300 PRC Crazy Jump

[Bare]

I'm in a real pickle here. Basically new 300 PRC barrel won't let me create rounds with a reasonable jump.
Basics:
Fire formed Lapua brass
230 gn A-Tips

Test cartridge touching the lands, COL is 3.861
To reach SAAMI max COL of 3.7 requires a jump of 0.161
What am I missing?

 

[spife7980]

Why do you care about loading to an arbitrary saami max length when you have actual measurements right there in front of you?

 

[918v]

I'm in a real pickle here. Basically new 300 PRC barrel won't let me create rounds with a reasonable jump.
Basics:
Fire formed Lapua brass
230 gn A-Tips

Test cartridge touching the lands, COL is 3.861
To reach SAAMI max COL of 3.7 requires a jump of 0.161
What am I missing?

That A-tips are like that.

If you want less jump at saami coal, use ELD-M.

 

[rustyinbend]

Back off the lands a couple of hundredths, load your best stuff, and go see how it shoots. The only problem is if in order to get near the lands, your bullet wouldn't have enough case neck to seat properly, but it doesn't sound like that would be the case. Bottom line ... load it and shoot it ... and see what happens.

 

[Bare]

Back off the lands a couple of hundredths, load your best stuff, and go see how it shoots. The only problem is if in order to get near the lands, your bullet wouldn't have enough case neck to seat properly, but it doesn't sound like that would be the case. Bottom line ... load it and shoot it ... and see what happens.

Thanks for the advice, RustyInBend. Yes, I'm running out of bearing surface. Figure I have 300 to 400 rounds before none at all. Assuming .007 erosion per 100.

 

[rustyinbend]

Thanks for the advice, RustyInBend. Yes, I'm running out of bearing surface. Figure I have 300 to 400 rounds before none at all. Assuming .007 erosion per 100.

I had the reverse of this problem with a new 300-WM barrel a few months ago. Had to send it back, with some dummy rounds included, so that they could expand the chamber to the proper length. McGowen did a good job fixing the chamber and it shoot great now. Not sure how a "too long" chamber would get fixed, other than to replace the barrel. Find out if they can try again, and I highly recommend sending some dummy-rounds sized to the bump and COAL that you need. Hopefully they'll step up, and fix it with a new barrel.

 

[TheOfficeT-Rex]

I don't fully understand, I have a couple questions:

How are you measuring touch?
What reamer did you have used?
How did you get fireformed brass? If you shot it, how's it shoot?

 

[parshal]

My AW2 reamer'd 300 PRC (saami throat) is .145 off the lands at mag length with 245 EOL. It hammers. It may be the best shooting rifle I own including dasher and BR. Load it to mag length and shoot it.

 

[Bare]

I don't fully understand, I have a couple questions:

How are you measuring touch?
What reamer did you have used?
How did you get fireformed brass? If you shot it, how's it shoot?

Hornady O. A. L Gauge
Gunsmith used reamer from Pacific Tool
Fire formed Lapua brass in the rifle discussed
.3 MOA with some tuning
But I'm going to run out of bearing surface in a few hundred rounds

 

[Evintos]

I'm in a real pickle here. Basically new 300 PRC barrel won't let me create rounds with a reasonable jump.
Basics:
Fire formed Lapua brass
230 gn A-Tips

Test cartridge touching the lands, COL is 3.861
To reach SAAMI max COL of 3.7 requires a jump of 0.161
What am I missing?

The better dimensions you should be measuring is where the bullet contacts the leade angle of the throat - which is the cartridge base to ogive dimension (CBTO). Reason why is bullet profiles differ and a secant ogive bullet has a much more slender and longer nose length which when measured out will give you a very long COL (cartridge base to bullet tip) and the illusion that it your barrel may have too long of a throat but your dimensions may very well be within specifications. The reason why is the bearing surface and contact point sits much farther back on a secant ogive bullet than tangent ogive bullet.

If within specs, your concerns about throat erosion should be alleviated.

 

[TheOfficeT-Rex]

Hornady O. A. L Gauge
Gunsmith used reamer from Pacific Tool
Fire formed Lapua brass in the rifle discussed
.3 MOA with some tuning
But I'm going to run out of bearing surface in a few hundred rounds

Try measuring again with the wheeler method (YouTube it, strip the bolt and make small seating die changes). I find the hornady tool convenient, but too dependent on “feel.”

Without a reamer print or spec, it’s hard to say the gunsmith had any affect or fault, unless he did not use the reamer you specified (or PTG sent the wrong one or otherwise made it wrong…). I don’t think he should have to eat any cost to “make it right.”

If I had a .3 moa gun, I’d shoot it till it opened up, then decide if I just need to retune, or set it back with a different freebore reamer. YMMV.

 

[918v]

It doesn’t matter. He’s going to make oal adjustments using a comparator or dial the seater die. Stripping the bolt for this is stupid.

 

[Kickin45]

I have heard pretty bad things about PTG reamer. I am having a new 300PRC barrel spun up right now and he mentioned he would use whatever reamer I wanted except PTG.

 

[Rio Precision Gunworks]

I have heard pretty bad things about PTG reamer. I am having a new 300PRC barrel spun up right now and he mentioned he would use whatever reamer I wanted except PTG.

Just make sure it has a .535 base. If you go with a minimum saami of .533 you might have some extraction/clicker issues. Some reamer makers like Manson are already doing something like .5345 which works as well. If not, then you can as for the AW2 version (Alex Wheeler as he's the one who figured the issue out early on).


We've had some come into the shop with issues and all it takes is spinning the wider base reamer by hand in the chamber to open it up, and solves the issue.

 

[Kickin45]

thanks Rio

 

[iceng]

I have heard pretty bad things about PTG reamer. I am having a new 300PRC barrel spun up right now and he mentioned he would use whatever reamer I wanted except PTG.

Theres a whole thread of people ragging on them. I wont use them, havnt for a looong time.