mattwill00]

So I got a brux barrel chambered by kelbly in 300 prc to put on an atlas tactical action. This was a “pre-fit” application if that makes a difference (action was already in my hands). I went ahead and started breaking in the barrel with a mild-ish load of retumbo under a 200 gr eldx with adg brass. At first I noticed a slight amount of pressure while chambering the virgin brass. I didn’t have to force the bolt down or anything but it’s definitely tight. My thought was maybe the adg brass was just a little large, and maybe the chamber a little small.

I went ahead and have shot 40ish rounds through the rifle with no signs of pressure at all. Brass prep was just chamfer/de-burr and running a mandrel to straighten the necks out. Last outing I had two round that refused to chamber. Also, the brass does not grow at all (in fact shrinks). Im beginning to think it’s the chamber job on this barrel. I’ll post a few numbers here. Let me know how these compare to your 300 prc brass and if I should be worried. Relatively new to putting rifles together btw. Have a go gauge coming from ptg, but I want to hear some other opinions here.

Unfired ADG:
Neck: 0.3335
Web: 0.5270
Base to datum: 2.194
OAL: 2.572

1x fired ADG:
Neck: 0.3415
Web: 0.5305
Base to datum: 2.1925
OAL: 2.571

Also here’s a pic of the base to datum on the rounds that don’t chamber.

 

[NevadaMike]

Rookie reloader here. I had a similar problem with ammo I loaded for a friends 30-06. I had not seated the primers fully so they were standing proud. You really had to look as it was not obvious.

 

[Wrench]

Is there any chance that you are seating with too much case crimp?

Screw the die body out 1 turn and make up the difference with the seater stem and see how it fits.

A shoulder swell can and does happen if the process is not correct.

 

[mattwill00]

Problem is the brass itself chambers a little tight without a bullet in it. Also I’m using a forester micrometer seater die seated one full turn out, and neck tension is .003. None of the rounds have been hard to seat.

I guess I’m confused on the shoulder swell. Are you saying I’m seating with too much tension, and that is crushing the shoulder, widening the junction between straight wall and shoulder? I would think this would shrink the base to datum, which in this case the base to datum is longer than the other brass by .004. Let me know if I’m way off track here. I also measured the shoulder junction and they are the same on the rounds that won’t chamber and the virgin brass.

 

[Harvey_NW]

Copied from SAAMI prints:
chamber headspace measurement - 2.2000 + .0100
cartridge base to datum - 2.204 - .007

Color the neck and shoulder of the case that won't chamber with a sharpie and give a few soft attempts to chamber it to see where it's making contact. By the numbers provided your chamber might need to be punched out a few thou.

 

[MTMeatHunter]

Following. I have a rifle that is doing the exact same thing. New brass or factory rounds chamber tight and actually measure SHORTER with a headspace comparator after firing it in the chamber. The rifle was at a gunsmith (who I don’t much care for) last week and the chamber checked out fine with the go/ no-go gauges. The smith told me basically not to worry about the tight brass. I don’t like it!

 

[mattwill00]

I’ve checked out the saami spec as well. Want to school me up on that? Why is the chamber spec 2.200 + .010, and the cartridge spec bigger than that at 2.204 - .007. It seems like if the chamber was on the small end (2.200) and the brass was on the large end (2.204) then it wouldn’t chamber? But it would technically still be “in spec”. I know this might be a different rabbit hole and I agree that my chamber might need to be reamed out a bit, I’m just curious on those numbers.

I’ll definitely try to color the round and see what’s going on. Also, primers are fully seated didn’t mean to ignore that post.

 

[Harvey_NW]

I’ve checked out the saami spec as well. Want to school me up on that? Why is the chamber spec 2.200 + .010, and the cartridge spec bigger than that at 2.204 - .007. It seems like if the chamber was on the small end (2.200) and the brass was on the large end (2.204) then it wouldn’t chamber? But it would technically still be “in spec”.

I honestly don't know, the reamer/chamber measurement is based of breech face so in my mind those are hard measurements that would be a discrepancy as you mentioned. Hopefully someone has better input. All I know is that breech face measurement is where prefits get hit and miss depending on how tight action manufacturers hold their tolerances.

 

[NevadaMike]

I may be missing it in your thread but If you search 300PRC and ADG sticking they had a batch a while back that had chambering problems in certain rifles. Fierce rifles in particular.

 

[mattwill00]

I know the 300 prc design leads itself to clickers as the web expands, but as far as chambering goes the specs on the adg that I have seem to fit the saami spec. Im leaning toward needing a little reamer work. I sent an email to kelbly. They’ve been super helpful and responsive when I was getting the original chambering and action purchase so I expect to hear something back next week. Hopefully they can clear some of this up.

 

[mattwill00]

Well, they did offer to ream out the barrel some more. Basically said the adg brass runs large (still within saami in my brain? But I could be wrong).

He also said that lapua brass would cure the issue. So instead of a wait on the reaming, I bought 100 pieces of lapua and I’m going to try that. Which leads me to my next question…

Does anyone have cartridge base to datum data on virgin lapua brass with a hornady comparator?

 

[mattwill00]

Go gauge came in. Found the culprit. Guess I can return that lapua brass now..