Oal and pressure question

[Jamnanc]

Loading hornady 168 bthp in commercial cases. Followed book data work up from 40.5 to 43.0 of h4895 in .3 increments. Loaded to 2.8 oal and the bolt wouldn't close. Took them home and ended up seating to 2.785 in order to get the bolt to close properly. Problem solved right?

Except that hat I started getting serious ejector marks and flattened primers at 41.5. Which shot pretty well. I'm thinking the bullet is still too close to the lans and causing pressure issues. So the question is if I push the bullet in farther will it increase pressure due to case capacity issues or lower pressure since it's going to have more free bore? I'd like to load a bunch of these based on their accuracy, but would like a little more pressure breathing room.

[Jamnanc]

44991
Not cratered, slightly flattened, no leakage. What say you.

[TheBelly]

What is the base-to-ogive length in your gun?

What is the trim length of the cases?

what is the headstamp on the cases?

What is the gun?

[Jamnanc]

I haven't measured base too give because I don't have the tools.

Trim length is 2.005.

Nosler brass once fired.

Savage 10fp-sr.

There are many posts about the savage having a short throat. I was expecting if I loaded to common lengths it would work and could go longer to cut jump down later.

[TheBelly]

The base to ogive measurement is pretty important to both pressures and accuracy.

[Hound]

I am having about the same issue with some 300BLK general 150gr and some .223 50gr ZMAX bullet loads. Other bullets load/shoot great to normal but when I try these two bullets in my gun(s) the bolt does not fully go home when I use the specs from the manuals. I tried to reduce the OAL length a bit but at a certain point don't know how far to push this. I just picked up an OAL gauge to get the numbers for my specific guns but have been on travel and have not had time to relax and go through the process yet. I don't want to be in a hurry when I do it and mess it up. I will be interested in the feedback here.

[TheBelly]

Try this:

http://youtu.be/GmDi7v530Og

[TheBelly]

When I did this, it was within 0.001" of the measurement I got when I used an actual cartridge length gauge.

[Jamnanc]

I will do this to confirm what I already know. Thank you for the link. The question I have is, can I load the same powder charge at 2.775 as I did at 2.80 without seeing a pressure spike, I know it matters in a pistol, to what degree does it affect a rifle case?

[TheBelly]

I will do this to confirm what I already know. Thank you for the link. The question I have is, can I load the same powder charge at 2.775 as I did at 2.80 without seeing a pressure spike, I know it matters in a pistol, to what degree does it affect a rifle case?

It matters.

I always start with the low end of the recommended charge weight and work up to a good group.

[Zombie Steve]

As you seat a bullet deeper, there's less case volume and pressures go up... as you already know. In 9mm, this is huge as there's very little case volume to start with. In .308, pushing back .005" or .010" isn't going to matter much at all. Bigger cases like .30-06 or .300 win mag even less. If the problem truly is that you're too close to the lands, what you're doing will lower pressures.

When you run into the bolt not closing, pull the cartridge out and look for marks on the bullet where the lands have scraped. If you don't see them, it's most likely a sizing issue (this happens eventually if you're just neck sizing). I generally neck size a few times, then give it a full length sizing again for just this reason.

Remember some bullets are just going to be longer than their counterparts. They aren't all the same. Set your die so that the long ones don't exceed 2.800" (for example). The majority of your bullets will come a few thousandths shorter, and some quite a bit shorter. It's a normal statistical bell curve. Depending on your level of OCD, you can sort them by weight and length.

[Jamnanc]

I smoked the bullet at the range with a marker. The bullet was definitely going into the rifling. I took them home and shortened them, the case is not touching, but the bullet definitely was. I will rework from a shorter oal after measuring per the video. Thanks guys.

[Zombie Steve]

Know what's nice when you rebarrel? The blank comes 27" or so, and the last inch or so isn't usable, so take what's cut off and ream it like the chamber. Custom case gauge that's an exact match for your throat / leade. I wish all rifles came with one, but that will never happen.

[spqrzilla]

As Zombie Steve describes above, the relationship between shorter OAL and higher pressure is not significant in rifle calibers as it would be in higher pressure pistol. At this point, the relationship is more dominated by the relationship between the initial contact of bullet to rifling and the pressure curve. Back off a bit should bring that down a bit.

[Tim K]

Know what's nice when you rebarrel? The blank comes 27" or so, and the last inch or so isn't usable, so take what's cut off and ream it like the chamber. Custom case gauge that's an exact match for your throat / leade. I wish all rifles came with one, but that will never happen.

My smith supplies one when he puts on a barrel. They are great tools. It's an exact match until you shoot a few thousand rounds. Throat erosion screws it up to the tune of about 0.003" - 0.005" per 100 rounds fired.

[Hound]

As Zombie Steve describes above, the relationship between shorter OAL and higher pressure is not significant in rifle calibers as it would be in higher pressure pistol. At this point, the relationship is more dominated by the relationship between the initial contact of bullet to rifling and the pressure curve. Back off a bit should bring that down a bit.

Got it that Rifle rounds are more tolerant and not thinking about pushing in 1" crazyness but 'typically' where is the danger zone when going under the posted OAL for a given round (understanding the larger the less it matters). On a .223 is it at .001, .01, .1, .5 etc? I am curious where you guys place your tolerances before the flags start going up.

[Zombie Steve]

Got it that Rifle rounds are more tolerant and not thinking about pushing in 1" crazyness but 'typically' where is the danger zone when going under the posted OAL for a given round (understanding the larger the less it matters). On a .223 is it at .001, .01, .1, .5 etc? I am curious where you guys place your tolerances before the flags start going up.

I generally try to go as long as I can without hitting lands or impacting feeding. The only time I've ever tried to see just how short is if I'm dealing with a really light / short bullet that I'm having trouble getting neck tension with. The old rule of thumb is one caliber width seated into the case (boat tail doesn't count as it's not touching the neck). I've never gone much more than that. If you're looking for some guide, check out the OAL for the lighter bullets for caliber in a manual. Beyond that I can't tell ya.

[Zombie Steve]

My smith supplies one when he puts on a barrel. They are great tools. It's an exact match until you shoot a few thousand rounds. Throat erosion screws it up to the tune of about 0.003" - 0.005" per 100 rounds fired.


He look like this?

http://ts3.mm.bing.net/th?id=HN.608009653775764886&pid=1.7


...and per 100 rounds? How overbore is the cartridge you're shooting?