Home Forums Reloading Big Game Rifles Tight chamber and pressure?

I just had a new rifle built on a 700 action and a pac nor bbl. .260 Remmy. It’s very accurate and shoots most everything I’ve Fed it so far into 1/2-3/4” groups. But it seems to have a tight chamber. Before I even fired it, it would not load factory new Hornady brass. Bolt wouldn’t quite close all the way. Once I ran the brass through my re sizing die it was fine.

Today while testing a load using H4350 and a Barnes 127 LRX at .080 off lands (mag length) I got pressure signs, ejector wipe, at just 42 gr of powder, which seems incredibly light. I’ve read about 45gr charges using same powder and bullet.

So my question is… Are having a tight chamber and easily seeing pressure signs related? Seems logical to me, but I’m also still rather new at this.

Seems to be lots of reports of Hornady ammo being oversized lately

Would be nice to KNOW the reamer specs. Could be a neck dimension is tight with insufficient bullet release clearance. This could show up with some pieces being so tight you have signs of pressure and sometimes with others working fine.

I encountered it once, a gunsmith told reamer maker to "tighten" up the specs so it would shoot its best. (later realized gunsmith didn't know squat about what he was asking for) Gunsmith and I had a deal for me to work up loads for his customer's rifle, a 6.5-284. I had no idea there was an issue with not enough clearance for bullet release. Some of the pieces of lapua brass worked fine and others showed signs of pressure. Happened to try fitting a bullet into a fired case and it was very tight. That had me asking what the neck dimension was....couldn't believe I was handed a rifle with tight chamber neck without being told. Had to neck turn the brass for proper release dimension.

As for not being able to close bolt on factory Hornady brass, IMO that is a headspace issue. Gunsmith might have made it on the tight side and Hornady brass shoulder is a few thousandths longer.

I would try to insert a bullet into the necks of fired cases. They should slide in easily. If not, then the neck of the chamber may be too tight--or the combination of chamber and case necks may be too tight.

I use a LOT of Hornady brass these days, and haven't found any "oversized" for the chamber. Have found a few cases with thicker brass "donuts" at the base of the neck, where it meets the shoulder. However, those have all been in cartridges where the necks are usually out-side turned for precision.

How short is the throat compared to SAAMI?

I have had several encounters with Hornady factory ammo being slightly "oversize" in some dimension.

I have had numerous .223 Varmint Express that would barely chamber in several different rifles, factory and custom. Other factory fits fine.

I have had several .270 WCF American Whitetail that chambered hard in several different rifles, factory and custom. Other factory fits fine.

I now have 25-06 American Whitetail that chambers hard in a brand new factory rifle. Other factory fits fine.

After firing, trimming, resizing and reloaded, it all fits just fine.

So a lil more info after hitting the range again today. At 42 gr H4350 and 127 LRX I get a light ejector mark or wipe every 3-5 pieces of ammo. Some pieces of fired brass are fine, then I get a light mark. 42.3 gr of powder puts ejector marks on the brass every time.

I also tried some 120gr TTSX. At 42 gr powder I got no pressure signs at all. At 42.3gr powder it acted like the above 127 LRX load at 42 gr. Got a light mark every few pieces.

I ordered some Lapua brass to try and will also try some factory ammo. Problem is, I’m almost scared to try factory ammo. Look at Barnes Vortx 120gr .260 specs. 2950 muzzle velocity! That MV is hotter by a good bit than ever their listed max load from their data sheets. So if I’m getting pressure signs without reaching max on their load data, their factory ammo appears to be even more high test! Should I be worried to give it a shot? Still scratching my head over this one. I don’t want to be limited to anemic ammo. I really hope I just got an odd batch of brass.

MD, a new bullet slides into a piece of fired brass fairly easily. Just some light finger pressure required.

No idea what the actual chamber measurements are other than they said it was cut to Saami specs.

I have 3 .308s, one is fitted with a Pac-Nor. Its chamber yields fired brass that has 1.4 grains less water capacity than the other two using the same brass. That will result in slightly more pressure with a given charge.

Another influence is a shorter throat.

With the Pac-Nor barrel, I reduced the load I was using in the other two by about .2 grains to get equal velocity.

What is the muzzle velocity of the 42g load?

??????????????

IMHO a bullet should slide in without any pressure as in fall by its own weight. Sounds like a tight neck/ thick necks from what has been said.

I don’t yet know. My local range doesn’t allow access beyond the firing line so I can’t set up my chrono. The range that does is an hour drive away. I realize that would tell me a lot I just haven’t had time to get there.

It doesn’t take much. Just a light touch and they drop right in.

I was asking (or attempting to) what his muzzle velocity was of the 127g LRX w/ 42g H4350 load.

This ^^^^^^

SDHUNTER,

No pressure (even "light finger pressure") should be needed to slide bullets into fired necks.

SDHNTR...after many, eight, PAC-NOR barrels in various cals, other than a 260, can tell you that I`ve learned to start at the low end of the powder charge with these barrels. We order pre-fit. They are tight.
As far as factory stuff goes, you may need to try more than one brand of ammo.

Can you inside neck ream?

Ok I dug out some more fired brass. Ttsx and gmx drop right in. The LRX seems to sometimes catch a bit on the cannelure rings but a light tap or shake and they drop.

I’m not familiar with “inside neck ream”. Please elaborate.

I understand starting light, I did that too. But got stopped short of max. Should I be spooked to shoot factory ammo? To follow my logic, Barnes 120 ttsx and H4350 max load on their data sheet is 2853fps, and I can’t reach it without pressure signs. Yet their Vortx factory ammo with the same bullet is published at 2950fps! See why I’m spooked?

So you are evidently saying that PacNor builds em tight as SOP? I assume for accuracy and I am getting good accuracy. Do I need to just resign myself to shooting anemic loads? Anything else I should try?

Try a new batch or brand of brass? Remember that this Hornady factory new brass wouldn’t chamber without a little force to push the bolt down. I had to full length size before they would chamber smoothly. I always full length resize anyway before shooting, but have never HAD to with other rifles to get new brass to chamber.

Should I throw caution to the wind and touch off some factory ammo? Think it’s safe given the load data concerns?

I’d also rather not pack this thing up and send it back as that’s a pain and deer season is close. I am excited to hunt this gun too. Im open to other ideas or things to try to narrow down the issue. Thanks for the feedback.

Do you have a headspace comparator? What does the headspace dimension measure?

new brass Vs. sized new brass Vs. fired brass

When sizing the new brass to chamber, what dimension(s) are changing? Just HS?